National Academies Press: OpenBook

Safe and Aesthetic Design of Urban Roadside Treatments (2008)

Chapter: Chapter 1 - Background

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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2008. Safe and Aesthetic Design of Urban Roadside Treatments. Washington, DC: The National Academies Press. doi: 10.17226/14171.
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2008. Safe and Aesthetic Design of Urban Roadside Treatments. Washington, DC: The National Academies Press. doi: 10.17226/14171.
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Page 4

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3Problem Statement and Research Objective 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 high- ways are at the center of a community that has developed around them. Increasingly, citizens of these communities have requested that highway corridors be redesigned using roadside solutions that enhance the appearance and, in many cases, the functional use of the highway roadside. Many of these solutions involve introducing roadside treatments such as trees, street furniture, and signs. In addi- tion to enhancing the appearance of these highways, some roadside treatments are intended to slow or “calm” traffic. However, many of these same features are considered fixed objects and will likely be located within the design clear zone. Recommended clear zone dimensions vary based on sideslope, design speed, and traffic volume; however, the generally wider road widths that are needed to include roadside treatments are usually difficult to achieve and impractical in constrained urban settings. As a result, designers often use minimum lateral offset distances that simply enable operational use of the road. Thus, introducing fixed objects—which can result in the re- duction of existing wider lateral offsets—can potentially have a direct impact on roadside safety. In addition, slowing traffic may cause changes in traffic operations. Therefore, it is crucial to informed decision making that the impacts of roadside enhancement designs be understood. There is also a need to identify designs that have performed in an acceptable manner and to develop new design guidelines that will lead to enhanced roadside environments and be forgiving to errant vehicles. These guidelines will provide the American Association of State Highway and Transportation Officials (AASHTO) Tech- nical Committee for Roadside Safety with critical information for the update of Chapter 10 of the Roadside Design Guide (1). The objectives of NCHRP Project 16-04, therefore, were to develop (1) design guidelines for safe and aesthetically pleasing roadside treatments in urban areas and (2) a toolbox of effective roadside treatments that can balance the safety and mobility needs of pedestrians, bicyclists, and motorists and accommodate community values. The guidelines devel- oped in this project were based on an evaluation of the effects of treatments such as poles, trees, landscaping, and other roadside features on vehicle speed and overall safety. The guidelines generally focus on arterial and collector-type facil- ities in urban areas with speed limits between 40 and 80 km/h (25 and 50 mph). Scope of Study This study includes two approaches for identifying the potential influence of urban roadside features on system- wide safety. The first approach was a corridor analysis of over 241 km/h (150 mi) of urban roadways, in which the re- search team examined historic crash information to identify common roadside crash conditions. Crashes were displayed on spot maps and also summarized individually for addi- tional analysis. The research team then used video to record the corridors and the placement of roadside features. The result of this corridor analysis is proposed urban control zones where the likelihood of crashes is significantly greater. This information has then been used to develop recom- mended guidelines for enhancing roadside safety in the urban environment. The second approach to evaluating the roadside safety problem was the assembly of case studies with crash type, crash severity, and before-after safety assessments. Ideally, a candidate case study would include the change of only one roadside feature so that the direct influence of that change on safety could be evaluated; however, such unique improve- ment projects are limited, so this case study task included general beautification projects with roadside enhancements C H A P T E R 1 Background

and excluded projects with major reconstruction. The results of these case study evaluations were mixed, but an agency seeking to perform a similar project can use the results to help understand the general safety performance that can be ex- pected following the completion of the project. Chapter 2 of this report summarizes current knowledge from literature on the urban roadside and objects commonly placed in the urban roadside environment. Chapter 3 sum- marizes the analysis procedures and subsequent findings for each task. Chapter 4 provides general research conclusions as well as future research needs identified during this research effort. In addition, this report includes four appendices. Appendix A provides detailed information about the urban control zone corridor sites. Appendix B includes the sum- mary statistics for the case study sites. Appendix C includes an urban roadside design toolbox, and Appendix D provides draft language for the urban chapter in the AASHTO Road- side Design Guide (1). Appendixes A, B, and D are available on the TRB website at http://trb.org/news/blurb_detail. asp?id=9456. Appendix C is appended to this report. 4

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TRB's National Cooperative Highway Research Program (NCHRP) Report 612: Safe and Aesthetic Design of Urban Roadside Treatments explores recommended design guidelines for safe and aesthetic roadside treatments in urban areas. The report also examines a toolbox of roadside treatments designed to balance pedestrian, bicyclist, and motorist safety and mobility.

NCHRP Report 612 includes four appendices, three of which are available online. The fourth, Appendix C, is included with the report.

Appendix A includes detailed information about the urban control zone corridor sites.

Appendix B includes the summary statistics for the report's case study sites.

Appendix C includes an urban roadside design toolbox, and

Appendix D provides draft language for the urban chapter in the AASHTO Roadside Design Guide.

Tables 19 and 20 on p. 43 of NCHRP Report 612 include incorrect information. The corrected tables are available online.

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