Weather could make holiday road trips even more tricky

State transportation officials and AAA Southern New England say that starting today South Shore travelers heading south to Cape Cod or north into Boston or New Hampshire should plan for extra traffic delays. But exactly when drivers should expect the worst traffic snarls is up in the air because of heavy rain predicted to roll in today and Friday.

Holiday travelers will face all the usual traffic bottlenecks with some added uncertainty from a looming storm this Fourth of July weekend.

State transportation officials and AAA Southern New England say that starting today South Shore travelers heading south to Cape Cod or north into Boston or New Hampshire should plan for extra traffic delays. But exactly when drivers should expect the worst traffic snarls is up in the air because of heavy rain predicted to roll in today and Friday.

“I would advise people to be particularly careful about watching the weather forecast and timing travel accordingly,” said Mary Maguire, director of public and legislative affairs for AAA Southern New England. “You don’t want to be out in major thunderstorms or heavy downpours. That just snarls traffic more.”

Maguire said AAA estimates 750,000 to 850,000 Massachusetts residents travel more than 50 miles from home on a typical Independence Day weekend. The organization is expecting that to increase 3 percent this year, though that depends on the weather.

Maguire said if the weather gets particularly bad, it could lead to fewer traffic jams if more would-be travelers stay home instead.

Route 3 south to the Cape, the Bourne and Sagamore bridges and Interstate 93 going through Boston and into New Hampshire are likely to be packed for much of today and Friday, said Michael Verseckes, a spokesman for the state Department of Transportation.

Verseckes said travelers should try to leave earlier in the morning and to download the free smartphone app RideWise to track real-time traffic conditions.

“We’re encouraging people to leave earlier if possible and also to download this app and use that as a tool to make decisions for their travel plans,” he said.

Boston announced Wednesday afternoon that it had moved up its fireworks display and Boston Pops concert on the Esplanade from Friday to tonight because of the weather forecast. People heading into the city are urged to take the MBTA, which will be free after 9:30 p.m.

The T will add extra cars on all subway lines beginning at 2 p.m. All trains and buses will be free after 9:30 p.m.

“The MBTA is well aware that its service is the preferred alternative for hundreds of thousands of people headed to the Esplanade,” MBTA spokesman Joe Pesaturo said in an email. “The MBTA has been doing this for decades, and we will be prepared again this year.”

Christian Schiavone may be reached at cschiavone@ledger.com or follow him on Twitter @CSchiavo_Ledger.