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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
| REPORT |
| This report is an archived publication and may contain dated technical, contact, and link information |
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| Publication Number: FHWA-HRT-17-070 Date: August 2017 |
Publication Number: FHWA-HRT-17-070 Date: August 2017 |
The objective of this study was to undertake a rigorous before–after evaluation of the safety effectiveness—as measured by crash frequency—of cable median barriers in combination with inside shoulder rumble strips along divided roads. The study used data from three States—Illinois, Kentucky, and Missouri—to examine the effects for specific crash categories, including total, fatal and injury (KAB and KABC), and cross-median crashes. The research team did not include crashes occurring at or related to an intersection and animal-related crashes.
In Illinois and Kentucky, inside shoulder rumble strips were present prior to the implementation of cable barriers; as a result, the evaluation in Illinois and Kentucky determined the safety effect of adding cable barriers on divided roads where inside shoulder rumble strips were already present. On the other hand, Missouri installed inside shoulder rumble strips and cable median barriers at about the same time (or within a few years of each other); therefore, the evaluation in Missouri determined the combined safety effect of cable median barriers and inside shoulder rumble strips. A disaggregate analysis of the results did not reveal any specific patterns, possibly because of the limited sample size for cross-median crashes.
Table 27 presents the recommended CMFs when the before condition included inside shoulder rumble strips. The B/C ratio for this treatment was 8.28. Table 28 provides the recommended CMFs when the before condition had neither inside shoulder rumble strips nor cable median barriers. The associated B/C ratio for this treatment was 4.14.
The findings of this study indicate that the introduction of cable median barriers resulted in a reduction in head-on, opposite-direction sideswipe, and cross-median crashes. At the same time, the cable median barriers led to an increase in total crashes and a reduction in injury and fatal crashes.
