Roundabouts vs. Signalised Intersections: A Safety Perspective from Australia’s AGRD01-21

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When designing road infrastructure, the choice between roundabouts and signalised intersections significantly impacts road safety and efficiency. While both designs have merits, their effectiveness depends on traffic conditions, user needs, and environmental constraints. The Guide to Road Design Part 1: Objectives of Road Design (AGRD01-21) provides comprehensive insights into designing safer roads, emphasizing intersections' role in road safety. Among the types of intersections discussed, roundabouts and signalised intersections are prominent for their distinct safety benefits and challenges.

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Benefits of Roundabouts

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1. Reduced Conflict Points

Roundabouts have fewer conflict points compared to signalised intersections. This streamlined design minimizes opportunities for high-severity collisions, such as right-angle (T-bone) crashes.

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2. Lower Vehicle Speeds

The circular layout of roundabouts naturally slows down vehicles, reducing both crash likelihood and severity. Slower speeds allow drivers more time to react to potential hazards.

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3. Continuous Traffic Flow

Roundabouts facilitate a continuous flow of traffic, reducing vehicle idling and congestion. This leads to shorter travel times and improved fuel efficiency, enhancing overall traffic management.

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4. Improved Pedestrian Safety

Splitter islands in roundabouts allow pedestrians to cross one direction of traffic at a time, improving safety compared to signalised intersections where pedestrians must navigate multiple lanes simultaneously.

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Advantages of Signalised Intersections

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1. Effective for High Traffic Volumes

Signalised intersections can handle high traffic volumes and complex movements more efficiently than roundabouts, making them suitable for dense urban environments.

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2. Enhanced Pedestrian Safety Controls

Traffic signals provide clear, timed instructions for pedestrian crossings, offering a structured environment for safe passage in areas with heavy foot traffic.

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3. Adaptability to Larger Networks

In sprawling urban areas, signalised intersections can be synchronized across multiple blocks, creating coordinated traffic flows and reducing stop-and-go movement.

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4. Space Optimization

Signalised intersections require less physical space compared to roundabouts, making them more feasible in densely populated or constrained areas.

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Safe System Approach in Intersection Design

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The Safe System approach emphasizes designing roads to accommodate human error while minimizing crash severity. Both intersection types align with these principles under specific conditions:

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• Roundabouts: By encouraging lower speeds and smoother traffic flow, roundabouts create a forgiving environment that mitigates the impact of driver mistakes.
• Signalised Intersections: In areas with heavy pedestrian or cyclist activity, traffic signals enhance safety by controlling interactions and providing designated crossing times.

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Factors Influencing the Choice of Intersection

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1. Traffic Volume

Roundabouts excel in managing moderate traffic flows, whereas signalised intersections are more effective for high-density traffic conditions.

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2. Road User Types

In areas with significant pedestrian or cyclist presence, signalised intersections may offer better safety through controlled crossings.

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3. Space Constraints

Roundabouts require larger footprints, making them less suitable for urban environments with limited space.

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4. Cost and Maintenance

Signalised intersections incur ongoing costs for electricity and maintenance, while roundabouts typically have lower long-term expenses.

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Conclusion

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The decision between roundabouts and signalised intersections depends on the specific needs of a road network. Roundabouts excel in safety and efficiency for moderate traffic, while signalised intersections are ideal for managing high volumes and diverse road user types. By applying the Safe System approach and considering contextual factors, road designers can optimize intersection designs to enhance safety and functionality for all users.