Traffic was brought to a standstill in Halls Head on Friday afternoon following a serious crash on the Mandurah Estuary Bridge.
The accident happened about 11.20am and involved two vehicles.
One of the vehicles rolled during the accident.
Emergency crews attended, with St John Ambulance treating drivers at the scene before transporting three to hospital.
No major injuries were reported.
The bridge was closed for close to an hour, with traffic diverted to the old Mandurah bridge, causing gridlock.
Investigations are under way.