Influence of Road Cross Section on Access Spacing

In 2003, the Transportation Research Board (TRB) published the Access Management Manual. This document was the first large-scale effort since the 1982 publication of Access Management for Streets and Highways published by the United States Department of Transportation. Both documents provided guidance about how access management can be successfully accommodated in a way that can enhance safety as well as traffic operations. Many of the techniques included in these manuals were developed based on mature research and the resulting recommendations and guidelines provided quantifiable information about how best to successfully provide access management. For example, these documents provided clear…

In 2003, the Transportation Research Board (TRB) published the Access Management Manual. This document was the first large-scale effort since the 1982 publication of Access Management for Streets and Highways published by the United States Department of Transportation. Both documents provided guidance about how access management can be successfully accommodated in a way that can enhance safety as well as traffic operations. Many of the techniques included in these manuals were developed based on mature research and the resulting recommendations and guidelines provided quantifiable information about how best to successfully provide access management. For example, these documents provided clear direction regarding the use and type of medians, and clearly identified the expected effectiveness resulting from converting a road without a median to one that includes a median. The Access Management Manual (TRB, 2003) also includes substantial information that can help an agency establish an access management program and incorporate a wide variety of strategies into this program. In the manual, access points include the intersections of public roads as well as driveway locations; however, most of the supporting research for the spacing of driveways is based on simple human factor and geometric principles that are applied for standard highway design procedures and have not been thoroughly evaluated for access spacing conditions based on a variety of road cross section and functional purpose configurations. The primary goal of this proposed research is to better understand how driveway spacing and the associated roadway cross sectional features influence safety and operations. Since the separation of conflict points will generally improve safety, it is critical that the transportation industry understand how to balance access spacing decisions that accommodate the needs of the adjacent land use while also enhancing safety. This proposed research effort, therefore, will be an initial effort to identify how drivers react to the increased workload demands when navigating a corridor with a variety of driveways and physical characteristics. To date, little research has focused on quantifying the various conflicts at driveway locations. This lack of research has been due to a number of data collection limitations. There are numerous combinations of road features that may influence assess spacing and identifying and studying these configurations is an onerous task. This research effort, therefore, proposes using a driving simulator supplemented with field analysis to try to identify critical cross sectional elements that must be included in consideration of access spacing decisions. The research team intends to use the outcomes of this research effort and incorporate any substantive findings into the national Access Management Guidelines (currently under development by members of the research team).