UK car insurance premiums fell by £100 over three months after the government announced changes to the way insurers calculate whiplash compensation last December.
The finding from comparethemarket.com is significant considering prices have typically fallen by just £65 between December and February over the last six years.
The researchers said whiplash reforms unveiled in the Civil Liability Act have had an "immediate" impact, despite the changes not actually taking effect until April 2020.
"This is the first good news for motorists in a long time, prices have been on a relentless upward march since 2012," comparethemarket.com head of motor insurance, Dan Hutson, said.
"A £100 drop in insurance costs between December and February indicated that a more structural reduction in premiums is taking place."
The researchers said that a decline in car registrations could also have contributed to falling premiums as insurers compete on price in a shrinking market.
However, they warned that the latest reduction does not necessarily mean there will be a significant reset of insurance costs in the coming months.
It is thought that a rise in insurance premium tax (IPT) could keep premiums comparatively high for the foreseeable future until any other mooted reforms are implemented.
But there could be a further fall in prices when the Ogden rate review is completed, according to the researchers, counteracting the punitive impacts of IPT hikes.
It was also found that the gap between the cheapest and average premiums now stands at £116, but that this is much higher for motorists aged between 17 and 24.
"The reduction in car registrations in the past six months suggests that insurers are having to compete more to win a larger share of a smaller market," Hutson continued.
"With the review of the Ogden personal injury discount rate now under way, there is hope for motorists keen to see further reductions of their premiums."