The Federal Highway Administration chose a Massachusetts engineering firm, CDM Smith and Associates, to help prepare its comprehensive study of truck size and weight limits.

The $2.3 million contract is the next step in the agency’s effort to finish the study by November 2014, as required by last year’s highway law.

The study will look at the safety and economic implications of changing the federal limits, including permitting six-axle, 97,000-pound combinations.

It will compare trucks operating at current size and weight limits to bigger and heavier trucks on the basis of crash rates and other safety risk factors, as well as the costs of effective enforcement, and the impact of the equipment on pavements and bridges. It also will look into the impact on truck-rail competition.

The agency said the study will be peer-reviewed before it is completed next fall, and that the public will have an opportunity to comment.

“This effort will ensure that DOT produces a report that is objective, data-driven, inclusive, and comprehensive,” the agency said in a statement.

The study is a compromise that arose from the highway law, MAP 21, that Congress passed last summer.

Trucking and shipping interests were pressing for a provision that would have given states the authority to permit the six-axle, 97,000 vehicles on Interstates. But they could not overcome opposition from safety advocacy groups and railroads, and had to settle for the study.

The issue will be front-and-center in the next highway bill, which is due about the same time the study is supposed to be done.

Rep. Michael Michaud, D-Maine, has said the study will give Congress the information it needs to vote on a size and weight provision in that bill.