why does adding more traffic lanes doesn’t help to alleviate traffic congestion?


why does adding more traffic lanes doesn’t help to alleviate traffic congestion?

In: 26

A number of reasons but here’s a couple big ones.

1. More lanes DOES lead to less congestion in any given lane, however because of this it leads to more people driving which more or less gets you back in the same neighborhood of where you started

2. Congestion is caused by way more than just “too many cars for a given number of lanes” – driver inefficiency/error (braking too hard/too early, not staying right if not passing, etc), onramps/offramps, conditions, and various other factors contribute. Adding more lanes doesn’t fix any of these problems (and in some cases can make things worse)

Drivers tend to be self-centered, and will gladly jam up all of the lanes if they think they can get past the vehicle in front of them.

In the vast majority of cases more lanes do reduce congestion. There are a small number of instances where it doesn’t due to poor road network design, but those are very much the exception. Unfortunately a lot of NIMBYs will use facts like this to block any new infrastructure construction, which is probably why you believe this misnomer.

A big part of it has to do with a phenomenon called induced demand. When you make driving easier and quicker, like by adding lanes or bypasses or freeways or reconfiguring intersections, you get more people into cars, until it reaches capacity and then you are back at square one, and then you end up with Los Angeles.

Because to beat peak congestion you would have to add like 12 lanes and 8 lane ramps and 6 lane side streets. You can’t build for peak hours because the rest of the time it is empty.

On normally sized roads, peak congestion causes the most cars possible to fill the road. At this traffic density, average traffic speed is about 40 mph. And due to variance in the speed of individual vehicles, speeds will drop as people brake and the braking action chain reacts backwards.

Cars do not run into traffic, cars are the traffic.

If you simulate a road where the only rules are 1) speed up if there is nothing in front 2) slow down if something is in front then you will get traffic bunching up just on the random speeds and braking action. Traffic clears from the front of a jam and builds from the back.

Add in one accident and it reduces lanes by at least 1 lane and makes everyone have to zipper over, limiting speeds all the way across the lanes.