When Matt Phelps of Groton got wind of the proposal to sharply boost fares on the commuter rail, he did the math this week.
Under the proposal, he will have to fork over $314 for a monthly pass, $64 more than he is paying now. He estimated that driving his Jeep to work every day would run him $280 a month.
The decision, he said, was simple: The Jeep it is.
“I’m not happy with the fact that I’ll be putting more CO2 in the atmosphere,’’ said Phelps, 47, who works at the Harvard-Smithsonian Center for Astrophysics. “But when it gets to the point where it’s a $30 or $40 difference in price between driving and taking the commuter rail, that trumps just about everything.’’
The MBTA’s latest budget-balancing proposal, which the T board could approve next week, includes an $11 to $64 increase in monthly fares for most commuter rail riders, along with an end to weekend service on the Greenbush, Plymouth/Kingston, and Needham lines.
Now, as commuters realize that a year’s worth of rides may approach $4,000, some have found that the fare increase will plunge them into the realm where it makes more financial sense to drive to work, even with the cost of gas and parking.
A report released Wednesday by the MBTA estimates that the proposed fare hikes and service cuts will result in a loss of at least 2.3 million commuter rail rides annually, a 7.2 percent decrease.
Spokesman Joe Pesaturo said MBTA officials hope the added revenue from fare hikes will allow for improved service, eventually attracting customers and allowing the commuter rail to maintain existing ridership.
“If some people decide to choose an alternative to commuter rail, we’ll aim to win them back by continuing to make improvements to service,’’ Pesaturo said in an e-mail.
According to a 2008-2009 passenger study by the MBTA’s Central Transportation Planning Staff, 94 percent of commuter rail riders live in a household with at least one vehicle. More than 75 percent said they have a household vehicle available for use instead of riding the commuter rail.
Richard Parr, director of policy at A Better City, said he is concerned about the impact the commuter rail fare hikes and service cuts will have on the city. But when compared with the MBTA’s initial proposals, announced in January, he knows it could have been worse.
“This is a good middle approach,’’ said Parr, whose organization is a nonprofit concerned with transportation and quality-of-life issues.
“Compared to what we were faced with a couple of months ago, this seems like a pretty reasonable proposal to put forward.’’
Marc Draisen, executive director of the Metropolitan Area Planning Council, said most commuter rail riders have the flexibility to choose their cars instead of the trains.
Draisen, who lives in Roslindale, has a personal stake in the matter: He typically takes the Needham train into Boston. That will no longer be an option on weekends.
A self-described “transit junkie,’’ Draisen said he is inclined to take a bus into town on weekends.
But he believes he is in the minority. Most suburban residents will drive into the city, further congesting Boston’s already crowded streets.
“It’s terrible, because this is a time in our country when we should be encouraging people to use public transit, because of gas, because of greenhouse gas emissions, because it is in many ways more convenient,’’ Draisen said.
Stephen Lawrence of South Plymouth typically spends two hours a day riding the Kingston train to Harvard Square. Wednesday, he decided to spend April commuting by car, a test run to see if driving will prove more cost-effective once train fares rise.
He plans to track his commuting expenses on Twitter using tag #CheaperFasterSmoother.
“I always used to think that doing the commute by car was just a ridiculous thing,’’ said Lawrence, who grew up in the United Kingdom. “Now, I’m looking at the numbers and going, ‘You know what? Commuting by car is not as bad as it looks.’ ’’
Waiting for his commuter rail train Thursday in South Station, Shyan Kao, 42, perused a newspaper, trying to discern how much his fare to Needham will increase.
Still, he said, it will not matter: Though he owns a car, he has no plans to start driving to work at the Massachusetts Eye and Ear Infirmary.
“I’m against the fare hikes, but there’s no parking here in the city,’’ Kao said. “What am I going to do? I can’t do anything.’’
Jeff Brown, 41, of Franklin said he was displeased to see the fare hikes (he’s facing a $52 increase, to $275 a month), but does not think ticket prices are high enough yet to warrant driving to work regularly.
Until the fees reach $350 a month, he said, he will choose the train, where he can get work done.
While Tina Morelli of Hyde Park has her complaints about the commuter rail - “the trains are in such bad shape,’’ she said - she does not want to deal with the hassles of driving.
Tim Simrell, 27, of Roslindale Village shared that view.
“It’s a convenience thing; it’s a gas thing,’’ Simrell said. “And you’d have to pay for parking anyway.’’
“Have you driven on 95 or 93 before 9 a.m.? It’s a nightmare,’’ said his friend, Michael Orlando, 30, who lives in Canton and takes the Stoughton line to work. “On the commuter rail, at least you get to take a nap.’’
But for Phelps, naps are a convenience he can no longer afford.
“It can be nice to take a nap on the train,’’ Phelps said.
“But $40 a month for the occasional nap isn’t really worth it.’’Martine Powers can be reached at email@example.com. Follow her on Twitter @martinepowers.