Re: Retaining Walls, extra lane could be in works for I-94

(This is a copy of the email that I sent to Eric Lawrence, author of the article linked to below.)

Hi Eric,

I’m incredibly concerned about the $2.9B MDOT plans you wrote about in Retaining walls, extra lane could be in works for I-94.

MDOT’s reason for widening the highway resonates well with common sense: if traffic is expected to grow, and the road is currently two lanes wide, then surely widening it to three lanes should help?

However, this ignores a well-known, subtle truth that many traffic engineers ignore known as “induced demand”. At its core, induced demand says that congestion effectively remains constant because, if you increase a road’s throughput, people will drive more and ultimately make the road as congested as it was before.

The Texas Transportation Institute summarized the phenomenon well in this study:

Metro areas that invested heavily in road capacity expansion fared no better in easing congestion than metro areas that did not. Trends in congestion show that areas that exhibited greater growth in lane capacity spent roughly $22 billion more on road construction that those that didn’t, yet ended up with slightly higher congestion costs per person, wasted fuel, and travel delay.

Because of induced demand, planners in Great Britain are no longer allowed to justify new highways on the basis of reduced congestion. Confusingly, in Michigan they still are.

I’m not suggesting that we let I-94 languish: if the road is in disrepair, then by all means it should be refinished. Perhaps it’s necessary to redesign some of the (treacherous) entrance ramps for the freeway. But before we embark on a 17 year project that costs enough money to kickstart a real light rail system for Detroit, we should strongly consider evidence that suggests that the current plan won’t have the desired effect.