Benefit-to-cost ratios for six dynamic message signs on two freeways ranged from 1.38:1 to 16.95:1 based on total crashes; however, hazard warnings posted during incidents were ineffective at reducing secondary crashes.

Experience with safety treatments on I-26 and I-40 in Asheville, NC

Asheville,North Carolina,United States

Summary Information

This project examined the benefits and costs of a series of dynamic message signs (DMS) installed on I-26 and I-46 in the vicinity of Asheville, North Carolina. As requested by the State Highway Patrol, three DMS units were installed on each interstate in problem areas where numerous secondary crashes were reported. The messages posted on each DMS were intended to warn motorists of incidents ahead and suggest alternate routes when applicable.

A naive before and after analysis was conducted to assess changes in crash rates relative to prevailing conditions of increased traffic and increased potential for crashes in each area.. The before period included crash data from June 1, 1998 through September 30, 2003 (5 years, 4 months) and the after period included crash data from July 1, 2004 through October 31, 2009 (5 years, 4 months). Data during construction (October 1, 2003 through June 30, 2004) was omitted from the analysis.

The focus area used to assess impacts at each site included roadway sections located 0.1 miles upstream from a DMS to 5 miles downstream of a DMS. Researchers tracked total crashes, rear end crashes, and run off road crashes. A primary goal was to assess impacts on secondary crashes (target crashes) defined as crashes that occurred in a time window of 30 to 120 minutes after an initial crash. The time window accounted for the time it would take the North Carolina DOT to confirm and post a new hazard warning message on a DMS (approximately 30 minutes) and the typical time required to clear an incident (approximately 2 hours).

Benefits were calculated based on the change in annual crash costs between the before and after periods. Operational and other benefits related to the project were not included in the analysis. The costs of the project were calculated from the actual construction costs and annual maintenance costs. Researchers noted that the evaluation did not account for other treatments that took place in the study area (i.e., installation of rumble strips) at the time of the evaluation.

  • The benefit-to-cost ratio for the I-26 treatment was estimated at 1.38 considering total crashes, and -0.15 considering only target crashes (secondary crashes).
  • The benefit-to-cost ratio for the I-40 treatment was estimated at 16.95 considering total crashes, and -1.04 considering only target crashes (secondary crashes).
Overall, safety improved after the DMS system was installed at each site; however, researchers concluded that the system was not effective at reducing the number of secondary crashes as expected.

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Hazard Elimination Project Evaluation: Evaluation of Six Dynamic Message Signs on I-40 and I-26 in Buncombe and Henderson Counties

Author: Simpson, Carrie L.

Published By: North Carolina DOT

Source Date: 12/17/2010

Other Reference Number: Project W-4440 and W-4444



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Goal Areas


Typical Deployment Locations

Metropolitan Areas


DMS, CMS, VMS, Changeable Message Signs, Variable Message Signs

Benefit ID: 2013-00840