More than half of the vans currently used to shuttle students throughout the Boston-area by the Phillips Brooks House Association (PBHA) will be forced to carry fewer passengers and stay off the highways due to safety modifications instituted in early January.

In response to National Highway Traffic and Safety Administration (NHTSA) warnings, PBHA removed the back seats from its four 15-passenger vans and restricted them from roads with speed limits over 35 miles per hour, including Storrow Drive and the Massachusetts Turnpike.

PBHA’s three remaining 12-passenger vans are still permitted to travel on the highway.

“In terms of the repercussions for programming, there are serious implications because our programs rely on vans to take volunteers and to take clients,” said PBHA President Ayirini M. Fonseca-Sabune ’04.

She added that the effect on the organization’s nine summer camps, which take place at 12 different locations and rely heavily on van service, may be even more severe.

Leaders of student volunteer groups said the modifications will increase travel time and could lead to a reduction in the size of some community service programs.

Stephen T. Ly ’04, the co-director of BRYE 1-2-1, a PBHA mentoring program, said with only 11 seats in each van, it will be difficult to find people to drive the additional vans needed.

“Right now I am going to do everything I can to prevent us from losing kids or from spending less time with them,” he said. “I am trying to minimize the effect by asking more from our volunteers.”

The new 11-person vans restrict the places Harvard’s volunteers will be able to travel, said Steven R. Griffin, a PBHA employee who coordinates van mainteance and teaches students how to drive the vans.

Budgetary constraints prevent PBHA from replacing the fleet immediately.

While removing seats from the 15-passenger vans did not cost anything, a new van will cost about $25,000, Griffin said.

“Everything comes down to money. If we had the money right now, we would buy new vehicles,” said Griffin. “Our goal is to replace them as soon as we can, but there’s a budgeting problem.”

Fonseca-Sabune said PBHA is committed to maintaining high-quality service despite the transportation setbacks.

“We’re working together to develop a plan that will allow us to continue serving the communities at the same level we have while also meeting Harvard’s new regulations,” she said. “We’ll look to the University as well as outside sources to help continue our programming at existing levels.”

And a van damaged beyond repair in a car accident last summer is slated to be replaced this semester, returning the total van count to eight, according to Fonseca-Sabune.