The National Transportation Safety Board is conducting a probe on a deadly milk tanker crash that occurred in Phoenix on Wednesday night.
The crash killed four and injured at least nine people.
The wreck occurred after the tanker failed to slow for traffic congestion, according to the Arizona Department of Public Safety.
A spokesperson with the transportation safety board said investigators will determine if the tanker had any advanced safety equipment and if so, how it performed in the crash.
If there were no extra measures taken, investigators will study the incident to see if it could have been prevented by safety devices.
At present, there are no federal requirements that semi trucks have forward collision warning or automatic emergency braking, even though the systems are becoming common on smaller passenger vehicles.
