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27 CHAPTER SIX CONCLUSIONS AND FUTURE RESEARCH NEEDS Most states developed tools or methodologies years ago that room for variation because they do not have specific determined the allowable weight limitations and vehicle di- enough provisions. mensions for permit vehicles in their jurisdictions. Some of the approaches that states have used are: Several conclusions can be drawn to summarize this syn- thesis study. Determine allowable permit axle and/or axle group weights by increasing Federal Formula B weights by In the United States, overweight vehicle permitting is some amount. operated through a highly complex system that involves Develop a permit design and analysis vehicle and set the many agencies at the state and local levels. The gov- allowable axle group weights based on the load effects erning policies and regulations vary extensively and of this vehicle. significantly in terms of permit type and processing op- Use locally developed methodologies to extrapolate al- eration. The industry has a strong interest in enhanced lowable permit weights from the bridge design loading. uniformity in this area. Use weight limitations that are legislated rather than de- Bridge evaluation for permit review as a step in the rived based on engineering concepts. permitting system also varies noticeably among the Use basic weigh policies of adjacent state(s) with state-level agencies, primarily as a result of variation modifications. in interpretation of the AASHTO Manual for Condi- tion Evaluation of Bridges (2000) and the referenced Note that these approaches not only establish the maximum AASHTO Standard Specifications for Highway axle and/or axle group weights, but may also affect the axle Bridges (2002), and possibly also as a result of the dif- spacing or number of axles required to carry the weight. For ferences in the computer software programs used. The instance, Federal Formula B considers the number of axles Southeastern Association of State Highway and Trans- in a group, whereas in some states the spread of the axles is portation Officials (SASHTO) study discussed in used as an important factor in permit review. chapter four shows that the difference in the allowable vehicle weight for one single case can be as high as These weight policies have evolved over the years to 40%. Note that the lack of specific provisions in these make accommodations for local industry needs and the needs specifications for the involved quantities has allowed of specialized vehicles and industries. The policies may be for the various observed interpretations. difficult to modify for the following reasons: Having electronic models of the bridges that can repeatedly be used for bridge evaluation is an effective The permit trucking industry has made an economic in- approach to enhanced uniformity for permit review. It vestment based on these policies. Changing the policies can reduce turnaround time for permit review, allow would change the interstate and intrastate competitive for more effort on examining other options for approv- playing field. ing the permit, and provide more consistent and accu- The personnel who developed these polices are no longer rate results. employed at the agencies. The present personnel are re- The multistate permit programs of the New England luctant to make significant changes without additional Transportation Consortium and SASHTO represent studies or electronic computer modeling of the bridges a successful model for improved uniformity in that would support the considered changes. Resources oversize/overweight permitting. In these programs, one are frequently not available for the studies or computer permit can be applied in all participating states for inter- models. state trips if the vehicle falls within the defined spec- ifications for dimensions, GVW, axle weights, and/or Some states now have various electronic computer mod- other parameters. els, which allow them more flexibility to make changes. This also contributes to the nonuniformity in permit weight As a result of this synthesis effort, the following needs were policies and practices. Apart from the policy differences, identified for further research in the area of improved the specifications for bridge evaluation also allow ample uniformity.

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28 Further understanding of the technical basis for issuing enhanced uniformity. For example, they could address those permits that do not require bridge evaluation cur- the differences in estimating the load distribution fac- rently practiced in many states is needed. This effort tor, dynamic impact factor, and live (vehicular) load po- should cover, for example, the vehicle configuration mod- sitioning. This effort could cover those bridges consid- els used in determining the thresholds for not requiring ered not ratable for a variety of reasons. It is also bridge evaluation, axle and axle group load limits, and ex- suggested that the details collected in the SASHTO sur- periences of the states with different thresholds. Next, it vey be fully understood in the context of this research would be helpful to develop rational methods and the effort, to identify the causal factors for nonuniformity needed electronic tools to perform screening, which could in bridge evaluation for permit review. easily be implemented in most states. This research effort Develop a national envelope vehicle based on the en- should include review of the computerized systems used velope vehicles of the New England Transportation by transportation agencies in Alabama, Nebraska, Ohio, Consortium and SASHTO, and the uniform vehicle of South Carolina, South Dakota, and West Virginia, which the Specialized Carriers & Rigging Association. This can analyze every bridge on any route given in the re- vehicle can be a candidate for a national permit pro- spective state. gram, which should cover a majority of permit vehicles Acquire quantitative understanding of the differences in in the country. the approaches, procedures, and software tools used for bridge evaluation in permit review, followed by the de- Resolution of these issues could improve the uniformity of velopment (or identification) of those that can achieve permit review for oversight/oversize vehicles.