So far, the industry has reacted positively, with rates filed by the state's 19 insurers showing an average reduction of 7.8 percent. Additionally, Progressive Insurance Company has announced that it will enter the market in May.

Massachusetts last attempted to move to a competition-based system in 1977, but the experiment lasted only five months. Ms. Burnes said that factors such as the economy and the state of the auto insurance market were different back then.

"The residual market was over 50 percent...Right now our residual market is about 4 percent," she noted.

"In addition," she added, "in 1977, the companies had about three months to get ready for the transition, and every policy renewed on Jan. 1, so they were trying to make the transition for all of the drivers in Massachusetts all at once."

Now, she said, the period from the day the draft regulation was issued until the first auto renewal was five months, "and the policies renew in a rolling way over the year, so that [insurers] did not have to get ready for four million drivers in three months."

Ms. Burnes added that "probably most important, we have been quite cautious about the transition so that we do have a whole set of transition rules before the system will really go into full effect."

Those transition rules include barring the use of credit scoring for rating and underwriting auto insurance for at least a one-year period.

"The credit [scoring] is in the final part of the regulation," she said, "which is to say that it won't be allowed unless I'm persuaded that it should be." She noted that she wants to see if there is a way to take advantage of the positive aspects of insurance scoring while avoiding the aspects that are harmful to consumers.

Ms. Burnes said the progress of the reforms will be studied before decisions on any further changes will be made.

"We don't know how it's going to play out," she said. "It seems to be playing out quite well for consumers. But I'm going to be cautious because I certainly don't want to repeat 1977."