LA Magazine reports that an unintended consequence of the popularity of the Los Angeles new Expo Light Rail line is that bus ridership along substitute routes has fallen sharply. Back in 2005, Nate Baum-Snow and I analyzed the impact of 16 new rail transit openings across the U.S. Our Brookings Paper is available here.
"We develop a simple model in order to fix ideas about the types of
responses one might expect to see in the data to new rail transit infrastructure.
The primary lesson from the model is that most mode switchers from car to
rail are likely to live far from the city center. The number of mode switchers
from driving will depend heavily on the travel speed on the rail line relative to
driving. Moreover, while some new rail commuters will switch from driving,
most are likely to be former bus users."
Does this sound familiar?
The new ridership on the Expo line (including myself) is cannibalized from the slower buses. The simple economics of transport mode choice asks the following Gary Becker question;
What is the full cost of each transport mode to get from point i to point j? Chose that mode that has the lowest cost.
The full cost includes;
1. out of pocket expenses on the durable (the car, parking, gas , insurance)
2. the time cost of the trip weighted by your value of time.
Cars are expensive with respect to $ cost but require less time (because they move at higher speeds than buses that stop and start).
Buses are slow but cheap and this is why poor people ride them (see Glaeser et. al. 2008).
Fast subways and fast light rail offer the best of both worlds but the rich still face a time cost from getting to station, waiting and walking from the destination station to their final destination. So, the marginal rider will be a bus rider.
Why does this matter? Boosters of the train have claimed that it will "mitigate traffic congestion". But even ignoring the Fundamental law of traffic congestion, this claim is false if the marginal rider is a bus rider.
Another under-appreciated point is that if bus demand declines, local unions won't allow bus drivers to be fired! So, progressive cities such as LA will have excess buses and drivers just driving around inefficiently with few passengers on board. Read my 2016 paper on this topic!
So, this means that when progressive cities build successful rail projects that their average cost per bus passenger mile traveled should increase. I think I will write a note studying this point!