The Hay Street Bridge in the Perth CBD will be raised in a $6 million project to avoid any more traffic-halting truck strikes.

The bridge beams that hover above the Mitchell Freeway are scarred by decades of truck strikes, the most recent in August 2018.

A truck crash at the Hay Street bridge on Mitchell Freeway. Credit:6PR

The bridge has been hit 20 times, with nine of those incidents within the past five years.

Each time an over-height truck strikes the bridge freeway traffic must be stopped while the resulting mess is cleaned up and an engineering assessment is completed.