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Safety considerations for electric vehicles and regulatory activities

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Abstract

This paper explores some potential hazards associated with electric vehicles and considers how the risks to users are mitigated by European Union and United Nations type-approval regulations. In doing so, it highlights any gaps in the regulations and the international efforts that are currently underway to close them. Vehicle hazards are the main focus for this work, and some consideration is given to the way they are likely to be used by the public. However, hazards relating specifically to infrastructure, such as vehicle charging or battery exchange are generally not included because they are likely to fall under a different regulatory framework.
EVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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EVS26
Los Angeles, California, May 6-9, 2012
Safety considerations for electric vehicles and regulatory
activities
Costandinos Visvikis
1
1
TRL, Crowthorne House, Nine Mile Ride, Wokingham, Berkshire, RG40 3GA, United Kingdom, cvisvikis@trl.co.uk
Abstract
This paper explores some potential hazards associated with electric vehicles and considers how the risks to
users are mitigated by European Union and United Nations type-approval regulations. In doing so, it
highlights any gaps in the regulations and the international efforts that are currently underway to close
them. Vehicle hazards are the main focus for this work, and some consideration is given to the way they are
likely to be used by the public. However, hazards relating specifically to infrastructure, such as vehicle
charging or battery exchange are generally not included because they are likely to fall under a different
regulatory framework.
Keywords: Safety, Regulation, Standardisation
1 Introduction
Electric vehicles have the potential to offer many
benefits to society such as improved air quality in
towns and cities and reduced carbon dioxide
emissions from road transport (depending on the
source of the electricity). However, they are very
different from conventional vehicles and present
some new safety hazards. Clearly, electric
vehicles are not inherently unsafe, nor will they
necessarily expose the public to greater risks than
internal combustion engine vehicles.
Nevertheless, there is always the potential for
unintended consequences whenever a new
technology is introduced. If such consequences
are to be minimised, then it is important that
vehicle safety regulations keep pace with new
technology.
For the purposes of this paper, “electric vehicle”
generally includes hybrids as well as purely-
electric vehicles. Hybrid vehicles combine
electric power from an on-board rechargeable
energy storage system (such as a battery) with an
internal combustion engine. Different degrees of
hybridisation are possible:
A “mild hybrid” switches the engine off when
the vehicle is stationary and then restarts when
the accelerator is pressed. Energy from
braking is stored and can be used to support
the internal combustion engine during
acceleration.
A “full hybrid” is capable of running on
battery power alone, although usually for very
short distances only.
A “plug-in hybrid” can be charged directly
from the grid and can run on electric power for
longer distances
An “extended-range electric vehicle” uses a
small internal combustion engine to charge the
battery rather than drive the wheels.
Purely-electric vehicles run on battery power only
and do not use an internal combustion engine or
liquid fuel.
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2 Road vehicle legislation
Most (if not all) regions of the world operate
some form of road vehicle legislation. However,
this paper focuses primarily on European Union
(EU) Directives and Regulations as well as
United Nations (UN) Regulations. The activities
of the main international standards bodies are
also introduced.
2.1 European Union type-approval
European Community Whole Vehicle Type-
Approval (ECWVTA) is the main form of
vehicle certification in Europe. The EU type-
approval system requires independent, third-
party approval covering all testing, certification
and conformity of production assessments. Each
member state of the EU must appoint an approval
authority to issue approvals and a technical
service to carry out the testing. The key principle
of the system is that an approval issued by one
authority will be accepted in all member states.
Directive 2007/46/EC (the Framework Directive)
applies to powered four-wheel vehicles including
passenger cars, goods vehicles and trailers
(lightweight, low-powered four-wheeled vehicles
referred to as quadricycles are not included;
instead, they fall within the type-approval
framework for powered two- and three-wheeled
vehicles).
The Framework Directive lists more than 40
separate EU Directives that the vehicle must
comply with in order to gain type-approval.
These specify performance requirements and
tests for various aspects of the vehicle ranging
from tyres through to exhaust emissions and
braking systems. The Framework Directive also
lists United Nations (UN) Regulations that are
considered to be acceptable alternatives to certain
EU directives.
European Union Directives are generally kept up
to date, but several EU Directives have started to
lag behind their corresponding UN Regulation,
particularly on the subject of electric vehicles.
However, EU type-approval is undergoing a
process of simplification in line with the
recommendations contained in the final report of
the CARS 21 High Level Group [1]. As part of
this process, EU Directives are being repealed
and replaced with a smaller number of EU
Regulations that apply directly in each member
state. These EU Regulations typically follow a
split-level approach, comprising two-parts:
Fundamental provisions are set out in an EU
Regulation laid down by the European
Parliament and Council and adopted through
the ordinary legislative procedure;
Technical specifications that implement the
fundamental provisions are laid down in one
or more separate EU Regulations adopted by
the Commission with the assistance of a
regulatory committee (typically comprising
representatives of EU member states, the
automotive industry, component
manufacturers and other stakeholders).
As an example of this split-level approach, in 2014
each of the separate EU Directives on vehicle
safety will be repealed by Regulation (EC) No.
661/2009 and replaced, where appropriate, with
reference to the corresponding UN Regulation. A
series of implementing regulations are also being
created where there is no UN Regulation that is
equivalent to the old separate EU Directive.
2.2 United Nations Regulations
UN Regulations (previously known as UNECE
Regulations) are administered by the World Forum
for Harmonisation of Vehicle Regulations
(WP.29), which is a subsidiary body of the United
Nations Economic Commission for Europe. The
regulations are based on the principles of type-
approval and of reciprocal recognition of approval
among participating countries. The legal
framework for the reciprocal recognition of UN
Regulations is set out in the 1958 Agreement.
UN Regulations generally provide for the approval
of vehicle systems and components, or for specific
aspects of a vehicle, but there is no “whole
vehicle” approval mechanism. Several UN
Regulations have been amended to include specific
provisions for electric vehicles. These include UN
Regulation 12 (protective steering), UN Regulation
13 and 13-H (braking), UN Regulation 51 (noise),
UN Regulation 83 (emissions), UN Regulation 85
(engine power) and UN Regulation 101 (CO
2
emissions). In addition, proposals to amend UN
Regulation 94 (frontal impact), UN Regulation 95
(side impact) have now been adopted. UN
Regulation 100 sets out specific provisions for
electrical power trains and was recently made
mandatory for EU type-approval.
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Some of the work of preparing amendments to
these UN Regulations, particularly those relating
to safety, was carried out by an informal working
group on Electric Safety, which was set up in
2008, and by “groups of interested experts” that
emerged from this informal working group.
2.3 United Nations Global Technical
Regulations
UN Global Technical Regulations are also
administered by WP.29. They are established
under the “1998 Agreement”, which is open to
countries that do not participate in the 1958
Agreement. For example, the United States does
not participate in, or recognise, UN Regulation
approvals. Vehicle legislation in the United
States operates on the principle of self-
certification whereby the manufacturer certifies
that their product complies with all the applicable
federal standards. Nevertheless, the United States
is a contracting party to the 1998 Agreement and
hence UN Global Technical Regulations are
compatible with both type-approval and self-
certification systems. This is generally achieved
by following a performance-based approach
when preparing the requirements.
A UN Global Technical Regulation is not a legal
document. However, a contracting party to the
1998 Agreement that voted in favour of
establishing a global technical regulation is
obliged to begin the process of transposing the
global requirements into their local legislation.
Contracting parties may adapt or modify the
specifications in a UN Global Technical
Regulation for their local legislation, but they
may not increase the levels of stringency or
performance.
The UN Global Technical Regulations that are
currently in place do not require special
provisions for electric vehicles because they
cover topics that are unrelated to the vehicle‟s
powertrain. However, a proposal was made at the
155
th
Session of WP.29 to set up two informal
groups on electric vehicles, under the 1998
Agreement, to create a basis for the possible
development of a UN Global Technical
Regulation. One group will focus on safety,
while the other will focus on environmental
aspects of electric vehicles.
The proposal envisages safety provisions for
electric vehicles that will cover electrical safety
in normal, everyday use as well as following a
crash. The in-use topics proposed are:
Occupant protection from electric shock;
Charging requirements;
Safety requirements for rechargeable energy
storage systems.
The post-crash topics proposed are:
Electrical isolation;
Battery integrity;
Best practices or guidelines for manufacturers
and/or emergency responders;
Battery discharge procedures.
The proposal recognises that the work already
carried out under the 1958 Agreement to amend
and update UN Regulations is a potential input to
this work.
2.4 International standards
While vehicle legislation is the main focus for this
paper, it is worth noting that a variety of
international standards are emerging for electric
vehicles, many of which deal with safety topics.
However, these are essentially voluntary industry
standards, unless a specific reference to the
standard is made in an EU Directive or Regulation
or a UN Regulation.
International standards work for electric vehicles is
largely being undertaken by two bodies: ISO
(International Organisation for Standardisation)
and the International Electrotechnical Commission
(IEC). Traditionally, standards work between these
bodies is shared according to the general principle
that all matters relating to electrical and electronic
equipment are reserved for IEC and all other
matters are reserved for ISO.
However, there are aspects of electric vehicles that
have the potential to fall under the responsibility of
both bodies, which brings the risk of duplication if
the work is not coordinated. A general consensus
was agreed between the two bodies in the 1990s
whereby ISO focussed on work relating to electric
vehicles as a whole, while IEC focussed on electric
components and supply infrastructure. Further
information about the basic division of work and
the key technical committees has been described
comprehensively elsewhere [2].
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More recently, in 2011, a memorandum of
understanding on the international
standardisation of electrotechnology for road
vehicles was signed to ensure ongoing
cooperation. The agreement describes two fields
of application:
On-board equipment and performance of
road vehicles;
Interface between externally chargeable
vehicles and electricity supply
infrastructure.
Briefly, the memorandum states that ISO is
responsible for all standardisation issues
concerning road vehicles and on-board systems,
but any standards should reference existing IEC
standards for electrical and electronic
components (unless vehicle-specific conditions
require otherwise). The memorandum cites
existing modes of cooperation in ISO/IEC
Directives, Part 1, clause B.4.2.2, for standards
relating to all interfaces between externally
chargeable road vehicles and the electricity
supply infrastructure.
3 Safety considerations and
regulatory activities
This section discusses some potential safety
considerations for electric vehicles. As noted, it
was not the intention to imply that electric
vehicles are unsafe or would expose the public to
greater risks than conventional vehicles. Instead,
the focus was on some general hazards and how
they are regulated under EU type-approval and in
UN Regulations under the 1958 Agreement.
3.1 Electrical safety in use
The voltages used in electric vehicles are
potentially very dangerous. However, a range of
safety features are typically used to ensure the
safety of occupants or other persons. Crucially,
the high voltage circuit is isolated from the
vehicle chassis (and any other conductors). This
means that a person would need to touch both the
positive and the negative sides of the circuit to
receive an electric shock. This would require a
loss of isolation on both sides of the circuit (i.e. a
double-fault). In fact, the ground-fault
monitoring system would detect any leakage of
current and would disconnect the high voltage
system from the rechargeable energy storage
system.
Safety requirements for electrical power trains are
set out in UN Regulation 100. It comprises
specifications and test procedures in four main
areas: protection against electric shock;
rechargeable energy storage systems; functional
safety; and determination of hydrogen emissions.
With regards to protection against electric shock,
the requirements generally apply to high voltage
buses when they are not connected to external high
voltage supplies. There are three main aspects:
protection against direct contact; protection against
indirect contact with exposed conductive parts; and
isolation resistance.
Vehicles may employ various means to prevent
direct contact with live parts, such as insulating
materials or physical barriers. UN Regulation 100
ensures that the conventional electrical protection
degrees (IPXXB or IPXXD) are enforced. For
example, the regulation specifies that live parts in
the passenger or luggage compartments must be
protected to a degree of at least IPXXD.
Enclosures in other areas must have a protection
degree of at least IPXXB. In each case, an access
probe is pushed against any openings of the
enclosure with a specified test force and must not
touch live parts. In the case of IPXXD, the probe is
a test wire, 1 mm in diameter and 100 mm long,
and in the case of IPXXB, the probe is a jointed
test finger, 12 mm in diameter and 80 mm long.
Protection against indirect contact with live parts is
closely related to the prevention of electrical faults.
The regulation requires that any exposed
conductive parts, such as barriers or enclosures,
are connected to the chassis to prevent dangerous
potentials being produced. The regulation also
specifies a limit for the resistance between all
exposed conductive parts and the chassis of 0.1
ohm when there is a current flow of at least 0.2
amperes.
Finally, detailed specifications are included for
isolation resistance. The specifications depend on
whether the power train comprises separate or
combined DC and AC buses. Limits are specified
according to the type of buses and their
connections, and test procedures are provided in an
annex.
UN Regulation 100 was updated and amended in
2010. The work was carried out by the UN
informal group on electric safety, which comprises
representatives from national governments, the
automotive industry, their suppliers and test
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institutes. The new version covers electrical
safety requirements for all types of electric
vehicles including purely electric vehicles,
hybrids and hydrogen fuel cell vehicles. It covers
both passenger and commercial vehicles,
provided their speed exceeds 25 km/h. The
regulation was officially made mandatory for EU
type-approval during 2010 and any vehicles that
meet its requirements should not pose an
electrical safety hazard during the normal
operation of the vehicle.
3.2 Electrical safety post-crash
A collision could compromise the electrical
safety measures described in the previous section
and could increase the risk of electric shock. For
example, electrical isolation might be lost such
that both the positive and negative sides of the
circuit come into contact with the vehicle
bodywork. If any of the occupants touched the
bodywork they would become part of the high
voltage circuit and would receive an electric
shock. However, it is likely that most electric
vehicles will be fitted with a device that
disconnects the rechargeable energy storage
system from the high voltage circuit in the event
of a crash. This is generally achieved by linking
the system to crash detection sensors used to
activate pre-tensioners and air bags. For example,
Justen and Schöneburg [3] describe the current
philosophy implemented by Daimler in
Mercedes-Benz hybrid and electric vehicles. Two
different switch-off strategies have been
implemented by Daimler: a reversible cut-off for
minor collisions and an irreversible cut-off for
more severe collisions. Another example is
provided by Uwai et al. [4], in a description of a
shutdown system developed by Nissan.
Disconnecting the rechargeable energy storage
system from the rest of the high voltage circuit
will reduce the risk of electric shock during and
following a crash, but it will also be important to
ensure that the rechargeable energy storage
system is not damaged in such a way that can
lead to a fire or an explosion. Furthermore,
discharging the rechargeable energy storage
system will be important for the safe handling
and recovery of the vehicle. This was illustrated
in the United States where an electric vehicle
caught fire three weeks after a pole impact test
[5]. The battery was damaged during the impact
and coolant leaked onto the electronic
components during the post-impact static roll of
the vehicle. The battery was not discharged
before the vehicle was placed in storage and the
ensuing fire destroyed the vehicle and several
others parked nearby.
Directive 96/79/EC and UN Regulation 94 set the
minimum requirements for the frontal impact
performance of cars. They both specify a frontal
impact test in which the car is propelled into an
offset, deformable barrier at 56 km/h. Similarly,
Directive 96/27/EC and UN Regulation 95 set the
minimum requirements for side impact
performance. They specify an impact test in which
a mobile deformable barrier is propelled into the
side of the car at 50 km/h.
There are no specific provisions for electric
vehicles in the EU Directives for frontal and side
impact. The test procedures and occupant safety
requirements could be applied to any vehicle,
regardless of power train type; however, there are
no specifications for the preparation of an
electrical power train or for the electrical safety of
the occupants during and following the impact. In
2009, a group of interested experts on post-crash
provisions for electric vehicles was formed. The
aim of the group was to derive amendments to UN
Regulations 94 and 95 so that they are appropriate
for the assessment of electric vehicles. The group
was formed mainly of experts in electrical safety
from the UN informal working group on electrical
safety and experts in crash safety from the UN
informal working group on frontal impact.
The proposals to amend UN Regulations 94 and 95
were completed in 2010 and adopted by WP.29.
With regards to the protection against electric
shock following the impact test, the amendments
specify four performance criteria:
Physical protection (IPXXB and resistance
between exposed conductive parts and
electrical chassis < 0.1 ohm);
Electrical isolation (minimum resistance
specified depending whether DC and AC
buses are separate or combined);
Absence of high voltage (≤ 30 VAC or 60
VDC);
Low electrical energy (< 2 Joules).
At least one of these four criteria must be met
following the impact test. However, the isolation
resistance criterion does not apply if more than one
part of the high voltage bus is unprotected (i.e. the
conditions of IPXXB are not met). This
requirement was added to prevent vehicles meeting
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the isolation resistance criterion and hence
gaining approval while presenting a risk of
electric shock (because more than one part of the
high voltage bus is accessible).
If the vehicle is equipped with an automatic
device that separates the rechargeable energy
storage system from the rest of the high voltage
circuit in the event of a crash, or a device that
divides the power train circuit, (one of) the
criteria must be met by the disconnected circuit,
or by each divided circuit individually after the
disconnect function is activated. However,
although the amendments include provisions for
vehicles with an automatic disconnect device,
there is no requirement to fit one. Two of the
four criteria to assess the projection against
electric shock can be met with no automatic
disconnect device: physical protection and
isolation resistance.
UN Regulations 94 and 95 will also now specify
requirements for the retention of the rechargeable
energy storage system and electrolyte spillage.
The requirements for the retention of the
rechargeable energy storage system depend on its
location. If it is located within the passenger
compartment, it must remain in the location in
which it was installed and all its components
must remain within its boundaries. No part of a
rechargeable energy storage system located
outside the passenger compartment can enter the
passenger compartment during the test. The
assessment is made by visual inspection only and
no guidance or tolerances are provided.
Electrolyte spillage within the passenger
compartment is not allowed in the amendments
to UN Regulations 94 and 95. Outside the
passenger compartment, it is limited to 7%;
except where open-type traction batteries are
fitted. For these batteries, spillage outside the
passenger compartment is limited to 7% up to a
maximum of 5 litres. These requirements are
valid over a 30 minute period, starting from the
point of impact. Batteries have traditionally
featured liquid electrolytes; however, solid
electrolytes have started to emerge. The
amendments do not distinguish between liquid
and solid electrolytes and hence the 7% limit
should apply in either case (if the requirement is
applied strictly).
The amendments to UN Regulations 94 and 95
will ensure that the electrical safety measures in
an electric vehicle are capable of functioning in a
collision (at least up to the severity of the
regulatory crash tests). Nevertheless, some residual
risks could remain. These are summarised below:
Validation of amendments
Although the amendments have been prepared by
experts, they have not been validated
experimentally. Performing a series of crash tests
(and/or obtaining data from manufacturers) would
help to confirm that the amendments are
appropriate and consider all the hazards.
Side impact taller vehicles
The side impact legislation does not apply to a
vehicle if the reference point of the lowest seat is
more than 700 mm from the ground. This
recognises that taller vehicles tend to perform very
well in side impact tests. While this could apply to
an electric vehicle too, the electrical components
might be damaged resulting in an electrical safety
hazard even when there is a low risk of collision
injury. Amending the legislation to require taller
electric vehicles to undergo a side impact test (i.e.
to assess only the post-impact electrical safety)
could potentially avoid this hazard.
Fuel leakage hybrid vehicles
The frontal and side impact legislation permits fuel
(or a substitute) to leak from the fuel system
following the impact test, but limits the leakage
rate to 5x10-4 kg/s (i.e. 30 grams/min). However,
hybrid electric vehicles could present a new hazard
due to their high voltage components, which can
generate enough energy to create a spark.
Adopting more stringent requirements for fuel
leakage with hybrid vehicles might reduce the risk
of fuel leaking from a hybrid vehicle following a
collision and coming into contact with high
voltage components.
Automatic disconnection of the electrical
energy source
An automatic disconnection device can be used to
provide protection, but it is not mandatory, and
other means of protection can be provided that do
not require an automatic disconnection device to
be fitted. The current performance metrics are less
design prescriptive, but there is a risk that they
may not perform in collision scenarios that differ
from the regulatory impact tests. A mandatory
requirement to fit an automatic disconnection
device could allow the protection against electric
shock to be controlled in a broader set of
circumstances.
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Structural integrity of the rechargeable
energy storage system
The amendments specify requirements to control
the movement of a rechargeable energy storage
system during the frontal and side impact tests,
but there are no requirements for its structural
integrity. Mechanical loading of a rechargeable
energy storage system can lead to shorting and
possibly rupture, with the risk of sparks, fire and
explosion. Amending the frontal and side impact
legislation to include post-impact structural
integrity requirements for the rechargeable
energy storage system would reduce the risk of
this potential safety problem.
Electrolyte spillage - limits
The limit of 7% specified for electrolyte spillage
outside the passenger compartment was derived
from other (national) legislation already in force.
However, it is unclear how much electrolyte
would be dangerous and whether the risk
depends on the type of battery chemistry and
electrolyte used. Prohibiting electrolyte spillage
outside the passenger compartment (as well as
inside) would avoid this potential safety problem.
Alternatively, further research would enable
appropriate limits to be created for different
battery types.
Electrolyte spillage - static roll
The amount of electrolyte that leaks might
increase if an electric vehicle rolls over following
a collision. Performing a static roll test following
the impact test would assess the potential for
electrolyte spillage in a broader set of
circumstances.
3.3 Crash compatibility of electric
vehicles
Electric vehicles are typically heavier than
equivalent internal combustion engine vehicles.
The rechargeable energy storage system (i.e.
batteries, capacitors, electromechanical
flywheels, etc) is the principal source of the
additional weight. A vehicle may also require
certain structural features to accommodate the
weight of the rechargeable energy storage system
and these features may add further weight
themselves. In the longer term, efforts will be
made to reduce weight elsewhere in the vehicle,
through better design and by incorporating new
technologies and alternative materials. However,
since there is also significant interest in reducing
the weight of conventional vehicles (to improve
their fuel economy), electric vehicles could remain
heavier in comparison.
There are numerous publications that discuss the
potential effects of vehicle weight on safety. The
basic physics is relatively straightforward: if two
vehicles of different mass collide, the heavier
vehicle will experience less deceleration than the
lighter vehicle. On that basis, occupants of heavier
vehicles are thought to face lower risks in
collisions than occupants of lighter vehicles [6].
The reality is more complex and various factors
can affect the secondary safety performance of a
vehicle in a collision, such as the structural
integrity of the passenger compartment, the “crush
space” available to absorb energy, the performance
of the restraint systems and the age and other
characteristics of the occupants. Nevertheless,
Talouei and Titheridge [7] found that a 100 kg
increase in mass decreases the risk of injury to the
driver in a two-car injury accident by 3 %. It could
be argued, therefore, that an electric vehicle will
offer secondary safety benefits to its occupants (in
certain circumstances). However, a heavier vehicle
will also be more “aggressive” and hence
increasing the mass of a particular vehicle could
increase the risks to occupants of other vehicles.
Preliminary research carried out by the Highway
Loss Data Institute in the United States found that
the odds of being injured in a crash are 25 percent
lower for people in hybrids than people travelling
in non-hybrid models [8]. However, while the
analysis included more than 25 hybrid and
conventional pairs, it was unclear how many
vehicles and collisions the finding was based on.
The relationship between vehicle mass and
occupant injury outcome is important; however,
some of the benefits associated with mass may
actually be related to size [9]. Clearly, mass and
size are closely linked (at least in current vehicles),
but they can have different effects. The size of a
vehicle, especially its front end, is key to its
performance in a frontal impact. A larger vehicle is
more likely to have a longer crush space to absorb
the collision. Broughton [10] found that the mean
risk of death for the driver of the smallest type of
cars (minis and superminis) is four times the risk
for the largest type (4x4s and people carriers).
Many of the first generation of purely-electric
vehicles are smaller, lighter vehicles (minis and
superminis). Some manufacturers have publicised
their electric vehicle development programmes for
larger vehicles, but it seems likely that this will
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remain the case in the short to medium term
(unless there is a significant energy storage
breakthrough). The composition of the car fleet
has already changed over the last 10 years. New
car registrations data published by the Society of
Motor Manufacturers and Traders (SMMT)
shows that the market shares of smaller cars
(minis and superminis) and larger cars (4x4 and
multi-purpose) have increased relative to
medium-sized cars [11]. However, Broughton
and Buckle [12] found that changes in the fleet
(between 1997 and 2003) appear to have had
only a minor contribution to the severity of car
accidents. Nevertheless, if purely-electric
vehicles penetrate the fleet in significant
numbers, the market share of small cars may
increase further relative to other vehicles. This
may have an effect on casualty statistics, unless
improvements in the “compatibility” of vehicles
can be achieved, potentially through better self
and partner protection requirements in the
legislative and/or consumer crash tests.
Another important aspect of vehicle
compatibility in a collision is the structural
interaction between the two vehicles. Proper
structural alignment over a common interaction
zone is essential to ensure that energy is absorbed
in the most effective way. Current electric
vehicles typically display a structural layout that
is comparable to that in conventional vehicles.
However, electric vehicles also present an
opportunity for innovation in vehicle design and
styling, particularly in purely electric vehicles or
range-extended electric vehicles (where there is
no need to mount a large, heavy engine in the
frontal compartment). Other developments such
as in-wheel motors could further reduce the need
for a conventional structural layout at the front of
the vehicle and hence in the longer term, there
could be greater diversity in the fleet.
The European 7th Framework Project, FIMCAR
(Frontal Impact and Compatibility Assessment
Research) is developing test procedures that will
encourage a common structural interaction zone
(www.fimcar.eu). The objective of the
researchers is for the measures developed to be
suitable for implementation in legislation. While
these procedures would reduce the risks
associated with poor structural alignment
between vehicles, they would not mitigate the
more fundamental risks associated with smaller,
lighter vehicles when they are in collision with
larger, heavier vehicles.
3.4 Rechargeable energy storage
systems
The rechargeable energy storage system is
arguably the key component of an electric vehicle.
Batteries are the most common type, but electric
double-layer capacitors and electro-mechanical
flywheels may also be used. Any type of
rechargeable energy storage system has the
potential to be hazardous if it is not designed
carefully, although concerns have been raised in
the literature about batteries in particular [13].
Hazards can emerge during the normal operation
of the battery or during conditions or events
outside its normal operating range. These include
electrolyte/material spillage if individual cell
casings are damaged, the battery‟s reaction to high
external temperatures and fire, and its electrical
properties, for example, under short circuit, over-
voltage and voltage reversal conditions.
UN Regulation 100 deals with the safety of electric
vehicles „in-use‟ and includes specifications that
relate mainly to the protection of users against
electric shock. There are some rudimentary
specifications for rechargeable energy storage
systems, which cover the protection against
excessive current and accumulation of gas. The
main requirement concerning excessive current is
simply that the rechargeable energy storage system
“shall not overheat”. However, if it is subject to
overheating, it must be equipped with a protective
device such as fuses, circuit breakers or main
contactors. Accumulation of gas is controlled by a
requirement to provide a ventilation fan or duct in
places containing an open-type battery that may
produce hydrogen gas.
UN Regulations 94 and 95 (frontal and side impact
respectively) are being amended to include post-
impact electrical safety requirements for electric
vehicles that will cover protection against electric
shock, retention of the rechargeable energy storage
system and electrolyte spillage following the
impact test. As noted in Section 3.2, the
requirements for the rechargeable energy storage
system consider only its movement during the
impact test.
There are no further safety requirements for the
rechargeable energy storage systems in electric
vehicles in EU type-approval. In contrast, the
energy storage system in conventional vehicles,
the fuel tank, must meet the requirements of a
specific EU Directive or corresponding UN
Regulation. These specify a series of component-
EVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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level tests and requirements for liquid fuel tanks.
Similar legislation is in place for hydrogen
storage systems. Developing type-approval
requirements for rechargeable energy storage
systems would harmonise the safety performance
of this key electric vehicle component and would
be consistent with the approach for other
vehicles.
A group of interested experts on rechargeable
energy storage systems was formed in 2010. The
group has prepared a proposal for a series of
amendments to UN Regulation 100 to specify
safety requirements and tests for rechargeable
energy storage systems. The proposals have been
submitted to the Working Party on Passive
Safety (GRSP) of WP.29 and will be discussed
during the 51
st
Session in Geneva on 21-25 May
2012.
The main topics covered by the performance
tests include:
Vibration;
Thermal shock and cycling;
Mechanical shock;
Mechanical integrity;
Fire resistance;
External short circuit protection;
Overcharge protection;
Over-discharge protection;
Over-temperature protection.
In general, there must be no evidence of
electrolyte leakage, rupture, fire or explosion
during each test. However, electrolyte leakage is
assessed by “visual inspection without
disassembling any part of the Tested-Device”.
Since a “Tested-Device” means a complete
rechargeable energy storage system or a
subsystem, including enclosures, it is possible
that electrolyte leakage from cells may not be
detected by this approach (i.e. if the leakage
remains within the main enclosure). This
assumes, therefore, that the principal hazards
relating to electrolyte result from leakage outside
the battery system and its enclosures.
Venting of gas would be permitted by these
requirements and is one means of reducing the
risk of explosion; however, at present, there are
no controls over the type of substances that may
vent, the quantity, and the areas of the vehicle
they may vent into. UN Regulation 100 already
specifies requirements to control the
accumulation of gas, but this is currently limited to
open-type batteries.
The test procedures in the proposed amendments
were derived mainly from ISO 12405 on lithium-
ion traction battery packs and systems (Part 1:
high-power applications, published in 2011, and
Part 2: high energy applications, in draft), with due
consideration also given to the lithium battery tests
in Section 38.3 of the UN Manual of Tests and
Criteria. It is unclear, therefore, to what extent the
procedures (and particularly the requirements) are
relevant for other battery chemistries. Furthermore,
it seems likely that additional procedures and
requirements will be needed to accommodate other
types of rechargeable energy storage systems (i.e.
capacitors and flywheels).
3.5 Acoustic perception
The acoustic emissions from a vehicle in motion
comprise three main elements: noise from the
engine and powertrain; noise from the interaction
between the tyres and the road; and finally, noise
made by air as it flows around the vehicle. At low
speeds (i.e. below 15 20 mile/h) the contributions
of tyre/road noise and aerodynamic noise are
relatively low and hence the powertrain noise is
responsible for most of the acoustic emissions
from the vehicle. Modern vehicles are quieter than
ever, due largely to ever more stringent legislative
requirements. Nevertheless, electric vehicles
typically generate less powertrain noise than
internal combustion engine vehicles.
The lower levels of powertrain noise from electric
vehicles might have implications for the safety of
other road users. For example, cyclists might use
auditory cues to the presence of a vehicle when
executing certain manoeuvres and pedestrians
might use auditory cues when crossing the road.
Visually-impaired pedestrians in particular may
rely on auditory cues. In certain environments (i.e.
where vehicles tend to travel at lower speeds), the
rates of cyclist and pedestrian casualties might
increase if electric vehicles become more
widespread. A study from the United States found
that hybrid electric vehicles engaged in certain low
speed manoeuvres were more likely to be involved
in collisions with cyclists and pedestrians than
internal combustion engine vehicles [14].
However, it was impossible to identify whether
each collision was a result of the cyclist or
pedestrian not seeing/hearing the car or vice versa.
EVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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More recently, a study from the UK found that
relative to the number of registered vehicles,
electric (including hybrid) vehicles were less
likely to be involved in a collision (of any kind)
than an internal combustion engine vehicle, but
were equally likely to be involved in a pedestrian
collision [15]. The authors concluded that while
this potentially supported the perceived increase
in pedestrian risk for electric vehicles, the
accident rates may reflect the usage patterns of
such vehicles.
It seems that the evidence for increased risks to
cyclists and pedestrians from electric vehicles is,
at present, not particularly strong. However, this
may change as more vehicles join the fleet
(particularly if they are used in urban
environments). In the meantime, various external
warning devices are starting to emerge for
electric vehicles [16]. A range of sounds,
including personalised sounds, have been put
forward, although sounds with similar noise
characteristics as conventional engines seem to
be the most favourable countermeasures [17].
The World Forum for Harmonisation of Vehicle
Regulations (WP.29) has determined that electric
vehicles present a danger to pedestrians and has
directed the Working Party on Noise (GRB) to
assess what steps, if any, might be taken to
mitigate pedestrian hazards (through acoustic
means or other means of communication). In
response, GRB has established an informal
working group on quiet road transport vehicles to
determine the viability of “quiet vehicle” audible
acoustic signalling techniques and the potential
need for global harmonisation. The use of “quiet
vehicle” recognises that many internal
combustion engine vehicles are quiet at low
speeds and may need to be included in any future
measures. The activities of the informal group
are ongoing and include a draft proposal for a
UN Global Technical Regulation on audible
vehicle alerting systems for quiet road transport
vehicles.
3.6 Electromagnetic fields
There is some public concern about the effects of
electromagnetic fields on human health,
particularly with respect to fields from mobile
phones and power lines. Some of the research
has produced contradictory results, but in
general, scientific evidence for any effect at the
intensity levels typically found in these situations
remains rather weak [18]. Nevertheless, the
International Commission for Non-ionising
Radiation Protection (ICNIRP) has published
exposure guidelines, based on the avoidance of
established biological effects of electromagnetic
fields.
Concerns have also been raised in the media about
the exposure of electric vehicle occupants to
electromagnetic fields [19, 20]. Electric and hybrid
vehicles give rise to particular concerns because
they use currents and voltages that are much higher
than those used in conventional vehicles, and
which can therefore potentially generate much
higher intensity fields. There is, however, very
little publically-available research on this topic.
One comparison of electromagnetic fields from
different modes of transport concluded that there
was no major difference in fields between electric
vehicles and conventional vehicles [21]. Another,
more recent, study measured electromagnetic
fields in hybrid cars, but found the levels to be
much lower than the ICNIRP guidelines [22]. An
ongoing European 7
th
Framework Project, called
EM-Safety, is also investigating this issue with the
aim of increasing public confidence in the safety of
fully electric vehicles with regards to their
electromagnetic fields (www.sintef.no).
At present, there are no type-approval
requirements for vehicles to address the potential
health effects of electromagnetic fields, arguably
reflecting the lack of any evidence of harm. The
type-approval EU Directive (and corresponding
UN Regulation) for radio interference is intended
to prevent problems with radio reception and with
the functioning of safety equipment on the vehicle.
Vehicle emissions are measured outside the
vehicle. The lowest frequency measured is 30
MHz, well in excess of the frequencies expected
from electric vehicle propulsion components.
3.7 Functional safety
Functional safety relates to the overall safety of a
system and is particularly important for complex
software-based systems. Electric vehicles typically
require greater use of distributed control systems
than conventional vehicles, which can be highly
integrated. However, the focus here is not on these
complex electrical and electronic systems. Instead,
consideration is given to the potential for
unexpected vehicle movements caused by drivers
(or others) being unaware that the vehicle is in an
active mode.
EVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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Electric vehicles could present some potential
functional safety hazards, particularly around the
safe operation of the powertrain by drivers. For
example, if the vehicle is stationary for a period
of time, say in a car park or similar situation, a
driver may forget that the vehicle is capable of
motion. They may leave the vehicle in this
condition, or they may unintentionally activate
the power train.
UN Regulation 100 includes basic functional
safety requirements that deal with the safety of
occupants, but also those outside the vehicle by
preventing (as far as possible) unintentional
vehicle movements. For instance, the regulation
requires that:
At least a momentary indication is given to
the driver when the vehicle is in “active
driving mode”;
When leaving the vehicle the driver must be
informed by a signal if the vehicle is still in
the active driving mode;
Vehicle movement by its own propulsion
system is prevented during charging as long
as the connector of the external power supply
is physically connected to the vehicle inlet;
The state of the drive direction control unit is
identified to the driver.
Several other functional safety requirements
were removed during the most recent amendment
of UN Regulation 100, possibly because
corresponding specifications for conventional
vehicles were not legislated.
As noted in Section 3.1, UN Regulation 100
applies only to passenger and commercial
vehicles (M and N category respectively).
Powered two- and three-wheelers and
quadricycles (L category vehicles) are not
included in the scope. However, the functional
safety hazards discussed above are relevant for L
category vehicles too. For example, a rider might
be sitting on an electric moped or motorcycle in
an “active driving mode” when another person
inadvertently (or intentionally) operates the
throttle. Some form of interlock would be needed
to prevent such an action.
4 Conclusions
1. It was not the intention of this paper to imply
that electric vehicles are inherently unsafe,
or would expose the public to greater risks
than conventional vehicles. Instead, the
focus was on some general hazards and how
they are regulated, particularly under EU type-
approval.
2. The main regulatory acts for EU type-approval
(i.e. EU Directives) tend to lag behind the
corresponding UN Regulations (which are
sometimes recognised as alternatives). This
“lag” is most noticeable when it comes to
provisions for electric vehicles in the safety
legislation.
3. The current approach in the framework
directive is to permit either the EU Directive
or the UN Regulation to be used. In 2014,
Regulation (EC) No. 661/2009 (the general
safety regulation) will come into effect. It will
repeal certain safety directives and will
include references to the appropriate UN
Regulation.
4. A proposal has been made to develop a UN
Global Technical Regulation on electric
vehicles. The proposal envisages safety
provisions for electric vehicles that will cover
electrical safety in everyday use as well as
following a crash. Adopting the proposal will
help to improve global harmonisation on the
safety of electric vehicles.
5. The voltages used in electric vehicles are
potentially very dangerous. However, a range
of safety features are typically used to ensure
the safety of occupants or other persons. In
addition, this aspect of the vehicle is regulated
under UN Regulation 100, which specifies
performance requirements and tests for
protection against direct contact, protection
against indirect contact and isolation
resistance.
6. A collision could compromise the electrical
safety measures in an electric vehicle,
increasing the risk of electric shock for the
occupants (or for the emergency services).
Proposals to amend UN Regulation 94 (frontal
impact) and UN Regulation 95 (side impact)
have been adopted that specify performance
criteria and measurement methods for
protection against electric shock post-impact.
7. Good compatibility is important in a collision,
regardless of the type of power train.
However, while electric vehicles are usually
heavier than equivalent conventional vehicles,
EVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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purely electric vehicles tend to be small cars
and hence there may be implications for our
casualty statistics if the public are
encouraged to downsize to these vehicles in
significant numbers. Furthermore, in the
future, electric vehicles may not require a
conventional structural layout, particularly if
there is a move towards in-wheel motors.
Although compatibility is not currently
considered in vehicle legislation, research is
underway to develop test procedures that are
suitable for legislation and will encourage a
common structural interaction zone.
8. There are a range of potential hazards
associated with rechargeable energy storage
systems. There are currently no safety
requirements for rechargeable energy storage
systems in EU type-approval. However, a
group of interested experts on rechargeable
energy storage systems has prepared
proposals for amendments to UN Regulation
100 to specify safety requirements and
performance tests.
9. The lower levels of powertrain noise from
electric vehicles might have implications for
the safety of other road users, such as
cyclists and pedestrians. Various warning
systems are starting to emerge and a UN
informal working group has been formed to
determine the feasibility of acoustic
signalling techniques and the need for global
harmonisation.
10. There is some public concern about the
effects of electromagnetic fields on human
health, particularly with respect to fields
from mobile phones and power lines.
Electric vehicles have the potential to
generate much higher fields than
conventional vehicles. However, limited
research has been carried out to measure
electromagnetic fields in the passenger
compartment of electric vehicles. In the
meantime, there are no EU or UN type-
approval requirements to deal with the
potential health effects of electromagnetic
fields in electric vehicles.
11. Electric vehicles could present some
potential functional safety hazards,
particularly around the unintended operation
of the powertrain by drivers. However, UN
Regulation 100 includes basic functional
safety requirements that should reduce the
likelihood (as far as possible) of unintentional
vehicle movements.
Acknowledgments
This discussion paper draws heavily from two
previous publications:
[1] Visvikis, C., Morgan, P., Boulter, P., Hardy,
B., Robinson, B., Edwards, M., Dodd, M. and
Pitcher, M. (2010). Electric vehicles: review
of type-approval legislation and potential
risks (Client Project Report 810). Retrieved
May 9, 2011 from http://ec.europa.eu/enter
prise/sectors/automotive/files/projects/rep
ort_electric_vehicles_en.pdf.
[2] Naberezhnykh, D., Gillan, W., Visvikis, C.,
Cooper, J. and Jones, M. (2011). Implication
of the widespread use of electric vehicles for
TRL (TRL Insight Report 010). Crowthorne:
TRL.
Any views expressed in this paper do not
necessarily reflect the views or policies of the
customers for whom these reports were prepared.
Whilst every effort has been made to ensure that
the matter presented in this report is relevant,
accurate and up-to-date, TRL cannot accept any
liability for any error or omission, or reliance on
part or all of the content in another context.
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EVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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Authors
Dinos Visvikis has a broad
background in vehicle safety research,
including research to inform changes
to policy, regulation and assessment
methods. He is currently Head of Low
Carbon Vehicle Safety at TRL and has
developed a detailed knowledge of
new vehicle technologies and their
potential implications for vehicle
safety. He contributes to various
regulatory working groups and
standards committees.
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When the permanent magnet synchronous machine (PMSM) based electric vehicles (EV) are in the postcrash situations, the dc-bus capacitor voltage requires to be reduced quickly for the sake of electric shock risk prevention. Currently, due to the advantages of low cost, compact structure, and high reliability, the pure-winding-based discharge strategies are attracting increasing attentions. However, there are no theoretical criteria for judging whether a pure-winding-based method is suitable for bleeding a particular PMSM-based EV drive, not to mention the rules for opting for an effective discharge strategy among the instant nonzero d -axis, zero q -axis (NDZQ), long-cycle NDZQ, and the nonzero d -axis, nonzero q -axis (NDNQ) current control techniques. This article discusses the applicable occasions of the instant NDZQ, long-cycle NDZQ, and NDNQ discharge methods based on parametric analysis. On this ground the principles for determining whether an EV drive can adopt a pure-winding-based method for discharge are given. Meanwhile, the implementation procedures of the proposed criteria are detailed clearly. Finally, the proposed selection criteria are used for evaluating five different EV drives so as to select the corresponding winding-based discharge strategy for each system, and the effectiveness is verified by simulation or experiments.
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The ever increasing global warming is affecting both the environment and quality of life. The dependency on the usage of fossil fuels for transportation and power generation sector is harming the environment in terms of greenhouse gas (GHG) emissions. To limit the use of fossil fuel, the world has to move towards a renewable, clean, and economical form of energy. In the transportation sector, the paradigm shift towards electric mobility is a step towards the same goal. For a developing country like Pakistan, due to the lacking charging infrastructure, load shedding of electricity, and high cost of non-renewable electrical energy, a country like Pakistan cannot go dependent on fully electric vehicles (EVs). The country has to shift from normal internal combustion engine vehicles (ICEVs) to hybrid electric vehicles (HEVs). This paper aims to select the most sustainable HEV in the context of a developing country, Pakistan. Using the multi-criteria decision making (MCDM) technique, i.e., fuzzy Technique for Order Performance by Similarity to Ideal Solution (TOPSIS), based on ten criteria and seven alternatives, it has been found that Toyota Aqua outperforms among all the other alternatives in terms of economic, social, and environmental perspective. Furthermore, to move towards hybrid technology, the government has to give relaxation in terms of customs duty and should encourage auto manufacturers to set up local industries of such vehicles in the country.
Technical Report
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Summary This report addresses external warning sounds for hybrid and electric vehicles. The purpose of adding external sound at low speeds is to minimise the risk from these quiet vehicles for pedestrians, cyclist and blind persons. The main perspective of the report is to describe signals and systems that minimises the risk and causes as low noise pollution and annoyance as possible. Based on background information about the hearing, sound propagation and the masking effect of the background noise, recommendations are given for the characteristics (levels, frequencies etc.) for optimal warning sounds. Four types of warning sounds and their usage are defined. Besides these recommendations a design guide for the warning sounds is given. Recommendations are given for external sound generation systems. It is found that such sys-tem needs to be based on at least two loudspeakers one pointing forward and one backward to minimize noise pollution and to make the signals audible in the driving direction. The warning sounds need to be optimized for audibility, suitability and annoyance. Listening test methods for this optimisation are described. The method for audibility defines the concept of dBALICE, i.e. the A-weighted sound pressure level of a warning sound that gives the same audibility level as a reference internal combustion engine sound. Instrumental measuring methods for documentation of signals and systems are defined. It is concluded that optimal warning sounds and good sound systems will make it possible to generate sufficient warning sounds with much less noise pollution than from vehicles with internal combustion engines.
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The electrically propelled vehicle makes use of various technologies and is thus faced with diverse standardization and regulation cultures. The relevant standardization landscape is a complex one, particularly if new energy vectors such as hydrogen are taken into account. The growing interest for the deployment of (hybrid) electric drive technology has given rise to specific standardization issues, which are being tackled by specific technical teams. Currently enforced rating standards to evaluate the performance of ground vehicles must in fact be adapted to hybrid electric vehicles, with particular problems arising when considering plug-in hybrids which use both fuel and mains electricity. New standards are needed to evaluate the potential benefits of the hybrid systems against the future vehicle requirements within specifically applicable bounds and regulations. The paper highlights current evolutions in the field, discussing the ongoing work programme of international standardization committees (particularly ISO TC22 SC21 and IEC TC69), and more particularly the interaction between these committees. Special attention will be given to a number of pending issues such as the definition of reliable performance and energy consumption tests for plug-in hybrid vehicles with both fuel and electricity energy supply, the specific need for infrastructure standardization and the impact of the introduction of new technologies such as hydrogen on vehicle safety standardization. The paper will report on activities in this field, providing direct feedback from the international standardization shopfloor, and will recommend specific work areas for standardization, highlighting the potential interaction of ongoing international standardization activities.
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Electricity is used substantially and sources of electric and magnetic fields are, unavoidably, everywhere. The transportation system is a source of these fields, to which a large proportion of the population is exposed. Hence, investigation of the effects of long-term exposure of the general public to low-frequency electromagnetic fields caused by the transportation system is critically important. In this study, measurements of electric and magnetic fields emitted from Australian trams, trains and hybrid cars were investigated. These measurements were carried out under different conditions, locations, and are summarised in this article. A few of the measured electric and magnetic field strengths were significantly lower than those found in prior studies. These results seem to be compatible with the evidence of the laboratory studies on the biological effects that are found in the literature, although they are far lower than international levels, such as those set up in the International Commission on Non-Ionising Radiation Protection guidelines.
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One way to improve vehicle's fuel economy is to reduce its weight. Reducing weight, however has other consequences. One of these is reduced vehicle size. Almost invariably, lighter vehicles are smaller. Reducing vehicle weight has also been associated with a reduction in occupant protection; the lighter the vehicle, the greater the chance of injury when a crash occurs. For this study, a data-based model is used to evaluate the independent effects of size and weight. This model is constructed using the NASS database and information obtained from NCAP tests. The results indicate that although mass is the dominant factor, size also has an effect; some of the observed reduction in safety benefits associated with mass reduction is actually an effect of size reduction. The model is also used to evaluate the effects of varying stiffness. A counterintuitive finding is that increasing the stiffness of the vehicle to reduce compartmental intrusion in severe impacts may not offer an overall improvement in safety. Finally, the model is used to give insights into the effects of reducing the variance of the mass distribution in the vehicle fleet. This shows that the smaller the mass distribution variance, the lower the injury risk.
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This research, conducted under the support of the Federal Electric and Magnetic Field Research and Public Information Dissemination (EMF RAPID) Engineering Program, characterized the extreme-low-frequency (ELF) electric and magnetic fields (EMF) which a traveler might encounter while using various forms of transportation. Extensive measurement of field level, frequency, temporal variability and spatial variability are reported for: conventional internal-combustion cars, trucks and buses; electric cars, trucks and buses; commuter trains; ferry boats; jetliners; airport shuttle trams; and escalators and moving sidewalks. Static magnetic field levels are also reported. Where possible, the source of the fields is identified. This effort extends extensive past work which investigated field in electrified trains, subways, light rail vehicles, and a magnetically levitated train by using similar protocols to characterize the complex ELF (3 Hz to 3000 Hz) electric and magnetic fields found in virtually all transportation systems.
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One interaction between environmental and safety goals in transport is found within the vehicle fleet where fuel economy and secondary safety performance of individual vehicles impose conflicting requirements on vehicle mass from an individual’s perspective. Fleet characteristics influence the relationship between the environmental and safety outcomes of the fleet; the topic of this paper. Cross-sectional analysis of mass within the British fleet is used to estimate the partial effects of mass on the fuel consumption and secondary safety performance of vehicles. The results confirmed that fuel consumption increases as mass increases and is different for different combinations of fuel and transmission types. Additionally, increasing vehicle mass generally decreases the risk of injury to the driver of a given vehicle in the event of a crash. However, this relationship depends on the characteristics of the vehicle fleet, and in particular, is affected by changes in mass distribution within the fleet. We confirm that there is generally a trade-off in vehicle design between fuel economy and secondary safety performance imposed by mass. Cross-comparison of makes and models by model-specific effects reveal cases where this trade-off exists in other aspects of design. Although it is shown that mass imposes a trade-off in vehicle design between safety and fuel use, this does not necessarily mean that it imposes a trade-off between safety and environmental goals in the vehicle fleet as a whole because the secondary safety performance of a vehicle depends on both its own mass and the mass of the other vehicles with which it collides.
Development of body structure for crash safety of the newly developed electric vehicle (Paper No. 11- rEVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium 13 0199)
  • H Uwai
  • A Isoda
  • H Ichikawa
  • N Takahashi
Uwai, H., Isoda, A., Ichikawa, H. and Takahashi, N. (2011). Development of body structure for crash safety of the newly developed electric vehicle (Paper No. 11- rEVS26 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium 13 0199). In: Proceedings of the 22nd International Technical Conference on the Enhanced Safety of Vehicles, 13- 16 June 2011, Washington, DC. Washington, DC: NHTSA.
Crash safety of hybrid- and battery electric vehicles (Paper No. 11-0096) Traffic Safety
  • R Justen
  • R Schöneburg
Justen, R. and Schöneburg, R. (2011). Crash safety of hybrid- and battery electric vehicles (Paper No. 11-0096). In: Proceedings of the 22nd International Technical Conference on the Enhanced Safety of Vehicles, 13- 16 June 2011, Washington, DC. Washington, DC: National Highway Administration (NHTSA). Traffic Safety
Risk in connection with electric vehicles
  • A Viladot
  • I Palsson
  • H Jonsson
  • H Torstensson
Viladot, A., Palsson, I., Jonsson, H. and Torstensson, H. (1999). Risk in connection with electric vehicles (SSPA Research Report No. 111). Gothenburg, Sweden: SSPA Sweden AB.