Illustration for article titled How the Downs-Thomson Paradox will ruin your commute

Anything that speeds up the daily commute has to be a good thing, right? Not necessarily. The Downs-Thomson Paradox shows that some things meant to improve a commute actually result in a slower trip for everyone.


Commuting sucks. Whatever shortens a commute is a good thing, right? That's not the position that Anthony Downs and J M Thomson take. They don't disagree because they think that longer commutes are better. They disagree because not everything that shortens a commute actually shortens a commute. Under the right conditions, expanding facilities can ruin everyone's schedule.

There are two basic choices for transportation, public transit systems and private cars. If both methods get too slow, it's generally easier to build an extra road, or make a regular road into a freeway, than set up an entirely new system of public transportation. Unfortunately, that extra road can make the car commute so very much faster than public transportation that people leave subways and pile into cars. Since public transport relies on public use to stay regular, eliminating demand will eliminate some parts of the system. As trains get less regular, more people pile into cars until both systems are slower than they were before the supposed improvements.


At least that's what Thomson and Downs theorize. The idea is dependent on certain conditions, like two modes of transport connecting the same destinations but not competing for the same roads. There also needs to be a healthy supply of people who can afford to travel using either public or private transportation. Still, there are plenty of debates, in different cities contemplating road expansions, whether there will be actual progress or will there will be nothing but this paradox. Which one do you think would apply to your city?

Image: Gonzalo Andrés

[Via Springer Science.]

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