Many challenges are encountered when designing highway projects that pass through urban areas. Arterial and collector highways are typically designed for moving vehicles as quickly and efficiently as possible. However, many times these highways are the centers of the communities that have developed around them. Increasingly, these communities have requested that these highways be redesigned using context sensitive solutions that enhance the appearance and, in some cases, the function of the highway.
Many of the context sensitive solutions involve introducing roadside treatments such as trees, sculptures, and signs. In addition to enhancing the appearance of these highways, these designs are often also intended to slow or "calm" traffic to enhance safety. However, many of these features are considered fixed objects, as defined in the AASHTO Roadside Design Guide
, and will often be located within the design clear zone. Recommended clear zone dimensions generally represent minimum offset distances. Thus, reducing existing, wider clear zones by introducing fixed objects even at the specified minimum distances recommended in the Roadside Design Guide
, reduces the recovery distance. In addition, slowing traffic may cause changes in traffic operations. Therefore, it is crucial that the impacts of these designs be understood so that decisions can be based on facts. There is also a need to identify designs that have performed acceptably and a need to develop new design guidelines that enhance the roadside environment while being forgiving to errant vehicles. These guidelines will provide the AASHTO Task Force for Roadside Safety with critical information needed to update Chapter 10 of the Roadside Design Guide
The objectives of this project are to develop (1) design guidelines for safe and aesthetic roadside treatments in urban areas and (2) a toolbox of effective roadside treatments that (a) balance pedestrian, bicyclist, and motorist safety and mobility and (b) accommodate community values. The guidelines will be based on an evaluation of the effects of treatments such as trees, landscaping, and other roadside features on vehicle speed and overall safety. The guidelines will generally focus on arterial and collector-type facilities in urban areas with speed limits between 25-50 mph.
Accomplishment of the project objective(s) will require at least the following tasks.
) Conduct a literature review of available information on the design, operational, and traffic calming effects, aesthetics, and safety performance of roadside treatments along urban arterials and collectors. (2
.) Conduct a survey of the states and selected cities to identify context sensitive roadside design treatments that have been implemented or are being considered for urban facilities. The availability of data relating to these treatments, such as location, crash histories, traffic volumes, operating speeds, site photographs and documentation, and community acceptance, will also be determined. The survey should also collect information on ongoing research efforts and urban clear zone policies. (3.
) Submit an interim report that summarizes the findings of Tasks 1 and 2, and includes an updated, detailed work plan and estimate for evaluating context sensitive roadside design treatments. The survey results will be used to identify highway projects where context sensitive solutions have been constructed. The plan will include a task to analyze the operational performance and crash history before and after implementation. Crash data associated with roadside treatments will be further investigated to identify properties that result in serious injuries. The plan shall also include a proposal to investigate the basis of the 4 inch maximum trunk diameter for roadside trees considered to be non-hazardous to errant motorists. (4
.) Meet with the NCHRP panel to review the Task 3 interim report, approximately 1 month after its submittal. Submit a revised interim report addressing the panel's review comments. (5.
) Execute the approved work plan. (6.
) Submit a final report documenting the entire research effort. The final report shall describe how the project was conducted and include (a) an appendix that contains the design guidelines for safe and aesthetic roadside treatments in urban areas and (b) a toolbox of effective roadside treatments that balance pedestrian, bicyclist, and motorist safety and mobility and accommodates community values.
The project has been completed. The final report has been published.
Product Availability: NCHRP Report 612: Safe and Aesthetic Design of Urban Roadside Treatments