All the right signals: the key metrics that could help you reduce congestion at intersections

If you’re a traffic engineer or transportation planner, you’re probably already familiar with the most challenging intersections in the urban areas you’re responsible for. Whether you sit in traffic on your way to the office, or listen to citizen feedback from those who do, you can likely name the most congested streets without prompting.

But if you’re aiming to eliminate bottlenecks and improve travel times, a deeper understanding of how the signalized intersections and corridors in your city are performing can be transformative. You may already use some of these key metrics to determine whether traffic is flowing through your intersections efficiently:

1. Dwell time: How long does each vehicle have to wait before they can move through the intersection?
2. Percentage of vehicles stopping: How many vehicles are stopping at the intersection?
3. Queue length: How far away from the front of the queue are vehicles when they stop at the intersection?
4. Speed: How long does it take for a vehicle to move from point A to point B?
5. Overall corridor performance: Average vehicle behavior throughout specific signalized corridors, including travel times and speeds across selected percentiles.

An extra layer of detail

Once you’ve uncovered these key metrics, consider drilling down into how different types of vehicles are behaving at the intersections in question. For example, heavy-duty commercial vehicles will almost always take longer to pass through intersections than smaller vehicles.

But if they’re taking even longer than expected, this could indicate there’s something about the intersection that causes large vehicles difficulties. For instance, they could be struggling to accelerate through a sharp turn. If this is the case, heavy-duty vehicles may be holding up other traffic and disproportionately contributing to the overall congestion.

The right tools will also tell you what percentage of the traffic is turning in each direction at the intersection. This is important because it may be that the backup for left-turning traffic is so long that it’s spilling into other lanes and affecting road users heading in other directions.

Being able to establish the purpose of the vehicles’ trips will inform your decision-making further. For example, a high percentage of vehicles may be heading to deliver goods to an industrial park which can only be accessed via this intersection – leading to further congestion.

Turning problems into solutions

Once you’ve established there’s a problem, you can start looking into solutions. For example, heavy-duty vehicles could be diverted elsewhere to improve the driving experience for them and other road users. Alternatively, you could update your traffic signal timing – extending your rush hour program to allow more heavy-duty vehicles to pass through at once.

And the analysis doesn’t stop once you’ve implemented a solution. The right tool will allow you to assess traffic conditions before and after you make your changes, allowing you to measure how impactful your solution was. Using this method, you can tweak and refine your approach until you reach maximum efficiency.

An advanced tool will even help you plan your response to incidents. For example, if a large collision happens on a freeway, it will give you visibility of what happened to signal and corridor traffic as a result. This will give you the insight you need to react and retime your intersection signals next time a similar incident takes place.

And when it comes to implementing longer-term solutions, you’ll have the data to back up your arguments, and gain the appropriate funding if you need it. This data is also a vital tool when fielding citizen feedback. You can compare citizens’ anecdotal evidence with data that confirms or contradicts their impression, and share these figures with them when discussing next steps.

Geotab ITS can offer you all the intersection insights mentioned in this blog, and more. Our Geotab Altitude platform gives you enhanced visibility into the efficiency of traffic signals, broken down by turning movement – so you can identify issues, make better decisions and improve efficiency.

Find out more about Intersections here, or get in touch today to discover how we can help your Department of Transportation achieve its goals.