More than 50 cars have been damaged by bricks and stones thrown from passing vehicles.
Witnesses say missiles have been hurled from oncoming cars on several rural roads on the Norfolk-Suffolk border, including the A146 and A143.
In one case, a driver said he "could have been killed" after hearing "an almighty bang" when a brick was thrown.
Suffolk Police said the incidents could be linked and described the attackers as "extremely irresponsible".
A spokesman said there had been more than 40 attacks in the area since 24 May, with a further 13 recorded since 1 June.
The force said a private patient transport ambulance was damaged on Tuesday.
David Thompson, 77, who runs Bungay-based taxi firm D-Way Travel, said he initially thought he had hit a pheasant on the A143 on 1 June until he realised an object had been thrown from a car coming towards him.
"I was approaching two cars - at 11 at night - about 100 yards apart," he told the BBC.
"I heard this almighty bang, and when I dropped my passenger off I found it was a brick and it was completely wedged under my engine.
"I don't know if they're young or old, they think it's a prank and they're getting away with it. I could have been killed."
Donne Bradley described how her windscreen was hit by a rock as she drove out of Flixton at 17:30 BST on 8 June.
She said she and her 11-year-old son were "showered with glass" when her car was "hit by a large rock from another oncoming car [and] the noise was awful".
"It's affected me quite a bit and is still happening," she said. "My son was quite shaken up, bless him."
A police spokesman said overnight patrols had increased and officers were "exploring the possibility that these incidents are linked".
Insp Liz Casey, of Lowestoft Police, said: "These incidents had the potential to cause road traffic collisions and in turn serious injury or damage.
"It is fortunate that no one has so far been hurt and the damage although, will be costly to victims, has not cost them their lives."
She added: "Such behaviour is extremely irresponsible, throwing any item into traffic puts lives at risk, and anyone found to be doing so will be firmly dealt with."
The force has issued an appeal for dashcam footage.