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OPPORTUNITY CHARGING OF BUSES. EFFECTS ON BUS OPERATOR COSTS AND USER PERFORMANCE

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Transit systems are a key strategy to reduce the use of private cars and mitigate congestion episodes in major cities. Transit networks can be operated by different kinds of transit technology (Bus, BRT, LRT or Subways). In recent years, the deployment of high performance bus systems (HPB) has provided competitive user travel times, comparable to Light Rail Transit Systems, at reasonable capital expenditures. However, there is already a pending issue to be addressed. As Subways and Light rail transit systems take the energy to move the rolling stock from electric power plants, the vast majority of HPB vehicles are powered by internal combustion or hybrid engines. Therefore, these bus systems are responsible for the emission of a huge quantity of pollutants that contributed to the global warming problem (GHG) or worsened the health of the citizens in metropolitan areas. In order to tackle this problem, the European Union are fostering the deployment of electric bus vehicles in the operation of European cities. Hence, the implementation of these electric buses, will contribute in the reduction of the fossil fuel consumption, carbon dioxide (CO2) emissions and local air pollution, by improving energy efficiency. Those standard buses (12 meters long) operating routes during a daily shift of 12 hours or less can be charged at bus garage (depot) at the end of the service. This slow charging operation takes 2-5 hours and does not have any effect on the user performance and does not imply further vehicles. However, for those bus routes requiring articulated buses or 12 hours or more of continuous service, the bus batteries should be charged during the service. This operation is known as opportunity charging. It consists of an on-street fast-charging operation of bus batteries and present two available schemes: (i) charging at ending / starting bus stops in each line direction and (ii) charging at intermediate stops of the bus route. The former scheme will maintain the in-vehicle travel time, but the time spent at ending stops (lay-over time plus slacks) is usually higher than the conventional diesel-engine powered vehicles. This fact causes that bus operator would need additional vehicles to operate the bus route at the desired headway. Additionally, when the required charging time is greater than the target headway, we would perform charging operations with multiple charging points in tandem or in parallel at the end of the route. This operating requirement is usually incompatible with the limited public space in urban areas. The latter scheme may increase both in-vehicle travel time and fleet size if the charging operation is made at stops with low passenger boarding rates. The aim of this paper is to analyse the effect of the opportunity charging constraints on the operation of bus services. The total number of resources (vehicles and chargers) as well as the travel time of users is assessed by an analytical model that resembles the bus operation for each electric charging scheme. This model is also able to estimate the corresponding operating variables for diesel buses. The aforementioned variables are translated into a monetary value in order to estimate the total cost of the bus system (in Euros per hour of service). The best bus technology is therefore found identifying the lowest value of the total system cost variable. The effects of opportunity charging have been estimated on the bus route H6 and H16 in Barcelona. The opportunity charging at the ending stops results to be the optimal charging scheme. It also implies a total cost reduction of 4,000 Euros/day, in comparison with diesel engine technology. This opportunity charging implies one additional vehicle due to the additional time spent at ending stops. Under perfect regularity, if the unit consumption rate is lower than 2.5kWh/km, the deployment of 1 charging station at each ending stop (1-1) is enough to guarantee the operation at the desired headway. However, if the energy consumption factor is greater than this threshold, the bus operator will need the 2-2 configuration (two servers at each stop). Nevertheless, if we consider the real time headway adherence of buses, the 1-1 configuration is not able to guarantee the dispatching of buses at the target time headway. In those cases, we need to deploy 2 chargers at each ending stop. The main conclusion is that bus regularity should be controlled in order to minimize the extra-cost caused by the electrification of buses.
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1
OPPORTUNITY CHARGING OF BUSES. EFFECTS ON BUS OPERATOR
COSTS AND USER PERFORMANCE
Dr.MiquelEstrada
AssociateProfessor,DepartmentofCivilandEnvironmentalEngineering,UPCBarcelona
TECH.
JosepMensión
DirectorCentralServicesandDeputyChiefOfficerofBusNetwoek,TransportsMetropolitans
deBarcelona
Dr.MiquelSalicrú
FullProfessor,StatisticsDepartment,UniversitatdeBarcelona
1. INTRODUCTION
Transit systems are a key strategy to reduce the use of private cars and mitigate
congestion episodes in major cities. Transit networks can be operated by different
kinds of transit technology (Bus, BRT, LRT or Subways). In recent years, the
deployment of high performance bus systems (HPB) has provided competitive user
travel times, comparable to Light Rail Transit Systems, at reasonable capital
expenditures. However, there is already a pending issue to be addressed. As Subways
and Light rail transit systems take the energy to move the rolling stock from electric
power plants, the vast majority of HPB vehicles are powered by internal combustion or
hybrid engines. Therefore, these bus systems are responsible for the emission of a
huge quantity of pollutants that contributed to the global warming problem (GHG) or
worsened the health of the citizens in metropolitan areas. In order to tackle this
problem, the European Union are fostering the deployment of electric bus vehicles in
the operation of European cities. Hence, the implementation of these electric buses,
will contribute to the reduction of the fossil fuel consumption, carbon dioxide (CO2)
emissions and local air pollution, by improving energy efficiency.
Those standard buses (12 meters long) operating routes during a daily shift of 12 hours
or less can be charged at bus garage (depot) at the end of the service. This slow
charging operation takes 2-5 hours and does not have any effect on the user
performance and does not imply further vehicles. However, for those bus routes
requiring articulated buses or 12 hours or more of continuous service, the bus batteries
should be charged during the service. This operation is known as opportunity charging.
It consists of an on-street fast-charging operation of bus batteries and present two
available schemes: (i) charging at ending / starting bus stops in each line direction and
(ii) charging at intermediate stops of the bus route. The former scheme will maintain
the in-vehicle travel time, but the time spent at ending stops (lay-over time plus slacks)
is usually higher than the conventional diesel-engine powered vehicles. This fact
causes that bus operator would need additional vehicles to operate the bus route at
the desired headway. Additionally, when the required charging time is greater than the
target headway, we would perform charging operations with multiple charging points
in tandem or in parallel at the end of the route. This operating requirement is usually
2
incompatible with the limited public space in urban areas. The latter scheme may
increase both in-vehicle travel time and fleet size if the charging operation is made at
stops with low passenger boarding rates.
The aim of this paper is to analyse the effect of the opportunity charging constraints on
the operation of bus services. The total number of resources (vehicles and chargers)
is assessed by an analytical model that resembles the bus operation for each electric
charging scheme. This model is also able to estimate the corresponding operating
variables for diesel buses. The effects of opportunity charging have been estimated on
the bus route H6 and H16 in Barcelona.
2. ESTIMATION OF OPERATING VARIABLES
The usage of electric vehicles will imply new operating schemes and kinematic
characteristics (acceleration, deceleration, commercial speed) that may vary both the
number and type of resources to be deployed in the bus route. In this section, the
operating issues to analyze the performance and agency cost of BEB electric buses in
comparison to ICE vehicles are presented on a given single route. This analysis is
based on the models explained embraced in Piccioni, C. and A. Musso (2017), where
the authors contributed in estimating the effects of opportunity charging in the
operation of urban bus lines.
For the sake of simplicity, we consider the route of Figure 1 that presents 2N bus stops
located along the whole length, where the position of each stop is denoted by s. Stops
s=1 and s=N denote the starting points for each route direction trip.
Figure 1. Schematic illustration of a bus route. Source: Estrada et al. 2016
Let M be the total number of buses operating the whole roundtrip. The gross
commercial speed of this bus route is estimated as the quotient of the route length (L)
over the vehicle travel time in each direction (R), excluding the time spent at the ending
stops of each direction. The total average travel time of a single bus (R) in both
directions can be estimated by Equation (1):
3
𝑅
𝑇
𝑟,𝑠
𝑇
𝑝,𝑠
𝑇
𝑠
𝑁
𝑠1
𝑇
𝑟,𝑠
𝑇
𝑝,𝑠
𝑇
𝑠
2𝑁
𝑠N
1
(1)
The expression of equation (1) is the sum of three time components in each segment
between stop s and s+1 for both route directions: the average running time (Tr,s), the
average time spent at intersections (Tp,s) and the average time spent at stop s (Ts).
Nevertheless, disruptions make it difficult to maintain the time-headway adherence of
buses and control the transit system performance. A traditional way to reduce this
effect is to introduce slack times in bus schedules at determined stops (holding points)
along the route, which affects the roundtrip travel time; and consequently the fleet size
M. In Estrada et al (2016) the slack time strategy is explained as the inclusion of an
additional amount of time in the bus schedule at certain stops.
Therefore, in Equation (2) the potential holding time (φs) is introduced in schedule at
stop s in order to compensate potential service disruptions (if it exists). Although slacks
could have been implemented at any stop s (s=1, …, 2N), bus agencies prefer that
holding times be performed only at the ending stop of each direction of service (also
called headers) to maintain time-headway adherence (s=N and s=2N). The reason is
that, at these ending stops all onboard passengers must alight, so the term does not
infer any additional travel time for passengers. Therefore, holding times are usually
φs=0 for s=1,..;N-1; N+1,..,2N-1.
𝑅
𝑅
φ
𝑠
𝑁
𝑠1

φ
𝑠
2𝑁
𝑠N
1
(2)
When we are wondering to estimate the fleet size needed, the roundtrip travel time
should consider the time spent by buses at the ending stop of each route direction AB
and BA (see Figure 1). At these ending stops s= 2N (A) and s=N (B) the bus schedule
usually encompasses the lay-over times θA and θB to let drivers rest for an amount of
time. This extra time is defined by a mandatory labour rule for each agency and it is
independent of the slack time devoted at holding points.
Finally, the total travel time (T) including those time spent at ending stops is determined
in Equation (3). The net commercial speed vc to be considered to estimate the fleet
size is defined by Equation (4).
𝑇𝑅′𝜑
𝐴
𝜃
𝐴
𝜑
𝐵
𝜃
𝐵
(3)
𝑣
𝑐
𝐿
𝑇𝐿
𝑇
𝑟,𝑠
𝑇
𝑝
,𝑠
𝑇
𝑠
𝜑
𝑠
𝑁
𝑠1
𝑇
𝑟,𝑠
𝑇
𝑝
,𝑠
𝑇
𝑠
𝜑
𝑠
𝜑
𝐴
𝜃
𝐴
𝜑
𝐴
𝜃
𝐴
2𝑁
𝑠N1
(4)
Therefore, the estimation of the fleet size (M) provided in Equation (5) will be composed
by a term that represents the minimal number of vehicles needed to provide a time-
headway (R/H), and an additional number of vehicles (B/H) to ensure the resting time
4
for the drivers at the ending stops and the holding times to perform the system
coordination by slacks along the route, where
𝐵𝜃
𝐴
𝜃
𝐵
𝜙
𝐴
𝜙
𝐵
𝜙
𝑠
𝑁
𝑠
1
𝜙
𝑠
2𝑁
𝑠
N
.
𝑀𝑇
𝐻𝑅𝐵
𝐻
(5)
In fact, the term B captures the sum of all unproductive times and should present a
number as low as possible to minimize inefficiencies.
2.1. OPERATING CONSTRAINTS CAUSED BY THE BATTERY
CHARGING SCHEMES
The average unit distance energy consumption of a bus depends on the weather
conditions, slope of the route, congestion, density of stops. It ranges between 1-2.5
kWh/km (12 meters long standard bus) and 2-4 kWh/km (18 meter long articulated
bus). In addition to that, BEB need to maintain the State of Charge (SOC) of their
batteries in a given domain of operation defined by the manufacturer (for example
0.2<SOC<0.8) to ensure the guaranteed cycle life (number of discharge-charge cycles
that the battery can handle). This fact, introduces more constraints in the operation
scheme of the electric route. Although there is enough room in the roof or base of the
bus chassis to accommodate the battery pack, the main limitation it’s the maximal
weight. Due to this fact, BEB vehicles cannot be in service during the whole daily shift.
It can be stated that there is not any fully- electric articulated bus of 18 meters of length
in the market (or even an articulated bus prototype) able to provide continuous service
(15-16 hours per day) with an initial charge at the bus garage. All of them need on-
route charging operations at charging stations located along the route to maintain the
actual SOC under the target domain.
Generally, there are three types of charging operation of the bus batteries depending
on the range of the vehicles:
Bus garage charging. This charging operation usually takes 2-5 hours (slow
charging) and is performed during the night period at bus garage, once the BEB has
finished the service.
Opportunity charging. This charging scheme is undertaken when the available SOC
range of the batteries does not allow the provision of the required daily vehicle mileage
between two consecutive charging operations at bus garage. In those cases, fast
charging stations should be deployed along the route to provide enough energy to
maintain the SOC level at the recommended values. Therefore, the charging operation
is made on-street during the service. There are two operations schemes known as
opportunity charging depending on the location of the charger points:
Opportunity charging at the ending stop of each route direction. The charging operation
can be made at the ending stops of the route direction, taking 3-8 minutes.
Opportunity charging at intermediate stops of a route direction. This option reduces the
battery weight and size. As there are several charging points along the route, the SOC
5
can be more frequently rebalanced with fast charging operation at bus stops. It allows
the usage of super capacitors in vehicles, elements of higher energy power and lower
energy capacity. In that situation, each charging operation can be done in 10-30
seconds.
The charging time at depot or, specially, at on-street charging stations, is the new
crucial decision variable in an electric operation system. This variable encompasses
one component needed to provide the target amount of electricity according to the
planned range between two consecutive charging operations. This electric charging
time
𝑇
𝑐ℎ,𝑥
is proportional to the length Lx travelled between two consecutive charging
points, to the vehicle energy consumption fc and to the inverse value of the recharging
speed of the station, S . Additionally, the initiation of the charging operation needs that
bus driver has parked the vehicle properly in the on-street charging platform and the
pantograph equipped in the vehicle (or other substitutive device) is fully spread out to
connect to the charging voltage arch. This operation takes an additional prepositioning
time Tpo. Therefore, the total time devoted to the charging operation (Tco,x) is defined
by the sum of the electric charging time and prepositioning time (Equation 6)
𝑇
𝑐𝑜,𝑥
𝐿
𝑥
𝑓
𝑐
S𝑇
𝑝𝑜
(6)
Depending on the value of this charging time estimated by Equation (6), the agency
cost might rise because more vehicles might be needed. Moreover, the total charging
time at the header stops will determine whether one or more charging points at these
stops are needed. We identified three different situations in which the number of
resources or the sequence of the charging operation may differ. The following
conditions have been analyzed considering a tough assumption: vehicles arrive
regularly at bus stops and the time headway adherence is excellent.
Case 1. The charging operation time needed at each ending stop A or B is lower than
the corresponding lay-over time
𝑇𝑐𝑜,𝐴 𝜃𝐴
,
𝑇
𝑐𝑜,𝐵
𝜃
𝐵
,
. In these cases, there is
enough time at bus headers to complete the charging time without introducing more
idle time in the schedule. The roundtrip travel time T is maintained by the expression
𝑇𝑅′𝜑𝐴𝜃𝐴𝜑𝐴𝜃𝐴
. Note that the slack time introduced in the target bus
schedule is not considered in this evaluation. Delayed buses can recover the headway
adherence with the vehicle ahead at the expenses of being held a time t at the ending
stop A, where
𝜃
𝐴
𝑡𝜑
𝐴
𝜃
𝐴
. A similar condition can be provided at bus header
B replacing the variables
𝜃
𝐴
;𝜑
𝐴
by
𝜃
𝐵
;𝜑
𝐵
.
Case 2. The charging operation time is higher than the lay-over time but still lower than
the headway, H (i.e.
𝜃
𝐴
𝑇
𝑐𝑜,𝐴
𝐻
or
𝜃
𝐵
𝑇
𝑐𝑜,𝐵
𝐻
). In these situations, buses
need to spend an additional time at charging or header stations to perform the charging
operation. The term of lay-over time, θA at bus header A should be replaced by the
charging operation time, Tco,A (in bus header B we need to replace lay-over times by
6
the corresponding charging operation time Tco,B). Consequently, the new roundtrip time
considering the time spent at bus headers (T’) is now defined by Equation (7).
𝑇𝑅𝜑𝐴𝜑𝐵max
𝜃𝐴;𝑇𝑐𝑜,𝐴
max
𝜃𝐵;𝑇𝑐𝑜,𝐵
(7)
Additionally, the additional number of vehicles needed to provide service is estimated
by means of Equation (8) with regard to a regular bus that only spent lay-over and
holding times at ending stops:
∆𝑀𝑇
𝑇
𝐻
(8)
Case 3. The charging operation time is higher than the target headway. In these
situations, we need to increment the number of charging positions or platforms at
ending stops and allow bus charging operations in parallel or tandem servers. Parallel
charging layout is not usually feasible in urban streets. Moreover, the deployment of
the tandem servers is also affected by the distance between two consecutive
intersections in a common block. Therefore, the maximal number of tandem servers
would be limited to 2-3 servers. In that way, if we refer the number of servers as Ns at
each ending stop, the necessary condition to allow the dispatching of vehicles at each
H time period is stated by Equation (9).
𝑇
𝑐𝑜,𝑥
𝑁
𝑠
𝐻
(9)
3. DISCUSSION
In this section, we will focus on specific bus route planning examples to quantify the
effects of electric operation. In fact, we will analyze the H6 and H16 bus routes of the
new bus system in Barcelona. To do so, we will consider the operation in perfect
headway-adherence.
H6 is a straight-shaped route that connects several university campus (Zona
Universitaria) and new business areas to residential districts (Fabra i Puig), running
along quite congested streets and avenues. The line presents a target time headway
of H= 4.72 min, with 23 buses operating the roundtrip service, and a total passenger
flow of 1400 pax/h in the period of study. The line has a mandatory layover time of 3
minutes and an additional slack time of s= 3 minutes for tackling bus bunching at each
ending stop of each route direction. The capacity of these buses is 134 pax/veh. The
line is 19.3 km long with 49 bus stops.
Additionally, we have also analyzed the H16 bus route that connects Zona Franca to
the Forum district along the sea front of Barcelona city. This line is 24.2 km long and
presents 67 bus stops. We consider the same layover time (3 minutes) at each bus
direction however the slack time is now higher (4 minutes). The layout and lengths of
each direction of service in both bus routes H6 and H16 are characterized in Figure 2
and Table 1.
7
Figure 2. Layout of the bus route H6 (left) and H16 (right) operated by TMB (major bus
agency in Barcelona city).
Table 1. Length of the direction trips in route H6 and H16.
Trip H6 route H16 route
Garage to origin A 15.86 km 4.11 km
One way trip, A-B 9.59 km 12.21 km
Return trip, B-A 9.74 km 11.99 km
Destination B to
Garage 4.08 km 12.88 km
We consider that these bus routes will be fully operated with the vehicle tested in the
Barcelona demonstration in the framework of ZeEUS project. This is a fully electric bus
of 18 meters of length manufactured by Solaris. Once the pilot test will have been
completed, it is supposed that the whole fleet in route H16 and H6 will consist of this
vehicle typology. The most important electric attributes of these vehicles will be the
following: a) the nominal capacity of the battery pack is 125kWh, b) the speed of the
charging station is 6.67kWh/min and c) the available SOC can be always kept equal
or higher than 40% (conservative value considered by the bus operator in the pilot
test). We will consider only charging points at the header stops. For the analysis we
consider six different alternatives of charging point layout:
Deployment of 1 charging point at route origin A – 0 charging points at route origin B .
Deployment of 0 charging points at route origin A – 1 charging point at route origin B.
Deployment of 1 charging point at route origin A – 1 charging point at route origin B.
8
Deployment of 2 charging points at route origin A –0 charging points at route origin B.
Deployment of 0 charging points at route origin A –2 charging points at route origin B.
Deployment of 2 charging points at route origin A –2 charging points at route origin B.
Additionally, we consider a given range of the energy consumption factor of (2.5; 3.5)
kWh/km. This range has been estimated considering the information provided by the
bus manufacturer from its in-house tests and the weather conditions in Barcelona.
Therefore, the electric feasibility range of the batteries has been verified for an energy
consumption variation of 0.1KWh/km. This range is supposed to encompass the real
consumption that these vehicles will have in real operation. Table 2 and Table 3
summarize the final results obtained in this energy consumption range for the proposed
charging schemes in route H6 and H16 respectively. The columns determine whether
the solution is feasible or not in terms of headway adherence (), and the SOC
consumption (, lower than 60%). The temporal suitability for charging the battery and
the maintenance of a convenient headway, depends on the charging and manoeuvre
or prepositioning time. This time should be lower or equal to the headway of the line.
If the scenario is time- feasible, the column will have a green “V”, otherwise it will have
a red “X”. The battery scheme is feasible (green “V”) in the scenario, as long as the
battery consumption in the trip under analysis does not exceed the 60% of the nominal
battery capacity. If this constraint is violated, a red “X” will be displayed in the column.
We also consider the integer number of vehicles needed to provide the service. In
those cases when the charging time is greater than the lay-over time, the number of
vehicles can be increased.
Table 2. Feasibility analysis of electric charging schemes in route H6 (Barcelona).
Table 3. Feasibility analysis of electric charging schemes in route H16 (Barcelona).
M
(veh)
M
(veh)
M
(veh)
M
(veh)
M
(veh)
M
(veh)
2.5 VV 24 XV24 XV24 VV24 VV24 VV 24
2.6 VV 24 XV25 XV25 VV25 VV25 VV 24
2.7 VV 24 XV25 XV25 VV25 VV25 VV 24
2.8 XV24 XV25 XV25 VV25 VV25 VV 24
2.9 XV24 XV25 XV25 VV25 VV25 VV 24
3XV24 XV25 XX25 XV25 XX25 VV 24
3.1 XV24 XV25 XX25 XV25 XX25 VV 24
3.2 XV24 XV25 XX25 XV25 XX25 VV 24
3.3 XV24 XV25 XX25 XV25 XX25 VV 24
3.4 XV25 XV25 XX25 XV25 XX25 VV 25
3.5 XV25 XV25 XX25 XV25 XX25 VV 25
2‐2
Chargingpointsdistributionscheme
Uni t
Consumption
(kWh/km)
1‐1 1‐0 0‐ 1 2‐0 0‐2
9
From the results of route H6 presented in Table 2, there are critical unit consumption
factors that define three different charging schemes. For low energy consumption (<2.8
kWh/km), the best charging point distribution scheme is the deployment of 1 charging
station at both ending bus stops (scheme 1-1 with chargers at Zona Universitària A
and Fabra i Puig B). This scheme only needs 24 vehicles to operate the service and
fulfil the dispatching of vehicles at the desired time headway as well as the sufficient
range of the batteries. When the energy consumption ranges between 2.8-3kWh/km,
there are two potential charging distributions: the 2-0 (or 0-2) and 2-2 scheme. The
former scheme has just 2 charging stations but needs an extra vehicle (25 operating
vehicles). The latter implies 2 extra charging stations but maintains the fleet size at 24
vehicles. Generally, for costs purposes, we will prefer the scheme 2-2 that reduces
one operating vehicle than reducing charging stations. This statement is also justified
by safety deployment reasons.
However, for unit energy consumption factors higher than 3 kWh/km, the only feasible
scheme is the deployment 2 charging stations at each origin and destination (A and B)
of the route. In that case, for energy consumption factors higher than 3.4kWh/km, the
route will need an extra vehicle (25 vehicles in service). The reason is that vehicles
must spend more time charging at ending stops and this fact increases the roundtrip
travel time.
The most restrictive constraint to ensure the feasibility of the service from the results
is the headway adherence (). In fact, 0-1 and 1-0 schemes never allow dispatching
bus vehicles at the desired headway. In those cases, the charging time at the bus
header is greater than the headway. However, all six charging schemes guarantee a
sufficient range for operating the two route directions. Some of them are not able to
guarantee the minimal available 40% of SOC in the trip between the more distant stop
with regard to the bus garage (schemes 0-1 and 0-2). In those cases, the origin of the
route without charging point (point A) is 15.96 km away from the bus garage, and the
bus had previously run the distance between points B-A in service (9.74 km).
The results in route H16 (Table 3) are more homogeneous since lay-over times at bus
headers and time headway are higher. These facts allows that charging operation can
be done simultaneously with the rest of drivers and vehicles are dispatched less often.
In that route, the most efficient charging scheme is the 1-1 for all energy consumption
factor domain considered. Schemes 1-0 or 0-1 can never maintain the target headway.
M
(veh)
M
(veh)
M
(veh)
M
(veh)
M
(veh)
M
(veh)
2.5 VV 20 XV21 XV21 VV21 VV21 VV20
2.6 VV 21 XV21 XV21 VV21 VV21 VV21
2.7 VV 21 XV21 XV21 VV21 VV21 VV21
2.8 VV 21 XV21 XV21 VV21 VV21 VV21
2.9 VV 21 XV21 XV21 VV21 VV21 VV21
3VV 21 XX21 XV21 VX21 VV21 VV21
3.1 VV 21 XX21 XX21 VX21 VX21 VV21
3.2 VV 21 XX21 XX21 VX21 VX21 VV21
3.3 VV 21 XX21 XX21 VX21 VX21 VV21
3.4 VV 21 XX21 XX21 VX21 VX21 VV21
3.5 VV 21 XX21 XX21 VX21 VX21 VV21
Chargingpointsdistributionscheme
Uni t
Consumption
(kWh/km)
1‐1 1‐0 0‐ 1 2‐0 0‐ 2 2‐ 2
10
4. CONCLUSION
The deployment of battery electric buses (BEB) will have an important effect on the
route operational planning. Some buses can provide 12-14hours of continuous service
between two consecutive charging operations. However, articulated buses or standard
buses operating long daily shifts (higher than 14 hours) currently need opportunity
charging to maintain the daily mileage.
The provision of BEB in busy bus routes with low time headways (headway less than
6 minutes) is a challenge. In case they need opportunity charging, the necessary
charging time at the ending stop of one route direction will require higher holding times
at final stops than in diesel buses. Indeed, this charging time would be usually higher
than the target headway. This fact would imply that multiple charging platforms at the
ending stop need to be deployed to perform charging operations simultaniously at
different vehicles. Although parallel charging servers would be preferable, the
limitations of urban layout only admit tandem charging points, distributed along the
right lane. On the other hand, if this charging operation is made at intermediate stops,
the dwell time at stops would be increased, causing higher passenger in-vehicle travel
times. In both opportunity charging alternatives (ending or intermediate stops), the
number of vehicles required to provide the service at the target headway can be higher
than diesel vehicles.
The effects of opportunity charging have been estimated on the bus route H6 and H16
in Barcelona. The opportunity charging at the ending stops results to be the optimal
charging scheme. This opportunity charging implies one additional vehicle due to the
additional time spent at ending stops. Under perfect regularity, if the unit consumption
rate is lower than 2.5kWh/km, the deployment of 1 charging station at each ending
stop (1-1) is enough to guarantee the operation at the desired headway. However, if
the energy consumption factor is greater than this threshold, the bus operator will need
the 2-2 configuration (two servers at each stop). Nevertheless, if we consider the real
time headway adherence of buses, the 1-1 configuration is not able to guarantee the
dispatching of buses at the target time headway. In those cases, we need to deploy 2
chargers at each ending stop. The main conclusion is that bus regularity should be
controlled in order to minimize the extra-cost caused by the electrification of buses.
REFERENCES
Estrada, M.,Mensión, J.,Aymamí, J.M., Torres, L. (2016). Bus control strategies in
corridors with signalized intersections. Transportation Research Part C 71, 500-520.
Piccioni, C. and A. Musso (2017). Deliverable 42.6. Training material for University
workshops. ZeEUS. Zero Emission Urban Bus System Project. European
Commission
... La recarga rápida de oportunidad durante el recorrido puede realizarse en las terminales (durante el servicio, luego de terminar un recorrido y previo a iniciar el próximo) o en paradas intermedias del circuito. Dependiendo del tiempo de recarga y la frecuencia del servicio, el primer método puede requerir mayor superficie y cargadores rápidos para recargar más de un autobús a la vez en las terminales; mientras que el segundo puede ralentizar el servicio, especialmente si los cargadores están instalados en paradas con bajos volúmenes de embarque y desembarque de pasajeros(Estrada et al., 2017).20 Para más detalles, ingresar en ZevAlliance (último acceso 14/08/2020). ...
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Following the growing trend for electric passenger cars, due to their lower environmental and climate impacts, a trend towards the electrification of public transport is emerging, particularly regarding urban buses. However, the reliability of the service offered by electric alternatives to diesel-powered buses and the costs of the related transition have not been fully explored. In this background, we simulated the transition to electric bus powertrains for two bus lines in Locarno (Southern Switzerland) and compared the currently available electric technologies and charging schemes, based on their level of operation and their overall cost. According to these simulations, "opportunity charging" schemes emerged as the most promising ones for such urban lines in Locarno. Nonetheless, in the short-term their introduction is still hindered by barriers, such as in particular: the lack of capability to guarantee the service in case of delays above three minutes, the higher cost (between 40% and 60% higher than Euro VI diesel buses, which is also hampered by cashback on diesel custom duties), the need for proper training by the transport company staff, and the time needed to install the charging stations.
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This paper proposes a new dynamic bus control strategy aimed at reducing the negative effects of time-headway variations on route performance, based on real-time bus tracking data at stops. In routes with high demand, any delay of a single vehicle ends up causing an unstable motion of buses and producing the bus bunching phenomena. This strategy controls the cruising speed of buses and considers the extension of the green phase of traffic lights at intersections, when a bus is significantly delayed. The performance of this strategy will be compared to the current static operation technique based on the provision of slack times at holding points. An operational model is presented in order to estimate the effects of each controlling strategy, taking into account the vehicle capacity constraint. Control strategies are assessed in terms of passenger total travel time, operating cost as well as on the coefficient of headway variation. The effects of controlling strategies are tested in an idealized bus route under different operational settings and in the bus route of highest demand in Barcelona by simulation. The results show that the proposed dynamic controlling strategy reduces total system cost (user and agency) by 15–40% as well as the coefficient of headway variation 53–78% regarding the uncontrolled case, providing a bus performance similar to the expected when time disturbance is not presented.