Austroads to update intersection sight distance guidance

Austroads has identified changes to intersection sight distance guidance in its road design framework, focusing on how visibility is assessed at signalised and unsignalised intersections.

The review found scope to clarify which sight distance models designers should use in different circumstances and to expand guidance for a wider range of road users beyond private cars.

Intersection design has become more complex as buses, cyclists and other users share road space once assessed largely through the lens of motor vehicle movement. Many existing methods remain valid, but the guidance should better reflect changes in vehicle types, transport technology and travel patterns.

The proposed revisions will feed into updates to the Austroads Guide to Road Design Part 4A, which covers unsignalised and signalised intersections. Expected changes include clearer treatment of available sight distance models, more detailed advice for signal failure scenarios and closer alignment with related technical standards.

Michael Nieuwesteeg, Road Safety and Design Program Manager at Austroads, said the review examined whether longstanding design assumptions still match the conditions road practitioners now face.

"Many of the principles that underpin intersection sight distance remain sound, but transport networks have evolved considerably. This work asks whether our guidance is keeping pace with the environments designers are working in today and the road users they are designing for," Nieuwesteeg said.

Practitioners currently draw on several sight distance models, each intended for different situations. Feedback gathered through the research indicated that industry wanted more direction on when and how those models should be applied.

Design questions

The review also looked at signalised intersections, including cases where traffic signals are not operating normally. This was identified as an area where existing guidance could be improved to help designers manage less routine operating conditions.

Nieuwesteeg said the work also sought to revisit assumptions that have shaped design practice over many years.

"Our aim was to challenge assumptions that have been embedded in road design practice for many years and give practitioners greater clarity to help them navigate increasingly complex designs," he said.

A broader finding was that visibility assessments need to account more clearly for the growing mix of users at intersections. Historic sight distance models have tended to focus on cars, while current transport networks require designers to consider interactions involving cyclists, public transport and other users within the same space.

That shift reflects wider changes in urban and suburban transport planning, where intersection layouts increasingly need to accommodate competing movements, safety requirements and different vehicle profiles. In practice, this means sight distance assessments may need to address a wider range of assumptions than earlier guidance.

Broader users

The issue is not only whether a driver can see approaching traffic, but whether the method used to assess visibility matches the way an intersection operates. Clearer guidance would help practitioners understand the assumptions behind each assessment approach and choose the most suitable one for the location being designed.

Nieuwesteeg said this was one of the central outcomes of the review.

"Good intersection design depends on more than applying a formula. Designers need to understand which assessment approach is appropriate, what assumptions sit behind it and how it relates to the people using the intersection. Providing that clarity is one of the most important outcomes of this work," he said.

The planned updates point to a more detailed review of intersection design guidance as transport agencies respond to changing road use. By focusing on model selection, signal failure conditions and the needs of users other than motorists, the work signals a broader reset in how visibility at intersections is assessed across the Austroads network.

The recommendations will inform future updates to the Austroads Guide to Road Design Part 4A: Unsignalised and Signalised Intersections.