Widening roads and building new lanes is seen as an obvious solution to traffic congestion. The idea is simple: if demand for rides is high and supply is limited, expanding capacity should allow more people to get around more easily and quickly.
However, research in the field of traffic indicates that this approach often has the opposite effect. A phenomenon known as “induced demand” explains why new road capacity quickly stops improving throughput. When road capacity increases, driving becomes more attractive as travel time and stress are reduced. As a result, more people are choosing to drive. Also, those who previously avoided the route due to congestion are now returning. Thus, the newly built capacity is soon filled, and the crowds return – sometimes even bigger than before.
According to some researches, as much as 80% of newly built capacities are already filled four years after construction.
Induced demand: When additional lanes create additional congestion
Induced demand implies that the new capacity is not only used for the existing number of drivers, but opens the door to latent, “suppressed” demand. People who previously chose alternative routes, means of transport or travel times due to excessive congestion are now returning to the road because it is less congested. And not only that – new drivers, who may not have even used a car before, decide to drive.
Experts note that this cycle leads to a vicious circle. The more we widen the roads, the more cars we have on the streets, and traffic remains the same or worsens further. California, for example, has been investing billions in expanding its highways for years, and the results are almost always the same – traffic congestion returns very quickly after the work is completed.
Alternative solutions: From public transport to smart politics
Instead of relying on traditional solutions, cities around the world are increasingly choosing alternative approaches to traffic management. One of the options is the introduction of traffic tariffs, like the “congestion charge” in London. This way drivers are charged extra to enter the city center during the busiest times. This system has successfully reduced the number of vehicles in traffic and increased the use of public transport.
Another important strategy is investing in improving public transportation. Faster, more reliable and affordable transportation can motivate drivers to leave their cars at home. Bicycle paths, pedestrian zones and integrated transport systems further reduce reliance on personal vehicles.
Conclusion: More asphalt is not a long-term solution
As long as cities rely solely on widening roads as a solution to congestion, they will face a recurrence of the problem. Induced demand shows that more space for cars leads to – more cars. A real shift in traffic flow comes through a combination of smart planning, alternative transportation options and changes in driver behavior.
