Access control design on highway interchanges
By: Hesham Rakha ... [et al.].
Contributors: Rakha, Hesham.; Arnold, E. D.; Virginia Transportation Research Council.; Virginia. Dept. of Transportation.
Series: VTRC -- 08-CR7; VTRC (Series) -- 08-CR7.
Publisher: Virginia Transportation Research Council
Published: 2008
Place of publication: Charlottesville, Va
Language: eng
Number of pages: 75
Subjects: Express highways -- Access control -- Standards -- Evaluation; Roads -- Interchanges and intersections -- Virginia -- Safety measures; Roads -- Interchanges and intersections -- Design and construction; Ramps (Interchanges)
Description: The adequate spacing and design of access to crossroads in the vicinity of freeway ramps are critical to the safety and traffic operations of both the freeway and the crossroad.  The research presented in this report develops a methodology to evaluate the safety impact of different access road spacing standards.  The results clearly demonstrate the shortcomings of the AASHTO standards and the benefits of enhancing them.  The models developed as part of this research were used to compute the crash rate associated with alternative section spacing.  The study demonstrates that the models satisfied the statistical requirements and provide reasonable crash estimates.  The results demonstrate an eight-fold decrease in the crash rate when the access road spacing increases from 0 to 300 m.  An increase in the minimum spacing from 90 m (300 ft) to 180 m (600 ft) results in a 50 percent reduction in the crash rate.  The models were used to develop lookup tables that quantify the impact of access road spacing on the expected number of crashes per unit distance.  The tables demonstrate a decrease in the crash rate as the access road spacing increases.  An attempt was made to quantify the safety cost of alternative access road spacing using a weighted average crash cost. The weighted average crash cost was computed considering that 0.6, 34.8, and 64.6 percent of the crashes were fatal, injury, and property damage crashes, respectively.  These proportions were generated from the field observed data.  The cost of each of these crashes was provided by VDOT as $3,760,000, $48,200, and $6,500 for fatal, injury, and property damage crashes, respectively.  This provided an average weighted crash cost of $43,533.  This average cost was multiplied by the number of crashes per mile to compute the cost associated with different access spacing scenarios.  These costs can assist policy makers in quantifying the trade-offs of different access management regulations.
Notes: Project manager, Eugene D. Arnold, Jr.

"January 2008"

Includes bibliographical references (p. 56-58).

Final contract report; March 2006-January 2008.

Also available online.

Sponsored by Virginia Department of Transportation 80596