Thieves caused delays and inconvenience for motorists after they stole batteries from temporary traffic lights in Bridgwater.
Work has been disrupted on two occasions after thieves struck on Friday (August 9) and Monday (August 12).
Somerset County Council is improving pedestrian access on Taunton Road with new signs and markings between the junctions for Rhode Lane and Wills Road.
Two-way temporary traffic lights have been in place at either side of the roadworks.
The thefts caused the traffic lights stay red, and sparked congestion and cancelled bus services.
Due to the thefts, Skanska, the company carrying out the maintenance on behalf of the council, has decided to remove the temporary lights each night.
A spokesman for Somerset County Council said: "Our contractor Skanska has reported the theft of traffic light batteries to Avon and Somerset Police following two incidents on Friday, August 9 and Monday, August 12.
"As well as being a criminal offence, this is disruptive to our work schedule which includes pedestrian safety schemes, and has caused delays and inconvenience for motorists.
"We would urge any member of the public who spots someone acting suspiciously at the site of ongoing roadworks anywhere in the county to please contact the police."
Councillor Leigh Redman called the incidents a shame and feared it could cause yet another delay to works.
Travel Somerset reports the roadworks will continue until Friday, August 23.
A spokesman for Avon and Somerset Police said: "I can confirm we have received reports of thefts of batteries from temporary traffic lights.
"Anyone who saw anything suspicious on this street is advised to call us on 101."
Witnesses who have any information about the incidents on either Friday or Monday should quote 5219182720 or 521918580, respectively.
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