National Academies Press: OpenBook

A Guide for Reducing Collisions Involving Heavy Trucks (2004)

Chapter: Section III - Type of Problem Being Addressed

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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
×
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
×
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
×
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Suggested Citation:"Section III - Type of Problem Being Addressed." National Academies of Sciences, Engineering, and Medicine. 2004. A Guide for Reducing Collisions Involving Heavy Trucks. Washington, DC: The National Academies Press. doi: 10.17226/23424.
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III-1 SECTION III Type of Problem Being Addressed General Description of the Problem Exhibit III-1 shows that crashes involving medium and heavy trucks predominately do not involve serious injury except for motorcycles and special vehicles, such as farm equipment on the road. Although the majority of large-truck crashes do not involve injury, the probability of a fatality is greater in large-truck crashes; for example, in 2001, 1.1 percent of large-truck crashes resulted in a fatality, versus 0.6 percent of the crashes involving all vehicles (FMCSA, 2003a; NHTSA, 2002). Moreover, the number of fatalities associated with large-truck crashes is a significant portion of all crash fatalities. In 2002, 434,000 large trucks (with a GVWR greater than 10,000 pounds) were involved in traffic crashes in the United States; 4,542 were involved in fatal crashes. A total of 4,897 people died (11 percent of all the traffic fatalities reported in 2002), and an additional 130,000 were injured in those crashes. One in nine traffic fatalities involved a heavy truck. Of these, most involved trucks with a GVWR greater than 26,000 pounds. EXHIBIT III-1 Maximum Severity for Vehicles Crashing with Medium- and Heavy-Weight Trucks 0% 20% 40% 60% 80% 100% Au tom ob iles Uti lity Ve hic les All Lig ht Tru cks Bu se s Mo tor cyc les Ot he r V eh icle s Pe rc en t M ax S ev er ity is fo r a Ve hi cl e Ty pe Fatal Incapacitating Non-Incapacitating Possible None Source: GES 1999Note: Medium and heavy weight > 4,536 kg GVWR

SECTION III—TYPE OF PROBLEM BEING ADDRESSED III-2 The trend of heavy-truck fatalities is shown in Exhibit III-2 (FARS, 2002). Generally, 80 percent of the fatalities result from a crash with another vehicle in transport. EXHIBIT III-2 Heavy-Truck Fatalities Heavy trucks have continued to account for between 11 and 13 percent of all traffic fatalities, with the largest proportion occurring to persons outside the truck (mostly occupants of other vehicles, but also nonoccupants, e.g., pedestrians and bicyclists). Of the fatalities that resulted from crashes involving large trucks, 79 percent were occupants of another vehicle, 7 percent were nonoccupants, and 14 percent were large-truck occupants. Of the injuries that resulted from crashes involving large trucks, 77 percent were occupants of another vehicle, 3 percent were nonoccupants, and 20 percent were large-truck occupants. Exhibit III-3 shows that, of the fatalities that resulted from two-vehicle collisions involving a large truck, the vast majority were passenger-vehicle occupants or light-truck occupants (the latter would include sport utility vehicles [SUVs] and pickup trucks). Large trucks were much more likely to be involved in a fatal multiple-vehicle crash—as opposed to a fatal single-vehicle crash—than were passenger vehicles (84 percent of all large trucks involved in fatal crashes, compared with 61 percent of all passenger vehicles). In 29 percent of the two-vehicle fatal crashes involving a large truck and another type of vehicle, both vehicles were impacted in the front. The truck was struck in the rear nearly 2.5 times as often as the other vehicle (17 percent and 7 percent, respectively). In 2001, large trucks accounted for 4 percent of all registered vehicles and 7 percent of total VMT (2002 registered vehicle and vehicle miles traveled data not available). In 2002, large trucks accounted for 8 percent of all vehicles involved in fatal crashes and 4 percent of all vehicles involved in injury and property-damage-only crashes (NHTSA, 2003). 0 1000 2000 3000 4000 5000 6000 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02 Year Nu m be r o f O cc u pa n ts Nonmotorists Multiple Vehicles Single Vehicle Other Vehicle Occupants Source: FARS 2002

SECTION III—TYPE OF PROBLEM BEING ADDRESSED In a multidimensional comparison of the quantitative crash experiences of various vehicle types, Wang et al. (1999) compared combination-unit trucks (tractor-trailers) with single-unit trucks (“straight” trucks) and all vehicles (predominantly cars, light trucks, and vans). Combination-unit trucks were found to have a markedly different crash involvement profile than that of vehicles in general. They have relatively low crash rates per mile traveled, but their high mileage exposures and the severity of their crashes combine to associate them with much greater crash costs per year and, over their operational lives, more than four times higher than most other vehicle types. This means that, from a cost-benefit standpoint, safety investments in tractor-trailers are likely to have much greater per-vehicle (or per- driver) benefits than similar investments in other vehicle types. Safety improvements to a fleet of tractor-trailers and/or their drivers have the potential to be much more cost- beneficial than similar investments in car or light-truck fleets of equal size. Single-unit large trucks (straight trucks) have a less dramatic crash picture than do combination-unit trucks. Like tractor-trailers, single-unit trucks have relatively low crash involvement rates per mile traveled, but unlike tractor-trailers, their mileage exposure levels are generally not high because they are used mostly for short local trips rather than long- haul trips. Their crashes tend to be more severe than those of light vehicles but less severe than those involving a tractor-trailer. Overall, their quantitative crash experience on an individual vehicle level is more similar to light vehicles than to combination-unit trucks. Consequently, the per-vehicle or per-driver benefits from safety investments in single-unit trucks are likely to be more similar to those of light vehicles than to those of combination- unit trucks (Wang et al., 1999). Specific Attributes of the Problem As stated above, large trucks are defined in FARS as those trucks having a gross vehicle weight rating (GVWR) of more than 10,000 pounds. This includes both combination- and single-unit trucks. Passenger vehicles have a GVWR of 10,000 pounds or less, but most are less than 5,000 pounds. Over 90 percent of trucks in fatal crashes are more than 26,000 III-3 EXHIBIT III-3 Fatalities by Vehicle Type in Two-Vehicle Collisions Involving a Large Truck Passenger Light Large Motorcycle Bus/Other/Unknown Source: FARS 2002

pounds. One analysis of trucks in fatal crashes found that almost half weighed more than 60,000 pounds at the time of the crash (FMCSA, 2000a). Obviously, the gross disparity in the weights of trucks and passenger vehicles places the occupants of the latter at a major disadvantage. In addition to weight per se, vehicle size, body stiffness, and bumper height contribute to the crash mismatch. The Nature of Heavy-Truck Crashes The General Estimate System (GES, operated by NHTSA) data for 1999 provide insights through the analysis of a variable called “critical event.” GES identifies the critical event that made the crash imminent (i.e., something that occurred that made the collision possible). A critical event is coded for each vehicle and identifies the circumstances leading to the vehicle’s first impact in the crash. GES does not provide the same classification for trucks as FARS, making direct comparisons difficult. However, Exhibit III-4 provides a picture of the nature of the critical events associated with all crashes involving a single-unit truck and a tractor truck (with or without its trailer). There are two kinds of critical events: those associated with the truck and those associated with the other vehicle or a person or object. For single-unit trucks, about 30 percent of the critical events were associated with the truck, while for the tractor it was about 36 percent. This means that something other than the involved truck was associated with the critical event in between 64 and 70 percent of the crashes for these two types of vehicles. The FMCSA/NHTSA Large-Truck Crash Causation Study is beginning to provide statistical reports from its in-depth crash reconstructions of a nationally representative sample of serious large-truck crashes. A preliminary report (Craft and Blower, 2003b) cites data on 158 two-vehicle crashes involving a large truck and a light vehicle. Of these crashes, the critical event (after which the crash is inevitable) was a truck driver action in 29 percent and an action of the other driver in 60 percent. The remaining 11 percent were associated with the roadway, weather, truck vehicle failure, other vehicle failure, or other/unknown events. In addition to the extensive crash data cited above, instrumented vehicle studies that directly record vehicle interactions in traffic have corroborated the crash data in regard to the source of most large-truck safety incidents. In an instrumented vehicle study of light- vehicle–heavy-vehicle interaction, Hanowski et al. (2001) captured and reviewed 142 driver errors (some of which resulted in near crashes) and observed that 117 (82 percent) were initiated by the actions of surrounding light-vehicle drivers, while 25 (18 percent) were initiated by the heavy-vehicle subjects in the study. The most common general error by drivers was allowing insufficient gaps or clearance, e.g., while making a lane change or left turn across the path of another vehicle. The distribution of types of critical events does not vary significantly between the two types of large trucks shown in Exhibit III-4 (although, as noted earlier, tractor-trailers usually have much greater mileage exposure and, therefore, a greater probability of most types of crash and incident involvement). Slightly more than 20 percent of the crashes involve encroachment by another vehicle into the truck’s lane, while slightly less than 15 percent of the crashes involve the truck encroaching on another lane. Less than 10 percent of the crashes involve critical events associated with truck maneuvers at an intersection (turning or SECTION III—TYPE OF PROBLEM BEING ADDRESSED III-4

SECTION III—TYPE OF PROBLEM BEING ADDRESSED Heavy-truck crashes differ from crashes in general in several important ways. As noted above, major problems are created by the actions of other drivers, who are often not aware of the special characteristics of heavy trucks. These larger, heavier vehicles require greater stopping distance, and rapid lane changes may cause jackknifing in articulated trucks. Trucks with multiple trailers (“doubles” or “triples”) are subject to problems with “rearward amplification,” sometimes referred to as the “crack the whip” phenomenon. Each point of articulation increases side-to-side sway by approximately 70 percent, so that multiple trailers, especially those using coupling devices with two points of articulation, can develop III-5 EXHIBIT III-4 Critical Event for Crashes Involving Single-Unit and Tractor Trucks 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Single Unit Tractor w/ or w/o Trailer Pe rc e n t o f T o ta l C rit ic al E ve nt s fo r t he B od y Ty pe Unknown Other Object or Animal Non-Motorist Another Motor Vehicle Encroaching Other Motor Vehicle in Lane Other Truck Factors Truck Maneuvering at Intersection Truck Over Edge of Roadway Truck Over Lane Line Truck Lost Control Source: GES 1999 Note: For medium and heavy weight > 4,536 kg GVWR crossing). Between 20 and 30 percent of the crashes have a critical event involving the other vehicle in the same lane as the truck.

SECTION III—TYPE OF PROBLEM BEING ADDRESSED III-6 considerable sway in the last trailer (just as the last person in “crack the whip” experiences the greatest forces). Direct comparisons of the crash experience of multitrailer to single- trailer trucks are difficult, because multitrailer truck use is largely limited to Interstate highways in the less-populated Western states. When other vehicles dart in front of and around heavy trucks, truck drivers may be forced to take avoidance measures that in turn may cause problems with controlling the truck. Of particular concern is the area around the truck that has been referred to as the “No-Zone” area. This space is especially dangerous for passenger vehicles, because it includes driver blind-spot locations as well as space required for the truck to decelerate. The No-Zone area includes the following areas: • Immediately behind the large truck and within its same lane; • Immediately in front of the large truck and within its same lane; • To the left of the large truck, adjacent to the cab and in the adjoining lane; and • To the right of the large truck, behind the cab and in the adjoining lane. An analysis of two-vehicle crashes involving a large truck and a passenger vehicle found that 35 percent of the crashes involved the passenger vehicle moving into the No-Zone area. Exhibit III-5 shows the distribution of these No-Zone crashes, based on 1996 data. EXHIBIT III-5 Estimated Potential No-Zone Crashes by No-Zone Area for 1996 (Pat Waller, www.nozone.org/mission/crash_est.htm) Estimated Total of No-Zone Percent of All Type of Crash Related Crashes Crashes Truck Encroaching—Non-Intersection 21,500 8.0 (Right and Left No-Zones) Truck Encroaching—Intersection 10,500 4.0 Front No-Zone 32,500 13.0 Rear No-Zone 25,000 10.0 Total Potential No-Zone 89,500 35.0 Total Two-Vehicle, Large Truck/Passenger Vehicle 258,000 100.0 Crashes Drivers of passenger vehicles cannot completely avoid moving into No-Zone areas, in that passing or being passed by a truck necessitates spending some time there. However, drivers should try not to remain in these areas any longer than necessary. In crashes between large trucks and passenger vehicles, passenger vehicle driver errors or other driver factors are about twice as likely to be cited as are truck driver errors or other factors (FHWA, 1999c; Blower, 1999). Heavy-truck drivers generally exceed highway speed limits less frequently and by smaller margins than do drivers of light vehicles (Tardif, 2003; NHTSA, 1991). In fatal crashes, truck drivers are much less likely than passenger vehicle drivers to be legally intoxicated. In 2002, only 2 percent of large-truck drivers involved in

SECTION III—TYPE OF PROBLEM BEING ADDRESSED fatal crashes tested for blood alcohol content (BAC) at or above 0.08, while at least 25 percent of drivers of other vehicles tested at the same levels (NHTSA, 2003). Drivers of large trucks were less likely to have a previous license suspension or revocation than were passenger car drivers (7 percent and 14 percent, respectively). On the other hand, almost 28 percent of all large-truck drivers involved in fatal crashes in 2002 had at least one prior speeding conviction, compared with 20 percent of the passenger car drivers involved in fatal crashes (NHTSA, 2003). As noted earlier, heavy-truck drivers have mileage exposures that are typically many times those of passenger car drivers, making comparisons of lifetime crash, violation, or incident involvements problematic. In analyses of 1998 two-vehicle fatal crashes involving a large truck and a passenger vehicle, important driver differences were found (FMCSA, 2000a). Exhibit III-6 summarizes some of the differences identified. It should be noted that, for driver-related factors, more than one could be identified for each driver. In fatal truck–passenger vehicle crashes, truck drivers are much less likely to be legally intoxicated, with only 1 percent or fewer having a BAC of 0.10 percent or higher, compared with 19 percent for passenger cars, 20 percent for light trucks, and 27 percent for motorcycles (NHTSA, 2001). However, because of the size, weight, and mileage exposure of the vehicles involved, even 1 percent of truck drivers operating with such high BACs is cause for concern. Safety belt usage is also much higher for truck drivers, based on crash reports. It is important to note that in a fatal crash involving a truck and a passenger vehicle, it is very likely that the fatalities occurred to the passenger vehicle occupants, so that reported belt III-7 EXHIBIT III-6 Characteristics of Drivers in Two-Vehicle Fatal Crashes Involving a Large Truck and a Passenger Vehicle, 1998 Driver Characteristic Heavy Truck Passenger Vehicle Driver < 26 years old 7.2 percent 24.2 percent Driver > 65 years old 2.4 percent 20.1 percent Invalid or no license 1.9 percent 10.2 percent Driver restraint use 76.4 percent 48.8 percent Driver alcohol use (any) 1.7 percent 18.8 percent Driver alcohol > 0.10 percent 0.6 percent 13.5 percent Driver factor recorded 26.4 percent 81.5 percent Failed to yield 5.3 percent 20.3 percent Ran off road/out of lane 4.8 percent 27.8 percent Driving too fast 3.8 percent 14.9 percent Failure to obey traffic devices 3.0 percent 12.1 percent Inattentive 2.7 percent 9.8 percent

usage may be more readily erroneously reported for the truck driver. Yet independent investigation based on vehicle points of contact and other physical evidence at the scene of the crash, as well as witness reports, verifies that the truck driver is less likely to have made the critical driver error in such crashes (Craft and Blower, 2003b; Blower, 1999). A report that focused on unsafe driving actions leading to fatal car-truck crashes again found that in such collisions the driver of the passenger vehicle is much more likely to be culpable (Kostyniuk et al., 2002). The report also found that, on the whole, unsafe driving actions that lead to fatal car-truck crashes are equally likely to lead to fatal car-car crashes. Indeed, five such factors, namely failing to keep in lane, failing to yield right-of-way, driving too fast for conditions or in excess of posted speed limit, failing to obey traffic control devices and laws, and being inattentive, accounted for about 65 percent of both car-car and car-truck fatal crashes. However, four factors were found to be more likely to lead to a fatal car-truck collision than to a fatal car-car collision: • Following improperly; • Driving with vision obscured by rain, snow, fog, sand, or dust; • Driving while drowsy or fatigued; and • Changing lanes improperly. These four factors accounted for only about 5 percent of all fatal car-truck collisions, however. By and large, the precrash scenarios of car-truck and car-car fatal crashes are similar. Truck crash probability may also be reduced by truck-focused programs. Of particular concern in heavy-truck crashes is the condition of the vehicle. In August 1996, Michigan initiated a program called FACT (Fatal Accident Complaint Team), in which investigations were conducted of trucks involved in fatal crashes. The program has been discontinued, at least for the present. Of 442 crashes occurring between program inception and February 2001, inspections were conducted on 354 fatal crash-involved trucks, or 80.1 percent, to determine the condition of the vehicle immediately prior to the crash. Trucks not inspected were either not available or so badly damaged that meaningful inspection was not possible. Analyses of these data by Blower (2002) show that in almost 66 percent of the cases, a violation was found for either the truck or the truck driver. Over one-third of all inspected trucks had at least one out-of-service (OOS) violation for either the truck or the driver. Considering just the mechanical condition of the truck, almost 55 percent had at least one violation, and 28 percent had at least one OOS violation. Although this rate is high, 31.8 percent of trucks inspected in Michigan under the Motor Carrier Safety Assistance Program (MCSAP) in the 3-year period ending June 2001 were placed out of service. This figure is comparable to findings from other states. Further analyses of FACT data reveal strong relationships between specific vehicle violations and crash types. In rear-end collisions, 27.3 percent of trucks that were struck had a brake violation, but 50 percent of trucks that were the striking vehicle had a brake violation. The only other vehicle inspection component associated with rear-end collisions was the lighting system. Here 15.4 percent of striking trucks had such violations, compared with 39.4 percent of the trucks that were struck, suggesting that truck conspicuity was a SECTION III—TYPE OF PROBLEM BEING ADDRESSED III-8

SECTION III—TYPE OF PROBLEM BEING ADDRESSED factor in the crash. In opposite-direction crashes, in which one vehicle encroached into the other vehicle’s right-of-way, almost half of the encroaching trucks (46.7 percent) had at least one brake defect, compared with only 19.7 percent of trucks that were encroached upon. Likewise, more encroaching trucks had an OOS brake condition than did trucks that were encroached upon. The other defect associated with truck encroachment in the opposite direction was steering. More encroaching trucks (26.7 percent) had preexisting steering defects than did trucks that were encroached upon (2.8 percent). Although high rates of vehicle defects, including OOS problems, are found in heavy trucks in general, large trucks in crashes have higher rates of vehicle defects that relate to the types of crashes involved. Clearly the condition of heavy trucks on the roadway is of concern, and anything states can do to improve vehicle condition should reduce crash probability. However, although truck mechanical deficiencies are overinvolved in crashes, mechanical failure is apparently not a frequent principal cause of crashes. Preliminary data from the FMCSA/NHTSA Large-Truck Crash Causation Study indicate that only about 4 percent of the sampled crashes involved a principal truck vehicle factor, such as a defective component (Craft and Blower, 2003b). Road-Related Characteristics Exhibit III-7 shows the distribution of fatal heavy-truck crashes by roadway functional class. About two-thirds occur on rural roads, and about a quarter occur on Interstate and expressway facilities. The split of crashes between minor and principal facilities is about equal, which indicates the likelihood that at least half of the crashes are occurring on nonstate highways. Exhibit III-8 further confirms the previous finding (FARS, 2002). It shows that the large majority of fatal heavy-truck crashes occur on two-lane roads. This is the case even though the majority of their travel is on Interstates or other divided highways (FHWA, 1999c). Exhibit III-9 provides further insight by comparing the types of heavy-truck collisions resulting in fatalities for two-lane and multilane facilities. The multilane facilities experience proportionately more rear-end crashes, while the two-lane facilities experience proportionately more head-on and right-angle fatal crashes. Exhibit III-10 depicts the variation in fatal heavy-truck collision type by time of day. The number of fatal heavy-truck crashes decreases in the evening and night hours, reflecting reduced volumes, but their proportionality changes. The change in proportions is exhibited in a different form in Exhibit III-11. These graphs demonstrate that rear-end crashes increase proportionately at night, while right-angle type crashes decrease. Evening-hour crashes can be related to many factors, including drowsy driving, driving under the influence, and inadequate lighting (both roadway and truck). Exhibit III-12 focuses on the issue of light conditions. The results suggest that artificial lighting at night is not associated with a significantly different distribution of collision types than that of unlighted road sections after dark. The daylight distribution is somewhat different, however, with greater percentages of front-to-side opposite direction and front-to- front crashes and smaller percentages of rear-end crashes. III-9

SECTION III—TYPE OF PROBLEM BEING ADDRESSED III-10 EXHIBIT III-7 Heavy-Truck Fatal Crashes by Functional Class EXHIBIT III-8 Number of Travel Lanes for Fatal Crashes Involving Trucks Rural Minor Collector 3% Rural Major Collector 11% Rural Local Road or Street 4% Urban Other Principal Arterial 11% Rural Principal Arterial-Other 20% Rural Minor Arterial 14% Urban Principal Arterial-Other Freeways or Expressways 3% Urban Principal Arterial-Interstate 9% Rural Principal Arterial-Interstate 14% Urban Local Road or Street 4% Urban Collector 2% Urban Minor Arterial 5% Source: FARS 2002 Two lanes 76% Three lanes 9% Four or more lanes 15% Source: FARS 2002

SECTION III—TYPE OF PROBLEM BEING ADDRESSED III-11 EXHIBIT III-9 Heavy-Truck Fatal Crashes: Manner of Collision for Two- and Multiple-Lane Roads No t C olli sio n w ith Mo tor Ve hic les Fro nt- to- Re ar Rig ht A ngl e Fro nt- to- Fro nt Fro nt- to- Sid e, O ppo site Two lanes Four or more lanes 24% 24% 19% 7% 12% 22% 14% 23% 18% 13% 0% 5% 10% 15% 20% 25% % o f C ra s he s Note: percents are for a given number of lanesSource: FARS 2002 0 50 100 150 200 250 6 a m to 9 a m 9 a m to No on No on to 3 p m 3 p m to 6 p m 6 p m to 9 p m 9 p m to Mi dn igh t Mi dn igh t to 3 a m 3 a m to 6 a m Period of the Day Nu m be r o f V eh ic le - Ve hi cl e Cr as he s in th e Pe rio d Front-to-Rear (includes Rear-End) Front-to-Front (includes Head-On) Front-to-Side, Same Direction Front-to-Side, Right Angle (includes Broadside) Front-to-Side, Right Angle (includes Broadside) Source: FARS 2002 EXHIBIT III-10 Fatal Truck Crashes: Number of Collisions versus Hour

Is nighttime driving more risky for trucks than day driving? An FMCSA-sponsored study by Hendrix (2002) attempted to measure and compare combination-unit truck fatal crash involvement rates per mile traveled over the 24-hour day. Determining the relative risk per mile traveled between night and day would help the trucking industry and drivers to schedule their trips more safely. The study used roadside weigh-in-motion data to estimate VMT by hour-of-day in four states. These exposure distributions were compared with FARS fatal crash distributions for the same states. The study found no significant differences across the 24-hour day, implying that each truck mile driven has a roughly equivalent fatal crash risk, regardless of the time of day. In contrast, passenger cars and light trucks had fatal crash rates between midnight and 6 a.m. that were several times their rates during the other 18 hours of the day, in part reflecting the higher probability of alcohol involvement during the overnight hours for car and light-truck drivers. SECTION III—TYPE OF PROBLEM BEING ADDRESSED III-12 EXHIBIT III-12 Heavy-Truck Fatal Crashes: Light Condition versus Manner of Collision EXHIBIT III-11 Fatal Truck Crashes: Percent of Collisions versus Hour 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 6 a m to 9 a m 9 a m to No on No on to 3 p m 3 p m to 6 p m 6 p m to 9 p m 9 p m to Mi dn igh t Mi dn igh t to 3 a m 3 a m to 6 a m Period of the Day Pe rc en t o f V eh ic le -V eh ic le C ra sh es in th e Pe rio d Front-to-Side, Right Angle (includes Broadside) Front-to-Side, Right Angle (includes Broadside) Front-to-Side, Same Direction Front-to-Front (includes Head-On) Front-to-Rear (includes Rear-End) Source: FARS 2002 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Daylight Dark but Lighted Dark Light Condition Pe rc en t o f C ra sh es O cc u rr in g Un de r In di ca te d Li gh t Co n di tio n Front-to-Side, Right Angle (includes Broadside) Front-to-Side, Opposite Direction Front-to-Side, Same Direction Front-to-Front (includes Head-On) Front-to-Rear (includes Rear-End) Source: FARS 2002

SECTION III—TYPE OF PROBLEM BEING ADDRESSED Exhibit III-13 depicts the manner of collision of fatal large-truck crashes as they relate to the location along the road. Only those collision types with significant frequency are shown. The fatal collisions at intersections are predominantly right angle, while rear-end crashes are overrepresented for intersection-related crashes (presumably primarily on approaches to intersections). Nonjunction crashes in this data set showed a proportionately greater presence of head-on crashes. The analysis of FARS data, for providing information regarding roadway and collision attributes, is a limited one. However, it demonstrates the value of detailed analysis of the data for a jurisdiction or area. PennDOT recently performed an analysis (Bryer, 2002) that provides a good example of what can be accomplished at the state level to increase understanding of the underlying crash factors and the applicability of candidate strategies. III-13 EXHIBIT III-13 Fatal Heavy-Truck Crashes: Location versus Manner of Collision 0% 20% 40% 60% 80% 100% Non-Junction Junction - Intersection Junction - Intersection Related Pe rc en t o f C ra s he s at Lo c a tio n T yp e Sideswipe - Opposite Direction Sideswipe - Same Direction Front-to-Side, Right Angle (includes Broadside) Front-to-Side, Opposite Direction Front-to-Side, Same Direction Front-to-Front (includes Head-On) Front-to-Rear (includes Rear-End) Source: FARS 2002

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 500 Volume 13: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan -- A Guide for Reducing Collisions Involving Heavy Trucks provides strategies that can be employed to reduce the number of collisions involving heavy trucks.

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