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Vehicle Speeds in Work Zones: An Objective and Subjective Analysis

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Dr. Ghulam H. Bham
Mohtaba Ale Mohammadi, PhD Candidate

Missouri University of Science and Technology

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Vehicle Speeds in Work Zones: An Objective and Subjective Analysis

  1. 1. Vehicle Speeds in Work Zones: An Objective and Subjective Analysis Mojtaba Ale Mohammadi, PhD Candidate Ghulam H. Bham, PhD Civil, Architectural and Environmental Engineering Missouri University of Science and Technology
  2. 2. DISCLAIMER The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. This document is disseminated under thesponsorship of the Department of Transportation University Transportation Centers Program, in the interest of information exchange. The U.S.Government assumes no liability for the contents or use thereof.
  3. 3. OUTLINE• Introduction• Data Collection Sites• Methodology• Results –Objective Evaluation –Subjective Evaluation• Conclusions and Recommendations 3
  4. 4. INTRODUCTION• Posted speed limits alone do not reduce vehicle speed• Drivers’ compliance reduces if speed limit is lowered by more than 10 mph or unreasonable speed limits• Most commonly used speed limit reductions are 0, 5, 10, and 20 mph• Different speed limits in work zones make enforcement difficult 4
  5. 5. OBJECTIVESObjective evaluation: vehicle speeds anddrivers’ speed limit complianceDrivers’ Assessment: drivers’ perceptionof speed limit and their complianceDOT Survey: work zone speed limit bestpractices 5
  6. 6. DATA COLLECTION SITES Waynesville I-44 West Bound, Right lane closed, Mile Marker: 152.8 August 13th, 2009 – Thursday 3 hours of data from 5 to 8 pm WZ Posted Speed Limit 60 mph Work Activity: Pavement Reconstruction Rolla I-44 West Bound, Right lane closed, Mile Marker: 185 October 2nd, 2009 – Thursday 5 hours of data from 12:15 to 7 pm WZ Posted Speed Limit 60 mph Work activity: Pavement Rehabilitation Lane width reduced by tubular markers 6
  7. 7. DATA COLLECTION SITES Pacific (WB & EB) I-44, Left lane closed, Mile Marker: 253 June 9th, 16th, 24th, 2010 – Wednesday, Wednesday, Thursday 20 hours of data from 6 to 11 am WZ Posted Speed Limit: 50 mph Work Activity: Addition of a New Lane Lane width reduced by pavement marking Data was also collected with no lane closure 7
  8. 8. DATA COLLECTION SITES Cuba I-44, West Bound, left lane closed, Mile Marker: 202.6 November 6th, 2009 – Thursday 5 hours from 11:30 to 4:30 pm WZ Posted Speed Limit 60 mph Work Activity: Rumble Striping Summary of work zone dataWork zone Lane closed Data WZ Speed limit ActivityWaynesville Right 3 hours 60 mph Pavement reconstructionRolla Right 5 hours 60 mph Pavement rehabilitationPacific (WB) Left 20 hours 50 mph Additional lanePacific (EB) Left 20 hours 50 mph Additional laneCuba Left 5 hours 60 mph Rumble striping 8
  9. 9. DRIVER SURVEY DATA• Collected at gas stations near work zones• Car and truck drivers surveyed: 118• Actual speed versus posted speed limit• Speed limit compliance of other drivers• Effect of construction activity on their speed• Preference for work zone signage 9
  10. 10. DRIVER SURVEY 18 Age distribution 16 14 12 10 Frequency 8 6 4 2 0 Age (years) Double <5 Trailer > 20 25% 7% 30% Passenger Single Car Trailer 69% 21% 5-10 Single 20% Unit RV 10-20 2% 1% 25% Driving experience (years) Vehicle Composition 10
  11. 11. DOT SURVEY DATATo identify common WZ practices of DOTS• WZ speed management policies• WZ activities that warrant a reduction in speedlimit• Factors influence WZ speed limit• Compliance levels 11
  12. 12. METHODOLOGYField Data Extraction-Sites were videotaped using HD video cameras-Autoscope system software used to extract vehicle free flow speeds (FFS)-FFS based on 5-second headway-FFS assumed to be normally distributed-Drivers were surveyed using a questionnaire near the Rolla and Pacific sites-DOTs were surveyed on their common practices related to work zone speed limits 12
  13. 13. METHODOLOGY Speed detector Movement detectors Count detector Autoscope software for extracting the vehicle speed 13
  14. 14. METHODOLOGYo Difference in speed of cars and truckso The effect of construction activity on vehicles speedo Effect of lane closure on vehicles (1-lane vs. 2-lane open)o Evaluate speed limit compliance 14
  15. 15. RESULTS:OBJECTIVE EVALUATION 15
  16. 16. OBJECTIVE EVALUATION Characteristics of Vehicle Speed – During Construction 80 Difference in mean speeds 70 Standard Deviation Mean 5.8 6.3 60 Percentage (%) 6.1 5.4 5.3 4.1 4.5 50 6.4 40 1.2 mph 2.0 mph *** 1.8 mph *** 2.6 mph ** 30 20 10 0 Car Truck Car Truck Car Truck Car Truck Waynesville WB Rolla WB Pacific WB Pacific EB *** Significant at 99% level of confidence ** Significant at 95% level of confidence 16
  17. 17. OBJECTIVE EVALUATION Characteristics of Vehicle Speed – During No-Construction 80 Difference in mean speeds 70 7.0 7.5 Standard Deviation Mean 4.7 4.9 60 7.1 6.6 6.7 5.4Percentage (%) 6.4 4.1 50 40 3.9 mph *** 4.1 mph *** 2.2 mph *** 1.8 mph *** 3.0 mph*** 30 20 10 0 Car Truck Car Truck Car Truck Car Truck Car Truck *** Significant at 99% level of confidence ^ One lane open = 1, Two lanes open = 2 *** Significant at 99% level of confidence; ** Significant at 95% level of confidence; * Significant at 90% level of confidence 17
  18. 18. OBJECTIVE EVALUATIONEffects of Construction Activity on Vehicle Speeds Difference in Standard Difference in MeanWork Zone Deviation # (mph) # (mph)Site Passenger Truck Trucks Passenger Cars Cars sWaynesville 1.18 1.19 4.0 2.2WBRolla WB 0.96 0.01 4.5 3.0Pacific WB 1.21 1.42 3.5 3.6Pacific EB 1.32 -0.44 4.7 2.8# Difference = speed with no construction – speed with constructionBold: Significant at 99% level of confidence 18
  19. 19. OBJECTIVE EVALUATION Speed Limit Compliance – During Construction Above Speed Limit > 5 mph Above Speed Limit 80 +6.78*** 70 +2.11** +1.47* +9.11***Percentage (%) +1.78** +1.38* 60 50 40 30 20 10 -14.56*** 0 -11.85** Truck Truck Truck Car Truck Car Car Car *** Significant at 99% level of confidence; ** Significant at 95% level of confidence; * Significant at 90% level of confidence 19
  20. 20. OBJECTIVE EVALUATION Speed Limit Compliance – During No-Construction Above Speed Limit > 5 mph Above Speed Limit 100 +30.50*** 90 +9.74*** +1.43* +8.85*** 80 +8.91*** +9.63*** +4.5*** 70Percentage (%) +1.43* 60 50 -7.13*** 40 30 -10.16*** 20 10 0 Car Truck Car Truck Car Truck Car Truck Car Truck Waynesville WB Rolla WB Cuba WB Pacific WB Pacific EB Work Zones *** Significant at 99% level of confidence; ** Significant at 95% level of confidence; * Significant at 90% level of confidence 20
  21. 21. RESULTS:SUBJECTIVE EVALUATION 21
  22. 22. DRIVER SURVEY How many miles in advance would you prefer to know about the presence of a work zone? How many miles in advance would you like to see the “Lane Closed Ahead” sign? How many miles in advance would you like to see the “Reduced Speed Limit” sign? >3 80 23 18 2-3 8 37 36Miles 1-2 12 26 32 0.5-1 13 14 < 0.5 1 0 20 40 60 80 100 120 140 Percent Drivers’ preference regarding location of WZ signs 22
  23. 23. DRIVER SURVEY 60 50 40Percentage (%) 30 20 10 0 Right after the first Before I see the work After I see the work Just before the taper "Lane Closed Ahead" zone zone sign Where drivers move out of the closed lane? 23
  24. 24. DRIVER SURVEY 100 16 20 40 36 80 Percent 60 80 84 40 60 64 20 0 Car Truck Car Truck Disagree Pacific (50 mph) Rolla (60 mph) Agree Did other drivers follow the speed limit? 24
  25. 25. DRIVER SURVEY Drivers Speed 5 7 (mph) 100 12 20 >60 80 48 50-60Percent 48 60 84 40-50 53 30-40 40 38 21 <30 20 20 14 10 16 5 0 Car Truck Car Truck Pacific (50 mph) Rolla (60 mph) Drivers’ speed through the work zone 25
  26. 26. DRIVER SURVEY Suggested Speed 100 5 7 7 Limit (mph) 21 26 80 27 70 65Percent 60 60 38 60 40 40 74 55 29 50 20 20 33 5 45 7 2 0 car truck car truck Pacific (50 mph) Rolla (60 mph) Speed limit suggested by drivers 26
  27. 27. DRIVER SURVEY• 92% of total respondents indicated construction activity reduced their speed• 80% found the work zone speed limit to be safe• 60% of participants indicated travel delay 27
  28. 28. DOT SURVEY – WORK ZONE PRACTICES• Twenty seven states responded to the survey• Major factors in determining the speed limit: – presence of workers, lane width, – roadway alignment, and type of activity• Seventy percent indicated a maximum reduction of 10-mph• Static speed limit signs are most commonly used• Best strategy to increase compliance is use of law enforcement• Regulatory signs found effective by 25% of the respondents 28
  29. 29. CONCLUSIONS• Passenger cars speeds higher than trucks by 1-2 mph• Construction activity significant effects speed – Passenger cars and trucks speeds reduce by 2-5 mph• With no-work zone construction activity, or construction activity not close to the open lane – More than 10% drivers traveled higher than 10 mph above the speed limit• Low drivers’ compliance with static speed limit• Reduced lane width using tubular markers significantly affected the speed of vehicles – Speed reduced 8 mph below the speed limit 29
  30. 30. CONCLUSIONS• Drivers agree that construction activity reduces their speed• Field data showed construction reduces speed• When most drivers traveled below the speed limit – They overestimate the number of other drivers that do not comply with the speed limit• When most drivers traveled above the speed limit – They underestimate the number of other drivers that do not comply with the speed limit 30
  31. 31. CONCLUSIONS• Higher compliance if WZ speed limit are consistent with drivers expectation• Drivers prefer well informed more than a mile ahead of WZ 31
  32. 32. RECOMMENDATIONS• Vary WZ speed limits with varying levels of traffic congestion• Use of variable speed limits for work zones with closed lanes and short-term construction activity periods• To reduce speed, tubular markers than pavement markings for separating the closed lane (construction area) from the open lanes 32
  33. 33. ACKNOWLEDGEMENT• The research grant from the Smart Work Zone Deployment Initiative (SWZDI) and Mid- America Transportation Center (MATC)• Ms. Victoria Woods, Mr. Tim Hellebusch and their staff at the Missouri DOT in data collection• Praveen Edara at University of Missouri at Columbia for sharing the DOT survey results 33
  34. 34. You can copy any of these graphics and paste them on other slides.
  35. 35. CREDITS Ghulam H. Bham, Ph.D.Civil, Architectural and Environmental Engineering Missouri University of Science and Technology Phone (573) 341-6286 Fax (573) 341-4729 Email: ghbham@mst.edu Slide design © 2009, Mid-America Transportation Center. All rights reserved.

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