By Michelle Durham

PHILADELPHIA (CBS) — Philadelphia police have arrested four men whom they say were observed by an off-duty officer removing a large drainage gate from the highway and placing it in their vehicle.

Penndot officials say the four suspects were employed by them as subcontractors, and note that between 60 and 70 of these cast-iron grates have been reported missing in the past year and a half.

According to Penndot spokesperson Gene Blaum, the grate in question was very large and worth about $1,000.   But besides the expense, he says, if the removal had gone detected it could have cost one or more lives.

“The results could be devastating,” he tells KYW Newsradio.  “It’s basically a hole in the highway that’s six feet long by two feet wide.  If a car came down the ramp too far over on the shoulder, there would have been a very, very serious accident.”

Blaum says Penndot continues to work with Philadelphia police as well as conducting its own investigation.

“We’ve had, over the past year and a half or so, grates mysteriously disappear along the I-95 corridor,” he says.

The four men charged are Norberto Rivera, 24, of the 2000 block of E. Allegheny Ave. in Philadelphia; Raul Rosario, 56, of the 400 block of N. 7th Street in Camden, NJ; Carlos Villegas, 54, of the 600 block of E. Willard Street in Philadelphia; and Edgar Manon, 24, of the 500 block of Alcott Street in Philadelphia.

How can a passing motorist tell if roadside work is being conducted for legitimate purposes?  Blaum says Penndot and its subcontactors always use cones and flags to protect workers from oncoming traffic — workers are never on the side of the road without that protection.