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Planning Guidance for the Installation and Use of Technology Devices for Transportation Operations and Maintenance

ENTERPRISE Transportation Pooled Fund Study

Curve Warning System Guideline 2 - High Risk Locations

Purpose: To influence driver behavior in horizontal curves where an excessive level of crashes are occurring.

The planning guideline for curve warning systems are presented as one tool to assist agencies in selecting deployment locations, and are not a replacement for the planning or design process. Also, prior to deploying a Curve Warning System, ensure the basic requirements of the MUTCD (2009 Edition Chapter 2C. Warning Signs and Object Markers) have been met at the location of concern.

Engineering judgment should be used to assess potential implications that may result from installation of Curve Warning Systems. This planning guideline does not mandate the use of Curve Warning Systems.

1a. Crash Rate Factor. The Crash Rate (crashes per million vehicle miles traveled) within the vicinity of the curve exceeds 1 crash per million vehicle miles traveled, when computed over a 3 year period.

Calculation: CR = (# of crashes * 106)/(Length * ADT*365Days*3 years). (1)

OR

1b. The curve has been identified as a location with a high probability for crashes, using the locally accepted crash analysis (e.g. one of the top 10 locations in the state most prone to curve related accidents, or on a list of areas most prone to crashes).

AND

2a. Speed Factor. The number of vehicles that has been observed to enter the curve at speeds that are considered unsafe is more than expected, based on the judgment of local engineers. (e.g., high profile vehicles entering rural curves at speeds believed to be unsafe, the 85th percentile speed exceeds the recommended or posted speed).

OR

2b. There is evidence of near misses and/or rapid deceleration either within the curve or in the approach to the curve. (e.g. pavement skid marks, scrapes along guard rails)

Reference:

(1) Oregon Department of Transportation. Myrtle Creek Curve Crash Analysis. 2008.