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Supporting information, experimental results, and analyses are provided in a series of appendices to this report as follows: A - Literature Review B - Development, Evaluation, and Ranking of M.O.E.s C - M.O.E. Field Validation D - Ancillary Enforcement Issues E - Effects of Axle Weight on Pavement Life F- M.O.E. Sampling Plan Development G - User Guide Software Help Screens H - Glossary of Tenns 2.0 TRUCK-WEIGHT ENFORCEMENT EFFECTIVENESS MEASUREMENT 2.1 Background Truck-weight enforcement programs are conducted to limit the amount of damage to the infrastructure and to improve public safety on the highways. These programs rep- resent a considerable effort to protect this country's investment in its pavement infra- structure. The level and value of truck weight enforcement activities are currently gauged by means of statistical measures such as: (! ~ the number of trucks weighed, (2) the num- ber of violators detected, and (3) the amount of fines collected. Such measures indicate level of effort, but not what is actually being accomplished as a result of that effort in teens of overall compliance web weight laws. A comprehensive examination of truck weight enforcement practice (U.S. DOT, 1993), over a four-year study penod, noted that on average over 144 million trucks were weighed annually, resulting in over 681 thousand citations. However, this comprehen- sive nationwide examination of enforcement-activity concluded that adequate informa- tion was not being collected to assess compliance trends. The DOT study documented a wide variation in the number of enforcement weighings between states, bearing no correlation with actual truck volumes. Moreover, sporadic changes in year-to-year enforcement activity further indicated the lack of uni 2
form practice. Highlights of the study noting inconsistencies with regard to truck weight enforcement practice between states are summarized as follows: I. Annual enforcement weighings Garaged from less that 20,000 in certain states to more than 5 million. 2. Within We sample of states conducting more Man 5 million weighings, Muck weight- sampl~ng rates vaned from 287 to 1,864 weighings per million vehicle miles of estimated truck travel miles. Thus, the sampling rate was seen to vary Mom state to state by a factor of 6.5. 3. Within Me above noted weighed-truck samples, citation rates vaned between .66 and 6.3 trucks per thousand. Thus, citation rates were seen to vary from state to state by a factor of 9.6. This wide divergence in enforcement practice confounds the problem of assessing compliance trends. It is not possible to gauge the impact of enforcement practice without a systematic data-sampling approach that is sensitive to the actual number of trucks in the traffic stream and to Weir degree of compliance with weight regulations. 2.2 Current Status The effectiveness of the nation's truck weight enforcement activity is not measured via any systematic sampling of truck volume, weight, and violation data. As a result, the elect of truck-weight enforcement programs is not known In terms of: (~) actual impact on weigh-law compliance, (2) effect on safety of truck operations, (3) pavement service life effects, or (4) cost-effectiveness of enforcement activity, e.g., associated cost-benefit in terms of pavement preservation. 2.3 Effectiveness-Measurement Requirements In order to determine what is actually achieved by truck weight enforcement ef- forts, it is first necessary to consider truck weight enforcement goals or objectives. Goals of state enforcement agencies, which operate truck weight enforcement activities, are the following: 3.
Deter truck operation in art overweight condition and/or operating with ~nappropnate axle spacing, Control pavement and bridge damage from overweight trucks, Protect the public from safety risks associated with overweight trucks, and Protect law-abiding truck operators from illegal competition. 4. Any benefit of the enforcement activity must then be recognized in terms of some, or all, of these goals. That is, a study to determine the effects of truck weight enforce- ment activities must be based on measures that reflect goals of the weight enforcement program. Typical output of a truck weight enforcement evaluation should indicate effects on compliance, e.g., instances and severity of overweight violations, and whether any en- forcement benefit is achieved in terms of reduced pavement wear. Moreover, it is necessary to systematically measure enforcement compliance in the context of actual truck exposure, e.g., total truck volume, so as to validly determine compliance (and consequences of non-compliance) within a given study area. Systematic observation procedures are required to ensure that the observed sample adequately char- acter~zes the overall truck population. 4
