By Donovan Slack and Mac Daniel, Globe Staff | September 4, 2005

A major discount bus carrier that shuttles passengers between Boston and New York rates significantly worse than the national average on two of three federal safety rankings, but state regulators say the bus line is safe.

Fung Wah Bus Transportation Inc., which had one of its buses burst into flames two weeks ago on a Connecticut highway just moments after passengers escaped, said it has run into some safety issues because it has been growing so fast, but it is now fixing any problems.

The company has risk ratings on driver safety and safety management that are close to the point that could trigger a federal investigation.

Fung Wah has a driver risk rating of 73. On the scale, 100 is the worst; 75 or above is considered at risk of being unsafe and can lead to an investigation.

Lucky River Transportation Corp., another low-cost carrier that runs the same Boston-New York route, has a driver risk rating of 74, according to ratings issued in July by the Federal Motor Carrier Safety Administration. Boston-based Kristine Travel & Tours Inc., another lower-cost carrier that used to run between Boston and New York under the name Travel Pack, had a driver risk rating of 97, one of the worst in the country.

It is not under investigation, federal officials say.

On the driver risk rating, the national average is 24. Among the higher-priced competitors, Greyhound scored 22, and Peter Pan Bus Lines rated 58.

The ratings, which are updated monthly and cover the previous 30 months, are based on drivers' records, including the number of traffic tickets and the number of times their logs show they spent too much time behind the wheel.

A score of 80 means that about 80 percent of carriers had better driver-safety records.