Photo Credit: Sundry Photography/


Ever Wonder What Causes Traffic Jams?

Written By: CarPro | Jul 10, 2024 2:00:00 PM

I drive a lot of DFW, area well known for heavy traffic.  Often when everything comes to a stop on a freeway, I wonder why.  It’s a beautiful day, there are no wrecks, yet traffic is bumper-to-bumper.  The people at Progressive Insurance have done research and bring us some thoughts on the causes of traffic jams. 
- Car Pro Show host Jerry Reynolds.


Raise your hand if you've been in a traffic jam today?  If yours isn't raised, you are likely in the minority.  Traffic jams are indeed a fact of life on many of our roads today. In fact, the just released INREX 2023 Global Traffic Scorecard reports that Americans lost an average of 42 hours to congestion last year, up 11% from 2022, costing $733 per driver.

Other interesting traffic trends:

  • Midday trips in the U.S. are up 23% compared to 2019, with nearly as many trips taken at 12:00 PM as there are at 5:00 PM.
  • Trip analysis indicates 10:00 AM to 4:00 PM is the new ‘9-to-5.’

Here are the report's top 10 most congested cities:

  1. New York
  2. Chicago
  3. Los Angeles
  4. Boston
  5. Miami
  6. Philadelphia
  7. Washington, D.C.
  8. Houston
  9. Atlanta
  10. Seattle

5 Causes of Traffic Jams

So what are the main cause of bumper to bumper traffic? Progressive Insurance lists construction, accidents, and rush hour as often the direct and observable causes of traffic jams. Road construction is often the issue when it requires lane closures or reduced speed limits. Car accidents are another for obvious reasons of traffic being blocked, emergency crews on scene or drivers slowing down to look at what's happening. And of course, traffic jams are common at rush hour,  since so many people are on the road at the same time. 

That brings us to "phantom traffic jams". Progressive says these are ones that doesn't have an obvious cause but they can have a slowing effect similar to any other traffic jam but without a triggering event such as an accident or lane restrictions. 

Here's a look at Progressive's list of 5 traffic jam causes:

Common causes of traffic jams

1. Car accidents

A car accident is one of the most obvious causes of traffic jams. While a serious accident can block the roadway, require emergency vehicles to come to the scene, and potentially even require traffic to be rerouted, a minor fender bender pulled off to the edge of the road can cause people to slow down enough to have a significant impact.

2. Road debris

Items falling off vehicles or been left in the road can lead to traffic tie-ups. When an 18-wheeler blows a tire, for example, bits of material could not only strike passing vehicles but remain in the roadway, requiring drivers to swerve and cause a chain-reaction slowdown. When driving on the highway, a team of workers might be deployed to clear the road, resulting in even more delays while they do their job.

3. Road construction

Construction projects are notorious for causing traffic jams. While smaller projects require drivers to go slower and merge into another lane, larger-scale ones require vehicles to be diverted onto another route. Cars detouring onto alternate routes can bring heavier-than-normal traffic, leading to traffic jams.

4. Rush hour

When a sudden influx of cars enters the highway in a short amount of time, traffic jams are soon to follow. In many cities, the morning commute to work and the afternoon/early evening commute home are prime factors causing traffic jams.

5. Phantom traffic jams

A phantom traffic jam occurs when a car slows down while driving — either by quickly braking or not keeping up with traffic speed — on a busy roadway. The braking also causes vehicles behind it to slow down, and the chain reaction can lead to traffic tie-ups. In this way, it can seem like a traffic jam is happening for no apparent reason.

Are traffic jams bad for your car?

Unfortunately, traffic jams aren't just annoying.  They can also be bad for your car. Progressive says driving in stop-and-go traffic might affect multiple aspects of your vehicle, including:

  • Battery and alternator system
  • Cooling system
  • Engine performance
  • Brake wear and tear
  • Drive (serpentine) belt
  • Fluid degradation
  • Excess fuel usage

To download the INREX Global Traffic Scorecard report click here.

Photo Credit: Sundry Photography/

Photo Credit: Sundry Photography/