Impact of Pavement Edge Line on Vehicular Lateral Position on Narrow Rural Two-Lane Roadways in Louisiana Xiaoduan Sun Jaehyun Park University of Louisiana at Lafayette Dean Tekell Nina Ludington Dean Tekell Consulting, L.L.C The 2007 Louisiana Transportation Engineering Conference Baton Rouge, February 13, 2007
Introduction Significant number of crashes occurred on rural 2-lane 2 highways each year in Louisiana The dominate type of crashes is ROR
Percentage of crashes by crash type and road width on Louisiana rural 2-lane highways 40% ROR Head-on Sideswipe 80% ROR Head-on Sideswipe Percentage 30% 20% 10% Percentage 60% 40% 20% 0% W< 20 20 W< 22 22 W< 24 W 24 Road Width (ft) 0% W< 20 20 W< 22 22 W< 24 W 24 Road Width (ft) (a) All crashes (b) Fatal crashes.
Crash rate by crash type and road width R (crashes per million VMT), 1.2 1.0 0.8 0.6 0.4 0.2 0.0 ROR Head-on Sideswipe W< 20 20 W< 22 22 W< 24 W 24 RF (fatal crashes per 100 million VMT),, 3.0 2.5 2.0 1.5 1.0 0.5 0.0 ROR Head-on Sideswipe W< 20 20 W< 22 22 W< 24 W 24 Road Width (ft) Road Width (ft) (a) All crashes (b) Fatal crashes.
Proper Proper pavement marking is considered one of inexpensive crash countermeasures
Purpose of Pavement Marking Marking edge lines intends to provide a visual guide which would help vehicles confining to the safer position within the travel lane.
Guidelines on Edge Line Implementation for Rural 2-Lane 2 Highways Previous MUTCD (1994) Updated MUTCD (2000) 1 Current LaDOTD Policy (1994) 2 Road Width No Requirement 20-ft or Wider 22-ft or Wider 1. MUTCD the Millennium Edition 2. LaDOTD Engineering Directives and Standards Manual (EDSM)
Concerned Issues Edge lines on narrow roadways MAY make motorists operate vehicles closer to the centerline, resulting in an increase of the risk of head-on and sideswipe collisions. A thorough investigation of this assumption on edge line marking implementation are necessary before LaDOTD generates a policy and begins implementation of the new edge line requirement contained in the latest edition of MUTCD.
Objective To investigate the impact of edge line markings on drivers behavior on narrow rural two-lane highways in Louisiana with traveled road width between 20 and 22 feet.
Measurements Vehicle lateral position Close to or crossing the road edge Close to or crossing over the centerline Maintaining a centralized position within the traveled lane Vehicle type (FHWA Schema F) Operating speed
Vehicle Lateral Position Road Edge Centerline
Measurement of Vehicle Lateral Position 0-1 ft 1-2 ft Centerline Road Edge 2 ft - Centerline Crossing Centerline
Data Collection Method After thoroughly experimenting with and evaluating several data collection methods, we used road tubes (also known as air-switch devices). If carefully designed, this method is more reliable, less intrusive, and easier to set up in the field than the other methods available.
Tube layout diagram
Site Selection Site ID State Highway # Alignment Speed Limit Pavement Width Pavement Condition Site 1 LA367 Tangent 55 MPH 20 Good Site 2 LA367 Curved 55 MPH 24 1 Good Site 3 LA 1113 Tangent 55 MPH 18.5 Poor Site 4 LA 98 Tangent 55 MPH 20 Good Site 5 LA 98 Curved 55 MPH 20 Good Site 6 LA 98 Tangent 55 MPH 21 Good Site 7 LA 354 Tangent 55MPH 21 Poor Site 8 LA 354 Tangent 55 MPH 2 20 Fair Site 9 LA 354 Curved 55 MPH 2 20 Fair Site 10 LA 354 Tangent 55MPH 20.5 Good 1. Partially road widened at the curve 2. Advisory speed limit of 45 MPH
Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Site 9
Results Speed Change 70 Speed Limit 55 MPH Advisory Speed 45 MPH BEFORE AFTER 60 Average Speed (MPH) 50 40 30 20 10 0 T1 T2 T3 T4 T5 T6 T7 C1 C2 C3 Study Sites
Results Position Change in 0-1 ft & crossing centerline % Crossing center line Decrease Increase % Close to road edge Increase Decrease Desirable Undesirable
Daytime changes (P(0-1) A - P(0-1) B 50% 40% (2nd qurdrant) (1st qurdrant) 30% 20% C2 10% T7 0% C1 T4 T6-10% T1 T3-20% C3-30% T2-40% (3rd qurdrant) (4th qurdrant) -50% -50% -40% -30% -20% -10% 0% 10% 20% 30% 40% 50% (P A (CL) - P B (CL) ) (a) Change in percentage 200% 150% (2nd qurdrant) (1st qurdrant) (b) Percentage change rate Δ = p A x p B x p B x 100% (P(0-1) A - P(0-1) B ) / P(0-1) B 100% 50% 0% -50% -100% -150% -200% (3rd qurdrant) T1 T3 T7 C1 C3 T4 T6 T2 (4th qurdrant) -200% -150% -100% -50% 0% 50% 100% 150% 200% (P (CL) A - P (CL) B ) / P (CL) B
(P(0-1) A - P(0-1) B 50% 40% (2nd qurdrant) (1st qurdrant) 30% 20% 10% C2 T7 0% C1 T6-10% T4 T1-20% T3-30% T2 C3-40% (3rd qurdrant) (4th qurdrant) -50% -50% -40% -30% -20% -10% 0% 10% 20% 30% 40% 50% (P A (CL) - P B (CL) ) Night Time Changes (a) Change in percentage 200% 150% (2nd qurdrant) (1st qurdrant) (b) Percentage change rate Δ = p A x p B x p B x 100% (P(0-1) A - P(0-1) B ) / P(0-1) B 100% 50% 0% -50% -100% -150% -200% (3rd qurdrant) T2 T4 T1 C1 T7 T3 T6-200% -150% -100% -50% 0% 50% 100% 150% 200% (P (CL) A - P (CL) B ) / P (CL) B C3 (4th qurdrant)
Results Position Change (between 1-foot and centerline) 100% 100% 80% 80% Percentage 60% 40% Percentage 60% 40% 20% 20% 0% T1 T2 T3 T4 T6 T7 C1 C2 C3 0% T1 T2 T3 T4 T6 T7 C1 C2 C3 Site Code Site Code Before After Before After (a) Daytime (b) Nighttime
Conclusions With the edge line, vehicles tend to move away from the road edge; thus, the risk of having a running-offroadway crash is likely to be reduced. The implementation of edge lines is likely to reduce the head-on and sideswipe collisions at night because of the reduced number of vehicles crossing the centerline in the nighttime. The benefit of having the edge line at night is significant since the distribution of vehicles is more centralized during this time period.
Conclusion With ROR being the most common and deadiest type of c rashes on rural narrow two-lane highways, the edge line marking does provide the positive guidance to drivers part icularly when visibility is compromised at night. Even tho ugh the crossing centerline counts at few sites increased d uring the daytime, it should not increase the frequency of head-on and sideswipe collisions since the traffic volumes at narrow highways are usually small less than 2,000 per day in this study. For instance, at site T2 where the increa se in the crossing centerline counts is the highest during th e day, the recorded ADT was only 78.
Future Work Conducting before-and-after crash analysis to see how the edge line actually affecting the crash frequency at these sites
Acknowledgment This study is a part of the research project Impact of Edge Line on Safety of Rural Two- Lane Highways, supported by the Louisiana Department of Transportation and Development (LaDOTD) through the Louisiana Transportation Research Center (LTRC). The authors wish to thank the project review committee at and LaDOTD and LTRC.
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