In Myrtle Creek, Oregon, an advanced curve speed warning system installed on I-5 reduced the speed of 76 percent of drivers surveyed.
Date Posted

Field Evaluation of the Myrtle Creek Advanced Curve Warning System

Summary Information

In Myrtle Creek, Oregon, the Department of Transportation prepared an evaluation of an advanced curve warning system (ACWS) deployed along a dangerous curve on Interstate 5. This warning system consisted of a radar unit for speed measurement and a dynamic message sign that displayed the speed of the vehicle. The evaluation report prepared in June, 2006 presents the results of a quantitative and qualitative before and after evaluation of a dynamic curve warning system deployed on both the northbound and southbound approach of I-5. Many of these deployments have been directed at improving truck safety for long downgrades or reducing rollover potential on curves. Despite additional warning signs and other modifications, some curves continued to exhibit higher than expected crash frequencies. ITS technologies such as advanced curve warning systems have the potential to enhance the effectiveness of static warning devices.


As part of the qualitative portion of the evaluation, an intercept survey of motorist perceptions of the advance curve warning system was conducted at the closest rest areas on both sides of the interstate. The southbound rest area was approximately 26 miles from the curve and the northbound rest area was approximately 35 miles from the curve. Surveyors were set up at the rest areas over a three day period to recruit willing motorists to fill out a two minute survey. The survey asked questions about recognition, importance, placement, and visibility.

The survey indicated:
  • Most drivers (76 percent) slowed down in response to the dynamic message signs that display their speed on each approach. Approximately half of the motorists surveyed who did not slow down indicated that they were already traveling below the advised speed.
  • 79 percent of drivers noted the sign was placed in an adequate location.
  • 84 percent of drivers thought the sign information aided in the safe navigation of the curves.
The quantitative evaluation involved obtaining speed measurements in the field using a laser speed detection and ranging device. Speed measurements were taken separately for vehicles and trucks. Data collection locations on the northbound and southbound sides were exactly the same for the before and after analysis to avoid any bias. Four data collection visits occurred prior to installation of the ACWS and three visits occurred after installation with conditions being similar for before and after.
  • The ACWS was effective in reducing the mean speeds of passenger cars and trucks by approximately three mi/h for the southbound direction and two mi/h for the northbound direction.
  • The distribution of vehicle speeds was statistically different with a lower number of vehicles in the higher speed bins.
The results of the evaluation indicate that the advanced curve warning system on I-5 in Myrtle Creek, Oregon is effective at reducing the speeds of the majority of vehicles entering the curve area.
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