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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- 59May 2019 (Version 1.1) Speed Reduction dB (A) Reduction from 70-60 km/h 1.8 from 60-50km/h 2.1 from 50-40km/h 1.4 Traffic Volume Reduction dB (A) Reduction 30% 1.6 40% 2.2 50% 3.0 75% 6.0 Table 3.2: Noise reduction effects of lowering traffic speeds and volumes 3.4.5 Noise and Air Pollution The primary source of widespread environmental noise in Ireland is road traffic. Traffic is also the main source of air pollutants in cities, towns and villages. Whilst air pollutants generally have declined in recent years, those pollutants associated with traffic have not, principally because of an increase in traffic volumes and congestion.15 Busy or congested roads can create pollution ‘hot-spots’ and can have a significant negative impact on adjacent street activities. Pollution can also seriously affect the attractiveness of walking and cycling along affected routes. The main factors which determine the level of road noise and air pollution are traffic volume, speed, levels of congestion and the proportion of HGVs. Many of these issues may be substantially addressed by directing large volumes of traffic (and in particular HGVs) away from cities, towns and villages via Urban Relief Routes (see Section 3.4.4 Relief Roads) and by reducing speeds (see Table 3.2). The creation of a permeable street network which promotes walking, cycling and public transport will also lead to reductions in vehicular traffic and less concentration of traffic and consequently of noise and air pollution. 15 Refer to Air Quality In Ireland (2009). SPEED AND NOISE REDUCTION TRAFFIC AND NOISE REDUCTION It is inevitable that some heavily-trafficked routes (such as Arterial streets) will pass through urban areas. Whilst traffic volume and noise have a significant impact on the value of place, there are many examples in Ireland of streets that carry significant volumes of through traffic at moderate speeds which retain a high place value (as per Figure 3.31 - Dorset Street). Whilst some mitigation measures can be provided through construction materials used on carriageway surfaces and within adjoining buildings, most integrated or place-based solutions should involve (see Figure 3.34): • Apply boulevard typologies with well planted medians and verges that reduce pollution16 and provide a buffer between the heavily-trafficked carriageway and the surrounding pedestrian environment. • Consider the use of multiple carriageways that separate through traffic from access traffic and parking. 16 Refer also to Effectiveness of Green Infrastructure for Improvement of Air Quality in Urban Street Canyons (2012).
- Design Manual for Urban Roads and Streets60 Figure 3.34: Examples of Urban Boulevard street typologies which mitigate the impacts of noise through place based design solutions. Through Carriageway Access carriageway Access carriageway Main Carriageway Median MedianMedianParking/ Verge Parking/ Verge MedianParking/ Verge At a broader level, land uses should be distributed in a manner that takes into account sensitivity to traffic noise: • Commercial or retail uses should be used to shield more sensitive receptors (i.e. residential uses). Such an approach complements the principle of integrated street design as it focuses commercial/ retail uses on Arterial and Link streets where public transport services are likely to be located. • Where residential uses are provided on the upper floors of buildings, aspects of the upper floors may be orientated so that they are perpendicular (i.e. at right angles) to the roadway. This will ensure a degree of overlooking, whilst deflecting the impacts of pollution (see Figure 3.35). Figure 3.35: Example of a development adjacent to a busy Arterial Street where residential development is provided over a commercial podium at street level. Parking/ Verge
- CHAPTER 4 - STREET DESIGN A more integrated approach to street design can create a ‘win-win’ scenario, where designers can enhance the value of place whilst calming traffic and improving pedestrian and cyclist comfort. To achieve this outcome, designers need to consider the multifunctional role of the street and apply a package of ‘self-regulating’ design measures.
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- 63May 2019 (Version 1.1) 4.0 Street Design 4.1 Movement, Place and Speed 4.1.1 A Balanced Approach to Speed Balancing the priorities Context and Function creates a shifting dynamic in street design. The UK Manual for Streets (2007) illustrates this relationship as a simple graph depicting some well known scenarios (see Figure 4.1). Key to the successful implementation of responsive design solutions is the issue of speed, particularly so with regard to pedestrian and cyclist safety, comfort and convenience (see Figure 4.2). Expectations of appropriate speed will vary greatly from person to person and there is little relevant research on this subject. Intuitively one would expect motorists’ tolerance of low-speed journeys to increase in intensively developed areas (i.e. from the Centres, to Neighbourhoods to Suburbs) and according to journey type (i.e. from Local to Link and to Arterial Streets. Designer must balance speed management, the values of place and reasonable expectations of appropriate speed according to Context and Function.1 In this regard: • Within cites, towns and villages in Ireland a default speed limit of 50km/h is applied. • Speed limits in excess of 50km/h should not be applied on streets where pedestrians are active due to their impact on place and pedestrian safety. • Lower speed limits of 30km/h are a requirement of Smarter Travel (2009) within the central urban areas, where appropriate.2 • Where pedestrians and cyclists are present in larger numbers, such as in Centres, lower speed limits should be applied (30-40km/ h). • Where vehicle movement priorities are low, such as on Local streets, lower speed limits should be applied (30km/h). 1 Further guidance in regard to special speed limits is available from Section 9 of the Road Traffic Act - Guidelines for the Application of Special Speed Limits (2011). 2 Refer to Action 16 of Smarter Travel (2009). Figure 4.2: Illustration from the Road Safety Authority showing the impact of vehicle speeds on pedestrian fatalities. This is of primary consideration when considering appropriate speeds and levels of pedestrian activity. Figure 4.1: Illustration from the Manual for Streets 2 (2010) depicting the relationship between place and movement in regard to some well know scenarios.
- Design Manual for Urban Roads and Streets64 • Local Authorities may introduce advisory speed limits of 10-20km/where it is proposed that vehicles, pedestrians and cyclists share the main carriageway. Design speed is the maximum speed at which it is envisaged/intended that the majority of vehicles will travel under normal conditions. In this regard: • In most cases the posted or intended speed limit should be aligned with the design speed. • In some circumstances, such as where advisory speeds limits are posted, the design speed may be lower than the legal speed limit. • The design speed of a road or street must not be ‘updesigned’ so that it is higher than the posted speed limit. Table 4.1 illustrates the broader application of design speeds according to Context and Function. Designers should refer to this table when setting speed limits and designing urban streets and urban roads to align speed limits and design speeds. Table 4.1: Design speed selection matrix indicating the links between place, movement and speed that need to be taken into account in order to achieve effective and balanced design solutions. ARTERIAL 30-40 KM/H 40-50 KM/H 40-50 KM/H 50-60 KM/H 60-80 KM/H LINK 30 KM/H 30-50 KM/H 30-50 KM/H 50-60 KM/H 60-80 KM/H LOCAL 10-30 KM/H 10-30 KM/H 10-30 KM/H 30-50 KM/H 60 KM/H CENTRE N’HOOD SUBURBAN BUSINESS/ INDUSTRIAL RURAL FRINGE CONTEXT PEDESTRIAN PRIORITY VEHICLE PRIORITY FUNCTION When applying these limits designers must also consider how effectively they can be implemented, as the introduction of more moderate and/or lower speed limits out of context and/or without associated speed reduction measures may not succeed.
- 65May 2019 (Version 1.1) Figures 4.3: Illustration of the links between place, movement and speed that need to be taken into account in order to achieve effective self-regulating street environments. CONTEXT FUNCTION SPEED DESIGN RESPONSE ARTERIAL 30-40 KM/H 40-50 KM/H 40-50 KM/H 50-60 KM/H 60-80 KM/H LINK 30 KM/H 30-50 KM/H 30-50 KM/H 50-60 KM/H 60-80 KM/H LOCAL 10-30 KM/H 10-30 KM/H 10-30 KM/H 30-50 KM/H 60 KM/H CENTRE NEIGHBOUR- HOOD SUBURBAN BUSINESS/ INDUSTRIAL RURAL FRINGE PEDESTRIAN PRIORITY VEHICLE PRIORITY 4.1.2 Self-Regulating Streets An appropriate design response can successfully balance the functional needs of different users, enhance the sense of place and manage speed in a manner that does not rely on extensive regulatory controls and physically intrusive measures for enforcement. In short, place can be used to manage movement. Such environments are referred to as being self-regulating. Within this selfregulating street environment the design response is closely aligned with the design speed (see Figure 4.3). Within Ireland, the Dublin Traffic Initiative: Environmental Traffic Planning (1995) was, perhaps, the first strategic document in Ireland to recognise the link between the street environment and driver behaviour. It cited the use of narrow streets and onstreet parking as traffic-calming tools. The Adamstown Street Design Guide (2010) draws upon research undertaken in regard to the UK Manual for Streets (2007) to advance this approach. It cited a combination of placebased psychological measures and integrated them with more traditional physical measures in order to create a self-regulating street environment (see Figure 4.4).3 3 Refer also to Section 2.2 ‘Safe Streets’ of the Adamstown Street Design Guide (2010). There is no set formula of how a package of psychological and physical measures should be applied. The design team must take into account that: • Physical and psychological measures are most effective when used in combination.4 • The more frequently and intensely physical and psychological measures are applied, the lower the operating speed. Analysis of the Road Safety Authority Free Speed Survey 2008, 2009 and 2011, inclusive showed that where there are few psychological and physical measures, average drivers regularly exceeded the posted speed limit. Conversely where these measures are more frequently and/or more intensely applied, driver speeds were lower and compliance with the posted speed limit was greater (see Figure 4.5). 4 Refer to Psychological Traffic Calming (2005).
- Design Manual for Urban Roads and Streets66 Figure 4.4: Extract from the Adamstown Street Design Guide. Illustration of the psychological and physical, or ‘hard’ and ‘soft’, measures that influence driver speeds and may be used to enhance place and manage movement. Close Proximity of Buildings (left) Continuous Street Wall (right) Active Ground Floor Uses (left) Pedestrian Activity (right) Frequent Crossing Points and Junctions (left) Horizontal and Vertical Deflections (right) Narrow Carriageways (left) Minimising signage and road markings (right) Reduced Visibility Splays (left) On-Street Parking (right) Tighter Corner Radii (left) Shared Surfaces (right)
- 67May 2019 (Version 1.1) Figure 4.5: Road Safety Authority Free Speed Survey and Street Characteristics The Road Safety Authority periodically undertakes free speed surveys throughout urban and rural Ireland. In 2008, 2009 and 2011 the speeds of some 9,500 vehicles along 23 streets within metropolitan Dublin were recorded. An analysis of the characteristics of the street environment at each of the 23 locations was carried out for the preparation of this Manual. This survey recorded the frequency and intensity of psychological and physical design measures that influence driver behaviour, such as those illustrated in Figure 4.4. The survey results demonstrated that the individual effectiveness of these measures varied. For example, as would be generally expected, the presence of deflections (such as ramps) had a strong influence on reducing speed. Results also showed that other ‘softer’ measures, such as a sense of enclosure, surveillance and activity created by a continuous line of development fronting directly onto the street, have a strong influence on lowering speed. Overall, the results demonstrated a strong trend whereby as the frequency and strength of the psychological and physical design measures increased, the lower the operating speed and the greater the level of compliance with the posted speed limit (see graphs A and B ). This trend was generally consistent for all road types including those which did not have ramps. Figure 4.2 illustrates that an increase in vehicle speeds from 50 km/h to 60 km/h nearly doubles the chance of a pedestrian fatality, should they be struck by a vehicle. Graph C is particularly significant in this regard as it illustrates that where there are limited psychological and physical design measures on streets with a speed limit of 50 km/h most drivers will exceed the speed limit by 10 km/h or more. Conversely where the frequency and strength of these measures are high full, or near full, compliance with the speed limit occurred. In many cases the average operating speed dropped below 40 km/h. LOWER MODERATE HIGHER 70 Km/h 30 Km/h 50 Km/h Frequency and Intensity of Psychological Conditions and Physical Constraints A. AVERAGE OPERATING SPEED LOWER MODERATE HIGHER 100% 60% Frequency and Intensity of Psychological Conditions and Physical Constraints B. % OF DRIVERS EXCEEDING SPEED LIMIT 80% 40% 20% C. % OF DRIVERS EXCEEDING SPEED LIMIT BY 10 KM/H OR MORE (50 km/h streets only) LOWER MODERATE HIGHER 100% 60% Frequency and Intensity of Psychological Conditions and Physical Constraints 80% 40% 20%
- Design Manual for Urban Roads and Streets68 In retrofit scenarios, designers must carefully consider the characteristics of the existing street environment prior to implementing selfregulating measures as: • The measures contained within this Manual should not be implemented in isolation as they may not fully address issues related to inappropriate driver behaviour on existing streets. • Designers should carry out a detailed analysis to establish the levels of intervention and design measures required in any given scenario (see Figure 4.6). Figure 4.6: Examples from Youghal, Co. Cork (left), and Dorset Street, Dublin City (right), of retrofitted design responses that are appropriate according to Context and Function. The narrow, enclosed and lightly trafficked nature of the street within Youghal is highly suited to a shared carriageway. The heavily trafficked nature of Dorset Street makes it highly suited to a Boulevard type configuration. AFTER BEFORE AFTER BEFORE For example, in many older Centres and Neighbourhoods, measures such as connectivity, enclosure, active street edges and pedestrian activity are generally strong. In these circumstances the design measures contained within this Manual may be readily applicable. The application of a holistic solution may be more challenging within a more conventional or highly segregated road environments. Under such circumstances a wider package of measures may need to be implemented. This Manual cannot account for every scenario that a designer will encounter. In addition to those examples contained in the ensuing sections, to assist designers in the process of retrofitting it is intended that a series of ‘best practice’ case studies will be made available as downloadable content.
Source Department of Transport, Tourism and Sport and Department of Housing, Planning and Local Government: Design Manual for Urban Roads and Streets (2019 (version 1.1)) · Licence the publisher's termsText read from the publisher’s PDF; tables, maps and drawings do not survive as text, and page numbers are the PDF’s (its first page is 1). Check the original before relying on a passage.