INTRODUCTION: Since 2006, INDOT has been preparing an annual fivepercent

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, stop-controlled 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, nonincapacitating/

possible, and 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.

FINDINGS: 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 the following:

presence of horizontal curves within the intersection vicinity,

traffic volume on the major road, land use, population

of the area surrounding the intersection, 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 left-turn 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.