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Is Design Guidance for Roads incomplete?

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A consultation on draft high level guidance for road design of streets in town and city centers in Northern Ireland ended in October 2013. The addition to the guidance through this proposal needs examples to allow designers to apply the high level guidance mentioned in practical situations. For mixed use developments in Northern Ireland designers have to apply the Design Manual for Roads and Bridge (DMRB) and seek formal departures and relaxations through the planning service in order to gain approval for proposals for a development. This is an unwieldy process and recognizing this, the authorities in England, Scotland and Wales have moved to provide design guidance. Northern Ireland has therefore fallen behind in in this respect. Seven case studies in the Belfast City Council area which is the largest council in Northern Ireland are used in this paper to provide a gap analysis in the existing legislation and suggest ways the current consultation proposal could be implemented on the ground.
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194
Proc. of the Second Intl. Conf. on Advances In Civil, Structural and Environmental Engineering- ACSEE 2014.
Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved.
ISBN: 978-1-63248-030-9 doi: 10.15224/ 978-1-63248-030-9-41
Is Design Guidance for Roads incomplete?
Dr. Robert Eadie, Dr. Phillip Millar and Mr. John Boyle
Abstract A consultation on draft high level guidance for
road design of streets in town and city centers in Northern
Ireland ended in October 2013. The addition to the guidance
through this proposal needs examples to allow designers to apply
the high level guidance mentioned in practical situations. For
mixed use developments in Northern Ireland designers have to
apply the Design Manual for Roads and Bridge (DMRB) and
seek formal departures and relaxations through the planning
service in order to gain approval for proposals for a development.
This is an unwieldy process and recognizing this, the authorities
in England, Scotland and Wales have moved to provide design
guidance. Northern Ireland has therefore fallen behind in in this
respect. Seven case studies in the Belfast City Council area which
is the largest council in Northern Ireland are used in this paper to
provide a gap analysis in the existing legislation and suggest ways
the current consultation proposal could be implemented on the
ground.
KeywordsHighways, Legislation, Design, Guidance
I. Introduction
TransportNI comprise the sections of the Department of
Regional Development (DRD), the overseeing authority in
Northern Ireland, that deal with Highway issues [1]. In the UK
the Design Manual for Roads and Bridges (DMRB) [2] is the
geometric design standard used for trunk roads including
motorways. The DMRB was initially produced in 1992 in
England and was subsequently adapted for Scotland, Wales
and Northern Ireland [3]. TransportNI are responsible for
overseeing its application in Northern Ireland. Two other
design guides have been jointly produced by TransportNI for
guidance on new residential developments and private
accesses:Creating Places (Residential Design) [4] and
Development Control Advice Note 15 (DCAN15) (Private
Access Design) [5]. The role of these documents in the
geometric aspects of design for Highways in Northern Ireland
is summarised in Table1.
Dr Robert Eadie and Dr Phillip Millar
University of Ulster
United Kingdom
Corresponding Author email r.eadie@ulster.ac.uk
Mr John Boyle
RPS Consulting Engineers
United Kingdom
TABLE I. CURRENT DESIGN GUIDANCE
This demonstrates a gap in the literature relating to mixed
use developments that do not have a residential section. The
Creating Places document [4] states “This guide is intended
for use in the design of all proposals for residential
development throughout Northern Ireland, from small-scale
infill housing schemes to major projects on large sites
incorporating a mix of uses. This limits the Creating Places
guidance to sites with a residential element.
II. Identified Gap in Guidance
The Creating Places document [4] was published in 2000
for Northern Ireland use only. In England and Wales, Design
Bulletin 32 [6] and Places Streets and Movement documents
[7] remained in use up to 2007, when the Manual for Streets
(MfS1) [8] was published. This defined a street as a highway
“that has important public realm functions beyond the
movement of traffic” and “Most highways in built up areas
can therefore be considered as streets”.
Early (2007) [9] highlighted that the publication of the
MfS1 [8] still did not close the knowledge gap for secondary
streets and stated that the Department of Transport was
considering drawing up new guidance on their design. Early
(2007) [9] clearly identified the gap in England and Wales by
stating that high streets, secondary retail streets and those
connecting residential areas fall between the Manual for
Streets and the DMRB which was prepared for motorways and
trunk roads.
Design Guidance
Geometric Applicability
Design Manual of Roads and
Bridges (DMRB)
Trunk Roads
Creating Places
Residential Developments
Development Control Advice
Note 15
Private Access Design
195
Proc. of the Second Intl. Conf. on Advances In Civil, Structural and Environmental Engineering- ACSEE 2014.
Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved.
ISBN: 978-1-63248-030-9 doi: 10.15224/ 978-1-63248-030-9-41
An attempt has been made to fill this gap in England and
Wales by the publication of Manual for Streets 2 (MfS2) in
2010 [10]. This states “MfS2 builds on the guidance
contained in MfS1, exploring in greater detail how and where
its key principles can be applied to busier streets and non-
trunk roads, thus helping to fill the perceived gap in design
guidance between MfS1 and the Design Manual for Roads and
Bridges (DMRB)”. MfS2 was published as a companion guide
to the Manual for Streets (MfS1)”.
Scotland followed in 2010, producing a policy statement
for Scotland called Designing Streets [11]. Again this was
predominantly for the design of residential streets but widened
the application of the design principles to include high streets
and other higher traffic volume streets in order to close the
gap.
In Northern Ireland the gap in the design guidance was
acknowledged in 2013 when the Urban Stewardship and
Design Guide (USDG) on design of streets was submitted for
public consultation [12]. However, this draft documentation
has not provided geometric design properties for streets. The
aim of the USDG is to establish the key principles behind
good place making. It is at a higher level than the calculations
required for street design seeking to inform those involved in
managing (stewardship) and making (design) urban places.
The design element concentrates on visualisation and access
rather than highway design. Therefore the status quo remains.
Early (2007) cites Duggan stating that Because there is a
policy gap the DMRB gets pulled down for secondary roads.”
Applying the rigour of highway design in the DMRB TD 9/93
Table 3 [2] for high speed roads in a mixed use development
can result in problems being created.
III. Case Study indicating
Problems with using DMRB for
Mixed Use Developments
RPS were appointed as consulting engineers for Titanic
Quarter in Belfast to prepare a detailed master plan for the
development [13]. One section of the design entailed a new
22.5m wide section of street with a 30mph speed limit in this
mixed use, residential, retail, office and leisure development.
To fit with the architectural master plan it was required to
provide reverse back to back 127m horizontal radii to fit
between the buildings.
Had the DMRB design criteria been applied, a 7% super
elevation would have been needed for this street creating over
1m of level difference from one side to the other. Coupled
with this level difference the super elevation would have
required to switch from one side to the other within a short
distance due to the reverse curve. This would upset the visual
appearance of the scheme.
This illogical approach to the design of this street
necessitated the application for formal departures from the
Overseeing Organisation to depart from the onerous DMRB
standards, which gives no consideration to a street lined with
trees and adjoined by apartments, shops and offices. This calls
for a separate design guide specifically for mixed use
developments. This paper seeks through correlating the results
of a number of case studies which used departures from the
DMRB standards with the codes in England to provide
guidance for certain street design criteria in mixed use
developments.
IV. Method
This paper reviewed seven randomly selected case studies
at existing locations in Northern Ireland where roads have
been designed, approved, constructed and operational for a
period of more than one year. However, the geometric
properties of these locations fail to meet the standards set out
in the DMRB and required relaxations of the DMRB design
standards. The case studies include accident statistics from the
Police Service of Northern Ireland to prove that reduced
standards can still be applied safely. The criteria used for
selection of case studies were:
1. The scheme was an existing city or town centre
street;
2. It included an existing city or town centre
junction, and;
3. Had geometry which is below the current design
standards.
The case studies from Belfast were:-
1. Sydenham Road Queens Quay in relation to a
relaxation for Horizontal Alignment and stopping
sight distance.
2. Donegall Quay Albert Square in relation to a
relaxation for Horizontal Alignment and stopping
sight distance.
3. Cromac Street in relation to a relaxation to cross-
section and lane width.
4. Victoria Street in relation to a relaxation to cross-
section and lane width.
5. Linenhall Street Donegall Square South in
relation to a relaxation for junction visibility
6. Adelaide Street Ormeau Avenue in relation to a
relaxation for junction visibility and on-street
parking.
7. Lisburn Road Osborne Drive in relation to a
relaxation for junction visibility and on-street
parking.
These case studies allow investigation of two sites for each
of horizontal alignment, cross-section and lane width, stopping
sight distance, and on street parking. Three examples of
relaxations for junction visibility are also provided.
196
Proc. of the Second Intl. Conf. on Advances In Civil, Structural and Environmental Engineering- ACSEE 2014.
Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved.
ISBN: 978-1-63248-030-9 doi: 10.15224/ 978-1-63248-030-9-41
V. Case Study 1 - Sydenham Road
/ Queens Quay - Horizontal
Alignment and stopping sight
distance
Figure 1 indicates the layout of this junction
Figure 1 Sydenham Road / Queens Quay
Traffic flows on this street were 1358 AM and 1405 PM.
The horizontal curvature at the junction is 30m. This is at the
entrance to the development alongside the car park and not
near any of the residential units on the mixed use
development. Therefore the curvature parameters from Table 3
from the DMRB should apply resulting in a minimum curve of
90m and super elevation of 7%. No super elevation is present
and the gully levels on both sides of the carriageway would
confirm this. This geometry is therefore sub-standard in terms
of the application of the DMRB design guidance.
Furthermore, the measured stopping sight distance around
the horizontal curvature is 60m. This would not seem to be
predominantly residential location as there are no apartments
or houses in direct vicinity therefore the stopping sight
parameters from Table 3 from the DMRB should apply
resulting in a required stopping sight distance of 90m with a
one step below desirable minimum of 70m.
Despite this the accident database indicates a single serious
accident between 2006 and 2010 with one casualty outside the
area of the red circle indicated on Figure 1, therefore not
directly related to the junction.
VI. Case Study 2 - Donegall Quay
Albert Square - Horizontal
Alignment and stopping sight
distance
Figure 2 indicates the layout of this junction
Figure 2 Donegall Quay / Albert Square
Traffic flows on this street were much heavier than Case
Study 1 at 2525 AM and 3047 PM. The horizontal curvature at
the junction is 21m. This area is predominantly office and
retail accommodation and again the curvature parameters from
Table 3 from the DMRB should apply. This again results in a
minimum curve of 90m and super elevation of 7%. Only a
slight super elevation is present evidenced in the gullies being
present only on the inside of the curve. This geometry is
therefore sub-standard in terms of the application of the
DMRB design guidance.
Furthermore, the measured stopping sight distance around
the horizontal curvature is 45m. Again this is not a
predominantly residential location and the parameters from
Table 3 from the DMRB should apply resulting in a required
stopping sight distance of 90m with a one step below desirable
minimum of 70m.
Again the Accident database indicates only a single slight
collision with a single casualty between 2006 and 2010. The
single casualty fell into the slightly injured category.
VII. Case Study 3 - Cromac Street -
cross-section and lane width
Figure 3 provides details of the street.
Figure 3 Cromac Street
2.54m
197
Proc. of the Second Intl. Conf. on Advances In Civil, Structural and Environmental Engineering- ACSEE 2014.
Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved.
ISBN: 978-1-63248-030-9 doi: 10.15224/ 978-1-63248-030-9-41
Traffic flows on this street were 2873 AM and 2310 PM.
There are retail units, houses and apartments in the vicinity of
this location. However, in the foreground of Figure 1 the street
does not directly serve these residential units therefore the lane
widths indicated in the DMRB Volume 6, Section 1, Part 2,
TD 27/05 and TD 9/93 Clause 5.65 should apply. There is no
specific guidance on lane widths within the DMRB for a 4
lane section of urban street with designers using the only
comparable cross section of the Dual 2 Lane Carriageway
(D2UAP) which is an urban all-purpose road and requires lane
widths of 3.65m and a central reserve. Cromac Street has 4
lanes, 2 in either direction with no central reserve.
Figure 4 provides details of the accidents in Cromac Street
from 2006-2010. The Accident database records the 4 not at
junctions as slight collisions with 14 casualties. A closer
examination of the locations of these incidents reveals that
these are the ones indicated on Figure 4 that are not at junction
locations or in queues of traffic leading to junctions.
This indicates that the lane width is not a criterion for the
majority of accidents on this stretch of carriageway. Casualties
were not in the killed, seriously injured or slightly injured
categories, indicating they were involved but injury was very
minor.
Figure 4 Accidents Cromac Street
VIII. Case Study 4 - Victoria Street -
cross-section and lane width
Figure 5 provides details of the street. Traffic flows on this
street were 2221 AM and 3736 PM. There are mainly retail
units and office accommodation in the vicinity of this location.
Again the lane widths indicated in the DMRB Volume 6,
Section 1, Part 2, TD 27/05 and TD9/93 should apply. There is
no specific guidance on lane widths within the DMRB for a 5
lane section of urban street.
Figure 5 Victoria Street
Designers use the only comparable cross section of the
Dual 2 Lane Carriageway (D2UAP) which is an urban all-
purpose road and requires lane widths of 3.65m and a central
reserve. This section would also require central reserve with
hard strips and a hard shoulder. Victoria Street has 5 lanes and
is one way which means no central reserve is provided.
Figure 6 provides details of the accidents in Victoria Street
from 2006-2010. The Accident database records the three
incidents not at junctions as slight collisions with five
casualties. The locations of these incidents are the ones
indicated on Figure 6 that are not at junction locations or in
queues of traffic leading to junctions.
This indicates that the lane width is not a criterion for the
majority of accidents on this stretch of carriageway. Again,
casualties were not in the killed, seriously injured or slightly
injured categories, indicating they were involved but injury
was very minor.
Figure 6 Accidents Victoria Street
198
Proc. of the Second Intl. Conf. on Advances In Civil, Structural and Environmental Engineering- ACSEE 2014.
Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved.
ISBN: 978-1-63248-030-9 doi: 10.15224/ 978-1-63248-030-9-41
IX. Case Study 5 - Linenhall Street
Donegall Square South in
relation to a relaxation for
junction visibility
Figure 7 provides details of the junction
.
Figure 7 Linenhall Street Donegal Square South Junction
At this junction the measured junction visibility provides
an x-distance of 4.5m and a y-distance of 90m. This is not a
predominantly residential area due to the presence of offices
and retail and it is also not a private access. Therefore neither
Creating Places nor DCAN15 are applicable. This means the
stopping sight parameters from the DMRB including those in
TD 9/93 Table 3 and TD 42/95 paragraphs 7.6c and 7.8 should
apply resulting in a junction visibility zone with an x-distance
of 9.0m and a y-distance of 90m. However a relaxation to
4.5m for the x-distance is allowable for lightly trafficked
simple junctions. The visual assessment has also shown that
there are trees, lamp posts and other obstructions within the
visibility envelope which would not be allowed.
Despite this the accident database indicates two slight
collisions between 2006 and 2010 with three casualties. Again,
casualties were not in the killed, seriously injured or slightly
injured categories, indicating they were involved but injury
was very minor.
X. Case Study 6 - Adelaide Street
Ormeau Avenue in relation to a
relaxation for junction visibility
and on-street parking.
Figure 8 provides details of the junction. At this junction
the measured junction visibility provides an x-distance of
4.5m and a y-distance of 90m. This is not a predominantly
residential area due to the presence of offices and retail and it
is also not a private access therefore neither Creating Places
nor DCAN15 are applicable.
Figure 8 Adelaide Street Ormeau Avenue Junction
This means the stopping sight parameters from the DMRB
including TD 9/93 Table 3 and TD 42/95 paragraphs 7.6c and
7.8 should apply resulting in a junction visibility zone with an
x-distance of 9.0m and a y-distance of 90m. However a
relaxation to 4.5m for the x-distance is allowable for lightly
trafficked simple junctions. The visual assessment has also
shown that there are trees, street lighting, and car parking
within the visibility zone which would not be allowed. There
is also a signalised pedestrian crossing in close proximity to
the junction which would not be allowed.
The accident database indicates three collisions in close
proximity to this junction between the years 2006-2010. The
collisions have been classified as one serious and two slight
collisions. Again, the three casualties were not in the killed,
seriously injured or slightly injured categories.
XI. Case Study 7 - Lisburn Road
Osborne Drive in relation to a
relaxation for junction visibility
and on-street parking.
Figure 9 provides details of the junction
.
Figure 9 Lisburn Road Osbourne Drive Junction
199
Proc. of the Second Intl. Conf. on Advances In Civil, Structural and Environmental Engineering- ACSEE 2014.
Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved.
ISBN: 978-1-63248-030-9 doi: 10.15224/ 978-1-63248-030-9-41
At this junction the measured junction visibility provides
an x-distance of 4.5m and a y-distance of 90m. The measured
junction visibility at Case Study No.7 is an x-distance of 4.5m
and a y-distance of 90m. This junction could be classed as a
private access from a residential area to a main road and
therefore DCAN15 should apply to this access. The
application of DCAN15 is then dependant on the traffic flow
using the junction. As the access has a traffic flow of over
1000 vehicles per day then the desirable minimum x-distance
should be 6m however this may be relaxed to 4.5m. The y-
distance for the access should be 70m based on a vehicle
speed of 31mph on the Lisburn Road. The visual assessment
has also shown that there are trees, car parking and street
lighting within the visibility envelope of the junction which is
not allowed.
XII. Conclusions and
Recommendations.
The case studies above support the following suggestions
in respect of design criteria for preliminary geometric street
design through interpolation of values from the DMRB and
MFS1/MFS2 and application of reasoning from the analysed
case studies. The case studies suggest a division of streets into
three main categories, Primary, Secondary and Shared
Carriageways having the following definitions:
1. Primary A main heavily trafficked street with
multiple lanes and used by pedestrians, cyclists, cars, delivery
vehicles and buses (Example - Case Studies 3 and 4).
2. Secondary A secondary access street with a
medium volume of traffic for access to developments used by
pedestrians, cyclists, cars and delivery vehicles (Example -
Case Study 1)
3. Shared Surfaces A minor street with low traffic
volume used by pedestrians, cyclists, cars and small delivery
vans (Example - Case Study 7).
The first two case studies support the determination of
proposals for horizontal and vertical alignment. The DMRB
TD 9/93 Table 3 [2] stipulates a minimum allowed horizontal
curve for a 50kph design speed of 90m with a super elevation
of 7%. The next radius above that is 127m with a super
elevation of 7%. The ratio of difference between these two
figures is 0.7. Manual for Streets 2 recommends minimum
radii on based on minimum v²/R values providing 28.28; this
could be adopted. Applying the ratio of difference of 0.7 to
90m gives a radius of 65m and a subsequent radius of 44m.
The case studies 1 and 2 indicate that these values would be
safe. The DMRB TD 9/93 Clause 4.1 [2] specifies a value of
6% gradient for single carriageways; this should be maintained
where possible. However Case studies 1 and 2 prove further
flexibility can be given for secondary and shared streets.
Desirable minimum lane widths of 3.65m should be
achieved as per DMRB TD9/93 Clause 5.56 on primary
routes. Case studies 3 and 4 indicate Clause 3.14 value of
3.5m at pinch points can also be safely reduced.
The MFS1Figure 7.1 [8] suggests an absolute minimum
value of 2.75m for lane width with no allowance for cyclists.
Case study 3 shows that narrow lanes of 2.54m can function
without a direct impact on safety. Therefore the minimum
value in the MFS1of 2.75m can be adopted for streets.
The minimum allowed stopping sight distance for a 50kph
design speed in the DMRB TD9/93 Table 3 [2] is 70m with a
one step below value of 50m. Manual for Streets provides a
Table 7.1 indicating 43M as the minimum including bonnet
length. From the evidence of Case Studies 2, 5, 6 and 7, 45m
is safe so the MFS1 value should be adopted.
Further work needs to be carried out to confirm the
findings of this limited number of case studies. Should the
work confirm the findings of this paper it is suggested that the
values proposed be incorporated into guidance for streets in
Northern Ireland in the proposed publication of the Living
Places document.
References
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