New Hampshire State Police are investigating the crash that happened about 10:30 a.m. Thursday on the on-ramp for Exit 5.
Theodore Takacs, 78, of Nashua, was on his motorcycle, heading down the Exit 5 northbound on ramp to go onto the highway when witnesses said he was passed by a black Chevrolet SUV.
The SUV hit the motorcycle, which rolled over and ended up on the shoulder of the ramp.
Tackacs was ejected and suffered severe head injuries. He was transported to Southern New Hampshire Medical Center in Nashua, but later taken by helicopter to a Boston area hospital for further treatment.
The SUV did not stop. Police are asking the public for help in locating it and the driver. The SUV should have scrape marks and paint transfer on its passenger side, according to state police.
Anyone with information about the crash should call Trooper L. Paul Lundt of Troop B in Bedford at 223-8668.