详情

Guidance for the Setting of Speed Limits

项目名称：	Guidance for the Setting of Speed Limits
摘要：	Speed management has long been a concern of transportation agencies, dating back to research from the 1960s which showed that vehicles traveling excessively below or above the speed limit were overrepresented in crashes on rural highways and interstates. Inappropriate speed limits are more likely to cause larger speed variability and a larger mean difference from the posted speed. It is desirable to achieve balance for safety between the various types of speed classifications: operating, posted, statutory, and design speed. Historically, research has shown that increases in speed differential tend to have more adverse safety impacts than higher mean speeds. Some evaluation studies have shown increases in traffic crashes and/or fatalities in some states where the statutory speed limit had been increased. However, other studies found either marginal or no changes in traffic safety, while others found safety improvements after speed limit increases. The repeal of the National Maximum Speed Law in 1995 led to a series of additional studies and statutory changes. Ideally, the design speed will exceed or match the posted speed and operating speed, but that is not always the case. While the design speed for an existing roadway is based on geometric features, posted speed limits have historically been established based on state statute or an engineering study. Engineering studies often consider the 85th percentile speed during free-flow conditions when determining the posted speed. In some cases, the 85th percentile speed is higher than the design speed. In these situations, the engineer is faced with the dilemma of determining a posted speed above the design speed without the ability to fully quantify the safety risk. NCHRP Report 504 identified general relationships between design speed, operating speed, and posted speed limit; however, it is unclear how these various speeds relate to safety performance. The objectives of this research are to (1) identify and describe factors that influence operating speed and (2) provide guidance to make informed decisions related to establishing speed limits on roadways. The guidance should address the following, at a minimum: 1. An approach for determining the relationship between operating, design, posted and statutory speeds and how the differences among them impact safety performance. This may also include quantitative and/or qualitative models to predict the safety performance associated with the differences between operating, posted, statutory and design speeds. Identification and classification of nationwide data including, but not limited to, geometric design, access density, signal density, traffic volume characteristics, and enforcement practices that may impact operating speed. 3. An analysis of the 85th percentile speed and other statistical measures and factors as appropriate methods for setting speed limits. 4. Implications of setting a speed limit lower than those recommended using the factors identified above. The focus of the research should be on roadway functional classifications of minor arterials and higher as defined by AASHTO.
状态：	Active
资金：	500000
资助组织：	National Cooperative Highway Research Program
项目负责人：	Bush, Mark S
执行机构：	Texas A&M Transportation Institute, College Station
主要研究人员：	Fitzpatrick, Kay
开始时间：	20161007
预计完成日期：	20190407
实际结束时间：	0