AASHTO Journal, 29 April 2016
The Federal Highway Administration’s truck size and weight limits study was delivered to Congress April 14, concluding more than three years of work on a report that was required by the 2012 MAP-21 surface transportation bill.
The issue of truck size and weight has been controversial for some time as advocates of larger vehicles point to greater efficiency that comes with larger loads. Opponents argue that larger and heavier trucks cause greater wear on infrastructure like roads and bridges and present greater safety concerns for truck operators and other road users.
FHWA’s report does not take a side in the debate, instead gathering data and identifying gaps where more data could help inform future policy decisions.
“Predictably, in a study in which there are so many components that cover different topics, there is no single bottom-line finding,” the report states. “One cannot responsibly take the figures derived from the discrete study areas and come up with a summary result that would yield a clear policy decision.”
However, FHWA cited the use of its Freight Analysis Framework data set, and improved computer models, as helping advance the current understanding of how truck size and weight impacts. In addition to the FHWA data, the study used pavement and bridge impact modeling software – AASHTOWare Pavement ME Design and AASHTOWare Bridge Rating, respectively – to help complete its technical report.
“Although FHWA’s technical work was able to employ the latest modeling techniques in a number of areas, the analytical work revealed very significant data limitations that severely hampered efforts to conclusively study the effects of the size and weight of various truck configurations,” the report states.
For instance, current state crash data systems do not include the operating weight of trucks at the time of a crash. Similarly, crash data systems also do not always identify a truck configuration at the time of a crash. Data gaps were also identified in other study areas including modal shifts, bridge impacts, composite pavement analysis and local roads.
While more data could help inform decisions, the report concludes that “Changes made by Congress regarding the size and weight of vehicles allowed on the Nation’s Interstate System are matters of policy. The work performed and the findings produced in this study can inform the debate on these matters but do not provide definitive evidence or direction to support any specific new change of direction in the areas of truck size and weight limitations. This work has helped identify the areas in which we are reminded that we need to know more, and that new technologies for data collection and sharing can offer us improved mechanisms for growing that knowledge.”
The study and its supporting technical reports are available at http://ops.fhwa.dot.gov/freight/sw/map21tswstudy/ctsw/ctswls_rtc_2016.htm.