WASHINGTON (Reuters) - As the Trump administration moves to freeze vehicle fuel efficiency standards, some regulatory officials have disputed the Transportation Department rationale that the plan would significantly cut traffic deaths, internal documents made public on Tuesday showed.

FILE PHOTO - Cars travel on city streets and highway overpasses in San Diego, California, U.S. in this February 10, 2016 file photo. REUTERS/Mike Blake/File Photo

The Transportation Department under President Donald Trump has proposed rolling back Obama administration rules requiring tough fuel efficiency standards and backs freezing the standards at 2020 levels through 2026.

In a June 18 memo posted by the Environmental Protection Agency on a regulatory website on Tuesday, EPA staff said they believed the plan would increase traffic deaths by 17 a year from 2036 through 2045 because of an increase in vehicle travel, rather than reduce deaths by 150 per year over that time as the Transportation Department contended.

The documents could give ammunition to environmental critics and states that oppose freezing the requirements.

Senator Tom Carper, a Democrat, said the documents suggested the proposal is “based on bogus science and fundamentally flawed assumptions. The administration’s own EPA itemized its technical concerns about the plan’s baseless claims, but DOT and the White House seems to have willfully ignored much of it.”

The EPA staff also concluded the plan would result in net societal costs of $83 billion, compared with the Transportation Department’s estimate of net benefits of $49 billion.

EPA spokesman John Konkus said the documents showed only “a fraction of the robust dialogue that occurred during interagency deliberations for the proposed rule” and noted the government is seeking comments on a variety of alternatives. The final proposal did not adopt those EPA staff fatality estimates.

The Transportation Department did not immediately comment.

The EPA made the documents public on Tuesday as it launched the formal regulatory process. Two people briefed on the matter said the proposal was expected to be published in the Federal Register early next week, kicking off a 60-day comment period.

The Transportation Department said in its Aug. 2 joint proposal with EPA that freezing the fuel standards would save at least 12,700 traffic fatalities by reducing the price of new vehicles and prodding people to buy newer, safer vehicles more quickly, or up to 1,000 deaths per year in the initial years that the rules are in place.

The administration has made reducing traffic deaths a key part of its argument that rules adopted in 2012 under President Barack Obama need to be rolled back. The administration has titled its proposed regulation the “Safer Affordable Fuel-Efficient Vehicles Rule.”

Emails among the documents posted showed EPA staffers in meetings questioned modeling by the Transportation Department’s National Highway Traffic Safety Administration (NHTSA). In a June memo, EPA called the NHTSA model “indefensible” and based on “unrealistic” assumptions.

EPA and NHTSA clashed over estimates about the future size of the U.S. vehicle fleet, total vehicle miles driven, automaker compliance costs as well as how long it would take consumers to recoup costs of buying fuel-efficient models, the emails showed.

The EPA document said the proposal could result in the loss of 27,000 to 35,000 jobs per year.

NHTSA said in a July 12 email to a White House office overseeing the proposal that the EPA criticism relied on a “developmental version” of its model and defended its analysis.

NHTSA said its “preferred option” would result in fleetwide fuel efficiency of 37 miles per gallon by 2026, compared with 46.7 mpg under the Obama rules, but reduce the cost of a new vehicle by $1,850 and save automakers more than $300 billion in regulatory costs. The Trump plan would hike U.S. oil consumption by about 500,000 barrels per day by the 2030s.

The Trump administration also wants to revoke California’s authority to set its own strict tailpipe emissions rules and mandate the sale of electric vehicles. California is moving ahead with setting its own rules, and 19 states said this month they will challenge the rollback in court.

Automakers want changes to address shifts in consumer demand but also favor efficiency requirements continuing to rise. They have urged California and federal regulators to negotiate an agreement that would avoid a lengthy legal battle.