The Amazing Truth About Freeway Congestion

You’d think that if your freeway is clogged up every rush hour, adding an extra lane would reduce the congestion. You’d be wrong.

And an uprising against Oregon state government plans to widen the I-5 freeway here in Portland may end up changing how cities around the country decide to use the hundreds of billions of dollars in highway funds coming to them from the Infrastructure Investment and Jobs Act.

A recent study of 100 US cities found that — between 1993 and 2017 — billions were spent to expand highway systems’ capacities by 42 percent, far faster than the cities were growing population-wise. But instead of reducing congestion, traffic delays actually went up by 144 percent.

The key to understanding this phenomenon is something called “induced demand.” Basically, it’s the idea that when you offer a population something nice, lots of people show up to use it.

Aaron Brown of NoMoreFreewaysPDX.com described induced demand to me on my program as being like when Ben & Jerry’s offers free ice cream and suddenly a quiet storefront area has a line around the block. When freeways are expanded, more people decide to use them, producing even more congestion.

The Rocky Mountain Institute, along with the NRDC and four other environmental groups has even put online an extraordinarily detailed induced demand calculator with databases for cities all around the country.