What is a Traffic Congestion or Traffic Jam?
Why does traffic congestion occur? They occur when the volume of traffic surpasses the available road capacity, a point known as saturation. This issue is a classic example of supply and demand imbalance. Major cities like London, New York, and Bengaluru are notorious for severe congestion. In cities such as Rome, Dublin, and Paris, drivers can spend around 10 days a year stuck in traffic, while in Moscow, it’s nearly 9 days. The implications are extensive: for instance, Indian drivers spend an average of 135 hours annually in traffic, leading to frustration, wasted fuel, and lost productivity, which collectively cost $22 billion each year. This equates to roughly 50 days of lost work per driver. Furthermore, traffic congestion exacerbates environmental problems by increasing emissions and air pollution, thereby contributing to climate change and health issues.
Road congestion is a widespread issue affecting cities globally, which is somewhat surprising given the diversity of urban landscapes. European cities typically feature dense urban cores, efficient public transportation (thanks to transport planning in the region), and limited road capacity. In contrast, American cities have extensive road networks spread over large areas with minimal public transport. Meanwhile, cities in the emerging world present a mix of vehicle types, mixed land-use patterns, and often have both dispersed areas and densely populated urban centers. Yet, they all experience traffic jams.
The Paradox of Traffic
Transport planners all around the world have tried lots of different measures to mitigate this problem: dense cities or dispersed cities, lots of roads or lots of public transport or lots of bike lanes or more information, or lots of different things, but nothing seems to work. But all of these attempts have one thing in common. They’re basically attempts at figuring out what people should do instead of rush hour car driving. They’re essentially, to a point, attempts at planning what other people should do, planning their life for them. Now, planning a complex social system is a very hard thing to do.
However, a complex social system has the ability to self-organize. When you try to solve really complex social problems, the right thing to do is most of the time to create incentives. You don’t plan the details, and people will figure out what to do, how to adapt to this new framework. And let’s now look at how we can use this insight to combat road congestion. Most solutions to traffic don’t actually solve the problem but just move it to a different location. And each solution brings more problems so what we find ourselves doing in traffic engineering is chasing our tail because when we make an improvement what happens more people want to come and use that because we’ve increased speeds, we’ve cut down travel time, so more people want to come, and we end up in the same situation that we were to begin with (Jevons Paradox).
The thing about traffic is that it slows down exponentially. This is a major driver for a lot of jams—a small addition of cars leads to a large addition in congestion—but it also makes solving traffic a bit easier since you only need to remove a small number of cars from the road. Traffic is a nonlinear phenomenon, meaning that once you reach a certain capacity threshold, congestion starts to increase rapidly. But fortunately, it also works the other way around. If you can reduce traffic even somewhat, then congestion will go down much faster than you might think.
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Solutions to the Conundrum of Traffic Congestion
1. Improvements in Physical Infrastructure
Road Expansion: Planners have known since at least the 1930s that adding more lanes does not solve traffic problems; it actually creates more traffic. Increasing road capacity doesn’t just accommodate existing cars; it attracts additional cars, a phenomenon known as induced demand. These new trips consist of people who previously used public transport or walked to their destinations but have switched to private vehicles due to the increased road capacity allowing for this change. This is induced demand at play: increasing supply leads to increased demand until congestion returns. Induced demand can develop over time, but there is also a related effect called latent demand, which can occur immediately when a new road opens. Latent demand refers to those who do not travel currently due to bad traffic but would like to if conditions improved.
A prime example of this is Katy Freeway in Houston, Texas (USA). In 2004, it was reported that the Katy Freeway was the second most congested road in America, which was a major embarrassment for Texas, prompting the state to invest $2.8 billion to expand the freeway to 28 lanes, making it the widest highway in the world. But from 2011 to 2014, travel times on the Katy Freeway increased by up to 55%.
What’s fascinating about roads is that this happens at a perfect 1 to 1 ratio. If the capacity of a road doubles, the amount of people using that road will also double. If it doubles again, the amount will again double. Of course, if you kept doing this over and over again you would eventually build a big enough road that there wouldn’t be any more cars to fill the road, but in the real world where demand for roads far outstrips supply, drivers will adjust to any change in road capacity.
Of course, you don’t want to take Braess’ Paradox too far. We do need some roads for our cars to travel down, and some highway expansions have reduced traffic jams. But planning and predicting traffic patterns definitely isn’t as easy as it might seem from the driver’s seat.
“Building more roads to prevent congestion is like a fat man loosening his belt to prevent obesity”
– Lewis Mumford
Traffic Evaporation: If adding more roads can slow traffic, could removing roads speed up traffic? There is a counterpart to induce demand called traffic evaporation where removing capacity from a road network doesn’t have to result in more congestion but can reduce the total amount of traffic. The most famous example is the removal of the Cheonggyecheon Expressway in Seoul where traffic improved after it was removed. After tearing down the structure it was replaced with a greenway with a stream running through it. Another famous example is the city of Boston where they removed a freeway in its city center in the 1990s, and replaced it with a boulevard with biking and bus lanes and more space to walk. In cases like this, commuters give up their cars and rely on public transit instead, while others find more efficient routes that they’d never explored when the highway was there.
Better Design: Better design of roads and intersections plays a crucial role in alleviating traffic congestion through various innovative approaches. Roads with varying widths, can create bottlenecks where multiple lanes merge into fewer lanes. This merging process often leads to slowdowns, accidents, and increased congestion. Additionally, variations in road width can create weaving sections where frequent lane changes disrupt the flow of traffic, causing further delays.
Roundabouts, Cul-de-sec, traffic islands, road intersections, offer a distinct solution by significantly improving safety and traffic efficiency. Unlike traditional intersections where high-speed head-on collisions are possible, roundabouts virtually eliminate these risks. But they are still able to maintain traffic flow consistency with a capacity comparable to traditional signalized intersections, handling up to 1800 vehicles per hour per lane.
On a larger scale, the diverging diamond interchange (DDI) represents another innovative design that enhances traffic management. By eliminating the need for vehicles to cross opposing traffic lanes when entering or exiting highways, DDIs reduce conflict points and improve safety. This design innovation not only facilitates smoother transitions onto highways but also enhances traffic flow efficiency. Studies by the US Department of Transportation have shown that DDIs allow more cars to pass through faster, regardless of traffic conditions, compared to traditional intersections. Furthermore, DDIs are more cost-effective to construct, offering significant savings in infrastructure investment.
2. Investments in Public Transport
The most important solution to traffic is to provide alternatives to driving. Driving isn’t inherently faster than other options, especially within cities. If driving is faster, it’s because most cities worldwide have heavily invested in infrastructure that prioritizes cars, making driving appear faster and more convenient. However, this approach has led to pervasive traffic jams, as highlighted by the Downs-Thomson Paradox, which posits that traffic will continue to increase until alternatives become faster and more appealing.
In cities like Amsterdam and Tokyo, where bicycles and trains respectively offer efficient transportation options, traffic congestion is mitigated. Conversely, in car-centric cities lacking robust public transit, driving remains the predominant choice despite its contribution to congestion.
The key lies in investing in and prioritizing public transportation systems. By improving bus, subway, tram, and train networks, cities can provide viable alternatives that reduce the reliance on cars. This shift not only alleviates traffic but also improves air quality, reduces carbon emissions, and enhances overall urban liveability. Political decisions play a crucial role in funding and supporting public transit, and overcoming historical underinvestment is essential to creating sustainable transportation solutions for the future.
Many governments worldwide often make the mistake of inadvertently providing competition to public transportation systems, seemingly unable to envision cities that prioritize alternative modes of transport over cars. In Nagpur, Maharashtra, India, for instance, the government constructed a double decker viaduct featuring a three-tiered transport corridor: the lower layer for an existing highway, the middle layer for a flyover highway, and the top layer for the Nagpur metro rail. This setup risks prioritizing car travel for those who can afford it, potentially limiting the metro’s ridership capacity.
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3. Incentivisation & Innovation
Congestion Pricing: Congestion pricing entails placing a cordon around a congested city area, requiring drivers to pay a fee to enter. This cordon can be a physical boundary with toll stations, or a virtual boundary enforced through spot checks or cameras on entry routes. The fundamental principle behind congestion pricing is that there are two costs to driving: money and time. When time alone isn’t a sufficient deterrent, adding a monetary charge can tip the balance, encouraging drivers to seek alternative transportation methods. This reduces the overall number of vehicles on the road, alleviating congestion and making urban travel more efficient for everyone. Prominent examples include Singapore’s electronic road pricing, the London congestion charge, and Stockholm’s congestion tax. The fees can be fixed, variable (higher during peak times), or dynamic (higher during actual congestion).
The city of Stockholm, spread across 14 islands, has numerous bridges that act as chokepoints, historically causing severe traffic congestion. The implementation of the congestion charge led to a 20% reduction in the number of drivers entering the central perimeter. Many opted for public transport, walking, or avoiding the area altogether. During the initial six-month trial, the daily number of drivers decreased significantly. When the charge was lifted temporarily, traffic levels nearly returned to their previous highs, but when reinstated permanently in 2007, daily traffic numbers plummeted once again. This demonstrates that even a small fee can significantly influence driver behavior, reducing congestion and improving travel times by up to 40%.
Parking: Parking restrictions make motor vehicle use less attractive by raising both monetary and non-monetary parking costs, thereby increasing competition for limited city or road space.
Most transport planning experts agree that free parking distorts the market in favor of car travel, exacerbating congestion. Thus reducing the amount of parking, we provide in core areas can incentivise people to use other forms of transportation to reach their destinations. Telescopic Charges based on rush hour timings can give similar results.
Ramp Signalling/Metering: A ramp metering system is a traffic management technique that uses traffic signals to regulate the number of vehicles entering a freeway during peak times. The aim is to reduce congestion, enhance traffic flow, and improve safety for drivers. This method “drip-feeds” merging traffic, typically allowing one car onto the freeway every five or six seconds. By controlling the number of cars on the highway, it maintains optimal traffic speeds. An experiment in Minnesota, where ramp meters were turned off for eight weeks, demonstrated their effectiveness: highway capacity decreased by 9%, travel times increased by 22%, speeds dropped by 7%, and crashes rose by 26%.
Remote Work/Flexible Hours: Implementing flexible work hours across various industries can significantly reduce road congestion during peak times and optimize the use of public transport. This approach has been successfully adopted in several cities worldwide, where employers stagger their employees’ work schedules to avoid peak-hour congestion. For instance, a flexible workplaces pilot was conducted in Brisbane, Australia, in 2009 to test the feasibility of a voluntary travel behavior change program aimed at managing congestion through either mode shift or peak spreading. During the one-month pilot, involving nearly 900 Brisbane CBD workers across 20 private and public sector organizations, there was a recorded shift of over 30% out of the morning and afternoon peak travel periods.
Intelligent Transport System: An intelligent transportation system (ITS) provides advanced services for various modes of transport and traffic management, helping users make safer and more efficient use of transport networks. In Qatar, a centralized road management system has been implemented to streamline operations and reduce corruption. This system manages all road-related works through a centralized authority, with strict guidelines and penalties for non-compliance.
Technologies like lane scanner cameras, road radars, and traffic flow management systems can optimize traffic flow and reduce violations. For instance, lane scanner cameras can detect improper lane changes, and traffic flow systems can regulate vehicle speeds to reduce congestion. Additionally, advanced number plates equipped with sensors can integrate with the traffic management system, eliminating the need for toll booths and aiding in data collection for future improvements. An automated system for issuing traffic penalties based on the violation’s location, time, and severity can further reduce corruption and increase efficiency. This system may also include automated highways, variable message signs, traffic counters, and active traffic management.
4. Urban Planning & Design
Mixed Land Use: Mixed land use planning helps reduce traffic by allowing residential, commercial, and business districts to coexist rather than being strictly separated by zoning laws. This integration makes it quicker and more convenient for people to walk or cycle to their destinations instead of relying on cars. In mixed-use neighborhoods, people are more likely to choose walking or cycling because amenities and workplaces are within close proximity. This contrasts sharply with suburban areas where everyone must drive down the same main roads to reach various destinations, leading to congestion. By bringing destinations closer together and providing alternative transportation options, mixed land use planning effectively reduces the reliance on cars and alleviates traffic congestion. In the long term, these policies build communities that are more efficient and accessible, placing people nearer to where they need to go.
Densification: Dense cities typically experience less traffic compared to urban sprawl due to their comprehensive and efficient public transit systems. In sprawling suburbs, where public transportation is limited and distances are greater, residents heavily rely on private vehicles. The expansion of highways in suburban areas fosters a cycle of dependence on cars. This leads to increased congestion and the continual need for more road expansions, escalating infrastructure costs and environmental impacts. In contrast, dense cities with mixed land use patterns concentrate amenities within walking or cycling distance, promoting sustainable transportation options and reducing overall traffic congestion and environmental footprint.
Transit Oriented Development: In urban planning, transit-oriented development (TOD) is a type of urban development that maximizes the amount of residential, business and leisure space within walking distance of public transport. It promotes a symbiotic relationship between dense, compact urban form and public transport use. It’s important to understand that induced demand isn’t just for cars, it can happen with any transportation infrastructure, when you create a transportation system that makes it faster, cheaper and more efficient to cycle or take public transit the majority of people will choose those options. The difference between induced demand for cars and induced demand for other modes of travel is that cars are extremely space inefficient. You can absorb a lot more induced travel demand on a subway line, tram line or bicycle path than you can in a car.
When a new train line is built people will arrange their lives around it people can and do change jobs or move houses because new public transit makes it more convenient so we can choose where we build homes and destinations right, we can build them along increasingly wide streets and highways inducing people to drive or we can build them within walking distance of rapid transit.
5. The Human Element
Different driving styles can have a big impact on the flow of traffic — and drivers tend to do a lot of things that make traffic worse for everyone around them, including themselves. Addressing human errors and inefficiencies in driving behaviors is crucial to improving traffic flow and reducing congestion on roads.
For example, improper merging practices can lead to longer backups and slower traffic progression. Zipper merging, where drivers use both lanes until the merge point and then take turns, optimizes road space and minimizes congestion by ensuring a smooth transition.
Tailgating, or driving too closely behind another vehicle, is another common issue that disrupts traffic flow. It increases the likelihood of accidents and sudden braking, causing chain reactions that lead to stop-and-go traffic patterns. These erratic movements create inefficiencies and safety hazards on the road.
A Phantom traffic jam occurs when a minor disturbance, like one driver braking slightly, causes a ripple effect in dense traffic, leading to a chain reaction of braking that propagates backward through the cars on the road. This results in stop-and-go waves that can travel for miles. When the density of cars exceeds a critical level, small disturbances are amplified due to dynamic instability, creating positive feedback loops. Drivers tend to brake harder and accelerate too quickly, worsening the traffic because they can’t anticipate conditions ahead.
Self driving cars equipped with data on traffic conditions ahead from connected vehicles or roadway sensors might be able to counteract phantom traffic in real-time. These vehicles would maintain a uniform speed, safety permitting, that matches the average speed of the overall flow, preventing traffic waves from forming. In situations where there’s already a traffic wave, the automated vehicle would be able to anticipate it, braking sooner and more gradually than a human driver and reducing the strength of the wave.
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Final Thoughts
As good as some of these solutions sound, there’s no one way to solve traffic. Addressing traffic congestion requires a multifaceted approach that goes beyond simply expanding road capacity. Effective solutions must focus on creating attractive alternatives to driving, such as improving public transportation, promoting cycling and walking infrastructure, and encouraging telecommuting and flexible work hours. While there is no singular solution to solving traffic woes, cities can significantly mitigate congestion through smart policies and innovative urban designs that balance road demand with sustainable transportation options. Experimentation with these solutions is essential to breaking the cycle of perpetual traffic congestion and fostering more liveable, efficient cities for the future.
