SMITHFIELD — Planning to drive a vehicle weighing more than six tons along Stillwater Road? Better not cross an aging culvert 400 feet north of the intersection of Ridge Road.

That’s because town engineer Kevin Cleary has discovered that the century-old granite culvert is in poor shape and needs to be replaced.

“It could fail any time,” he reported to the Town Council last night.

Cleary told the council that he has notified the pertinent town departments and has had signs posted warning of the new weight limit. The limit is expected to affect fire trucks, school buses and snowplows, all of which are likely to exceed six tons.

The council authorized him to seek bids for a replacement.

Cleary said he discovered the deteriorating condition of the culvert by accident, when he was inspecting the area in May on a visit to a proposed housing development. He said he got permission from Town Manager Dennis G. Finlay to hire a structural engineer to check the culvert, and the engineer, Maguire Group, recommended the six-ton cap.

“It’s not in good condition,” he told the council. “It could fail at any time, and the engineers agree.”

Cleary called the structure “functionally obsolete” and “potentially hazardous,” and said, “It should have been replaced 30 years ago.”

He said the work could be inserted into the budget for the next fiscal year.

In another action, the council authorized John Ratcliffe, acting public works director, to seek bids to purchase three trucks and a new boom arm for cutting roadside vegetation.

Ratcliffe said the heaviest of the trucks would replace a 1983 dump truck. “It has parts from Scandinavia that are no longer available,” he said.

One pickup truck with a snowplow package would replace an 11-year-old model that is proving unreliable, he said. Another would replace a similarly aging pickup operated by the Water Department.

Ratcliffe, on a suggestion by Councilman Bernard A. Hawkins, said he would look into what may be available in the way of vehicles powered by alternate fuels, such as natural gas.

tmorgan@projo.com