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23 Rocky Mountain doubles, triple-trailer combinations, and trailer truck crashes than for those involving one-trailer CTs. Turnpike doubles. The United States and Canada have com- Taken together, this and the earlier studies do not permit a plex sets of rules and limitations regarding use of LCVs and "bottom line" determination of the overall crash risk of HPVs other HPVs. In the United States, LCVs generally are per- relative to conventional CTs. mitted in western states but not in most eastern states. A more detailed discussion of HPV configurations and rules for use Earlier in this section, the results of two survey questions is beyond the scope of this report. Individual carriers, how- on the relative safety of larger versus smaller trucks were ever, often have some flexibility in the size and configura- covered. The safety-manager survey also included a question tions of trucks they employ. on whether carriers actually used higher-capacity vehicles, and how users rated them for safety effectiveness. Only 17 of From a carrier perspective, the most compelling HPV 77 respondents reported using HPVs in their fleets. User rat- rationale is efficiency. A 2008 comparative study by ATRI ings of their safety effectiveness were generally high, how- analyzed HPV versus conventional CT efficiency under var- ever; the mean rating was 3.9 on a five-point scale. ious weight, travel, and load scenarios (ATRI 2008). In one comparison, ATRI found that moving 1,000 tons 500 mi with Using Full Vehicle Load Capacity conventional 80,000-lb tractor-semitrailers would require 42 trips and 3,889 gal of fuel. Using a Rocky Mountain Regardless of a truck's or bus's legal load capacity, it would double weighing 120,000 lb would require just 27 trips, a appear to make sense to use the vehicle's full capacity rather 36% reduction, and 3,215 gal of fuel, a 17% reduction. Envi- than to operate partially empty vehicles. The benefits of oper- ronmental benefits from reduced carbon emissions parallel ating vehicles at full capacity are much like the benefits of the fuel savings. Safety benefits would arise from requiring reducing empty miles, as discussed earlier. Fully loaded trucks fewer vehicles and trips to haul the same amount of freight, are less likely to experience wheel lockups and associated thus reducing exposure to crash risk. An Australian study jackknifes and other loss-of-control incidents (Moonesinghe (Moore 2007) found the HPV crash rate per freight ton-mile et al. 2003; Knipling 2009). Loaded vans are less likely to be to be less than one-half that of regular CTs. affected by crosswinds than empty ones (Rossetti and Johnsen 2008). On the other hand, heavier vehicle loads increase stop- Two Canadian studies (Tardif and Barton 2006; Montufar ping distances (Clarke et al. 1991), thus potentially increasing et al. 2007) looked at HPVs classified as LCVs. Both con- rear-end and forward-collision risks. Heavier loads also raise cluded that LCVs offer both productivity and safety benefits if vehicles' centers of gravity slightly, adding to rollover risks their operations are closely and intelligently controlled. The (Moonesinghe et al. 2003). The "bottom line" probably favors Alberta Infrastructure and Transportation study (Montufar full loads, though the benefits cannot be stated categorically. et al. 2007) analyzed Alberta LCV crashes over a 7-year period and determined crash rates and LCV crash risk factors. They compared LCV crash rates per VMT with those of light vehi- ONBOARD COMPUTERS AND MOBILE COMMUNICATIONS cles and three other truck configurations, including standard doubles. LCVs had the lowest overall crash rate of all the Commercial vehicle onboard computers and mobile communi- vehicle types examined. This meant an even greater advan- cations offer a wide range of potential applications for opera- tage over other truck configurations in crash rate per ton-mile, tions and safety. Many of these applications are beyond the because the LCVs carried more cargo. The Tardif and Barton scope of this report. Most notably, this report does not address (2006) study reviewed the use of Turnpike Doubles in Canada. collision-avoidance systems, such as forward-collision warn- They found the Turnpike Double incident rate for seven large ings, lane-departure warning systems, and side object detec- fleets to be 0.24 incidents per million km (equivalent to 0.39 tion systems. It also does not address the technical details of per M VMT), compared to an overall CT rate of 0.46 incidents onboard computers and wireless communications systems. The per million km (0.74 per M VMT). The report cited other data term telematics comprises onboard sensors, networks, soft- indicating that doubles have similar or better crash rates ware, GPS, and wireless communications, which are becoming than tractor-semitrailers in similar operations. Both Canadian commonplace in today's commercial vehicles (Strah 2009). groups suggested superior driver training and qualifications as Much of the MCES focuses on mobile communications used to reasons behind the observed lower crash rates for HPVs com- support various operational efficiencies (Belella et al. 2009). pared to conventional CTs. HPV drivers tend to be more senior The focus here will be on those specific telematic applications and have superior safety records. They generally receive higher mentioned by motor carriers in project surveys and interviews, pay than drivers of CTs in comparable operations. which relate to both operational efficiency and safety. These were discussed primarily with regard to safety benefits, though HPV crashes do have higher severity potentials than those some concerns were expressed about safety losses owing to of other trucks because of their weight and number of trail- driver distraction. ers. Using LTCCS statistics, Zaloshnja and Miller (2007) found the average crash harm (including both human and Commercial vehicles have been equipped with "comput- material components) to be considerably higher for multi- ers" for about 2 decades, at first in the form of electronic