Review of U.S. Department of Transportation Truck Size and Weight Study - Second Report: Review of USDOT Technical Reports (2015)

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55 7. ENFORCEMENT AND COMPLIANCE MAP-21 requires the USDOT study to “evaluate the frequency of violations in excess of the Federal size and weight law and regulations, the cost of the enforcement of the law and regulations, and the effectiveness of the enforcement methods” [Section 32801(a)(3)]. The USDOT study responds to this part of the charge with three assessments: a summary of U.S. trends in truck size and weight enforcement spending, frequencies of weighings and citations, and measures of enforcement effectiveness; a comparison of enforcement costs in states where vehicles exempt from federal weight limits operate with costs in states where the federal limits apply; and an estimate of the effects on enforcement costs of allowing the alternative configurations to operate nationwide based on estimates of costs of weighing specific vehicle types. Responsiveness to the Questions Identified by Congress The USDOT study’s interpretation of the enforcement evaluation charge is as follows: “The purpose of this study is to assess the cost and effectiveness of enforcing TSW limits for trucks operating at or below current Federal truck weight limits as compared with enforcement costs and effectiveness for alternative truck configurations in six scenarios” (Compliance, 2). The legislative language does not explicitly call for an evaluation of the effect of allowing alternative configurations on enforcement; however, USDOT’s examination of how enforcement costs would be affected by the alternative configurations is relevant to the study charge to evaluate safety and infrastructure impacts of the alternative configurations. The report provides a thorough summary of available data on trends in enforcement expenditures and unit costs, numbers of weigh scales in operation, and frequencies of weighings and citations (Compliance, 45–79), addressing the legislative charge to evaluate the frequency of violations and the cost of enforcement. The effectiveness measures used in the study are defined as follows: “Three pertinent

56 relationships are established, namely: the weighing cost-efficiency ([non-WIM] weighings per personnel cost), the weight violation citation rate (citations per weighing), and the relationship between citation rate and enforcement intensity (measured as the number of weighings per truck vehicle-miles of travel (VMT))” (Compliance, 3). The last measure, the impact of enforcement on violations, appears closest to answering the enforcement question that would be most relevant to Congress: Is the level of enforcement sufficient to reduce violations to a tolerable level? (The tolerable level would depend on the safety and infrastructure costs of violations and the cost of enforcement.) The conclusion of the USDOT study that directly addresses the legislative charge to evaluate enforcement effectiveness is the following: “The relationship between citation rate and enforcement intensity revealed that the citation rate decreases as enforcement intensity increases (i.e., more weighings per million truck VMT), but reaches a point of diminishing return. Moreover, those States that conduct a higher proportion of portable and semi-portable weighings generally have a lower overall enforcement intensity and a higher citation rate” (Compliance, ES-6–ES-7). The USDOT report makes a worthwhile beginning at understanding the relationship between enforcement effort and outcomes (Compliance, 79– 83) but stops short of establishing the relationship. It concludes that “measuring enforcement effectiveness in terms of a citation rate is complex because both relatively low and relatively high citation rates could be interpreted as a reflection of an effective enforcement program” (Compliance, ES-7). Therefore, the report does not fully address the charge to evaluate the effectiveness of truck weight enforcement. Methods and Data Measures of Enforcement Effectiveness The indicator of effectiveness used in the USDOT study, the relationship between weight violation citation rate and enforcement intensity, uses the frequency of citations as a proxy for frequency of

57 violations. However, as the report points out, citations can be a misleading measure of violations. A relatively high rate of citations in a state may indicate a relatively high frequency of violations or it may indicate that the state’s enforcement program is highly efficient at catching violators. To establish the relationship between enforcement and violations, a direct measure of violations is necessary. WIM data, if installations were appropriately sited and operated, would be an ideal source of information on the frequency of overweight vehicles. (To determine violations, corrections would be needed to account for legally permitted overweight vehicles. The measurement errors in WIM readings that prevent their use as evidence for legal citations are not an obstacle to the use of the data to monitor enforcement effectiveness.) The report does not exploit WIM data to assess the overall frequency of weight violations (although WIM data are used to compare frequency of violations of the control and alternative configurations). The authors may have concluded that limitations of presently available WIM data make the data unsuitable for this purpose. Enforcement Cost Estimates The report’s description of the method of computing the change in enforcement costs in the alternative configuration scenarios (Compliance, 13–14, 57–58) is not detailed enough to allow the calculations to be reconstructed. The alternative scenario enforcement costs appear to depend on estimates of (a) the average enforcement personnel cost per truck weighed today, (b) the ratio of the personnel time required to weigh an alternative configuration to the time required to weigh a five-axle tractor-semitrailer, and (c) the change in the volume of trucks by configuration in the scenarios. The report states (Compliance, 8) that no attempt was made to allocate state enforcement expenditure data between weighing and safety inspection (both of which occur at the same roadside stops). Therefore, the estimates appear to be based on an average cost that includes the personnel cost of safety inspections but takes into account only time changes due to weighing. A complete estimate would have included the cost of any changes in average safety inspection

58 time in the alternative scenarios. The results of the inspection and violation analysis in the safety technical report (Safety, 76) suggest that inspection times may differ, although, as explained in the review of the safety technical report above, any observed differences in violation rates in that analysis may be the result of differences in operator characteristics rather than in vehicle configuration. Inspection of more complex vehicles (triples replacing double-trailer configurations or six-axle tractor-semitrailers replacing five-axle tractor-semitrailers) might be expected to require more personnel time per vehicle. 13 Recommendations Knowledge of the relationship between weight enforcement effort and frequency of weight violations would be of great value in planning and budgeting enforcement programs. USDOT should continue the analysis of this relationship begun in the truck size and weight study. The analysis should determine the relationship between enforcement effort and frequency of violations as observed in WIM or other nonenforcement weighing data, as well as the relationship between enforcement effort and frequency of citations. The analysis must be deepened to distinguish relative effectiveness of alternative methods and strategies of enforcement. In any future truck size and weight study, estimates of enforcement costs should explicitly account for costs of safety inspections as well as costs of weighings. 13 The change in total enforcement time is the difference between the time per inspection multiplied by the frequency of inspections in the alternative configuration scenario and time per inspection multiplied by the frequency of inspections in the base case. If truck traffic volume declines in the alternative configuration scenario because the alternative configuration has greater capacity than the control vehicle, then the frequency of inspections, for a constant enforcement intensity, will decline.