United States Department of Transportation
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Analysis and methods of improvement of safety at high-speed rural intersections.
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2012-04-01
[PDF-39.47 MB]
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Alternative Title:Joint Transportation Research Program Technical Report Series : Civil Engineering
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Edition:Final report.
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Abstract:Since 2006, INDOT has been preparing an annual five‐percent report that identifies intersections and segments on Indiana
state roads that require attention due to the excessive number and severity of crashes. Many of the identified intersections are two‐way, stopcontrolled
intersections located on high‐speed, multi‐lane, rural roads. Some contributing design and human factors have been identified while
other factors still await investigation. Multivariate ordered probit models have been developed to help identify additional factors of the
frequency and severity of crashes. These models can estimate how much different factors increase the frequency of crashes at several levels of
injury severity (fatal/incapacitating, non‐incapacitating/ possible, property‐damage‐only). They have a unique ability to account for unobserved
but common conditions that affect all of the crash severity levels. Recommendations for safety countermeasures are made based on both of
these research results and our study of published reports of other authors.
The statistical analysis was performed on 553 existing intersections in Indiana and 72 existing intersections in Michigan using crash data reported
during a four‐year period. The identified safety factors include: presence of horizontal curves within the intersection vicinity, traffic volume on
the major road, land use, population of the area surrounding the intersection, and the minor road functional class (traffic volume on minor road
unknown), nearby at‐grade railroad crossings, intersection conspicuity to drivers on the major road, acceleration lanes for both left and right
turns, median width, intersection angle, and number of intersection legs. These results are in line with other research results as documented in
the literature review. Based on the results of this and other studies, recommendations are made to improve safety at new intersections as well as
at existing intersections. For new intersections, construction of medians wider than 80 feet is suggested. Where this is not possible and a
narrower median needs to be constructed, adding a parallel acceleration lane for vehicles turning left from the minor road is suggested.
Intersections should be placed at a sufficient distance from horizontal curves and from at‐grade railroad crossings. Solutions with indirect leftturn
lanes (Michigan U‐turns, J‐turns) are recommended. At existing intersections experiencing excessive numbers of crashes involving vehicles
from the minor road, median closure should be considered or a median opening should be restricted to certain maneuvers. Median acceleration
lanes can be added in order to allow a two‐stage maneuver for left turns from the minor road. Enhanced guide and warning signage can be used
to improve intersection conspicuity; adding road illumination can especially help at night. The practice of adding left‐ and right‐turn bays should
be continued as this is a proven intersection safety improvement practice. Applying these countermeasures may help improve safety and avoid
the construction of expensive grade separations. Finally, advanced intersection collision avoidance systems, such as road‐side dynamic signs
warning drivers on the minor road about a short gap on the major road, should be the subject of pilot studies in Indiana. Experiments in other
states have indicated that these systems help drivers choose safe gaps.
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