WASHINGTON – A massive highway bill that serves as a road map for federal transportation projects in the next six years passed the Senate last week without any amendment to boost truck weight limits on Interstate 95 north of Augusta.

The amendment, sought by Sen. Olympia Snowe, R-Maine, would allow trucks heavier than 80,000 pounds to run all the way from the New Hampshire line to an exit from the interstate close to the controversial West Old Town Landfill.

Instead, heavy trucks must leave the interstate at Augusta and wind their way through various towns and on various state- and locally maintained roads that allow up to 100,000-pound loads.

The federal limit is 80,000 pounds.

The weight differences stem partly from rules that grandfathered older highway systems. Massachusetts, which allowed heavier trucks on its roads before the interstate system existed, is still able to let them travel on I-95.

Maine secured an exemption for the Maine Turnpike because no federal dollars were used to build the original highway.

The turnpike portion ends just south of Augusta, however, so the 80,000-pound limit kicks in from that point north.

Snowe and other members of Maine’s congressional delegation have been trying to extend the exceptions.

Last week, the Senate passed a bill that authorizes some $318 billion in federal highway aid to the states.

Snowe’s amendment would have allowed Maine a waiver from federal restrictions on truck weight limits on interstate highways for a three-year period. If it were found to have a positive impact on safety, it would become permanent.

The amendment was rejected, but a spokeswoman said the senator would now attempt to push it through when competing House and Senate versions of the bill are worked out in conference committee.

The Senate approved its version Thursday. The bill would authorize an increase in spending on highways, mass transit and road safety nationwide by some 40 percent over the next six years, compared with the six-year program soon to expire.

It passed the Senate by enough of a margin to overcome a threatened presidential veto. The White House has said the Senate bill far exceeds the administration’s own $256 billion proposal and would add to the already record-high federal deficit.

On the House side, Rep. Michael Michaud, a Maine Democrat who sits on the House Transportation Committee, and Rep. Tom Allen, D-Maine, have backed a measure that would allow the state to raise truck weight limits on interstates. The bill is in committee. Snowe and Sen. Susan Collins, R-Maine, last year filed a similar bill in the Senate.

Monica Castellanos, spokeswoman for Michaud, said pushing for higher weight limits is a priority. “This is really about safety, about big roads going around small roads. We need to get them out of our towns and onto interstates.”

Dale Hannington of the Maine Motor Transport Association said raising truck weight limits is important from an economic development standpoint. He said lower truck weight limits slow down businesses and keep them from wanting to set up shop in Maine.

“As much as 90 percent of the freight in Maine is carried through trucks,” said Maria Fuentes of the Maine Better Transportation Association.

Some communities including Bangor face the possibility of 100,000-pound trucks traveling to and from landfills. Officials say carrying the waste in smaller trucks would cost millions more each year, and would double the number of vehicles on state and local roads.

A state Department of Transportation spokesman said it is safer and more effective to allow five- and six-axle trucks to travel on interstates than on secondary roads.

However, national safety groups have long lobbied with some success to freeze federal weight limits on interstates, citing safety. The Coalition Against Bigger Trucks says heavier trucks are more prone to collisions and rollovers. The group also points out that freezing truck weight limits at current levels would save $326 million in infrastructure costs annually because bigger trucks cause more damage to roads and bridges.