Some engineers may find the recommendations in the new Design Manual for Urban Roads and Streets to be radical, but they will lessen the car’s dominance and make more room for people, write Seán McGrath and Robert Curley
Civil

 

Seán McGrath, BE MIEI, Fingal County Council and Robert Curley, BE MIEI, Kildare County Council

In March 2013, the Department of Transport, Tourism and Sport (DTTAS) and the Department of the Environment, Community and Local Government (DECLG) jointly published the Design Manual for Urban Roads and Streets (DMURS), a new guidance document setting out an integrated and holistic approach to road and street design in our cities, towns and villages. The use of DMURS is mandatory on all urban roads and streets with a speed limit of 60 km/h or less and it replaces the use of the DMRB in urban areas.

Historically, towns have grown up around transport nodes, such as river crossings, and crossroads. Consequently, streets in towns have always had a dual function – first as a transport corridor and second as a place to do business or a place to live. This second function is referred to as a ‘place function’.

For some roads/streets, one function may dominate (e.g. motorways versus pedestrianised shopping streets). However, most roads/streets in urban areas will have both a transport function and a place function (e.g. O’Connell Street, Ranelagh). The DMURS attempts to balance the two functions, thereby recognising the needs of all users of the street.

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Traditional street design in Ireland has largely been influenced by the Buchanan Report (Traffic in Towns, 1963), which envisaged a highly segregated and structured street network. Amongst its recommendations were the segregation of motorised vehicles from pedestrians, the provision of distributor roads with restrictions on frontage development and a restriction on the movement of through traffic within neighbourhood cells.

These recommendations followed from the perception that cars and pedestrians were fundamentally incompatible and that by maintaining strict segregation, a safer road environment would be created. This approach has been widely implemented throughout the country and has resulted in the proliferation of frontage-free roads. However, the level of segregation envisaged by the Buchanan Report has proved to be difficult and has not delivered the intended safety benefits.

DMURS calls for an integrated approach to street design that incorporates not only what could be considered traditional engineering elements (such as geometric parameters), but also elements of urban design and landscaping that instinctively alter driver behaviour, resulting in lower speeds and thus a safer environment for all road users.

For some time, there has been a gap in the available guidance and standards for the design of urban roads and streets. This gap has, in many cases, led to the application of DMRB standards almost as a default. The DMRB, although an invaluable tool for road design, was never designed for urban areas. It almost exclusively addresses transport function, with little regard to place, and it does not cater for the lower design speeds that are appropriate in urban areas.

In order to address this, in 2009 the DTTAS and the DECLG decided to prepare a new national design standard for urban roads and streets. A multi-disciplinary project team comprised of architecture, engineering, planning and urban design professionals from South Dublin, Kildare, Fingal County Councils and Cork City Council was tasked with preparing the new document.

KEY PRINCIPLES

In order to achieve the balanced approach to street design promoted in DMURS, four key design principles have been set out: connected networks, multi-functional streets, a pedestrian focus and a multi-disciplinary approach.

  • Connected networks

Figure 1: Creation of a structured and permeable grid network as a multi-layered process

DMURS requires increased permeability within street networks, particularly for pedestrians and cyclists. A street hierarchy based on the movement function of arterial, link and local streets (where arterial streets have the highest movement function and local streets the lowest), combined with a consideration of the place context of any given part of a street (such as urban centres, neighbourhood areas and suburban areas), allows designers to create a structured and permeable network of streets in a layered approach, demonstrated in Figure 1.

Connected networks have certain advantages over the traditional approach. They result in reduced travel distances, particularly for slower modes, thus increasing the attractiveness of walking and cycling for shorter trips. More frequent entrances to a neighbourhood cell can reduce the footprint of individual junctions and streets, reducing the potential for community severance that can result from distributor type roads. In addition, increased permeability can provide more even distribution of traffic and reduced congestion as traffic is no longer concentrated on a small number of critical streets or junctions.

  • Multi-functional streets

Figure 2: User hierarchy that promotes and prioritises sustainable forms of transport

Designers need to consider the multi-functional role of the urban street and apply an integrated approach to design that will provide an improved environment for pedestrians by managing traffic speed without the need for physically intrusive enforcement measures (such as the ubiquitous traffic calming ramp). To achieve this, DMURS aims to create ‘self-regulating’ streets; i.e. streets where place, function, urban design, landscaping and engineering design can all be used to reduce speeds.

There is a range of measures such as: the creation of a sense of enclosure through appropriate building-height to street-width ratios, active frontage, the limited use of signage and line marking, planting, street furniture and the choice of materials and finishes can all be combined with more traditional physical measures, such as street geometry, to bring about reductions in speed.

  • Pedestrian focus

DMURS sets out a user hierarchy (illustrated in Figure 2) that prioritises sustainable travel modes. Walking is the most sustainable mode of transport and prioritising design for pedestrians will help to create a safe, comfortable and attractive pedestrian environment, which in turn will reduce the number of shorter trips taken by private car. Furthermore, as all trips begin and end on foot, all road users benefit from enhanced pedestrian facilities.

Footways should be kept clear of obstructions, a minimum width of 1.8 metres is required, and street furniture and planting should be provided for in strips along the frontage of buildings or in verges adjacent to the carriageway, an example of which can be seen in Figure 3. Pedestrian crossings should be conveniently located.

Figure 3: Example from Castlebar, where the verge acts as a designated space for street furniture, public lighting and trees, keeping the footway clear of obstacle

Corner radii must be minimised to ensure that crossing points are close to desire lines, to reduce crossing distances and to reduce vehicular speeds. However, achieving a comfortable and attractive pedestrian environment goes beyond simply providing the minimum requirements of DMURS; it must be an intrinsic part of a design from the outset.

  • Multi-disciplinary approach

DMURS recommends that design teams should include a broad range of professionals, depending on the nature and scale of the plan/project and the available resources. The design team may include engineers, planners, urban designers, architects, landscape architects and heritage/conservation officers.

In order that the team functions effectively, a collaborative and professional approach is required by all. It is not the case that engineers will cede control of projects that they control to architects or planners, or vice versa, rather that using the knowledge of a broader team of professionals, working together, will result in final designs that are better for the broad range of functions of an urban street.

PRACTICALITIES

Streets and networks that are designed in accordance with DMURS will have some of the following characteristics:

  • Residential areas will no longer be a series of cul-de-sacs which are linked to the general road network by a single access. Instead, they will be accessible from multiple points;
  • There will be no frontage free distributor roads, with long uninterrupted straights and high boundary walls;
  • Carriageway widths, especially in residential areas, will be narrower, but footpaths and verges may be wider;
  • All junctions will have tighter radii, especially those where the side road serves a residential area;
  • Pedestrian delays will be included in the calculation of optimum traffic signal timings. Consequently, traffic signals will have lower cycle times;
  • Signalised junctions will no longer provide left turn slip roads with dividing islands. Instead, junctions will be more compact and more pedestrian friendly;
  • Pedestrian barriers will be rare.

The Design Manual for Urban Roads and Streets provides the latest guidance on the design of roads and streets in urban areas. It appeals to many professions – engineers, planners, urban designers and architects. It gives guidance at both the strategic and the detailed design levels. It takes into account the many complex and often competing functions of streets in our cities, towns and villages.

Some designers, especially some engineers, may find the recommendations radical. In particular, the principle that road safety is achieved not by segregating vehicles from pedestrians, but by using urban design to slow down vehicles, is new and challenging. However, the recommendations in DMURS are backed up by evidence and experience from the UK, mainland Europe and, increasingly, from Ireland.

The DMURS will change the appearance of our urban roads and streets with less domination by cars and more space for people, which will benefit everyone.

Seán McGrath, BE MIEI, qualified from UCD in 1985. He worked in consultancy in the UK, Middle East, the Caribbean and Ireland. He subsequently joined the Dublin Transportation Office and the Quality Bus Network Project Office and is now a senior executive engineer in Fingal County Council’s planning and strategic infrastructure department.

Robert Curley, BE MIEI, qualified from DIT in 2006. He worked in a Dublin-based consultancy firm before joining Kildare County Council in 2007, where he is a design engineer in the transportation department.

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  Seán McGrath, BE MIEI, Fingal County Council and Robert Curley, BE MIEI, Kildare County Council In March 2013, the Department of Transport, Tourism and Sport (DTTAS) and the Department of the Environment, Community and Local Government (DECLG) jointly published the Design Manual for Urban Roads and Streets (DMURS), a new guidance...