Lessons on street design from Abu Dhabi

Gulf region takes context-sensitive roadway design to a new level.

Designing streets properly is a challenge not only in North America but also across much of the globe. It is an issue that a team of us have recently made progress on in the Emirate of Abu Dhabi in the development of the Abu Dhabi Urban Street Design Manual.

The standard approach in the US, the United Arab Emirates, and elsewhere relies on the “functional street classification” system — which, because of its limitations, should perhaps more accurately be called the “dysfunctional street classification system.” This system, accepted by most transportation departments, defines the vehicular movement requirements of the street — basically the curb-to-curb requirements. Its greatest drawback is that it does not address context or what may best serve the local community.

The Congress for New Urbanism (CNU) has long recognized that streets should be designed to reflect and respond to their local surroundings. Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities (CSS), a 2006 publication produced by the Institute of Transportation Engineers in partnership with CNU, was a breakthrough, encouraging designers to take a more responsive approach to street design in an urban environment.

CSS recognized that streets may need to change along their length to reflect adjacent land-use changes. For example, main streets with a high vehicular carrying capacity generally traverse a range of land uses, ranging from residential to commercial to high-density mixed use in town and city centers.

Alternative street classification system
During the development of the Abu Dhabi Urban Street Design Manual, the issue of street classification became a main area of debate for the project team. The CSS document contains a number of very good examples of how context and capacity can be dealt with. However, our team concluded that none of the existing guides or manuals provided the required mix of land use, density, and vehicular capacity needed to clearly direct designers on how to respond to varying types of land use.

The Transect approach, adopted in CSS, recognizes a linear progression through defined “context zones,” but we found that this approach did not account for large scale, single use development areas that are a common element of the local planning and development process in the Emirate of Abu Dhabi. Another issue was the descriptive terminology used in “typing” particular streets.

To describe a street type, those of us in Abu Dhabi felt that two distinct characteristics, or influencing factors, needed to be recognized: planning context and vehicular capacity. For this reason a two-name convention was developed. The first part of the name is based on the urban land-use and density context, the second part on vehicular capacity requirements.

This approach led to a long list of street types based on context and capacity, which at first did not seem to be any more useful than the traditional functional classification approach. It was only with the adoption of a matrix-based identification system that the system became more coherent.
The matrix applies the context, defined by the land use and density, against vehicular capacity. This pairing provides a relatively simple way to classify street types encountered in most urban scenarios.

Vehicular capacity – street family names
The vehicular capacity names were relatively easy to develop: Urban streets generally have high, medium, or low vehicular traffic volumes and need to be designed accordingly. This capacity was therefore applied to the following naming convention:
Boulevard: 3+3 lanes, high vehicular capacity
Avenue: 2+2 lanes, medium vehicular capacity
Street: 1+1 lane, low vehicular capacity
Access Lane: 1+1 or single shared lane

These street family names are familiar to most designers, some of who may not agree with the very definitive descriptions applied. For example a Boulevard is generally understood to be a wide, median divided arterial thoroughfare and to have service or access lanes connected and parallel to the main street. However, since the intention was to develop an urban street design manual specific to Abu Dhabi with a clearly explained naming convention, this street family naming system was accepted locally.

Land use and density – context names
The development context was defined by considering the land use and density (expressed in building height) of development along a street frontage leading. The result was the following context names:

City: High-density mixed use
Town: Medium-density mixed use
Commercial: Medium-density office or retail use
Residential: Low-density residential use
Industrial: Low-density industrial use

An additional frontage type, that of “no active frontage.” was also included to cover areas where little pedestrian activity was anticipated. Both land use and density are important considerations when understanding and designing for anticipated pedestrian activity along a street. The Abu Dhabi Manual places the needs of pedestrians first.

Street typology matrix
With the context and family names defined, the street typology matrix moved into a more complete form (see table at the top of this column). This matrix allowed the majority of streets, the so-called “80 percent standard streets,” to be easily defined. For example, a heavily trafficked street in a predominantly designated commercial area would be defined as a Commercial Boulevard and the design requirements from the table at the bottom of this page would be applied to it.

Additional matrix information
Once the basic matrix was developed, it became apparent that additional information could be illustrated using this format. A matrix approach was therefore applied to junction spacing and vehicle operating speed. Street speeds are easily inserted into the street typology matrix; they allow designers to identify the required changes in operating speed based on changing land use.

The use of a matrix classification system has allowed the Abu Dhabi Urban Street Design Manual to discard the traditional functional classification system. Street design in Abu Dhabi will be based on the activity that occurs in the public realm — as defined by the adjacent land use and pedestrian movement requirements — as much as, if not more than, by vehicular capacity. This, it is hoped, will allow Abu Dhabi street designers to respond to different urban environments and provide the emirate with a valuable tool — one that can be used to create walkable, sustainable cities that rival the best in the world.

Flexibility and adaptability
It is also recognized that the matrix classification system is very flexible and can be adapted for any specific series of land uses or vehicular capacity requirements. In this way the matrix can be developed to reflect the specific needs of all street design requirements. It is expected that the adoption of this system will assist in the development, design and construction of truly context-driven streets.

Colin Hill is a civil engineer, educated in the United Kingdom, who has been in Abu Dhabi for 10 years. For the past three years he has been director of transport at Otak International, working on design and planning projects in the Gulf region. Rudayna Abdo is director of planning in Otak’s Abu Dhabi office.
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