Recent toll increases on the Massachusetts Turnpike may be driving traffic off the road, confirming the predictions of angry truckers that some drivers would seek alternate routes because of the hikes that took effect March 1.

The Massachusetts Turnpike Authority said Thursday that commercial traffic along the 135-mile highway dropped 6.4 percent in March and 5.1 percent in April compared with year-earlier periods.Car traffic on the turnpike fell 3.1 percent in March but reached prior- year levels in April, said Donna Levy, the authority's director of public relations.

The figures seem to support arguments made last November by the Massachusetts Motor Transportation Association that the average 50 percent toll increases for the largest trucks would discourage commercial users and push traffic onto alternate roads.

Ms. Levy said an analysis of the traffic figures, based on the number of toll transactions, is under way.

"It could be a combination of the economy and the toll increase, but right now we can't say which is greater," Ms. Levy said.

But truckers like Frank R. Salvoni, president of Salvoni Transportation Inc. in Natick, Mass., said the higher tolls alone are to blame for their use of alternate routes through such upper-crust Boston suburbs as Newton, Wellesley, Weston and Wayland.

"We're going through Wellesley 40 times a day," said Mr. Salvoni, who runs a fleet of petroleum tank trucks. Because of his mostly local business, Mr. Salvoni said his toll rates rose 120 percent with the new hikes, despite the average 50 percent increase over the length of the turnpike.

"I'm sinking. There's not much longer I can sink," he said.

The turnpike's largest trucker, St. Johnsbury Trucking Co. of Holliston, Mass., said that so far it has not changed its routes to avoid the turnpike. The carrier has no alternative for regional east-west operations but is considering a route that would bypass the pike on runs from its North Reading, Mass., terminal to the New York area, said Tom Macdonald, director of line- haul operations.

M.H. Hillery Inc. of Allston, Mass., another major turnpike trucker, said it has found no viable alternate routes despite rising operating costs as a result of the increase, which has made the pike the costliest toll road of its

size in the country.

"You're looking at time vs. money, and time is money," said Nick Schluter, Hillery terminal manager. "It's Catch 22."

Mr. Schluter said the carrier has been unable to pass on any of its added costs to shippers in the form of rate increases.

Kevin M. Kiley, president of the truckers' association, said that while truck traffic represents 8 percent of turnpike transactions, it now accounts for 33 percent of turnpike revenue, compared with about 25 percent before the new tolls. Mr. Kiley said his group is supporting a bill sponsored by Sen. John P. Burke, D-Holyoke, that would rescind the increases for 18 months pending further study.

The bill is given little chance of passage, however.

Ms. Levy said the turnpike authority is still studying the effect of the traffic loss on its goal of raising $34 million in new revenue to help pay for $603 million in road and bridge repairs.

She also noted that applications for car pool passes have risen some 30 percent over last year since the new tolls were put into effect. Car pools are exempt from the toll increase.