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Traffic is the bane of every driver on the road. It can turn what should have been a twenty-minute drive into a two-hour slog through the smog and mire accompanied by beeping horns and blinking brake lights.

But how does a traffic jam start, and is there any way to avoid it? Here are the seven root causes of traffic jams:

7 Root Causes of Traffic Jams

Traffic Incidents

Traffic incidents include roadside accidents, breakdowns, and other events that disrupt the regular flow of traffic. Oddly enough, this can include incidents that happen away from the road entirely.

Studies have shown that human behavior causes us to slow down and observe incidents outside our lanes out of curiosity. If you’ve ever slowed down to catch a glimpse of a crash site that wasn’t even in your lane, you’ve definitely experienced this. This tendency to slow down builds up along the rest of the road as more cars approach the area. The longer the disturbance continues and the more cars are on the road, the higher its likelihood of causing a traffic jam.

interstate with few cars driving
To avoid traffic jams, you should train yourself to drive at a consistent speed with a good amount of distance between you and vehicles in front of and behind you.

Work Zones

Work zones include construction and repair zones along the road. These areas can lead to certain lanes or routes being closed. Besides reducing the space for vehicles, work zones also force you to do more stop-and-go driving. These include lane mergers and shifts. These small pauses will again add up over the hundreds of cars passing the same stretch of road, leading to mass slowdowns.


When the rain starts pouring down and you decide to slow down to navigate the road better, you can see weather causing traffic in real time. All the other drivers in your vicinity will likely make similar decisions, showing just how effective weather is at starting a traffic jam. Whether it’s icy roads or thick fog, you’ll naturally want to take it slow to avoid accidents.

Demand Fluctuations

Monday morning traffic is a perfect example of a traffic demand fluctuation. These fluctuations happen when the number of vehicles on the road goes beyond what the road usually handles. Work zones and special events sometimes cause fluctuations in smaller roads as well. Both these causes shift vehicles onto roads that aren’t usually utilized as heavily as main roads.

Special Events

Special events such as parades or presidential motorcades can be fun for you to watch, but they can also cause a lot of traffic. These events block off certain roads, forcing vehicles to use other streets and avenues that aren’t used to the traffic. This can cause surges in these areas, overwhelming the systems in place.

Traffic Control Devices

Traffic lights, railway crossings, and signages are just some of the traffic control devices you can observe. These are made to mediate and help the flow of traffic, but when one of these devices is poorly timed or placed, they can cause a lot more harm than good. For instance, a stoplight with a long green light for a low-traffic lane can cause traffic to form on heavier lanes that don’t have enough time to empty.


Bottlenecks are areas on the road that restrict the flow of traffic. This often happens because the road has reached its capacity, with more vehicles than it can handle. There are two types of bottlenecks to look out for:

Physical Bottlenecks

Physical bottlenecks are areas like mergers, toll booths, and roadway alignments. When combined with other traffic jam causes, physical bottlenecks can also include open highways blocked up by traffic or other areas that wouldn’t automatically be considered part of this section.

Behavioral Bottlenecks

Interestingly enough, drivers like you can also cause bottlenecks through the sheer force of natural behavior. For instance, studies show that driving at constant speeds with some distance between vehicles is the best way to avoid traffic perturbations. These are small but sudden braking or lane changes that cause other vehicles to slow down.

However, drivers tend to tailgate anyway, and they have a difficult time sticking to a single speed with other drivers around. This tailgating results in the buildup of traffic perturbations, which can lead to a phantom traffic jam. Phantom traffic jams happen on the open road with no visible causes like weather or work zones.

Lane mergers are another example. Although merging one side at a time like a zipper is the most efficient way to merge lanes into an exit, most drivers will ignore this and line up on whatever side the exit is on without a second thought. Actions like these are what cause behavioral bottlenecks.

cars stuck on a merging lane
Physical bottlenecks like mergers, toll booths, and roadway alignments can sometimes cause traffic jams.

How to Avoid Traffic Jams

Now that you know the answer to the question “how does traffic even start,” it’s time to learn how to avoid it if you can. While engineers work on minimizing traffic jams with self-driving cars, you can work on decreasing traffic by increasing your awareness of behavioral bottlenecks.

Ideally, you should train yourself to drive at a consistent speed with a good amount of distance between you and vehicles in front of and behind you. This will help prevent traffic perturbations by letting you wait out more minor stops and bumps from cars in front of you while moving. It’ll also keep your minor stops and bumps from affecting the car behind you. As a result, Other cars won’t be roped into stop-and-go driving, keeping traffic from building up along the road.

You can also make use of location and pathfinding apps to find out the best route with the least amount of traffic during rush hour.

Finally, try to commute more or walk/bike when you need to go somewhere local. If everyone did this, traffic would be less heavy.

Lisa Conant, Automotive Features Reviewer at
Reviewed By Lisa Conant

Automotive Features Reviewer at

Lisa Conant grew up in Canada around a solid contingency of gear heads and DIY motor enthusiasts. She is an eclectic writer with a varied repertoire in the automotive industry, including research pieces with a focus on daily drivers and recreational vehicles. Lisa has written for Car Bibles and The Drive.

CarParts Research Team
Written By Research Team

Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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