TRENTON - Amtrak is going to break the speed limit in the Northeast Corridor.

The rail service announced Monday that it will operate test trains overnight at 165 m.p.h. in four stretches from Maryland to Massachusetts.

Acela Express equipment will be used for the tests, which were to start at about 10:30 p.m. Monday in New Jersey and will continue into next week, Amtrak spokesman Cliff Cole said.

All the locations may one day have regular 160-m.p.h. service; the current top speed limit is 150 m.p.h.

Amtrak said tests need to be performed at 5 m.p.h. above what is expected to be the maximum operating speed.

Two test locations - from Perryville, Md., to Wilmington, and from Trenton to New Brunswick, N.J. - currently have a speed limit of 135 m.p.h. The two others - in Rhode Island from Westerly to Cranston and in Massachusetts from South Attleboro to Readville - have 150-m.p.h. limits.

The same areas, totaling just over 100 miles, were used for tests reaching 165 m.p.h. in the 1990s before the introduction of high-speed Acela service, Cole said. Federal regulations required another round of testing, he said, to further raise the top speed limit.

Cole said the tests, with cars equipped with instruments to collect a variety of data, will not affect normal rail operations because they are scheduled at a time of minimal rail service.

In New Jersey, track, electric power, signals and other systems are to be upgraded over the next several years to improve reliability and to permit regular train operations at faster speeds, as part of a $450 million project funded by the federal high-speed rail program.