Design manual
Design Manual for Urban Roads and Streets
The design of roads and streets within urban speed limits.
Department of Transport, Tourism and Sport and Department of Housing, Planning and Local Government · 2019 (version 1.1) · 165 pages
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- 99May 2019 (Version 1.1) Figure 4.52: Extract from the National Cycle Manual (2011) which illustrates the appropriate use of integrated or segregated cycle facilities according to the volume and speed of traffic. 4.3.5 Cycle Facilities This Manual and the National Cycle Manual (2011) (NCM) promote cycling as a sustainable form of transport and seek to rebalance design priorities to promote a safer and more comfortable environment for cyclists. To achieve these goals, the NCM recognises the importance of slowing vehicular traffic within cites, towns and villages, and advocates many of the measures contained within this Manual, such as narrower vehicular carriageways and tighter corner radii. The principle source for guidance on the design of cycle facilities is the NCM published by the National Transport Authority. The NCM provides designers with a comprehensive set of design measures aimed at achieving an overall quality of service that is appropriate to user needs. Figure 4.52, from the NCM, provides an overview of the integration and segregation of cycle traffic within the carriageway based on vehicle speeds and traffic volumes. For example: • On lightly-trafficked/low-speed streets, designers are generally directed to create Shared Streets where cyclists and motor vehicles share the carriageway • On busier/moderate speed streets, designers are generally directed to apply separate cycle lanes/cycle tracks. Designers must also have regard to the measures contained within this Manual when applying the NCM. For example: • To minimise the width of vehicular carriageways from kerb to kerb, preference should be given to the implementation of Raised Cycle Lanes or Raised Cycle Tracks over those design solutions where cyclists and vehicles are at grade.
- Design Manual for Urban Roads and Streets100 Figure 4.53: Example of a narrow verge between a cycle track and on-street parking. This verge provides a buffer that protects cyclists from opening doors. 0.75-1.0m • Cycle facilities on most streets within Centres, Neighbourhoods and Suburbs will need to be integrated with on-street parking. Pages 138-139 and 149 of the NCM illustrate how this can be achieved with Cycle Lanes. Figures 4.53 and 4.54 illustrate this with regard to a Cycle Track. • To reduce clutter, the use of hatching, bollards and signage associated with cycle facilities should be minimised within areas with a higher place value such as Centres, Neighbourhoods and Suburbs. A similar logic may be applied in respect of the requirements for signage and line marking within the NCM as with the application of the Traffic Signs Manual (2010), refer Section 4.2.4 Signage and Line Marking. The NCM also makes several references to the Traffic Management Guidelines (2003). As the Traffic Management Guidelines precede this Manual many of these references may no longer be relevant and designers should refer to the corresponding principles, methods and standards contained within this Manual.29 29 For comparison between the road classification system used within the National Cycle Manual (2011) and Traffic Management Guidelines (2003) designers should refer to Table 3.1. Figure 4.54: Extract from page 86 of the National Cycle Manual illustrating how to re-establish from an Off Road Cycle Track to Cycle Lane on approach to a junction. This design can be adapted to cater for onstreet parking by placing spaces within the green area or verge between the vehicular carriageway and Cycle Track.
- 101May 2019 (Version 1.1) 4.4 Carriageway Conditions 4.4.1 Carriageway Widths Research from the UK has found that narrow carriageways are one of the most effective design measures that calm traffic.30 The width of the vehicular carriageway is measured from kerb to kerb or from the outside line of a Cycle Lane or from the edges of parking spaces (where the latter facilities are provided). Designers should minimise the width of the carriageway by incorporating only as many lanes as needed to cater for projected vehicle flows and by reducing the size of individual lanes to meet predominant user needs (see Figure 4.55). In this regard: • In new designs the standard lane width on Arterial and Link Streets should lie in the range of 2.75m to 3.5m. Within this range the preferred values are 3.0m and 3.25m. The selected values within the overall range will depend on the following: - the function and context of the street - the number of large vehicles using the street - access requirements and frequency of accesses - the overall number of lanes - the need for lane width reductions at pinch points • The standard carriageway width on Local streets should be between 5-5.5m (i.e. with lane widths of 2.5-2.75m). • Where additional space on Local streets is needed to accommodate additional manoeuvrability for vehicles entering/ leaving perpendicular parking spaces, this should be provided within the parking bay and not on the vehicle carriageway (see Section 4.4.9 On-Street Parking and Loading). • The total carriageway width on Local streets where a shared surface is provided should not exceed 4.8m. 30 Refer to Figure 7.16 of UK Manual for Streets (2007). On heavily-trafficked Arterial and Link streets with multiple lanes (see Section 3.4.5 Noise and Air Pollution) in urban areas designers should consider the street as Boulevard with a median that is no less than 2m wide to provide areas of pedestrian refuge and allow for the planting of large trees. When carrying out upgrades, or trafficcalming works on existing streets, the first priority of authorities should be to narrow existing carriageways where they exceed those standards listed above. This will not only calm traffic, but will free up additional space within the street reserve to widen footpaths, insert cycle lane/tracks, provide bus lanes, street trees and on-street parking (all of which will further contribute to traffic calming).
- Design Manual for Urban Roads and Streets102 FIGURE 4.55: CARRIAGEWAY WIDTHS (note: Illustrations do not include cycle facilities) Carriageway widths for heavily-trafficked Arterial and Link streets in boulevard configuration. Main carriageway suitable for moderate design speeds. Includes access lanes with a lower design speed. 6-6.5m 6-6.5m6-6.5m 6-6.5m2.75-3m 2.75-3m Standard carriageway widths for multi lane Arterial and Link streets in boulevard configuration, including bus lanes. Standard lane/carriageway widths for multi lane Arterial and Link streets, including bus lanes. Range for low to moderate design speeds. 5.5-6.5m3-3.25m 3-3.25m Carriageway width for Local streets with a shared surface carriageway. Standard carriageway width for Local streets Carriageway width for Arterial and Link streets frequently used by larger vehicles. 6.5-7m 5-5.5m 4.8m Standard carriageway widths for Arterial and Link streets. Range for low to moderate design speeds. 5.5-6.5m
- 103May 2019 (Version 1.1) 4.4.2 Carriageway Surfaces The material, texture and colour of the carriageway are important tools for informing drivers of driving conditions. Research has found that the use of robust surface materials (such as block paving) can reduce vehicle speeds by 4-7 km/h alone.31 The use of paving, imprinted or looser materials (combined with no kerbing, see Section 4.4.8 Kerbs) is one of the clearest ways of reinforcing a low-speed environment and of signalling to all users that a the main carriageway is to be shared (see Figure 4.56). The use of such surfaces also adds value to place, particularly in historic settings. With regard of surface types: • The use of standard materials, such as macadam/asphalt should generally be confined to streets with moderate design speeds (i.e. 40-60km/h). • Where low design speeds (i.e. 30km/h) are desirable changes in the colour or texture of the carriageway should be used periodically, such as at crossings or at strategic locations, such as Focal Points. • Where shared carriageways are proposed (i.e. 10-20 km/h) changes in colour and texture should be applied to the full length of the street. The use of robust finishes may also be used, on all streets, for the full carriageway where large numbers of pedestrians congregate. Such treatments should be considered in Centres (i.e. along shopping streets), in all urban areas around Focal Points and adjacent to schools, squares, parks and other areas where vulnerable pedestrians are present (see Figure 4.57). Designers should also consider the use of at-grade material changes (up to 25mm in height) such as at crossings, particularly on streets with more moderate speeds and where the aim is not to require large reductions in speed but to alert drivers of a change in driving conditions ahead (see Figure 4.58). 31 Refer to Section 7.2.15 of the UK Manual for Streets (2007). Figure 4.58: Examples from Tallaght, Co. Dublin of a robust surface material (including a slight vertical deflection) designed to add value to place and increase pedestrian safety by alerting/slowing vehicles on approach to the crossing. Figure 4.57: Example from Chapelizod, Co. Dublin, where the carriageway has been paved adjacent to a square in a village centre to add value to place and calm traffic in an area of higher pedestrian activity. Figure 4.56: Example from Adamstown, Co. Dublin of a shared surface ‘homezone’ adjacent to a school. Paving materials, combined with embedded kerbs encourage a low speed shared environment.
- Design Manual for Urban Roads and Streets104 Figure 4.59: Left turning slips (left) generally offer little benefit in terms of junction capacity and increase the number of crossings pedestrians must navigate. They also allow vehicles to take corners at higher speeds, exposing pedestrians and cyclists to greater danger. Where a large number of turning movements occur, left turning lanes (right) with tighter corner radii should be used. 4.4.3 Junction Design Junction design is largely determined by volumes of traffic. As noted in Section 3.4.2 Traffic Congestion, the design of junctions has traditionally prioritised motor vehicle movement. Designers must take a more balanced approach to junction design in order to meet the objectives of Smarter Travel (2009) and this Manual. In general designers should: • Provide crossings on all arms of a junction. • Reduce kerb radii, thereby reducing crossing distances for pedestrians and slowing turning vehicles (see Section 4.3.3 Corner Radii). • Omit left turn slips, which generally provide little extra effective vehicular capacity but are highly disruptive for pedestrians and cyclists. Where demand warrants, they may be replaced with left tuning lanes with tighter corner radii (see Figure 4.59). • Omit staggered crossings in favour of direct/single phase crossings (see Section 4.3.2 Pedestrian Crossings). • Omit deceleration lanes. These are not required in low to moderate speed zones (i.e. up to 60km/h). • Include pedestrian, cyclist and bus passenger delays in the optimisation of traffic signal phasing and timings. This will almost certainly lead to a reduction in cycle times. • Minimise waiting with pedestrain cycle times of no more than 90 seconds at signalised junctions (see Section 4.3.2 Pedestrian Crossings). Designers should also have regard to Context and Function when selecting junction types (see Figure 4.60). Junction design will also need to be considered in conjunction with crossing types and ratio of flow to capacities (see Sections 4.3.2 Pedestrian Crossings and 3.4.2 Traffic Congestion).
- 105May 2019 (Version 1.1) Traffic Signals These can provide a wide range of capacities depending on the widths of the approaches, the presence of bus lanes on approach, cycle times and turning traffic flows. Traffic signal junctions can include pedestrian phases and advanced stoplines for cyclists, thus making them safer. Traffic Signals should generally be used at all junctions between Arterial and Link streets. Where pedestrian activity is particularly high (such as within a Centre or around a Focal Point), designers may apply all-round pedestrian phase crossings with diagonal crossings. Roundabouts These have a wide range of capacities depending on the size and geometry of the roundabout, its approaches, and turning traffic flows, but are generally lower than signalised junctions. Large roundabouts are generally not appropriate in urban areas. They require a greater land take and are difficult for pedestrians and cyclists to navigate, particularly where controlled crossings/cycle facilities are not provided, and as such, vehicles have continuous right of way. The use of large roundabouts (i.e. those with radii greater than 7.5m) should be restricted to areas with lower levels of pedestrian activity. Where large roundabouts currently exist, road authorities are encouraged, as part of any major upgrade works, to replace them with signalised junctions or retrofit them so that are more compact and/or pedestrian and cycle friendly, as is appropriate. The use of more compact roundabouts (i.e. those with a radii of 7.5m or less) may address many of the issues highlighted above and may also be useful as a traffic-calming measure. These may be considered where vehicle flows are not sufficient to warrant full signalisation, such as on Links, and pedestrian activity is more moderate, such as in Suburbs and Neighbourhoods, provided they are appropriately fitted with the appropriate pedestrian crossings. JUNCTION CONTROL Figure 4.60: General junction selection based on the optimising pedestrian and cyclist movement whilst also balancing the needs of motor vehicle users. Standard Signalised Junctions. Areas of moderate pedestrian/high-moderate vehicular activity. Signalised junction with all-round pedestrian phase crossing. Areas of high pedestrian and vehicular activity. Mini or shared roundabouts with informal crossings. Areas of low pedestrian activity. Uncontrolled Junctions. Areas of lower/moderate pedestrian and vehicular activity. Priority Junction. Areas of lower/moderate pedestrian and vehicular activity.
- Design Manual for Urban Roads and Streets106 Section 4.8 of the National Cycle Manual (2011) also contains further guidance on the design and use of roundabouts to make them more pedestrian and cycle friendly. With regard to the application of these models. • Where compact roundabouts are proposed, designers may apply the Mini or Shared roundabout models. • The use of large roundabouts, such as the Segregated Track on Roundabout or Fully Segregated Roundabout, should be restricted to areas where pedestrian activity is low (as noted above). The application of these models may be acceptable where it is proposed to retrofit an existing roundabout to make it more pedestrian and cycle friendly. Designers may also consider the use of shared space/informal roundabouts within low speed environments, such as Centres. These junctions incorporate the design characteristics of a shared space junction (i.e. no kerbs, paved surfaces etc) with circular features placed at the centre and edges. Examples of roundabout type features (sometimes referred to as ‘roundels’) have been successfully implemented in the UK on heavily trafficked junctions with the effect of enhancing place, calming traffic and increasing cyclist/pedestrian mobility (see Figure 4.61). Priority Junctions (i.e. Stop and Yield junctions). These generally have low capacity and are appropriate for low to medium flows. They should generally be applied where Local streets meet Arterial or Link streets. Uncontrolled Junctions These generally have low capacity and rely on informal communication between drivers. They should generally be used where vehicle flows are low, such as those between Local streets. Designers may also consider the use of shared space junctions at busier junctions within low speed environments, such as Centres. There are also examples of uncontrolled shared space junctions which cater for higher flows without signalisation (see Figure 4.62 and Section 4.3.4 Pedestrianised and Shared Surface Streets). Figure 4.61: Examples from Ashford, UK (top) and Poynton, UK (bottom). The placement of a circular features with the shared space/ traffic calmed environment creates an informal roundabout with fewer restrictions pedestrian/ cyclist movement when compared to more conventional types (image sources: Hamilton- Baillie Associates and Ashford Borough Council). regulations that would have imposed black and white chevrons and reflective stripes on his corten steel centrepiece sculpture. Not-a-roundabout, the tree grilles and the bollards have been installed, but not all of his superb granite seats seem likely to be commissioned due to pressure on scheme finances. Nayan Kulkarni conducted a zonal study that provided a rationale for the colour and intensity of Flume the linear floorscape sculpture by Simeon Nelson, runs down Bank Street and east along Elwick Road, making an artistic link between the town centre and the International Station. It is an elegant work that adds an intelligent presence to street scene. rking with many good artists small. A key consideration that s the previous experience re well aware that the timing the Ashford project would essure to complete their d then their detailed design e. was to facilitate the integrated come a part of the new e also wanted to introduce do this we created a brief programme of challenging transport theme. After y was selected and his ost O took Ashford by storm. d significant works for the UK, including Portland Centre. His work with the n section of the ring road, a een re-scheduled for the future be found on prominent sites hought his bold style, with ms, would work well with the cape architects Whitelaw laboration allowed John to its entirety and contribute his Simeon Nelson is an artist with an interest in the shared languages and underlying aesthetic concerns that occur within different art forms. He also has a passion for exploring how humans and nature interact, and his work frequently involves collaborations with structural engineers, biologists, dancers and others. In his work he uses analogies and metaphors from science, philosophy and theology, made manifest in physical (often fractal) forms. Michael Pinsky takes on the multiple roles of artist, activist, planner and provocateur, and social space as much as physical space provides the context for his work. In response to a brief, which asked him to mark the passing of the ring road, and to explore issues of public space through sometimes playful and subversive means, he conceived a multi-artist temporary works programme that was delivered during the middle of the construction period, which resonates in Ashford to this day. Inevitably Breaking Boundaries had both wins and losses. Not every collaboration proved to be a ‘marriage made in heaven’, yet some thrived wonderfully well and are still thriving and developing in other projects, in Ashford and elsewhere. This is invariably the way with integrated design team working. Some relationships spark the creative process and produce much more than the sum of the parts. Others never quite get there and the Figure 4.62: Example from Coventry, UK of a shared surface uncontrolled junction. The level of traffic using the junction would normally warrant some form of control, however, its traffic calmed nature allows for drivers to communicate with each other and pedestrians to establish movement priorities (image source: Hamilton-Baillie Associates).
- 107May 2019 (Version 1.1) 4.4.4 Forward Visibility Forward Visibility, also referred to as Forward Sight Distance (FSD), is the distance along the street ahead which a driver of a vehicle can see. The results of research carried out by Transport Research Laboratory UK (TRL) for the UK Manual for Streets (2007) found that reducing forward visibility is one of the most effective measures used to increase driver caution and to reduce speeds.32 The minimum level of forward visibility required along a street for a driver to stop safely, should an object enter its path, is based on the Stopping Sight Distances (SSD). The SSD has 3 constituent parts: • Perception Distance: The distance travelled before the driver perceives a hazard. • Reaction Distance: The distance travelled following the perception of a hazard until the driver applies the brakes. • Braking Distance: The distance travelled until the vehicle decelerates to a halt. The perception and reaction distances are generally taken as a single parameter based on a combined perception and reaction time. The formula for the calculation of SSD is: SSD = vt + v2/2d 32 Refer to Section 7.4.4 of UK Manual for Streets (2007) and UK Manual for Streets: Redefining Residential Street Design (2006). Design Speed (km/h) SSD Standard (metres) 10 8 20 15 30 24 40 36 50 49 60 65 Forward Visibility on Bus Routes Design Speed (km/h) SSD Standard (metres) 10 7 20 14 30 23 40 33 50 45 60 59 Forward Visibility SSD STANDARDS Table 4.2: Reduced SSD standards for application within cities towns and villages. Reduced forward visibility increases driver caution and reduces vehicle speeds. Where: v = vehicle speed (m/s) t = driver perception-reaction time (s) d = deceleration rate (m/s2) SSDs have generally been applied according to those contained within the NRA DMRB TD 9 which where derived from the UK DMRB Manual of the same name using a perception reaction time of 2 seconds, and a deceleration rate of 0.25g, or 2.45 m/ s2. TRL found these SSD values to be overly conservative as they underestimated driver reaction times, deceleration rates and did not take into account actual road design details.33 Based on this research, a driver perceptionreaction time of 1.5 seconds, and a deceleration rate of 0.45g, or 4.41 m/s2, should be applied with design speeds of 60 km/h and below. For larger vehicles such as HGVs and buses, a deceleration rate of 0.375g, or 3.68 m/s2 should be applied. A revised set of reduced SSDs, based on the parameters included in the UK Manual for Streets (2007), are presented in Table 4.2. The reduced SSDs should be applied according to the design speed of a street (see Section 4.1.1 A Balanced Approach to Speed) at junctions and along the alignment of a street (see Sections 4.4.5 Visibility Splays and 4.4.6 Alignment and Curvature, respectively and Advice Note 3 - Geometric Standards. 33 Refer to Manual for Streets: Evidence and Research (TRL Report 661) (2007).
- Design Manual for Urban Roads and Streets108 4.4.5 Visibility Splays Visibility splays are included at junctions to provide sight lines along the intersected street to ensure that drivers have sufficient reaction time should a vehicle enter their path. Visibility splays are applied to priority junctions where drivers must use their own judgement as to when it is safe to enter the junction. Junction visibility splays are composed of two elements; the X distance and the Y distance. • The X distance is the distance along the minor arm from which visibility is measured. It is normally measured from the continuation of the line of the nearside edge of the major arm, including all hard strips or shoulders. • The Y distance is the distance a driver exiting from the minor road can see to the left and right along the major arm. It is normally measured from the nearside kerb or edge of roadway where no kerb is provided. The procedure for checking visibility splays at junctions is illustrated in Figure 4.63. An additional check is made by drawing an additional sight line tangential to the kerb, or edge of roadway, to ensure that an approaching vehicle is visible over the entire Y distance. 1: VISIBILITY SPLAY (no constraint on overtaking) 2: ALTERNATIVE VISIBILITY SPLAY (constraint on overtaking) Figure 4.63: Forward visibility splays refer to an X and Y value. The X value allows drivers to observe traffic on the intersected arm. The Y value allows the driver of a vehicle to stop safely should an object enter its path, and is based on the SSD value. Longer X distances allow drivers more time to observe traffic on the intersected arm and to identify gaps more readily, possibly before the vehicle comes to a stop, thus allowing increased vehicle speeds through junctions. Furthermore, a longer X distance may encourage more than one vehicle on the minor arm to accept the same gap even where it is not ideal that they do so. Neither circumstance is desirable in urban areas. The attention of a driver should not solely be focused on approaching vehicles and the acceptance of gaps. The pedestrian/ vulnerable road users should be higher in the movement hierarchy For this reason, priority junctions in urban areas should be designed as Stop junctions, and a maximum X distance of 2.4 metres should be used. In difficult circumstances this may be reduced to 2.0 metres where vehicle speeds are slow and flows on the minor arm are low. However, the use of a 2.0 metre X distance may result in some vehicles slightly protruding beyond the major carriageway edge, and may result in drivers tending to nose out cautiously into traffic. Care should be taken to ensure that cyclists and drivers can observe this overhang from a reasonable distance and manoeuvre to avoid it without undue difficulty. 1 2 1 Y distance X distance Constraint on overtaking? Y distance 1 2 1 Constraint on overtaking? X distance Y distance X distance 1 1 2 Constraint on overtaking?
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