GREENWICH — Some say truck drivers like the Pennsylvania man at the wheel of the tractor trailer that stopped short of a low-hanging Merritt Parkway overpass — causing the death of a Stamford man whose car slammed into the back of the big rig this week — should understand the highway’s restrictions.

Others believe more needs to be done to deliver the message.

Signs prohibiting commercial vehicles from entering the highway sit on every on-ramp along the route, according to the state Department of Transportation. Some have height markers. None of the overpasses — including the Stanwich Road bridge in Greenwich where the accident occurred Thursday morning — can accommodate large vehicles.

Kevin Nursick, a spokesman for the DOT, said Friday a $4.25 million project to upgrade and replace all of the signs along the approximately 32 miles of the Merritt Parkway will begin later this month. Nursick said the federally funded initiative, which is expected to take about a year to complete, will also enhance the language of the highway’s restrictions on all of the entrance ramps.

Nursick also said the DOT plans to submit a report to the state Legislature by Jan. 1 with potential options to “improve notifications of the height restrictions on the Merritt —obviously to help reduce the number of incidents occurring with trucks illegally using the parkway.”

The Pennsylvania driver had not been ticketed or charged as of Friday, State Police said. The crash shut down the Merritt Parkway for hours as police documented the fatal scene.

“They are professionals. They're supposed to understand the signage around them,” Nursick said of truck drivers. “There’s really no excuse for them to get on to the Merritt Parkway if they are driving one of those vehicles that are restricted.”

Family members of the crash victim, Akija Elezaj, 62, declined to comment at their Turn of River home in Stamford on Friday.

Elezaj’s death underlined the danger of commercial vehicles on the Merritt Parkway.

More often, the crashes are not fatal — just a major inconvenience.

“That is where the majority of our problems happen in my career,” Deputy Greenwich Fire Chief Kevin Millette said. “The drivers are lost and not paying attention to the signs and the next thing they see there is a bridge they won’t fit under.”

State Police Troop G receives 911 calls each day reporting commercial vehicles on the parkway. Many of them are driven by non-commercial drivers, like people who rent a U-Haul to move their belongings.

“They are just following their GPS, not realizing that the vehicle they just rented is not allowed on that parkway,” State Trooper Sgt. Robert Derry said. “This also goes for (all types of) trailers being towed on the parkway.”

Most of the 911 callers are locals who’ve read the “no commercial vehicle” of “passenger cars only” signs many times, Derry said. Most of the offenders are from out of state. Because they’re not using the box trucks for work, many feel the signs aren’t meant for them.

“I believe that there’s a signage issue that's not really getting the message out to the traveling motorist about being on the parkway with these illegal vehicles,” he said.

A DOT-led group that’s studying the signage could recommend changes in the future, Derry said.

Those changes are more difficult to implement than on other roads for the same reason commercial vehicles are banned: the Merritt is a “scenic” road. That’s meant no billboards, and no clearance markers on some of the charming, arching overpasses — including the one where Elezaj died.