Characteristics of Traffic Accidents in Highway Work Zones

Characteristics of Traffic Accidents in Highway Work Zones A DETAILED ANALYSIS OF WORK ZONE ACCIDENTS REPORTED ON NEW YORK STATE DEPARTMENT OF TRANSPORTATION CONSTRUCTION PROJECTS ESTABLISHED THE PREDOMINANT TYPES OF WORK ZONE TRAFFIC ACCIDENTS AND THEIR RELATIVE SEVERITIES AND COSTS. THE RESULTS ARE USEFUL FOR HIGHWAY PRACTITIONERS TO IMPROVE WORK ZONE TRAFFIC SAFETY WITH A COST-EFFECTIVE PERSPECTIVE. INTRODUCTION The U.S. highway infrastructure is deteriorating at an increasing rate due to rising travel demand beyond earlier projections. In 2001, 2.8 trillion vehicle miles were traveled in the United States, compared to 1.5 trillion miles in 1980, an increase of 83.0 percent. 1 This has necessitated more frequent pavement rehabilitation and geometric improvements in addition to regular maintenance to sustain the highway infrastructure at desired service levels. This increase in highway construction operations has resulted in more work zones and, consequently, more accidents resulting from work zones. In 2001, 989 work zone fatalities and 47,000 severe injuries were reported in the United States. The attention of transportation agencies now is focused on examining and revising existing safety measures and developing innovative ways to increase safety on U.S. highways during periods of reconstruction. The research presented in this feature includes detailed statistical analyses of 6,044 traffic accidents reported on New York State Department of Transportation (NYSDOT) construction projects from 1989 to 2001. The objective is to identify the predominant and most frequent accident types. This information, based on real data, can be utilized to develop recommendations for minimizing traffic accidents in work zones. LITERATURE REVIEW Several studies have been conducted during the last two decades to identify the types and characteristics of work zone traffic BY SATISH MOHAN, PH.D. AND WESLEY C. ZECH, PH.D. accidents. 2 8 Currently, practitioners use the Manual on Uniform Traffic Control Devices (MUTCD) and the Federal Highway Administration s (FHWA) best practices guidebook as references for recommendations and guidance on the implementation of potential work zone countermeasures. 9, 10 However, none of these studies or publications has quantified the severity of the various accident types or given their yearly trends. Therefore, optimal solutions to work zone traffic accidents have not been identified and implemented. The lack of such information in the literature is the primary reason for the research reported in this feature. NYSDOT HIGHWAY WORK ZONE ACCIDENT DATA All accident data utilized in this research were obtained from NYSDOT Construction Safety Summary Reports from 1989 through 2001. 11 The 13 years of work zone traffic accident data included 123 fatal and 5,921 nonfatal traffic accidents. Traffic accidents are defined as accidents involving a vehicle, pedestrian, bicycle, or motorcycle traveling through a work zone. 12 All accidents that occurred from 1989 to 2001 were reported by construction groups in the various regions of New York in accordance with the Manual for Uniform Record Keeping on Construction Contracts (MURK Part 1C). MURK Part 1C is a section of the NYSDOT Safety and Health Program Manual, which provides NYS- DOT construction division employees with the guidelines and procedures to follow after an accident occurs on a construction project. In all of the NYSDOT construction reports, accidents are categorized by four injury severity types. In this feature, all traffic accidents are classified accordingly by one of the four severity types: Fatal: an accident resulting in one or more deaths. Hospital-level: an accident resulting in injury or injuries that required the injured to be transported to the hospital and (i) admitted or (ii) their status was unknown after transport. ITE JOURNAL ON THE WEB / APRIL 2006 73

SOURCE: NYSDOT Construction Safety Summary Reports, 1989 2001. Table 1. Yearly trends of NYSDOT work zone traffic accidents (1989 2001). Accident category: Total traffic accidents Injury severity Year Fatal Hospital Minor None/unknown Total 2001 10 81 129 283 503 2000 9 88 189 408 694 1999 9 134 139 406 688 1998 8 170 159 436 773 1997 10 166 136 324 636 1996 9 142 109 333 593 1995 12 90 125 235 462 1994 10 92 118 230 450 1993 9 74 78 172 333 1992 7 66 62 151 286 1991 10 89 42 156 297 1990 7 74 51 99 231 1989 13 35 10 40 98 Total 123 1,301 1,347 3,273 6,044 SOURCE: NYSDOT Construction Safety Summary Reports. Figure 1. Annual growth of work zone traffic accidents (NYSDOT). Minor: an accident resulting in the injured person either (i) being transported to the hospital and released, (ii) treated on the scene, or (iii) complained of pain or having visible injury, but declined treatment. None/unknown: an accident resulting in no injury, resulting in property damage only, or for which there was a lack of information in describing the injury. Table 1 includes yearly data on traffic accidents, categorized by injury severity, reported on NYSDOT construction work zones during the period from 1989 to 2001. NYSDOT started collecting work zone accident data in 1989. Accidents in the first year of the program were underreported and, therefore, are excluded from the trend analyses given in Figure 1. Figure 1 illustrates the yearly growth of these traffic accidents for each of the four injury severities. As shown, total traffic accidents increased at a rate of 16.3 percent from 1990 to 1998, then declined at a rate of 15.4 percent from 1998 to 2001. Hospital-level injury accidents increased at a rate of 11.0 percent from 1990 to 1998, then declined at a rate of 28.0 percent from 1998 to 2001. Minor injury accidents increased at a rate of 15.3 percent from 1989 to 2001. Fatal injury accidents seem to have no definable trend, ranging from 7 to 13 per year from 1989 to 2001. Types of Work Zone Traffic Accidents Table 2 presents 8 years (1994 2001) of work zone traffic accident types reported on NYSDOT work zone construction projects, categorized by the injury severity levels defined above. Detailed breakdowns describing the accident classification and location of various traffic accident types were not reported in the NYSDOT safety summaries prior to 1994. Therefore, data between 1989 and 1993 have been excluded from Tables 2 and 4, and trend analyses are plotted in Figure 2. Table 2 places traffic accidents into seven categories, each of which includes several accident types. Multi-vehicle accidents accounted for the maximum number (60.7 percent) of total injury accidents. This accident type represented 35.1 percent of fatal, 59.4 percent of hospital-level, 60.4 percent of minor and 62.1 percent of none/ unknown injury accidents. Single vehicle construction feature/object was the second most frequent accident category, accounting for 12.7 percent of total injury accidents. The third highest category, motor vehicle construction vehicle/equipment, accounted for 10.6 percent of total injury accidents. Single vehicle other accidents accounted for 8.7 percent. This category represented the highest fatal injury accident category, with 23.4 percent of total fatal injury accidents. The other two accident categories, pedestrian/bicyclist/ motorcycle and worker on foot motor vehicle, accounted for 6.1 percent of total injury accidents combined. Specific major accident types within the broader categories described above also were examined. Other single vehicle 74 ITE JOURNAL ON THE WEB / APRIL 2006

run-off-road (ROR) was the most fatal accident type, resulting in 23.4 percent of all fatal injury accidents approximately two times higher than the next two accident types. The second highest fatal accident type, accounting for 11.7 percent of fatal injury accidents, was head-on/sideswipe in opposite direction. Multi-vehicle collisions at an angle accounted for 10.4 percent of all fatal accidents reported in NYSDOT highway work zones. The next three accident types each accounted for 9.1 percent of the fatal injury accidents: rear-end; construction equipment struck by vehicle inside work zone; and vehicle ROR striking temporary concrete median barrier/roadside traffic control device. Out of 963 hospital-level traffic injury accidents, rear-end accidents accounted for 372 (38.6 percent), approximately 4.7 times greater than each of the next two accident types: other single vehicle ROR (representing 8.3 percent of total hospital-level injury accidents) and multi-vehicle collision at an angle (accounting for 8.0 percent of total hospital-level injury accidents). Also, Table 2 shows that rear-end accidents accounted for 45.2 percent of total minor injury accidents, which was six times greater than the next accident type. Other single vehicle ROR accidents accounted for 7.6 percent of total minor injury accidents. Multi-vehicle at an angle accounted for 6.3 percent of total minor injury accidents. Rear-end accidents also represented 45.6 percent of total none/unknown injury accidents, and were reported 5.6 times more frequently than the next accident type. Sideswipe in same direction accidents accounted for 8.1 percent of total none/unknown injury accidents. Other single vehicle ROR accounted for 7.6 percent of none/unknown injury accidents. Table 2. Project-related traffic accidents in NYSDOT work zones. Injury severity None/ Fatal Hospital Minor unknown Total Total Accident type % % % % number % Multi-vehicle 35.1 59.4 60.4 62.1 2,915 60.7 Rear-end accident 9.1 38.6 45.2 45.6 2,088 43.5 Head-on/sideswipe in opposite direction 11.7 3.5 1.8 1.5 104 2.2 Multi-vehicle collision at an angle 10.4 8.0 6.3 3.8 255 5.3 Other 3.9 9.2 7.1 11.3 468 9.7 Single vehicle construction feature/object 10.4 9.3 9.4 15.4 610 12.7 Vehicle run-off-road striking temporary concrete median barrier/ 9.1 5.4 3.2 5.6 244 5.1 roadside traffic control device Other 1.3 3.9 6.2 9.8 366 7.6 Motor vehicle construction vehicle/equipment 9.1 10.4 7.6 11.9 507 10.6 Construction equipment struck by vehicle inside work space 9.1 5.6 4.3 4.8 236 4.9 Other 4.8 3.3 7.1 271 5.6 Single vehicle other 23.4 9.0 7.9 8.5 417 8.7 Other single vehicle run-off-road 23.4 8.3 7.6 7.6 385 8.0 Other 0.7 0.3 0.9 32 0.7 Pedestrian/bicyclist/motorcycle* 13.0 6.1 6.4 0.4 151 3.1 Worker on foot motor vehicle 9.1 4.4 7.5 0.5 144 3.0 Other/unknown 0.0 1.3 0.7 1.3 55 1.1 TOTAL 100 100 100 100 4,799 100 SOURCE: NYSDOT Construction Safety Summary Reports, 1994 2001. Corresponding FHWA NYSDOT injury comprehensive FHWA accident severity severity costs ACCIDENT COST ANALYSES AND RANKINGS Table 3 lists the comprehensive costs (in 1994 dollars) per accident severity, based on unit costs developed by FHWA. 13 Although these cost figures were developed 10 years prior, the costs represent the most currently available accident costs reported by FHWA and were utilized in this study to rank various accident types. The equivalent NYS- DOT injury accident severities corresponding to the FHWA severities also are included in Table 3. Accident frequencies summarized in Table 2 were multiplied by the cost figures in Table 3 to compute an aggregate cost for each accident by all severity types. Table 4 ranks the top 10 accident types reported in Table 3. Total unit costs per accident. Fatal Fatal $2,600,000 Severe Hospital-level $180,000 Slight Minor $19,000 None, unknown/pdo None/unknown $2,000 SOURCE: FHWA Motor Vehicle Accident Costs Technical Advisory, 1994. NYSDOT construction work zones by cost. As shown in Table 4, the following six traffic accident types in highway work zones had the highest associated costs: Rear-end Other single vehicle ROR Multi-vehicle collision at an angle Construction equipment struck by vehicle inside work space ITE JOURNAL ON THE WEB / APRIL 2006 75

Table 4. Ranked traffic accident types in NYSDOT work zones. None/ Percent Fatal Hospital Minor unknown Cost total Accident type % % % % (millions) cost Rear-end accidents 9.1 38.6 45.2 45.6 $97.1 24.3 Other single vehicle run-off-road 23.4 8.3 7.6 7.6 $63.2 15.8 Multi-vehicle collision at an angle 10.4 8.0 6.3 3.8 $36.2 9.1 Construction equipment struck by vehicle inside work space 9.1 5.6 4.3 4.8 $30.0 7.5 Single vehicle run-off-road striking temporary concrete median barrier/ 9.1 5.4 3.2 5.6 $29.1 7.2 roadside traffic control device Head-on/sideswipe in opposite direction 11.7 3.5 1.8 1.5 $28.5 7.1 Multi-vehicle left turn accident 3.9 5.2 4.6 3.1 $20.8 5.2 Pedestrian struck by vehicle 7.8 2.9 0.9 0.0 $17.9 4.5 Sideswipe in same direction 0.0 3.6 2.3 8.1 $10.9 2.7 Other 15.5 18.9 23.8 20.3 $66.3 16.6 Total 100 100 100 100 $400.0 100 Figure 2. Trends of yearly frequencies of major traffic accident types. Vehicle ROR striking temporary concrete median barrier/roadside traffic control device Head-on/sideswipe in opposite direction These six accident types, each of which accounted for greater than 7.0 percent of total costs, accounted for 72.8 percent of all fatal, 69.4 percent of all hospital-level, 68.5 percent of all minor and 68.9 percent of all none/unknown injury accidents, and cost $284.1 million in 8 years, (71.1 percent of the total cost of traffic accidents). Rear-end accidents stand out as the single most expensive accident type, costing $97.1 million, and were the most reported accident type, 43.5 percent of all traffic injury accidents (see Table 2). YEARLY TRENDS OF MAJOR ACCIDENT TYPES AND THEIR POTENTIAL SOLUTIONS To understand the progression of the six major traffic accident types listed above, Figure 2 presents their yearly trends. Possible causes and some potential solutions are described for each accident type. Potential solutions have been extracted from MUTCD, the FHWA best practices guidebook and the judgment of the authors. The information ascertained from literature reviews on work zone safety also guided this effort. Potential solutions offered are of a generic nature and will have to be tailored to each unique work zone situation and location. Rear-End Accidents Rear-end accidents showed an increasing linear trend of 19.7 percent per year from 1994 to 2001. These accidents resulted in an 8-year cost of $97.1 million, 24.3 percent of the total costs. The primary reasons for rear-end accidents include: differentials in vehicle speeds; limited sight distance; inadequate advance warning; driver inattention; low visibility; and traffic congestion. Work zone traffic controls and other procedures that reduce vehicle speeds significantly and can result in large speed differentials should be re-evaluated to minimize differentials in vehicle speeds. Public outreach and educational pro- 76 ITE JOURNAL ON THE WEB / APRIL 2006

grams along with speed enforcement procedures may minimize the occurrence of rear-end accidents. Other Single Vehicle ROR Accidents Other single vehicle ROR accidents displayed a decreasing trend of 1.3 percent per year for the period from 1994 to 2001. These accidents accounted for 15.8 percent of the total costs. Also, single vehicle ROR striking temporary concrete median barrier/roadside traffic control device accidents declined at a rate of 3.1 percent over the study period, accounting for $29.1 million in total costs. Potential causes of ROR accidents include: inadequate roadway geometrics; excessive vehicle speeds; inadequate clear zones; and lack of channelization devices. Practitioners may want to investigate the use of innovative advanced traffic management procedures, installing temporary traffic barriers and speed management techniques as potential solutions to ROR accidents. Multi-Vehicle Collision At an Angle These accidents showed a downward linear trend of 0.5 percent and cost $4.5 million per year. Possible causes include: poorly designed intersections; driver error or confusion; inadequate merge lengths; or inadequate sight distances. Some suggested potential solutions to avoid these accidents are public outreach and educational programs, advanced traffic controls and adequate geometric designs of intersections. Construction Equipment Struck By Vehicle Inside Work Space These accidents displayed a declining trend of 0.9 percent. Accidents resulting from vehicles striking construction equipment tend to be more severe due to the large size of the construction equipment and high vehicle speeds. These accidents may occur because of driver error or confusion; excessive vehicle speeds; inadequate physical barriers around the work space; or poor traffic management. Potential solutions to minimize vehicle intrusions are speed management; utilization of temporary concrete barriers to provide positive physical protection between the vehicles and construction equipment; and adequate pavement markings to properly direct highway traffic through the work zone. Head-On/Sideswipe in Opposite Direction Head-on/sideswipe in opposite direction accidents had a 2.0 percent decreasing annual trend from 1994 to 2001. These accidents may be the result of redirection of traffic; improper or inadequate lane shifts; poor traffic management; or any other abrupt change in road geometry. To avoid the occurrence of headon/sideswipe in opposite direction accidents, practitioners should consider advance traffic controls, innovative flagging techniques and proper speed management procedures. CONCLUSIONS The research reported in this feature identified and ranked major highway work zone traffic accident types and plotted their yearly trends. It was found that six of the traffic accident types accounted for 72.8 percent of all fatal, 69.4 percent of all hospital-level, 68.5 percent of all minor and 68.9 percent of none/unknown injury accidents and for 71.1 percent of the total costs of traffic accidents on NYSDOT construction work zones. Total traffic accidents increased at a rate of 16.3 percent from 1990 to 1998, but progressively declined at a rate of 15.4 percent from 1998 through 2001. Yearly trends of the major accident types indicated that only rear-end accidents increased; other accident types declined at 0.5 to 3.1 percent per year. Also, rear-end accidents were noted as the single most expensive accident type based on the combination of frequency and severity. The primary reasons for rear-end accidents are: differentials in vehicle speeds; limited sight distance; inadequate advance warning; driver inattention; low visibility; and traffic congestion. Work zone traffic controls that reduce the speeds of vehicles significantly and can result in large speed differentials should be considered to decrease the speed differentials. Safety measures for reducing other accident types as suggested in this feature include: providing adequate merge lengths; utilizing temporary concrete barriers around the work space; and posting advanced traffic controls. The results in this feature provide real statistics on traffic accidents reported on NYSDOT construction work zones and can guide highway agencies all over the nation in prioritizing their safety efforts for maximum benefits. Ranking accident types along with accident trends will enable practitioners in studying problem areas over time and in evaluating the effectiveness of any safety measures. Rear-end accidents were noted as the single most expensive accident type based on the combination of frequency, severity and corresponding costs. Practitioners should develop specific countermeasures for each accident type because each type relates to an area of the work zone, especially rear-end accidents. References 1. Federal Highway Administration (FHWA) Highway Statistics Publications (1992 2001). Accessible via www.fhwa.dot.gov/ policy/ohpi/index.htm. 2. Hall, J.W. and V.M. Lorenz. Characteristics of Construction-Zone Accidents. Transportation Research Record, No. 1230 (1989): 20 27. 3. Pigman, J.G. and K.R. Agent. Highway Accidents in Construction and Maintenance Work Zones. Transportation Research Record, No. 1270 (1990): 12 21. 4. Garber, N. and T. Woo. Accident Characteristics at Construction and Maintenance Zones in Urban Areas. Report No. VTRC 90- R12. Virginia Transportation Research Council, January 1990. 5. Ha, T. and Z.A. Nemeth. Detailed Study of Accident Experience in Construction and Maintenance Zones. Transportation Research Record, No. 1509 (1996): 38 45. 6. Pal, R. and K.C. Sinha. Analysis of Crash Rates at Interstate Work Zones in Indiana. Transportation Research Record, No. 1529 (1996): 43 53. 7. Bryden, J.E. and L. Andrew. Work Zone Traffic Accidents Involving Traffic Control Devices, Safety Features, and Construction Operations. Transportation Research Record, No. 1650 (1998): 71 81. 8. Daniel, J., K. Dixon and D. Jared. Analysis of Fatal Crashes in Georgia Work Zones. Transportation Research Record, No. 1715 (2000): 18 23. 9. Manual on Uniform Traffic Control Devices. Washington, DC, USA: FHWA, 2003. ITE JOURNAL ON THE WEB / APRIL 2006 77

10. Work Zone Operations Best Practices Guidebook. Publication No. FHWA-OP-000-010. FHWA, April 2001. 11. New York State Department of Transportation Construction Safety Program, 1989 2001 Summary Reports, Construction Division, Albany, NY, USA. 12. Bryden, J.E. and L. Andrew. Serious and Fatal Injuries to Workers on Highway Construction Projects. Transportation Research Record, No. 1657 (1999): 42 47. 13. Technical Advisory: Motor Vehicle Accident Costs. FHWA, 1994. Accessible via www.fhwa.dot.gov/legsregs/directive/techadvs/ t75702.htm. SATISH MOHAN, Ph.D., is an associate professor in the Department of Civil, Structural, and Environmental Engineering at the State University of New York (SUNY) at Buffalo. He obtained a bachelor of technology (Hons) from IIT Khargpur in India (1959), an M.S. from Kansas State (1975) and a Ph.D. in civil engineering (1978) from Purdue University. His research efforts have focused in the areas of construction safety, construction delay analyses and lean construction. WESLEY C. ZECH, Ph.D., is an assistant professor in the Department of Civil Engineering at Auburn University. He obtained a bachelor of science in civil engineering (1995), an M.E. in civil engineering (1999) and a Ph.D. in civil engineering (2004) from SUNY Buffalo. His research efforts have focused in the areas of work zone safety, construction safety and GIS technology in the field of transportation. 78 ITE JOURNAL ON THE WEB / APRIL 2006