BOSTON (CBS) – National Grid is facing a wrongful death lawsuit in a fatal accident on Interstate 495 last year.

WBZ NewsRadio 1030’s Mark Katic reports

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Sharon Wang of Westford was driving with her mother and two children on 495 in Southboro on August 12, 2011 when they were passed by a National Grid truck pulling a backhoe on a trailer.

The 17,000-lb. backhoe suddenly fell off and landed on top of Wang’s minivan, crushing it.

Wang and her children were hurt and her mother, 72-year-old Xjaoyun Jiang, was killed.

“I could not reach my children, but I could hear them screaming,” Wang said Wednesday at a news conference announcing the lawsuit.  “I could not even respond to their call for help.  For an hour we were trapped.  It was the worst hour of my life.”

National Grid admitted after the accident it was test-driving the truck at the time because of safety concerns expressed by employees.

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The lawsuit contends National Grid put out an internal memo warning that their new dump trucks had difficulty towing backhoes.

The family believes that was nothing short of negligent by running the test on a busy highway on a Friday afternoon.

Attorney Brad Henry said National Grid has been arrogant not reaching out to them.

“The only response we received from National Grid was a letter from a lawyer in New York instructing the family to preserve the vehicle as evidence,” he told reporters at the news conference.

They’re seeking monetary damages and safety reforms.

“We extend our deepest sympathies to Mrs. Jiang and her family.  Because this is pending litigation, we cannot comment further at this time,” National Grid spokeswoman Jackie Barry said in a statement to WBZ-TV.

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The Worcester County District Attorney’s office said the accident is still under investigation.