Why aren't highways wider

Studies have consistently shown that increasing highway capacity provides only a respite from traffic congestion; eventually the increased capacity will encourage more usage. It is a positive feedback loop.

               Physically there are several issues to consider:

• 20 lane highways would cost an incredible amount to construct.
• 20 lane highways would also require proportionally higher maintenance and replacement costs when compared to normal sized highways.
• A 20 lane highway built in or around a major urban center would require a very wide, continuous piece of land, approximately 300' wide. Typically a piece of land like this isn't available to be developed, so you'd have to buy a tremendous amount of land/property, increasing costs further.
• An extremely wide highway of this sort would require very, very large and complex intersections to allow drivers to exit and enter. Imagine being in the 10th lane from the right and you realize you need to get to an exit off the right most lane in a quarter mile. You'd have to switch lanes ten times in a very short period of time. This is a daunting proposition to say the least.

There are other non physical reasons why this isn't done, first among these is that most locations simply don't require so much highway capacity.