How do traffic jams on highways occur?

Question

Just wondering?

Answer 1

Accidents.

Gawkers.

Construction.

Narrowing lanes, requiring merging.

On ramps too close to Exit ramps.

(Many are being corrected)

Mechanical breakdowns.

Illegal cutting in and out of traffic by some drivers, requiring hard braking by others.  This slows heavy traffic.

I'm sure there are more.

Answer 2

people dont know how to merge properly.

Answer 3

There are a number of ways that a traffic jam can occur.  The most popular though, are accidents/rubberneckers, bottlenecks/to many drivers, and road construction.  In my experience the first reason is the most common.  Usually someone has to pull over to the side of the road for one reason or another.  As that person is sitting there taking care of whatever caused them to pull over in the first place, people tend to slow down to take a look at whats going on.  This just compounds until traffic slows to a crawl, or worse.  I know people who have been involved in accidents on the freeway because they were hit by someone who was paying more attention to the side of the road, then what was in front of them.  

The second reason is simply to many drivers for the roads.  If you are in CA you know exactly what i am talking about.  The roads across the US were made and designed back in the 50's and 60's, and were more than able to support the amount of drivers on the road.  However, we now have about 10+ times the amount of drivers we had back then, and the roads simply can't handle the traffic load.  Many of the fixes for this problem have only made things worse, if you have even seem an area where it goes from six lanes to two, then you have seen them.  Which leads to the third most popular reason, road construction.  The constant construction that goes on to aleviate the traffic situation tends to leave construction zones.  When you have people going 65-75 mph and suddenly have to slow to 45, cars start to pile up since cars are approaching the construction zone quicker than people are exiting it.    

Just remember that there are plenty of other reasons as well, like people geting pulled over (Which causes rubbernecking, and people tend to slow down because cops are near).  There are also those who can't drive and talk on the phone at the same time.  But i think you get the point...