The human reaction time causes several unnecessary traffic jams nowadays. While there will always be accidents and physical barriers that prevent a smooth flow of traffic 24/7 and this is a reality that we will always have to live with. However, slow reaction times create traffic jams that never had to occur in the first place and make traffic jams caused by other factors much worse.

There are two ways in which slow reaction times are problematic:

  1. When several cars have come to a halt (i.e. at a traffic light) and they can finally move again, each driver only starts driving after they see the driver in front of them moving (who must have also done so after a similar reaction time). The result of this is that if the reaction time of a driver is x and we have n cars, the time it takes for all n cars to start moving again is nx. However, if all drivers in the queue started accelerating at the same time (at the same rate), we parallelise their reaction times instead of compounding them, meaning that it would only take x time for the cars to start moving again. However, this is practically impossible as humans cannot coordinate this to avoid crashes and getting all drivers to put the gas pedal down at the same time itself is a logistical nightmare.
  • When a car is moving and it slows down suddenly before continuing to drive again (this could because by a pothole or a car cutting across on a motorway), due to the reaction time of the driver behind, they will have to break even harder to compensate for the distance they drove during their reaction, meaning they will also therefore end at a slower speed than the car in front. This starts a chain reaction until a car comes to a halt, creating a traffic jam. This traffic jam then takes a while to memory as a result of the first problem above 

All of this means that traffic jams are very common at intersections and also on busy roads such as the motorway where more cars join a traffic jam before those at the front can accelerate and things return to usual.

However, by changing the way we drive, it is possible to go some way to mitigating this problem. If all drivers are equidistant such that the car in front of them is an equal distance from the car behind. Ideally, this distance should be based on the break-reaction times (the distance travelled in the time it takes to think and then break). Maintaining this equal distance maximises the time you have to react if a car in front of you breaks so that you overbreak less while also doing the same for the driver behind you. The closer you are to car in front of you, the more likely you are to break far harder than you need to, come to a halt, and start a traffic jam. So at the very least, traffic jams are less likely to build-up quickly or in the best-case scenario, some traffic jams won’t happen in the first place. Maintaining the right distance in accordance with the break-reaction time would only serve to make this system even better.

However, this is a near-impossible solution as humans cannot see the car behind them and would struggle to keep an equal distance. In addition, their length perception is not awfully accurate and so they can’t necessarily keep the right distance apart. Finally, the largest issue is human psychology. There are many impatient drivers who only maintain a few metres distance will exist however little this will reduce their journey time by. Moreover, they are unlikely to care about leaving a traffic jam behind them when they want to get to their destination quicker as humans prioritise short-term gain over long-term goodwill. Therefore, we need a system that does not involve humans at all if we ever want to eliminate these traffic jams.

The obvious solution is self-driving cars – a fully automated system which can make accurate distance measurements and can react in a matter of nanoseconds. In a fully automated system where all cars are connected to a network that oversees all traffic, it is easy to see how we can coordinate this to prevent traffic. However, even in a system where we have a mix of human drivers and self-driving cars, there is still a positive impact.

A fully automated system carries many interesting possibilities. If we have smart roads occupied entirely by self-driving cars connected to one large network, every car can have a planned journey to minimise heavy traffic on certain roads and ensure a quicker journey. Even if a tree falls on a road for example, this system can easily coordinate cars to move backwards and find another route to reach their destination. This not only helps eliminate traffic jams with human causes, but also reduces the effects of traffic jams with other causes. In addition, at intersections, there is no need for cars to come to a halt at a traffic light as cars can coordinate so that cars can keep driving from all 4 directions with such precision that they can avoid a crash. Also, on highways, if a car does have to break for whatever reason, the car behind can react instantly and not break too hard, thus not creating a traffic jam. The capabilities of a totally automated system are unlimited and eliminating traffic jams is just one of them.

However, this is still quite hopeful (in the near future), but even as the first self-driving cars are being rolled in, we can still find advantages of this. Even if we have to deal with slow human reaction times, at least self-driving cars won’t contribute to the problem and make it worse. They can still keep an equal distance between cars, making the previously discussed solution easier to carry out. In addition, at an intersection when the light has gone green, we can still get a partial parallelisation where as soon as the driver in front has started accelerating, the self-driving car reacts immediately and also accelerates, so these two cars are still parallelised, even if it’s not the entire queue.

Another solution to traffic jams is simply finding more space for cars to move. If there isn’t a heavy flow of cars, then there is less of a chance that if a driver does have to break for whatever reason, there will be a driver right behind them who also has to break and starts the chain reaction that causes a traffic jam. If cars are very spaced apart, then these human reaction times cease to make as much of a difference. Solutions such as that Elon Musk has proposed to have roads on several different levels (even underground) could have the unintended consequence of alleviating traffic jams. Elon Musk has even toyed with the idea of automating these underground systems by having pods which can take a car underground and whizz them across at speeds of up to 120mph. As we’ve seen, automating this system is far from a bad thing.

At the end of the day, there could be many solutions to traffic jams. Our slow reaction times are one of the largest issues concerning traffic, and whether it is self-driving cars or multi-layer highways, anything that removes or reduces the impact of human reaction times will go a long way to ending traffic jams once and for all.


CGP Grey (2016) The Simple Solution to Traffic. Available at:

Brown, D. ‘How self-driving car or adaptive cruise control could ease traffic jams’. USA Today. 2019. Available at:

‘Elon Musk unveils underground tunnel prototype’. CBC News. 2018. Available at:

About the author