The Federal Highway Administration has chosen the types of vehicles it will compare in its comprehensive study of truck sizes and weights, and is gathering reams of data on how these configurations would affect safety, infrastructure, enforcement and competition among the modes.

It is an ambitious effort ordered by Congress in the last highway bill. The aim is to produce an analysis that will help Congress make an informed decision about federal truck size and weight limits in the next highway bill, due next October.

The agency will not recommend any particular changes, said Tom Kearney of the FHWA Freight Analysis and Research Team. The research is intended to identify the impact of any changes, he said.

The selection of the vehicle types is a key decision.

In a webinar update on the study conducted Wednesday, the agency explained that it will compare six different vehicles to the two standard workhorses of the industry, the 5-axle, 80,000-pound tractor-semitrailer, and the 6-axle, 80,000-pound tractor pulling two 28-foot or 28.5-foot trailers.

The first variation will be a 5-axle rig with a gross weight of 88,000 pounds.

The second will be the 6-axle, 97,000-pound unit that some in the industry are promoting as the logical expansion of the long-time federal size and weight limits. The third will be a 91,000-pound version of that unit.

The fourth will be a 6-axle, 80,000-pound combination of a tractor pulling two 33-foot trailers.

The fifth: a 7-axle, 105,500-pound combination of tractor and three 28-foot or 28.5-foot trailers.

And the last will be a 9- or 10-axle, 129,000-pound combination with three 28-foot or 28.5-foot trailers.

The webinar provided a status report on the study and was an opportunity for stakeholders to participate. Many of the questions came from representatives of groups that have strongly opposed any increase in federal size and weight limits, and indicate the issues that will shape the political debate once the study is done.

For instance, there is much concern about how a change in the limits might affect the competitive balance within trucking, and between trucking and rails.

The research team explained that in addition to estimating the distribution and volume of any freight shift that might occur, it will look at the energy, emissions and traffic implications as well.

It will estimate the total logistics costs for the control vehicles and compare them to estimates for the alternative configurations.

This prompted a question from Ryan Bowley of the Owner-Operator Independent Drivers Association, who wanted to know what steps the researchers are taking to look at the impact on small carriers. OOIDA has opposed any increase in the limits.

Jim March, a consultant on the research team, replied that the study won’t look at different segments of the trucking industry. He acknowledged that small carriers typically are slower to adopt new equipment configurations than bigger, better financed carriers, but said the researchers don’t have a good way to analyze that.

Another OOIDA official, Tom Weakley, asked if the agency is going to consider the environmental impact of having to do more highway repairs due to bigger, heavier trucks.

An agency official said the study will cover energy consumption and emissions from the trucks themselves, but that it’s beyond the scope of the study to look at the impact of highway repair.

Another trucking concern was aired by Mary Phillips, senior vice president of legislative affairs at American Trucking Associations, which supports giving states more flexibility to increase size and weight limits.

Phillips asked if the study will account for profit margins as well as costs in its analysis of freight shift between trucks and railroads.

“In many cases, traffic will not shift if the non-trucking mode opts to lower shipping rates to retain the traffic,” she said.

Scott Greene, a study team member from the Federal Railroad Administration, said the analysis will take this into account.

The discussion of the safety implications of revised size and weight limits drew questions from the safety advocacy community, which adamantly opposes any increases.

John Lannen, executive director of the Truck Safety Coalition, asked the researchers how they will account for bias among organizations that are providing carrier data and also support higher limits.

The response was that the agency is committed to doing an objective, fair study. The researchers are collecting data from carriers in order to fill an information gap, but that data will be balanced by additional information from the states and commodity flow studies.

One limitation in the data that’s available is that police accident reports do not contain information about the size and weight of the truck, the researchers said.

Henry Jasny, general counsel for Advocates for Highway and Auto Safety, wanted to know if the study will take into account that fleets running longer combination vehicles use experienced drivers with more training and higher pay.

David Harkey, a consultant to the study from the University of North Carolina, said these factors will be included in the research.

The study appears to be on track for its scheduled completion date next November. Two more public meetings are planned, and a peer review process is slated to begin in the spring.

FHWA maintains a robust website with volumes of information about the study.