BOSTON -- Safety changes are being made in the wake of two accidents on Big Dig Ramps, where vehicles plunged over the side, killing one man and seriously injuring two.

NewsCenter 5's Gail Huff reported that a new, independent review will be conducted into the safety of some of the ramps on Interstate 93 even though officials have assured the public that federal safety requirements have been met on the highway.

The state is hiring a consultant with no connections to the Big Dig to study the configuration of the ramps and to determine whether additional safety enhancements are needed. In addition, new speed signs will be posted on the road alerting drivers to the sharp curves. The caution signs will be posted on the ramps where the ramps occurred and also on a ramp that links the Tobin to Storrow Drive. They will be reminders to motorists that they should not exceed 25 mph on the ramps.

A tractor-trailer truck veered off the ramp from the Tobin Bridge Monday, falling 70-feet to the ground below. The driver is still hospitalized in critical condition. State Police said they believed speed was a factor in the accident.

It was the second accident on the ramp in less than a month. On March 19, another car plunged off the road. The driver survived but his passenger was killed. Police said speed was likely a factor in that accident as well.