Sen. Susan Collins on Thursday announced a breakthrough agreement that would allow the heaviest trucks in Maine to travel on federal highways, taking them off many back roads and downtown streets.

The agreement would allow trucks weighing up to 100,000 pounds on federal roads in Maine for the next 20 years. While Maine now allows those heavier trucks on state roads, federal regulations only allow trucks weighing up to 80,000 pounds on the interstate system here.

“This has been a long, long difficult slog. Bringing it to fruition feels really good,” Collins told the Bangor Daily News. “This is first and foremost a public safety issue, as all the law enforcement groups in Maine are quick to attest, it will make a real difference to allow the trucks to use the federal highways, rather than being diverted onto secondary streets and downtown roads.”

The heaviest trucks now have to leave federal highways and travel on state roads, affecting towns including Freeport, Saco and Old Orchard Beach when they are forced off I-95 and I-295. But the problem is most noticeable north of Augusta, particularly in Bangor and Brewer, where the heaviest trucks are banned from I-95 and I-395 and often rumble through city streets, navigating tight turns.

Collins noted that a big truck traveling from Hampden to Houlton on I-95 rather than Route 2 would avoid 300 intersections, 86 crosswalks, 30 traffic lights, nine school crossings and four railroad crossings.

Bangor Police Chief Ron Gastia said when a recent pilot program was in place allowing heavy trucks on federal roads in Maine, there was a huge decline in the number of trucks on city streets. Now that it’s over, the perception is that there’s even more big trucks in Bangor than before.

And the problems become even bigger in the winter when the road widths narrow and surfaces can be slippery.

“These trucks can’t stop on a dime,” Gastia said. “Getting them away from pedestrians and the congested city streets is just essential.”

The change is also important to Maine’s business community. Companies that ship goods in or out of the state have long complained that they are at a competitive disadvantage because other states in the region, such as New Hampshire, Massachusetts and New York, allow the heavier trucks on federal roads, as do the provinces of Quebec and New Brunswick.

Collins said the new agreement also would benefit the environment because trucks use less fuel when they’re on the interstate and produce less greenhouse gases as well.

“This is a win-win for the economy, for energy and the environment, but most of all for public safety,” she said.

The agreement was greeted with enthusiasm by the Maine Motor Transport Association.

“The Maine economy moves by truck and the success of Sen. Collins to get this through Congress is tremendously welcome news, especially for the professional truck drivers who have communicated to us that they want to use the safer interstate system because it decreases their interactions with other vehicles and pedestrians if they are able to avoid secondary roads,” said Brian Parke, president and CEO of the association, in a statement. “They would rather not have to go past driveways and through towns to deliver their loads.”

It was the public safety argument that swayed her fellow senators and representatives, said Collins, as well as support from educational groups that wanted to cut down on the number of big trucks passing by schools.

The agreement is part of the transportation bill, which provides funding for the next year. Collins said she has been working on this issue for the better part of a decade and the final stretch didn’t get any easier.

While Collins had language in the Senate version of the transportation bill allowing the heavier trucks, the House version did not. So when a conference committee she was a member of had a series of meetings to merge the two bills, Collins had to continue to fight to get the language accepted by representatives of both houses. She was offered a one-year exemption, but Maine already ran a one-year pilot program allowing the heavier trucks which expired last December. Meeting after meeting, said Collins, she brought up her issue until it finally was accepted.

Collins worked with Sen. Patrick Leahy, D-Vt., on the agreement, which also allows such trucks on federal roads in that state.

Collins said the transportation laws and how they are applied came about in a patchwork fashion, leaving Maine and Vermont “like two islands in which these trucks were not allowed on the roads.”

In 2005, then-Sen. Judd Gregg of New Hampshire got a truck weight exemption for his state by working on the Appropriations Committee, said Collins. So when she became a member of that committee in 2009, she headed down that same road.

“Until I got on Appropriations, I didn’t have the means to get this done,” she said. “Then I got on the Transportation Subcommittee, and moved up in seniority to ranking member.”

Both the Senate and House are expected to vote on the transportation bill next week and President Barack Obama is expected to sign it into law Nov. 18. The bill also has, as a rider, the continuing resolution that allows for funding the entire federal government — so it likely will move swiftly along, Collins said.

She warned that it is not a done deal until the bill was signed by the president.

“Something can always go wrong at every step,” she said. “But this is a huge breakthrough.”

Once the president signs the bill, she said, heavier trucks would be permitted on the federal roads immediately. There may be some minor alignments necessary between state and federal laws, Collins said, but she has spoken with Gov. Paul LePage and he’s taking actions to make that happen.

Collins said opposition to the group has come from highway safety activists who would like to ban trucks weighing more than 80,000 pounds from all federal highways. But in Maine the trucks must have a sixth axle to more evenly distribute weight and add to their stopping power, she said. Opposition also has come from railroad companies in other parts of the country, she said.

“It’s an issue that constituents have brought up to me for so long — literally, for probably a decade,” said Collins. “For the next 20 years, we’re in good shape.”