SOUTHBOROUGH — A National Grid trailer hauling a backhoe was out on a test drive amid safety concerns when it toppled onto a minivan in Southborough on Friday, according to a company spokeswoman.

State police said a 2010 Freightliner truck towing a 2007 Case backhoe/front-end loader on a trailer was traveling south on Interstate 495 at about 1:15 p.m. when the backhoe rolled off of the trailer and landed on top of a 2000 Toyota Sienna.

National Grid spokeswoman Debbie Drew said it was unclear what caused the crash but that the dump truck was being test driven at the time, according to media partner WCVB-TV, Channel 5.

“This was a new model of dump truck which National Grid was continuing to evaluate and test drive following some safety considerations which had been identified by our employees,