SALEM — Eliminating nighttime and weekend commuter rail and bus service would deliver a devastating blow to traffic, the environment and tourism on the North Shore, a regional economic group said yesterday.

The North Shore Alliance for Economic Development criticized a contingency plan by the MBTA to cut commuter rail service all day on weekends and on weeknights after 7 p.m. The plan would also slash bus service in half on weeknights after 8 p.m. and all day on weekends.

"I think the cuts would be absolutely devastating on the North Shore from Boston all the way up to Rockport and Newburyport," said Bill Luster, president of the alliance, a newly formed, private nonprofit representing about 30 North Shore communities.

The alliance sent a letter to the MBTA yesterday detailing the impact on the North Shore and plans to send memos to North Shore mayors and town managers today, Luster said.

In it, Luster claims the cuts would spike traffic volume on major highways, add to air pollution and devastate tourism.

On the roads, there would be more vehicle trips along Routes 1, 128 and 1A and Interstate 93 as more commuters who usually take the train at night would opt to drive instead, adding to "an already perilous peak-hour commute," Luster said.

Drivers seeking to avoid those heightened traffic jams would try to find shortcuts on local roads, jamming those up, as well. That could lead to dwindling property values as communities become overburdened with commuter traffic, and local businesses would suffer as patrons stay away during rush hour, according to Luster.

Environmentally, auto emissions would rise with more cars on the road, and so would the threat for car crashes.

The public transportation cuts would also hurt tourism by decreasing the number of day trips to places like Salem, Gloucester, Rockport and Newburyport on the weekends and hurt nightlife across the North Shore.

It would also hurt low-income workers and college students who rely on public transportation as their only way to get around, according to Luster.

"We are saying we understand how bad things are, but don't look there," Luster said. "It's too significant of a cut."

A spokesman for the state's Executive Office of Transportation did not return a message left yesterday evening.

Luster's group is taking the cuts seriously because the beleaguered MBTA is facing a $160 million budget gap, he said. The point of the letter is to establish a dialogue with the MBTA, he said.

"We understand there are going to be discussions on revenue, toll hikes, gas tax," he said, "and we want to be involved in that discussion."

Staff writer Chris Cassidy can be reached at ccassidy@salem news.com.