Roads and intersections are an important form of land use and an integral part of the transport network. They aim to provide safe passage for all road users and mitigate congestion issues.

Below we will dive into the different types of intersections and how we at Marvel approach analysing which type will best meet the specific requirements for each project.

Following Austroads Guide to Traffic Management (AGTM), intersection selection needs to consider safety and operational performance to maximise mobility. Another way of looking at this is to develop the safest practicable treatment that also provides an acceptable level of mobility.

It is imperative to develop a deep understanding of the following considerations before designing an intersection:

• Type of road user
• Topography andland availability
• Environment andheritage
• Physicalconstraints

Key inputs such as traffic volumes, crash data, pedestrian routes and design speeds can be used to determine the most appropriate type of intersection choice such as unsignalised, signalised, or a roundabout.

It is important to also liaise with stakeholders who may be impacted by a new or upgraded intersection, as community feedback can provide vital information that determines the form and function of intersection.

Let’s look at the three main types of intersections.

Unsignalised intersections

Based on key inputs such as traffic volumes, pedestrians, crash data and design speeds, we can determine the most appropriate intersection type is unsignalised. Now what?

 Well, there are plenty of unsignalised intersection types to choose from, as defined in AGTM Part 6:

• Basic
• Channelised
• Staggered T-intersection
• Seagull– uses a T-intersections
• Wide median treatment
• Two-staged crossing
• Offset right-turn lanes
• Intersections with service roads.

 The adopted unsignalised intersection arrangement is based on land availability, traffic demand, approach roads, median arrangement and safe crossing points. Sight distance requirements must be met at all intersections.

 As you can see, there are many variables that go into designing an unsignalised intersection. Engineering judgement and best practice are critical when advising infrastructure authorities on the most appropriate intersection choice.

Signalised intersections

If you've reviewed all your key input information and determined that you can't achieve a safe intersection design without signals, look no further than Austroads Guide to Road Design (AGRD) Part 4 and AGTM Part 6.

Signals are adopted at intersections to address road safety or traffic and transportation operational issues. Design of signalised intersections must consider:

• Space available for concurrentright turns
• Proximity to other intersections
• Storage / queuing
• Pedestrian treatments
• Signal phasing.

Safe intersection performance is based on adequate visibility, minimising potential for conflict, managing priority movements and speeds, and clear design layouts (AGTM Part 6). Signalised intersections can provide additional mobility to the transport network by controlling access for incident management, supporting freight and public transport, and contributing to network-wide congestion management strategies.

The Marvel team have extensive experience working on signalised intersection installations and upgrades, having collectively designed 100+ across our vast project backgrounds (including Coomera Connector Stage 1, M1/M3/Gateway Merge, M1 Pacific Motorway Upgrade South (VL2T), M1 Pacific Motorway Upgrade North Stage 2 (SD2GM), Gateway Upgrade North and Kingsford Smith Drive Upgrade – to name a few!)

However, it’s not just the major projects that require signalised intersections. Recently, we were involved in the planning and optioneering of a safety upgrade at the Cunningham Highway, Ipswich-Rosewood Road intersection. Considering safety at the forefront of this project, and factoring in the existing land use, community feedback and existing congestion issues, a signalised intersection was determined to be the best for project outcome. The team worked with consultants and TMR through the options analysis phase, quantifying costs and benefits, and designing a safe and compliant final arrangement.

Roundabouts

The final intersection type is roundabouts.

Roundabouts are efficient at controlling speeds and the flow of traffic using multiple variables. As all traffic entering the roundabout must give way to the right, they improve road safety by reducing the number of conflict points between vehicles. The elements needed to design a roundabout include:

• Number of legs
• Number of entry, circulating and exit lanes
• Central island and circulating carriageway diameter
• Entry and exit geometry
• Superelevation.

Roundabouts are the safest form of intersection control for motorists (AGRD Part 4B), however the same cannot be said for pedestrians and cyclists, as they do not have priority on this type of intersection. When designing your roundabout, you can enhance the safety of pedestrians and cyclists by designing sufficiently wide splitter islands, prohibiting parking on approaches for sight distance, and providing zebra or signalised crossings on approaches.

Choosing and designing an intersection requires careful consideration of numerous factors to ensure safety, efficiency, and long-term sustainability. The Austroads Guide to Traffic Management and Austroads Guide to Road Design offer comprehensive, well-defined guidance to support critical decision-making throughout the design process. By collaborating closely with clients and engaging with the community, engineers can create intersections that not only meet technical standards but also address local needs and priorities.

Feel free to reach out to us if you are looking for expertise in intersection design.

‍