Police have warned drivers to take care after concrete blocks, wood and barbed wire were found placed deliberately in roads in Essex.
Nine incidents have been reported in Tiptree since December 20, Essex Police said.
The obstructions have been left on unlit sections of roads and have caused thousands of pounds' worth of damage to four cars and a bus.
Chief Inspector Nick Lee said: "The first couple of reports of items found were thought to be debris that had fallen in the road, but it is now clear that there has been a pattern to these incidents and the items have been deliberately placed in the road with the intention of causing danger to motorists.
"We have been very fortunate so far that no motorists or other road users have been injured but the damage caused to vehicles has been significant, and it is only down to luck that we have not ended up having to deal with a serious incident.
"The stupidity involved in carrying out these acts beggars belief and I want to catch those responsible as soon as possible."
Officers would like to speak to two white men, aged 20 to 30, seen wearing camouflage trousers and an orange and grey top, and a woman, aged 20 to 30, wearing grey and black clothing.
Anyone with information is asked to contact Essex Police on 101 or 999 in an emergency.