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
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:
- Chicago IL
- Boston MA
- New York City NY
- Toronto ON
- Philadelphai PA
- Miami FL
- Los Angeles CA
- San Francisco CA
- Washington DC
In London vehicles lost on average 156 hours per year due to congestion whereas in Washington it was 83 hours.