Truck crashes into M4 overpass closing two of three lanes

The truck driver who sparked hours of traffic chaos on the M4 Motorway this morning has copped a hefty fine and lost six demerit points from his driver's licence.

Police and RMS crews were called to the Bennet Road overpass at Colyton at 2.15am after the truck's overhead crane smashed into the bridge.

The 32-year-old left the crane extended at 5.8, two metres too high to fit under the bridge.

The incident caused two eastbound lanes of the M4 to be shut down for most of the morning, triggering significant traffic delays in western Sydney.

At one stage, the traffic snarls stretched back at least 11km, with the cars not clearing until about 11am.

Engineers were called in to assess the bridge for damage and remove the concrete and loose tiles. Each tile weighs about 50kg alone.

9NEWS understands the engineers also assessed whether any repair work needed to be carried out on the bridge tonight.

Highway Patrol Chief Inspector Phil Brooks said the truck driver dropped some framework for roadworks early this morning but had left the crane in an upright position.

"The driver then drove down the road and struck the Bennets Road overpass," Insp Brooks said.

"Police and RMS have defected the truck and it will have to undergo a further inspection.

"A further investigaton will take place with a view to prosecuting that driver or using the crane in an upright position."

The truck driver has been fined $2319 in addition to losing six demerit points for failing to heed the bridge height limitations.

"This incident highlights the need for trucks to be safe on our roads," he said.