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CHAPTER 1
Background
Problem Statement The objectives of NCHRP Project 16-04, therefore, were
and Research Objective to develop (1) design guidelines for safe and aesthetically
pleasing roadside treatments in urban areas and (2) a toolbox
Many challenges are encountered when designing highway of effective roadside treatments that can balance the safety
projects that pass through urban areas. Arterial and collector and mobility needs of pedestrians, bicyclists, and motorists
highways are typically designed for moving vehicles as quickly and accommodate community values. The guidelines devel-
and efficiently as possible. However, many times these high- oped in this project were based on an evaluation of the effects
ways are at the center of a community that has developed of treatments such as poles, trees, landscaping, and other
around them. Increasingly, citizens of these communities roadside features on vehicle speed and overall safety. The
have requested that highway corridors be redesigned using guidelines generally focus on arterial and collector-type facil-
roadside solutions that enhance the appearance and, in many ities in urban areas with speed limits between 40 and 80 km/h
cases, the functional use of the highway roadside. (25 and 50 mph).
Many of these solutions involve introducing roadside
treatments such as trees, street furniture, and signs. In addi-
Scope of Study
tion to enhancing the appearance of these highways, some
roadside treatments are intended to slow or "calm" traffic. This study includes two approaches for identifying the
However, many of these same features are considered fixed potential influence of urban roadside features on system-
objects and will likely be located within the design clear zone. wide safety. The first approach was a corridor analysis of
Recommended clear zone dimensions vary based on sideslope, over 241 km/h (150 mi) of urban roadways, in which the re-
design speed, and traffic volume; however, the generally wider search team examined historic crash information to identify
road widths that are needed to include roadside treatments are common roadside crash conditions. Crashes were displayed
usually difficult to achieve and impractical in constrained on spot maps and also summarized individually for addi-
urban settings. As a result, designers often use minimum lateral tional analysis. The research team then used video to record
offset distances that simply enable operational use of the road. the corridors and the placement of roadside features. The
Thus, introducing fixed objects--which can result in the re- result of this corridor analysis is proposed urban control
duction of existing wider lateral offsets--can potentially have zones where the likelihood of crashes is significantly greater.
a direct impact on roadside safety. In addition, slowing traffic This information has then been used to develop recom-
may cause changes in traffic operations. Therefore, it is crucial mended guidelines for enhancing roadside safety in the urban
to informed decision making that the impacts of roadside environment.
enhancement designs be understood. There is also a need to The second approach to evaluating the roadside safety
identify designs that have performed in an acceptable manner problem was the assembly of case studies with crash type,
and to develop new design guidelines that will lead to enhanced crash severity, and before-after safety assessments. Ideally,
roadside environments and be forgiving to errant vehicles. a candidate case study would include the change of only one
These guidelines will provide the American Association of roadside feature so that the direct influence of that change on
State Highway and Transportation Officials (AASHTO) Tech- safety could be evaluated; however, such unique improve-
nical Committee for Roadside Safety with critical information ment projects are limited, so this case study task included
for the update of Chapter 10 of the Roadside Design Guide (1). general beautification projects with roadside enhancements
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and excluded projects with major reconstruction. The results well as future research needs identified during this research
of these case study evaluations were mixed, but an agency effort. In addition, this report includes four appendices.
seeking to perform a similar project can use the results to help Appendix A provides detailed information about the urban
understand the general safety performance that can be ex- control zone corridor sites. Appendix B includes the sum-
pected following the completion of the project. mary statistics for the case study sites. Appendix C includes
Chapter 2 of this report summarizes current knowledge an urban roadside design toolbox, and Appendix D provides
from literature on the urban roadside and objects commonly draft language for the urban chapter in the AASHTO Road-
placed in the urban roadside environment. Chapter 3 sum- side Design Guide (1). Appendixes A, B, and D are available
marizes the analysis procedures and subsequent findings for on the TRB website at http://trb.org/news/blurb_detail.
each task. Chapter 4 provides general research conclusions as asp?id=9456. Appendix C is appended to this report.
