Sidewalk/Street Design

Article

"Streets and their sidewalks, the main public places of a city, are its most vital organs."

The quote above from Jane Jacobs describes the critical role streets and sidewalks play in our communities. Our streets and sidewalks are the centerpieces around which great places can be developed. In addition to facilitating the movement of people and traffic, the design, layout, size, and style of streets and sidewalks have a direct impact on the overall character and feel of a place.

Consider, for example, the street shown in the image at right.

While a variety of characteristics help shape this great street, the type, texture, and color of the pavement undoubtedly play a significant role.

Imagine how this street would look with a standard, generic pavement type and sidewalk - the character changes dramatically!

Credit: css.org

In the image at right, the pavement striping, color, width, and streetscape amenities found in the corridor largely contribute to the area's appeal.

Also note that the bike lane has been designed in a contrasting color to increase driver awareness and enhance the street's aesthetic character. Although such details are often overlooked when considering street improvements, their impact on the streetscape can be striking.

Street Width:

In a great street, how much space should be allocated for pavement? Vehicular capacity needs, bicycle lane or shoulder provisions, and the design vehicle/desired design speed for the facility influence the appropriate street width for a corridor. Capacity considerations will generally govern how many lanes are required for vehicular traffic, while the facility's target speed and design vehicle influence how wide each lane should be. The presence and type of median treatments and the need to provide bicycle lanes will also influence overall street width.

Capacity generally refers to the quantity of vehicular traffic a street is able to carry at a chosen level of service (LOS).

It is important to recognize the relationship between roadway width and the target level of service set for a facility.

For example, if the target performance for a given roadway is set at LOS B, the number of lanes needed to accommodate through-traffic and turning movements will be much higher than if the target is set at LOS at E. In many cases, setting higher level of service targets will result in a much wider street. Setting lower targets (i.e. tolerating more congestion on a given facility) can help limit street width and/or free up space for non-vehicular, multimodal treatments.

For many of the place types considered in this guide, namely Downtown Main Streets, Small Town Downtowns, Mixed-Use Districts, and Civic/Educational Corridors, vehicular mobility is a lesser priority; therefore it may be appropriate to design narrower streets with lower vehicular capacity. Roadway planners should work with local agencies, businesses, and residents when determining specific requirements for each place. See the Capacity section of this manual for more information.

Vehicular Travel Lane Width:

Based on the perception that wider lanes are safer, the St. Louis region has historically used 12-foot travel lanes for most streets. Although wider lanes are typically safer for higher-speed travel, at the lower speeds which are more common in the place types discussed in this guide, lane width has less effect on safety and operations. Recent studies show that at speeds of 35 mph or less, there is very little difference in substantive safety performance for lane widths of ten, eleven, and twelve feet.

Narrower travel lanes can also have a traffic calming effect on a street by causing vehicles to drive slower; conversely, wider lanes often encourage motorists to travel above the facility's target speed.

Because this guide focuses on place types where slower speeds are desirable (e.g. downtown areas and mixed use districts), lane widths under twelve feet are recommended. (Lane widths less than 10' are not recommended). Tables 6.2 and 6.3 of the ITE publication Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities provides excellent design parameters for arterial and collector streets. These tables recommend a lane width of 10-11 feet for the majority of place types, including those discussed in this guide. Chapter 9 of the ITE publication also provides useful guidance on lane width.

Bicycle Lane Considerations:

A bicycle lane should be provided along streets which are designated bicycle routes, whenever feasible. When bicycle lanes are not possible due to existing right-of-way constraints, a wider outside travel lane should be considered. A shared bicycle-parking lane may be provided along streets needing bicycle lanes and on-street parking. General width recommendations are as follows:

Dedicated bicycle lane: minimum width is four (4) feet with an open shoulder or five (5) feet when bordered by a curb, guardrail, or other roadside barrier
Wider outside travel lane
Shared bicycle-parking lane: 12' (7' for parking, 5' for bicycle travel)

Sidewalk Width:

A number of (often conflicting) forces influence the appropriate width for sidewalks along a given corridor, including the current or anticipated pedestrian presence, abutting land uses, and utility requirements. See Chapter 3.2.3 of AASHTO's Guide for the Planning, Design, and Operation of Pedestrian Facilities for more guidelines on establishing a suitable sidewalk width in various types of corridors.

Although the minimum clear width required for sidewalks is four (4) feet, most of the place types discussed in this guide, especially those with a significant pedestrian presence will elect to include wider sidewalks.

See the Pedestrians section of this manual for place-type-specific recommendations on sidewalk width. The table at right, from Oregon Metro's "Creating Livable Streets," also provides excellent guidelines for minimum width requirements as they relate to other elements of the streetscape.

Credit: Oregon Metro

Aesthetic Treatments:

Choosing the appropriate width for streets and sidewalks, although important, is just one of many considerations in creating attractive, livable streets and places.

Various design treatments, such as colored or textured pavement, brick pavers, cobblestones, and granite curbs can be used to visually enhance the streetscape, as shown in the images at right and below.

Credit: css.org

Credit: greatstreets.org

Credit: Charlier Associates

Credit: greatstreets.org

Although these treatments typically cost more to construct, they help create a much more attractive place, which can be an investment that pays dividends in local economic return.

Some treatments, such as the cobblestone midblock pedestrian crossing shown below, can also have traffic calming effects at key locations.

Credit: CH2M HILL

Credit: CH2M HILL

Linking the design of these treatments with the architectural character of surrounding land uses creates an even more attractive and cohesive corridor.

Treatments such as raised brick pavers or cobblestones should not be used in bicycle lanes, as they can be hazardous or uncomfortable for bicyclists to navigate.

Likewise, decorative sidewalk treatments should not interfere with ADA compliance. The image at right is an example of an attractive, ADA-compliant treatment.

Inserting artistic design treatments intermittently, rather than along the entire sidewalk (as shown in the image below, at left), is a cost-effective way to enhance the streetscape.

When linked with the surrounding land uses, colored sidewalks (as shown in the image below, at right) can be a great way to revamp a corridor. This treatment is generally less expensive than pavers or other special material applications.