What is Traffic Congestion?

Traffic Congestion is a traffic phenomena characterized by slower vehicle speeds, longer trip times and increased queuing of vehicles.

What causes traffic congestion?

Traffic congestion occurs when the number of vehicles is larger than the capacity of a road or intersection. As a result vehicles pile up, velocity decreases and trip time increases. The point at which road or intersection capacity equals traffic demand is referred to as saturation.

Traffic demand often grows over time, thus traffic congestion can occur simply because the road or intersection capacity has not been designed for the actual traffic demand especially during peak hours. Negative conditions like rain, snow, construction works or accidents can reduce the capacity of roads and intersections.

Common types of congestion include:

• Congestion caused by Traffic-Influencing Events: Weather conditions like rain or snow, construction works or accidents can reduce the capacity of roads and intersections.
• Gridlock: This means that all roads leading to a major intersection become blocked, making it impossible for any cars to pass through the intersection.
• Bottleneck: This happens when a certain section of road becomes too narrow for all cars, causing some to slow down or even stop completely.
• Shockwave: This occurs when one car suddenly slams on its brakes, causing several other cars behind it to also slow down or stop.
• Congestion caused by special Events: Certain events such as football games or concerts can cause increased traffic due to the influx of large numbers of people coming into the area.

What is the difference between traffic congestion and traffic jam?

Traffic jam describes the situation when traffic is completely halted. Thus, a traffic jam is worse then traffic congestion.

How can Traffic Congestion be Classified

Level of Service (LOS) is a metric which classifies congestion depending on its severity.

Effects of Traffic Congestion

Traffic congestion has significantly negative effects. It causes:

• Increased carbon emissions as a result of idling in traffic
• Increased vehicle consumption which results in higher fuel cost
• Increased trip duration reduces the time spend productively
• Trip Delays can result in missed appointments
• Increased chances of road accidents
• Wear and tear on vehicles as a result of idling in traffic and frequent acceleration and braking
• Emergency vehicles have longer trip times to reach accidents and bring wounded people to the hospital

How can traffic congestion be mitigated?

Traffic can ether be reduces by increasing road system capacity or by reducing demand.

Increasing the road system capacity can be done by planning, designing and building roads and intersections with higher capacity but also through using existing infrastructure more intelligent.

Intelligent Transport Systems (ITS) are systems to provide smart means of transportation. ITS continuously monitor traffic conditions such as demand, weather and accidents. The obtained information is then used to actively managing traffic and reduce congestion and accidents.

Some measures to increase capacity or mitigate the negative effects of traffic congestion with ITS include:

• Hard shoulder running
• Variable message signs
• Emergency vehicle preemption
• Parking management and guidance systems
• V2X communication
• Coordinated Traffic Adaptive Signals
• Transit Signal Priority
• Automatic accident detection

The video below shows how intelligent video analysis can be used together with regular security cameras to obtain real time information about traffic flow and congestion. The insights generated by such solution can be used to optimize the traffic control to changing traffic patterns.

Reducing the traffic demand can be done by:

• Promoting modal shift to public transport
• Promoting modal shift to cycling
• Promoting the concept of 15 minute cities
• Car sharing
• Autonomous driving

Political initiatives to reduce traffic congestion

Political initiatives and programs such as the European Green Deal and the US Bipartisan Infrastructure Law aim to reduce the emission of CO₂ in the transport sector.

Top 20 Cities with highest traffic delay times worldwide in 2022

According to an study by Inrix the top 20 Cities with highest traffic delay times worldwide in 2022 are:

1. London
2. Chicago IL
3. Paris
4. Boston MA
5. New York City NY
6. Bogota
7. Toronto ON
8. Philadelphai PA
9. Miami FL
10. Palermo
11. Monterrey
12. Dublin
13. Rome
14. Los Angeles CA
15. San Francisco CA
16. Istanbul
17. Brussels
18. Medellin
19. Bucharest
20. Washington DC

In London vehicles lost on average 156 hours per year due to congestion whereas in Washington it was 83 hours.

Further Reference:

• FHWA: Traffic Congestion and Reliability: Trends and Advanced Strategies for Congestion Mitigation