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Page 31
Suggested Citation:"Chapter Four - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Impacts of Speed Limiter Device Installations on Commercial Trucks and Buses. Washington, DC: The National Academies Press. doi: 10.17226/14211.
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Suggested Citation:"Chapter Four - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Impacts of Speed Limiter Device Installations on Commercial Trucks and Buses. Washington, DC: The National Academies Press. doi: 10.17226/14211.
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Page 33
Suggested Citation:"Chapter Four - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Impacts of Speed Limiter Device Installations on Commercial Trucks and Buses. Washington, DC: The National Academies Press. doi: 10.17226/14211.
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CONCLUSIONS Speed Limiters and Safety There is adequate literature on the role of large-truck speed in terms of crash severity, but less empirical data relating to the use of speed limiters to meaningful reductions in total crashes because the percentage of crashes that occur above 65 mph is relatively small. However, the statistical impact could increase over time, as indicated by Insurance Institute for Highway Safety data showing that the number of trucks traveling over the 75 mph speed limit rose from 8% to 14% during the period from 1996 to 2006. Published studies indicate that both traveling above the posted speed limit and speed variance among vehicles increase crash exposure. Speed limiters, by restricting speed at or near the speed limit, also create such variances in speed relative to other traffic. This is particularly prevalent in truck–car interac- tions where research shows that car speeds exceed posted speed limits at higher levels than do trucks. Although this situation requires additional objective data, the Study Team found little in the way of published data that addresses the safety impacts of speed limiters on commercial motor vehicles. The most definitive results on the effectiveness of speed limiters comes from the United Kingdom, which showed that the crash involvement rate for speed-limited heavy trucks fell 26% between 1993 (when mandated) and 2005. U.K. authorities noted that other contributing factors may have influenced the decline, but concluded that speed limiters at least played a significant role. Although extensive objec- tive data exist regarding the use of intelligent speed adop- tion speed limiters in European field trials, the differences between the application settings (arterials and residential streets versus highway), operational mode (personal versus commercial), and drivers (private citizens versus profession- als) are such that these results are not deemed relevant to this study. Speed Limiter Utilization Mandated speed limiters are an established component of safety policy in Europe and Australia. In Europe, the require- ment for speed limiters has been extended to include not only large trucks, but also medium-sized trucks. This is indicative of European authorities’ level of conviction that speed lim- iters improve safety. 32 In the United States almost all large trucks (Class 6–8) man- ufactured in the last 5 to 7 years have the ability to govern speed using the engine control module (ECM). However, the per- centage of fleets that use the ECM speed limiter functionality appears to be approximately 65% across the industry. At the sector level, there are more tangible differences, with larger fleets and private fleets being the primary users. Finally, whereas some survey respondents indicated a desire to receive insurance industry benefits, insurance com- pany interview data conducted by American Transporta- tion Research Institute (ATRI) and FMCSA show hesitancy by insurers to offer “front-end” premium discounts to carriers utilizing speed limiters. The general position of commercial insurers is that users of limiters will benefit “after the fact” from lower crashes and/or crash costs. Although this position presently differs from personal auto insurance, which credits users of seat belts, anti-lock brakes, and other safety devices, there is some informal indication that greater amounts of empirical data on the use of limiters might positively influence commercial insurers. Qualitative Analyses Given the paucity of published objective results, the experi- ences of fleet safety managers and owner–operators are the best available sources of information. Two previous surveys plus a written survey conducted in the current synthesis shed some light on the issues. Note that the current study had a low response rate (approximately 7%). The survey can best be described as a small population convenience survey of the commercial motor vehicle (CMV) industry; as such, the results may not be representative and should be interpreted with this in mind. It is not known whether the survey responses are repre- sentative of the overall trucking and motor coach industry. In the ATRI study, researchers found it difficult to mean- ingfully compare fleet safety data before and after speed lim- iter installation owing to the low number of respondents that provided objective safety data. However, qualitatively both the ATRI and Owner–Operators Independent Drivers Association (OOIDA) surveys illustrate that safety is a primary motivation for either adopting or avoiding speed limiters. Those carriers using speed limiters saw benefits in terms of both safety and fuel economy, whereas those choosing not to use speed limiters cited concerns with car–truck speed differential. The OOIDA study focused strongly on driver issues and in particular noted that 81% of drivers reported that they would rather drive for a CHAPTER FOUR CONCLUSIONS

33 company without speed limiters. In the survey conducted for this synthesis, labor concerns were also cited by non-users as a strong reason for not using speed limiters. In the written survey, a large majority of respondents used speed limiters in at least some of their vehicles. Their pri- mary motivation for using speed limiters was noted as reduc- ing the top speed of the vehicle to improve both safety and fuel economy. In addition to reducing vehicular crashes, sev- eral respondents also indicated that they viewed speed lim- iters as a fatigue management tool. The surveys indicated that speed limit settings on the speed limiters were within a fairly narrow range of about 4 mph (65 mph to 69 mph). Safety was selected as the pri- mary consideration for determining the set speed, followed by fuel mileage. Tampering has been cited by some as a con- cern with speed limiters. Depending on the survey, 22%–27% of respondents reported such tampering. The written survey documented anecdotal evidence of large percentages of truck drivers (with speed-governed trucks) exceeding posted speed limits in zones posted below the speed limiter set speed to “make up time.” Survey results strongly supported the existence of this phenomenon, although respon- dents disagreed on whether the effect resulted from speed lim- iters or overall driving habits. Without additional research that cross references speeding with speed limiter/non-speed limiter use, it is difficult to determine the relationship. If the former effect is valid, application of intelligent speed adoption-type methods could be effective; that is, speed limiters that dynam- ically adjust to changing speed limits as the vehicle traverses its route. Overall, a positive picture emerges from speed limiter users who participated in the written survey. Fifty-six percent of respondents indicated speed limiters were either “success- ful” or “very successful” in reducing crashes, and 64% reported speed limiters were either “successful” or “very suc- cessful” in reducing speeding violations. In operational terms, speed limiter users believed that limiters were either “suc- cessful” or “very successful” in reducing tire wear (44%) and increasing fuel economy (76%), whereas 84% indicated that “seldom” or “very seldom” did on-time delivery get reduced. Fleet safety managers indicated that driver attitudes toward speed limiters were largely neutral (64%), whereas 23% were positive. Recognizing the seriousness of the ongoing driver shortage, it is also noteworthy that 77% viewed the impact of speed limiters on driver hiring and retention as neutral. Qualitatively, 96% of respondents indicated speed lim- iters did not negatively affect safety or productivity. When asked whether fleet operations “overall” have been improved by speed limiters, 64% were positive, whereas 24% chose a neutral stance. Thus, synthesizing and examining the results from the series of questions on safety and other benefits of speed lim- iters, this group of respondents overwhelmingly reported note- worthy benefits with relatively few drawbacks. Clearly, speed limiter user respondents considered speed limiters an impor- tant part of their overall fleet management operations. Al- though the majority of respondents perceived the systems as reducing crashes, no respondents indicated any quantitative data that would support their perceptions. However, ATRI’s industry crash data shows that crash severity is highest among large truck crashes where speeds exceeded 45 mph. In summary, these results provide strong anecdotal evi- dence that speed limiters were beneficial to fleet operations; however, the results suggest cost reductions associated with fleet operations and high-severity crashes were greater than for a reduction in the frequency of large truck crashes. POTENTIAL STEPS FOR AN EMPIRICAL STUDY OF SPEED LIMITER USE Although this synthesis provides a general understanding of speed limiter use in CMV operations, as well as of generalized impacts, it does not provide a methodological comparison of before and after results applied uniformly across predefined truck and bus fleet operations. An in-depth, empirical study is needed to collect objective and subjective data in the com- mercial truck and bus industry with regard to the safety effec- tiveness of speed limiters. Such a project might consist of the following steps. • Detailed Survey of Implementation Programs A detailed survey of the commercial truck and bus industries, working with industry associations and manufacturers of speed limiter devices, to discover and classify technologies and techniques used in past application of speed limitation in commercial trucks and buses. In addition, more detailed information is needed on the active use of (versus simply the existence of) speed limiters by fleet sector, size, driver expe- rience, carrier policies and enforcement, and other key vari- ables. These data can then be used to extrapolate benefits to the larger fleet and CMV driver populations once additional empirical research data are obtained. • Selection of In-Depth Survey Population Development of a detailed survey population, based on a strat- ification of fleet size classes (e.g., large, medium, and small), operational types (long haul, short haul, less-than-truckload, private, and for hire), or by commodity types, driver categories, and overall safety performance classifications. • Development of Evaluation Schema Development of a set of quantitative and qualitative evalua- tion criteria and factors for analysis, including both safety per- formance and economic factors as a minimum, to serve as a basis for before and after comparisons, so that results of speed limiter technology application can be determined. Formal

partnerships with industry would be useful to ensure that sen- sitive internal safety data can be collected and analyzed. • Development of Survey Analysis Schema Development of an attitudinal and perception survey for use with the population of drivers and fleets, which would then be evaluated in the expanded study effort, would be useful. Content could include views on program success, perspectives on safety benefits and economic impacts, and evolution of atti- tudes of management and drivers over implementation period. These qualitative data could be compared and corroborated with industry/fleet data as a validation tool. • Selection of Populations of Survey and Control Fleets A selection of appropriate fleets would be an important part of the evaluation. Possible categories could be (1) fleets that have implemented speed limiters in the past 5 years, (2) fleets that are planning implementation, and (3) control fleets. • Conduct Analysis of Survey and Control Fleets An essential step would be to conduct analyses of the survey and control fleets, including evaluation of impacts, and atti- 34 tudinal and perception surveys. If feasible, identification of promising targets for fleets that have not yet implemented speed limiter application, but are willing to work in a pre- application and post-application evaluation of results in a one-year time frame, would be ideal. • Development of Best Practices Recommendations One outcome could be the development of a set of best prac- tices for implementing a speed reduction program, to include detailing key factors that could lead to success of such a pro- gram. This effort could also identify the relationships of speed limiters to an overall fleet safety management culture and best practice use and commitments. • Consultation with Insurers of Truck and Bus Fleets As an additional component to this investigation, selected insurers of truck and bus fleets could be involved to (1) develop an understanding of insurance company views of speed limiter use and implementation and how this technology, with ade- quate empirical data, may influence a priori risk evaluation and loss-pick ratings, and (2) develop and design aggregated data sets relating to safety efficacy results of speed limiter technologies.

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TRB's Commercial Truck and Bus Safety Synthesis Program (CTBSSP) Synthesis 16: Safety Impacts of Speed Limiter Device Installations on Commercial Trucks and Buses explores issues associated with speed limiters including measurable safety impacts, metrics, and degree of benefit. Speed limiters, also described as speed governors, are devices that interact with a truck engine to only permit the attainment of a pre-programmed speed.

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