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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- 69May 2019 (Version 1.1) Figure 4.7: Measurements that indicate the sense of enclosure by way of building height to street width ratio and the percentage of the street wall that is solid. BUILDING HEIGHT TO STREET WIDTH RATIO CONTINUITY OF THE STREET WALL 1 1 Ratio of 1:1 - Very strong sense of enclosure (street trees optional) 2 Ratio of 1:2 - Strong sense of enclosure (supplementary street trees desirable) 1 75%+ solid - strong sense of enclosure (street trees optional) 75% solid - moderate sense of enclosure (supplementary street trees required) 3 Ratio of 1:3 - Moderate sense of enclosure (supplementary street trees required) 1 4.2 Streetscape 4.2.1 Building Height and Street Width Sense of enclosure is generally measured as a ratio where the height of a building (measured from front building line to front building line) is measured against the width of a street. Consideration needs to be given as to how consistently this ratio applies along the length of the street through the creation of a street wall. The street wall refers to how continuous the sense of enclosure is along the street. Enclosing streets with buildings helps to define them as urban places, creates a greater sense of intimacy5 and promotes them as pedestrian friendly spaces that are overlooked. This sense of intimacy has been found to have a traffic-calming effect as drivers become more aware of their surroundings. Designers should seek to promote/maintain a sense of enclosure on all streets within cities, towns and villages (see Figure 4.7). In this regard. • A strong sense of enclosure should be promoted in large Centres. The most effective way of achieving this is with a building height to street width ratio greater than 1:2 and street wall that is predominantly solid (allowing for intermittent gaps only). • A good sense of enclosure can also be achieved with a building height to street width ratio of 1:3 and a street wall that is 75% solid, provided a continuous line of street trees are planted along the street. This approach may be more desirable in smaller Centres or Neighbourhoods where maintaining a more human scale is desirable. • A strong sense of enclosure may be difficult to achieve where the total street width exceeds 30m wide, such as on Boulevards. In such circumstances design teams should emphasise the sense of enclosure with the planting of continuous rows of large closely planted street trees. 5 Refer to Section 07 of the Urban Design Manual (2010).
- Design Manual for Urban Roads and Streets70 • Within established areas creating a strong sense of enclosure may result in building heights that would conflict with those of the surrounding area. In such circumstances designers may emphasise enclosure though other design measures, such as the planting of street trees. • The planting of street trees should also be considered as a retrospective traffic calming measure in existing contexts where levels of enclosure are traditionally weaker, such as in Suburban areas. • The planting of street trees may also be desirable within Transition Zones (see Sections 3.4.1 Wayfinding and 3.4.4 Relief Roads), in advance of Gateways and within Rural Fringe areas as an advance warning to drivers of changing conditions ahead. The measures illustrated in Figure 4.7 should not be strictly viewed as quantifiable. For example a moderate building height to street width ratio, in addition to a moderate continuity of street wall, does not equate to a strong sense of enclosure. Rather they should be viewed as complementary, i.e. a strong sense of enclosure is created where both elements are strong. The relationship between building height and street width is also key to creating a strong urban structure, by increasing building heights in proportion to street widths. This will also promote greater levels of sustainability and legibility by placing more intensive development along wider/busier streets, such as Arterial and Links streets, to support public transport routes and highlight their importance as connecting routes, respectively (see Figure 4.8). Additional building height may also be used at junctions to create a ‘book end’ effect (see Figure 4.9). This approach will assist in slowing vehicles as they approach junctions and will improve legibility by highlighting connecting routes throughout the network. Figure 4.8: Plan illustrating how taller buildings (purple) are placed along busier routes (and around major spaces) to enclose streets and reinforce the structure of the area. Figure 4.9: Reinforcing junctions with additional building height will assist in slowing vehicles as they approach junctions and will improve legibility by highlighting connecting routes throughout the network.
- 71May 2019 (Version 1.1) 4.2.2 Street Trees Street trees are an integral part of street design as they contribute to the sense of enclosure, act as a buffer to traffic noise/ pollution and enhance place. A trafficcalming effect can also be achieved, where trees are planted in continuous rows and their canopies overhang, at least in part, the vehicular carriageway. Street trees can also be used to enhance legibility by highlighting the importance of connecting routes and distinguishing one area from another through variations in size and species selection. The planting of trees should be considered as an integral part of street design. In general, the size of the species selected should be proportionate to the width of the street reserve. For example (see Figure 4.10): • Larger species, with a canopy spread greater than 6m will be best suited to wider streets, such as Arterial and Link streets. • Smaller species with a canopy spread of 2-6m will be best suited to narrower streets such as Local streets. Designers may seek to vary this approach in keeping with the characteristics of a place. For example: • Sparse planting may be more appropriate in a Centre, enhancing its urban qualities. • Smaller species may be more appropriate where buildings are located in close proximity to the street edge carriageway (i.e. to take account of overshadowing, growth restrictions). • Larger species may be desirable within Suburbs, to enhance the greener character associated with these places. To be effective, trees should be planted at intervals of 14-20m. This may be extended periodically to facilitate the installation of other street facilities, such as lighting. Designers should also consider the impact of root growth. Tree roots may need to be contained within individual tree pits, continuous soil planting strips or using other methods to restrict growth under pavements/toward services. TREE SIZE AND STREET RESERVE Small Street Reserve - Smaller Species 13-15m 2-3m 2-3m 17-21m 2-3m 4-6m Moderate Street Reserve - Smaller Species 19-23m 4-6m 3-5m 22-25m 4-6m 3-5m 30m+ 6-10m 4-6m 26-30m 6-10m 4-6m Large Street Reserve - Larger Species Figure 4.10: General guide to the canopy width and clearance height for street trees.
- Design Manual for Urban Roads and Streets72 4.2.3 Active Street Edges Active street edges provide passive surveillance of the street environment and promote pedestrian activity. This should be a principle aim of the design team. Increased pedestrian activity also has a traffic-calming effect as it causes people to drive more cautiously.6 Designers should seek to promote active street edges on all streets within cities, towns and villages. The most effective way to promote pedestrian activity is to place buildings in close proximity of the street (see Section 4.2.1 Building Height and Street Width) with a high frequency of entrances and other openings. In this regard (see Figure 4.11): • To maximise activity in Centres the street edge should be lined with development that promotes a high level of activity and animation such as retail, commercial or other appropriate uses. To maximise the effectiveness of these uses, setbacks should be minimised (for example 0-3m) and a high frequency of entrances provided (for example every 5-10 metres). • Where larger retail/commercial floor plates are proposed at ground floor level an active street edge may be achieved by creating multiple entrances and/or wrapping them with smaller perimeter units that front on to the street (see Figure 4.12). • Arterial and Link streets through intensively developed Neighbourhoods may also sustain retail/commercial activity, particularly on corner locations. • Higher levels of privacy are desirable where residential dwellings interface with streets. This may be provided via a small setback (for example 1-3 metres) which incorporates planted strip that defines public and private space (see Figure 4.13). • Residential development will also promote on-street activity where individual dwellings (including ground floor apartments) are ‘own door’ accessed (see Figure 4.14). 6 Refer to Section 2.2.5 of the UK Manual for Streets (2007). Figure 4.11: Measures that indicate active and animated street interfaces. FRONTAGE TYPE AND FREQUENCY OF ACCESS 0-3m setback strong street presence SETBACK TO THE PEDESTRIAN FOOTWAY 4-6m setback more moderate street presence Higher frequency retail/commercial - high level of activity and animation 5-10m Moderate frequency retail/commercial - more moderate level of activity and animation 11-16m Own door residential - more moderate level of activity and animation 5-8m
- 73May 2019 (Version 1.1) Figure 4.12: Illustration of how a larger retail/ commercial unit can be accommodated within a block whilst promoting an active street edge that is also overlooked from the upper levels. Larger Floorplate Smaller units ‘wrapped’ around perimeter Development ‘Cap’ Figure 4.13: Privacy strip to the front of residential development. The strip provides a buffer and clearly define the private domain from the public. Figure 4.14: A fine grain residential environment where all ground floor dwellings are directly accessible from the street via ‘own door’ entrances. Note, in this instance access to upper floors is provided via internal lobby areas. • Greater flexibility in regard to setbacks may be needed in existing areas where they are defined by an existing pattern of building lines • The inclusion of in-curtilage parking within front gardens (i.e. to the front of the building line) may result in large building setbacks that substantially reduce the sense of enclosure. In addition to the above, designers should avoid a scenario where parking dominates the interface between the building and the footway (see Section 4.4.9 On-Street Parking and Loading). In addition to the above, further advice with regard to the creation of active street edges may also be taken from the Urban Design Compendium.7 7 Refer to Section 5.1.2 Building Lines and Setbacks and Section 5.2 Animating the Edge, UK Urban Design Compendium (2000).
- Design Manual for Urban Roads and Streets74 4.2.4 Signage and Line Marking The principal source for guidance on signage and line marking is the Department of Transport Traffic Signs Manual (TSM) (2010), which categorises signage and road marking into four main categories: • TSM Chapters 2 and 4: Information Signs that give directions and distances to destinations or which provide other information that may be relevant to road users; • TSM Chapter Section 5: Regulatory Signs that give instructions, prohibitions or restrictions which road users must obey and indicate the existence of a Road Traffic Regulation or implement such a Regulation, or both. • TSM Chapter Section 6: Warning Signs are used to alert the driver to a danger or potential danger on the road ahead. • TSM Chapter Section 7: Road Markings are defined as markings on the surface of the road for the control, warning, guidance or information of road users and may either be used on their own or to supplement associated upright signage. Regulatory Signs can be further divided into three main groups: • Mandatory Signs are used to indicate that a road user must take a certain action. For Example ‘Stop’, ‘Yield’ or ‘Keep Left’. • Restrictive Signs to indicate a limit must not be exceeded. For Example ‘50 km/h Speed Limit’ or ‘Weight Limit 3 tonne’. • Prohibitory Signs to indicate something which must not be done. For Example ‘No Right Turn’ or ‘No Parking’. The implementation of a self-regulating street environment means that the reliance on signage or line marking to direct or instruct people is significantly reduced. As noted in the Manual for Streets (2007)8, there may also be traffic-calming benefits of a ‘less is more’ approach to reinforce lower design speeds. For example, the removal of centre line markings has been found to reduce vehicle speeds and the number of accidents.9 With reduced signage drivers must navigate the street environment with full regard to their own behaviour and the behaviour of others around them. An emphasis on the values of place also requires the visual impact of signage to be considered in order to reduce visual clutter. The TSM warns against over providing signage and line marking. Section 1.1.10 of the TSM states in relation to signage in general, ‘signs should only be erected where there is a demonstrable need, because unnecessary, incorrect or inconsistent signs detract from the effectiveness of those that are required and tends to lead to disrespect for all signs’. There is also a limit to how many signs/line markings drivers can absorb in a short period. To define where designers are allowed to employ discretion, Section 1.1.12 of the TSM states that: • ‘Shall’ or ‘must’ indicates that a particular requirement is mandatory; • ‘Should’ indicates a recommendation; and • ‘May’ indicates a permissible option. 8 Refer to Section 9.1.7 of the Manual for Streets (2007). Designers should also note that the Manual for Streets recommended monitoring streets where little or no signage is used to confirm its effectiveness. 9 Refer to Improving Traffic Behaviour and Safety Through Urban Design, Civil Engineering (2005).
- 75May 2019 (Version 1.1) Figure 4.16. Kensington High Street, London, UK, where as part of upgrade works, a major decluttering exercise took place which included removing all guardrails, minimising signage and line marking. It is notable that upon completion of the works, vehicle speeds decreased and the incidence of accidents decreased by 43% (2003-2005). Left image source: Kensington and Chelsea Borough Council. Figure 4.15: Walworth Road, Central London, UK, before (top) and after (bottom). The street carries over 20,000 vehicles per day and as part of major upgrade signage and line marking were minimised (image source: Southwark Council). Designers should use this discretion with regard to the self-regulating characteristics of streets and the impact of signs/line marking on the value of place when applying the TSM. In this regard: • Minimal signage is required on Local streets due to their low speed nature and low movement function. The generally lightly trafficked nature of these streets means that the use of signage can be minimised, and in some cases eliminated altogether. • The requirements for signage on Arterial and Link streets will be higher than on Local streets. The use of signage should be kept to the minimum requirements of the TSM, particularly where place values are very high, such as in the Centre context. Designers may have concerns about minimising signage on streets that carry higher volumes of traffic, but there are many successful examples where the amount of signage provided has been significantly reduced (see Figures 4.15 and 4.16).
- Design Manual for Urban Roads and Streets76 With regard to signs and line marking more generally (see Figure 4.17): • Signage structures should be rationalised. Individual sign poles may be better utilised and signs should be clustered together on a single pole.10 • Non-regulatory, and in particular Information Signs, signage may be embedded within street surfaces or incorporated into other items of street furniture. • Local authorities should undertake periodic decluttering exercises to remove unnecessary repetitive and redundant signage.11 • The size of individual signs should generally be to the minimum specification stated in the TSM for the particular speed limit. • The use of Warning signs should be limited as they are generally not required in built-up areas where potential hazards are clearly legible and vehicles travel at lower to moderate speeds. Warning signs should be installed only if an engineering assessment indicates a specific need for improving road safety for users and it is clear that the sign will be effective.12 10 Refer to Action 16 of Smarter Travel (2009) which requires the rationalisation of signage poles 11 Refer to UK Department for Transport Local Transport Note 1/08. Examples of guidelines are available from www.english-heritage.org.uk 12 Refer to Sections 6.1.17 and 6.1.19 of the Traffic Signs Manual (2010). Figure 4.17: Example of the improvements to a streetscape that can be achieved where signage and line marking are substantially reduced. Note all changes have been made within the scope of the TSM. BEFORE AFTER • Designers should minimise the duplication of signage and/or road marking. Where signage and road markings provide the same function, preference should be given to the provision of road markings only, unless specifically required by the TSM. In general, road markings are more legible for drivers and have less of a visual impact on the streetscape. • The use of signage and/or road marking that duplicate existing regulations should be avoided and may lead to confusion. For example the use of double yellow lines around corners to reinforce the standard prohibition on stopping within 5m of a road junction may lead to misinterpretation that loading is generally permitted.13 Designers should also note that a Regulatory sign may not be required as a ‘regulation’ or a ‘mandatory requirement’. Designers may conclude that a Regulatory sign may not be needed due to the self-regulating nature of the street and/or in order to reduce the overall amount of signage used. 13 Refer to Section 7.6.5 of the Traffic Signs Manual (2010).
- 77May 2019 (Version 1.1) 4.2.5 Street Furniture Street furniture serves many purposes that relate to both place and function and includes a variety of commonly found items within a street such as public art, lighting, bollards, guardrails, seating and cycle parking. Whilst items such as public art may be of place value only, many other items, if well designed, provide a place and function value (see Figure 4.18). In general, the provision of street furniture must be considered as part of the overall design of street. In this regard: • The placement of street furniture should be considered as part of a wider strategy, such as part of an integrated landscape plan or series of street typologies. • Street furniture should be placed within a designated zone, such as a verge (see Section 4.3.1 Footways, Verges and Strips) • The items used should be chosen from a limited palette that promotes visual cohesion (see Section 5.2.1 Policy and Plans), while contrasting with the background to assist the visually impaired. • The number of items used should be balanced with other facilities (including signage and line marking) to reduce clutter. • Existing items of historic value which promote local character should be clearly identified (see Section 4.2.8 Historic Contexts). Guardrails An integrated approach to street design will substantially reduce the need for obtrusive physical barriers such as guardrails. For example, the alignment of crossing points with desire lines will eliminate the need for guardrails to redirect pedestrians (see Section 4.3.2 Pedestrian Crossings) In this regard: • Guardrails should not be used as a tool for directing and/or shepherding pedestrians. Figure 4.18: An example from Drogheda, Co. Louth, where well placed street furniture has a functional role that also provides a major contribution to the streetscape and value of place.
- Design Manual for Urban Roads and Streets78 Figure 4.19: Items such a bicycle racks, seating and/or bollards are less intrusive elements that can be used to guide pedestrians toward crossing points and reduce illegal kerb mounting. • Guardrails should only by installed where there is a proven or demonstratable safety benefit, for example where people may inadvertently step onto the carriageway (e.g. at a school entrance).14 Where the potential need for guardrails is identified (such as via a Road Safety Audit), designers should review their design as this need may highlight inadequacies in the design (such as the failure to take proper account of pedestrian desire lines). Designers should also consider the use of street furniture that may guide pedestrian movement and also contributes to the sense of place and provide amenities (see Figure 4.19). Authorities should remove unnecessary guardrails on existing streets. The removal of individual sections of guardrails should be the subject of a rigorous and well documented assessment process. Further guidance in regard to the removal of guardrails may be obtained from, UK Guidance on the Assessment of Pedestrian Guardrail (2012 update) and UK Department for Transport Local Transport Note 2/09 (see Figure 4.20). The National Cycle Manual (2011) also recommends the removal of guardrail as it poses a safety risk to cyclists.15 Once guardrails have been removed monitoring should be undertaken to ensure the works have had the desired effect. Designers may have some concerns in regard to the removal of guardrails on busy streets due to their perception as effective ‘crash’ barriers. However, guardrails are only effective at stopping vehicles at very low speeds and therefore may provide a false sense of security resulting in pedestrians and vehicles both paying less attention.16 14 Refer to UK Department for Transport Local Transport Note 2/09: Pedestrian Guardrailing, for further guidance. 15 Refer to Sections 1.1.4, 4.4.1.2-4.4.1.4 and 4.4.4 of the National Cycle Manual (2011). 16 Refer to UK Guidance on the Assessment of Pedestrian Guardrail (2012). Figure 4.20: Before and after images near Kings Cross station, London, extracted from the TfL document Assessment of Pedestrian Guardrails. TfL have undertaken a wide program of guardrail removal throughout the streets of London.
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.