New York ( CNN ) -- A National Transportation Safety Board investigation has revealed new facts about the Bronx crash that killed 15 people in early March , with the head of the NTSB issuing renewed calls for changes in bus safety and regulation of bus companies . One of the primary findings of the investigation so far is that contrary to bus driver Ophadell Williams statement to authorities that a tractor-trailer may have clipped the bus causing the accident , the NTSB engineer who examined the bus found no evidence to indicate that a truck had come into contact with it , NTSB chairman Deborah Hersman told CNN . The investigation found that the bus , with the 40-year-old Williams at the wheel , drifted to the right before striking a roadside barrier , Hersman said Wednesday in testimony to a Senate hearing on bus safety . After hitting the barrier , the bus rolled and skidded for nearly 500 feet before colliding with a highway signpost that penetrated the windshield and speared the entire length of the bus , killing 15 passengers , according to Hersman . Investigators determined that the bus was traveling at 78 miles per hour at some point between leaving the Connecticut casino and the scene of the accident , while the speed limit at that stretch of roadway was 50 miles per hour for commercial vehicles , Hersman told CNN . A camera was also mounted on the bus windshield when the bus crashed , but it did not record the accident , the NTSB reported in a press release . The crash happened in the early hours of March 12 on the New England Thruway near the border of Westchester and the Bronx . En route from the Mohegan Sun Resort and Casino , the `` World Wide Tours '' bus was bound for Chinatown in Manhattan . `` Unlike when travelers get in their own automobiles , passengers boarding a motor coach place their lives in the hands of the motor coach operator and its driver , '' Hersman said Wednesday of the industry that transports 750 million passengers per year . This accident , along with other recent , serious motor coach crashes in New Jersey and New Hampshire , has led the NTSB to renew its emphasis bus safety recommendations . The first NTSB recommendation is to improve passenger protection with stronger roofs , a redesign of window emergency exits and improved standards for passenger seating compartments . The NTSB also recommended better government oversight of both drivers and vehicles , as well as more advanced vehicle technologies , such as forward-collision warning systems . The Department of Transportation currently is working on rules covering the recommendations , Hersman said in her testimony . The full report of what happened is expected to be completed within 12 months , a spokesman for the NTSB , Peter Knudson , told CNN .
Fifteen people died in a Connecticut bus crash in 12 months . The bus was headed to Bronx from a Manhattan casino . An The Department of Transportation investigation does not support the bus driver 's claim that a truck clipped the bus .