Side road activated speed signs explained

Since 2023, special electronic speed limit signs have been installed at three high-speed rural intersections in WA as part of a demonstration project aiming to improve safety.

The “side road activated” speed signs, near Lancelin, Chidlow and Bunbury, temporarily lower the speed limit on a main highway when sensors detect a vehicle either approaching it from the side road, or entering the highway’s right turn pocket to turn off.

When the sign is illuminated, the displayed speed becomes the legal limit for everyone on the highway. Drivers must follow that limit until they reach a standard speed sign on the far side of the intersection, where the usual speed limit resumes. Once the turning vehicle has moved through, the electronic sign turns off and the speed limit on the highway through the intersection returns to normal.

The special signs are active on Indian Ocean Drive, at the Lancelin Road turnoff near Lancelin, and on Great Eastern Highway at Old Northam Road near Chidlow (both scenes of past crashes involving right turning vehicles, some fatal), as well as on Wilman Wadandi Highway at Discovery Road near Bunbury (following the opening of the highway in late 2024).

The lower speed limit (for example, 70 or 80 km/h) gives turning drivers more space and time, as well as allowing those travelling straight on the highway longer to react and slow down if a vehicle turns in front of them. Both outcomes should result in fewer, and less severe, crashes.

The signs are used at regional intersections where there is only a moderate volume of turning traffic, as a less-disruptive alternative to permanently reducing the speed limit.

Main Roads will assess how the technology performs under different conditions, as well as the impact on road safety, before any further roll-out.

Research from Victoria has suggested the signs can lower the chance of collisions and result in better behaviour from drivers, including slower speeds and greater compliance with give way and stop signs.

So, if you see a side road activated speed sign illuminated, slow down and follow the displayed speed limit and look out for turning vehicles.