Patch is being told that a tractor trailer truck and a van have rolled over on 495 southbound near the Tadmuck Road bridge at approximately 9:05 p.m. on Monday night.
Serious injuries are being reported.
We are heading to the scene now to assess the damage, we will provide more information as it becomes available.
UPDATE - 10:33 p.m. - 495 South was backed up to approximately Hunt Road in Chelmsford from the crash site near the Tadmuck Road bridge as of 9:55 p.m.
Motorists are advised to seek alternate routes.
Local police and fire officials are on the scene, we will have more information as it becomes available.