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17 0.1 0.38 Undivided Roads 0.9 Divided Highways 0.62 Exposure Incidents FIGURE 4 Undivided and divided roads. An extension of the earlier findings and logic applies to roads. Several use routing software maximizing travel on these the toll road avoidance strategy known as "diversion." Diver- roads. Others pre-plan trips in detail, including road choices. sion (Short 2006) occurs when trucks or other vehicles eschew toll roads to avoid paying the tolls. Often this is on a parallel undivided highway. There are about 2,800 mi of toll AVOIDING WORK ZONES roads within the 42,800-mi Interstate highway system, and about 1,800 additional mi of non-Interstate toll roads (Short 2006). Many toll roads operate at below-capacity volumes, in part as a result of diversion. No one knows how many trucks and other vehicles divert from these roads to avoid tolls, or the effects of diversion on overall crash rates. It is important that carriers and drivers carefully weigh their road choices by factoring relative crash risks into their decisions. In 2008 there were about 10,000 large-truck crashes in work zones, about 3% of all truck crashes. These included 166 fatal In the safety-manager surveys, "maximizing travel on Inter- crashes, 4.4% of the total of 3,733 for the year (FMCSA states and other freeways" was among four factors tied for Analysis Division 2010). About one-fourth of all work zone the highest mean rating (+1.8 on a -3.0-to-+3.0 scale) of fatal crashes involved a large truck. Roadway- and traffic- the 11 driving situations and practices presented. Its opposite, related crash threats in work zones include constricted lanes, maximizing travel on low-speed roads, received the lowest narrow or absent shoulders, makeshift signs, and traffic back- mean rating (-1.1). For other experts, the corresponding val- ups where light vehicles may dart in front of trucks to move up ues were +1.7 (the second highest rating for 15 practices pre- in the queue. An FHWA website ( sented) and -1.6 (the highest negative rating). With regard to contains crash data, research reports, driver training materials, toll reimbursements to drivers, 66 of 78 responding carrier rep- and other information on work zone safety, including infor- resentatives indicated that they provided "EZ Pass transpon- mation on major highway work projects. ders and/or reimbursement of toll charges to drivers/OOs [owner-operators]." The practice received an average rating of In the same naturalistic driving data as discussed earlier 3.8 on the five-point safety effectiveness scale. (Hickman et al. 2005), trucks drove in highway work zones in only 8 of 1,072 randomly selected exposure-point obser- On the other-expert survey, a respondent provided the vations (0.7%). During the same driving, they had 55 of 914 following comment (with no sources cited for statistical traffic conflicts in highway work zones (6.0%). Although statements): these data are based on relatively few work-zone observa- tions, they suggest greatly elevated risk. The calculated The biggest single determinant of overall safety is risk exposure. odds ratio for conflict involvement in this data set is 8.5 Interstates, because they are divided trafficways with no at-grade intersections, are 400% safer than U.S. and State routes. More [(55/8)/(859/1,064) 8.5]. than 70% of fatal truck crashes occur on these latter roads, not Interstates where all the enforcement attention and focus takes The elevated crash risk in work zones is not specific to place. Carriers operating mostly on non-Interstate roads are much more at-risk than those that predominantly travel up and trucks. Khattak et al. (1999) found that changes in crash rates down Interstates. during the construction were about the same for cars and trucks. Truck crash severity was not increased by roadwork, Almost all of the case study carriers equip their vehicles but work zone crashes tended to involve more vehicles than with toll transponders and actively encourage travel on divided those on normal roads.