Adolescents have been seen throwing rocks off the bridge at vehicles travelling along the bypass below.

Police have stressed the dangers involved in the activity, and urge anyone who witnesses anyone throwing rocks at vehicles to contact them immediately.

The crime has been the focus of recent State legislation, which has resolved to push ahead with plans to increase the maximum gaol term to 14 years for offenders caught throwing rocks at cars.

The debate raged following the case of 22-year-old Nicole Miller, who was hit by a rock while travelling on the Princes Highway on the State’s South Coast on July 22 last year.

Ms Miller was sitting in the back seat of the car when she was hit by the rock, which was the size of a brick.

She suffered extensive injuries and was left in a coma, then unable to use her left hand and arm.

She also suffers a permanent ringing in her right ear, and has a titanium plate in her head to protect her skull.

The offender, Peter Hodgkins, was sentenced to a maximum gaol term of four years with a non-parole period of two years.