Study Details
Study Title: In-Service Performance Evaluation of Median Cable Barriers in Iowa
Authors: Savolainen et al.
Publication Date:MAY, 2018
Abstract: Median crossover crashes occur when errant vehicles depart from their intended lane of travel on divided roadways and traverse the median, ultimately striking a fixed roadside object or vehicle traveling in the opposite direction. These crash types are commonly associated with high-severity injuries due to the increased travel speeds and sharp impact angles experienced when a vehicle crosses the median. These crash types are caused by a wide variety of factors, including drowsiness, weather impacts, driver distractions, impaired driving, loss of control, and other factors. A common countermeasure selected by agencies to reduce the risk of cross-median crashes is median cable barriers. These high-tension cable barrier systems are designed to absorb the impact forces when struck by errant vehicles, reducing the vehicles’ speeds and containing them within the barrier system. While prior research has shown median cable barrier to be effective in various settings, Iowa has unique differences in topography, weather conditions, and other factors that motivate the need for additional research. This study involved an in-service performance evaluation to assess the efficacy of median cable barrier systems that have been installed in Iowa to date. In addition to examining impacts on traffic crashes, injuries, and fatalities, the study also involved an economic analysis of the cable barrier systems. The results show that median cable barrier systems have significantly reduced the number of fatal and severe injury crashes across the state. While these reductions have been accompanied by significant increases in less severe crashes, particularly property damage-only collisions, the barrier systems have been shown to provide a significant return on investment. The results of this study suggest that further implementation of median cable barrier systems is warranted. As such, installation guidelines are recommended based on various combinations of median width and annual average daily traffic.
Study Citation: Savolainen, P. T., T. J. Kirsch, R. Hamzeie, M. U. M. Johari, and E. Nightingale. "In-Service Performance Evaluation of Median Cable Barriers in Iowa." Report No. InTrans Project 15-546. Iowa Department of Transportation. Ames, Iowa. (May 2018).
Study Report: Download the Study Report Document
Comments: This study produced CMFs using two methods, cross-sectional regression and simple before-after methodology. Only the cross-sectional CMFs are included due to the fact that they have a higher reliability than the simple before-after CMFs.
CMFs Associated With This Study
Category: Roadside
Countermeasure: Increase Median Width
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
 |  | Cross median | All | Principal Arterial Other Freeways and Expressways | All |
Countermeasure: Install cable median barrier
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.38 | 62 | | Cross median | K | Principal Arterial Interstate | Not specified |
| 0.69 | 31 |  | Cross median | A | Principal Arterial Interstate | Not specified |
| 0.74 | 26 | | Cross median | B | Principal Arterial Interstate | Not specified |
| 1.11 | -11 | | Cross median | C | Principal Arterial Interstate | Not specified |
| 2.08 | -108 | | Cross median | O | Principal Arterial Interstate | Not specified |
Category:Speed management
Countermeasure: Raise posted speed
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.13 | -13 | | Cross median | All | Principal Arterial Other Freeways and Expressways | Not specified |
