MEANS TO REDUCE OPERATING SPEEDS ON CURVES Adam Vest Kimley-Horn Dr. Nikiforos Stamatiadis, P.E University of Kentucky Basic Idea Provide driver with clues to impact operating speed Reduce proliferation of signs Improve effectiveness of traffic control devices Objectives Evaluate effectiveness of currently used selected warning signs and pavement edge lines Determine traffic control combinations that could affect operating speeds Review of Literature Transverse lines Can reduce operating speeds effectively Act as a visual warning Most studies showed speed reductions Pavement markings Wider edge lines not so promising 1
Review of Literature (cont d.) Warning signs Benefits increased when coupled with other warning signs or devices Additional warning signs or devices draw attention Flashing lights increase visibility and reduce speeds Review of Literature (cont d.) Additional markings usually help in reducing speeds Great variation among sites Flashing lights draw attention Site Selection Site Example Selection criteria sharp rural curve history of speed related crashes long tangent section no vertical grade no intersecting roadways or commercial activity 2
Curve Treatments Existing Treatment Warning Sign with Flags Sign with Flashers New Warning Sign Flashers both Signs Post Delineators 3
Speed Measurement HI-STAR Vehicle Magnetic Imaging gtraffic Analyzers Chevrons Large Arrow Speed Measurement Layout Distance between Stations (m) Site 1-2 2-3 1 60 65 2 120 120 3 75 75 1 2 3 Analysis Approach Speeds at each measurement location Speed differences between locations Speed differences between first and last locations Day-night comparisons 4
Analysis Measures Site 2, Average Speeds Average speed Difference among treatments Standard deviation Difference in speed consistency/spread 85 th percentile speeds Difference among treatments t t Speeds over 85 th percentile speeds Difference for high speeds Average Speed (mph) 55 50 45 40 35 30 51.7 48.9 46.3 51.0 47.6 44.6 No Treatment Warning Sign w/ Flags 52.3 51.9 48.7 48.7 45.9 Warning Sign w/ Flashing Lights 45.3 52.5 52.5 48.3 44.5 New Sign Both Signs w/ Flashing Lights Treatments 49.3 45.7 Post Delineators 52.0 1 2 3 47.5 43.4 Transverse Lines C umulative Percentages Site 2, Location 3, Cumulative Dist. 100 No Treatment 90 Warning Sign w/ Flags Warning Sign w/ Flashing Lights 80 New Sign Both Signs w/ Flashing Lights 70 Post Delineators Transverse Lines 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 Group Median (mph) Speed Reduction 1-3 (mph/%) Treatment Site 1 Site 2 Site 3 Ei Existingi -7.7/15.1 77/151-6.3/12.2 63/122-5.0/9.3 50/93 Flags -7.6/14.9-6.9/13.4-5.4/10.0 Lights -- -7.1/13.5-5.9/10.6 New Sign -7.7/14.8-7.5/14.3-5.9/10.8 Both Lights -- -8.7/16.4 87/64-5.7/10.5 57/05 Delineators -8.0/15.4-7.5/14.2-4.2/8.0 Transverse -7.7/14.9-9.0/17.3-3.2/6.1 Arrow -7.5/14.6 -- -- Chevrons -- -- -5.3/10.1 5
Standard Deviation (mph) Treatment Site 1 Site 2 Site 3 Ei Existingi 80 8.0-6.6 66 58 5.8-5.0 50 55 5.5-5.2 52 Flags 8.7-6.7 5.7-4.7 6.0-5.5 Lights -- 6.2-5.4 5.7-4.9 New Sign 6.5-4.8 6.2-5.0 6.0-5.0 Both Lights -- 6.1-5.4 5.8-5.1 5.1 Delineators 6.4-4.8 6.4-5.3 5.9-5.4 Transverse 6.8-5.1 6.1-5.6 5.6-5.0 Arrow 6.1-4.8 -- -- Chevrons -- -- 5.7-5.4 85 th Percentile Speeds 1-3 (=/> %) Treatment Lee Greenup Henry Ei Existingi 16.5/17.2 13.3/16.93/16 92/142 9.2/14.2 Flags 16.1/18.0 15.0/19.2 10.0/15.3 Lights -- 13.4/17.6 10.4/14.7 New Sign 16.2/19.8 15.3/18.4 11.5/15.3 Both Lights -- 16.4/20.0 64/200 11.5/15.2 5 Delineators 17.0/20.5 13.9/19.1 7.9/11.3 Transverse 16.2/20.6 16.0/20.7 6.1/10.8 Arrow 16.0/20.8 -- -- Chevrons -- -- 10.3/15.5 Conclusions Some treatments moderately reduce operating speeds Flashing lights are effective, especially with the use of the new combination sign Transverse lines showed promising speed reductions Several treatments affected the over 85 th percentile speeds more than any other measure Night time reductions were greater for flashing lights (as expected) 6