Officers attached to Bathurst Highway Patrol were conducting speed enforcement on the Mount around 11.40am on Saturday when they spotted a red Holden SS Commodore speeding on Conrod Straight.

Police allege the driver was clocked at 140km/h, 80km/h over the posted speed limit, as he overtook a motorcyclist travelling in the same direction.

Police stopped the vehicle and spoke with the driver, a 19-year-old man from Harrington Park, in Sydney's south-west.

He produced a NSW CP2 provisional driver's licence and was breath tested, which returned a negative result.

The driver's licence was confiscated and suspended for six months and he was issued a number of traffic infringements, including exceeding the speed limit by 45km/hr; not complying P1/P2 high performance vehicle restrictions; not complying with P2 licence conditions (not displaying P-plates); and overtaking a vehicle when unsafe.

The incident came on the first day of Operation Slowdown, a high visibility police operation targeting bad driver behaviour over the long weekend.

Police Commissioner Michael Fuller said there would be extra police conducting enforcement activities on roads across the state.

"Operation Slowdown will see our Traffic and Highway Patrol officers targeting speeding, drink and drug driving, driving while fatigued, mobile phone, helmet and other traffic offences," Commissioner Fuller said.

Double demerits remain in place on NSW roads until 11.59pm Monday night.