Why Expanding Roads Fails to Reduce Traffic Congestion(nominalnews.com) |
Why Expanding Roads Fails to Reduce Traffic Congestion(nominalnews.com) |
> Overall, VKT in the US doubled from 1983 to 2003, from 7,700 VKT to 15,900 VKT for interstate highways. For major urban roads, a similar pattern occurred – VKT went up from 15,000 to 30,000. In the same time span, the number of lane kilometers of interstate highways remained basically constant, while on major urban roads, it went up from 3,800km to 6,500km.
I don’t know how someone can trot out this stat and then claim with a straight face that new lanes cause congestion. What this states is that car traffic doubled over a 20 year period, and it doubled whether lane capacity increased (cities) or not (interstates).
In the extreme case, as road coverage approaches 100%, the city stops containing buildings so the traffic will drop towards zero, so there’s actually a balance point somewhere, but roads are quite inefficient for high density cities, so probably the balance point would be less about fulfilling traffic demand and more about reducing the demand by demolishing most of the city.
Basically, an extra lane temporarily reduces congestion. The main cost of congestion to road users is time. Since now it's faster to travel, you're more likely to do an extra car trip. You continue taking extra car trips, until the cost in time is the same as pre-road expansion.
The question then is are the extra car-trips valuable.
In fairness, I have not read the 37 page paper yet. Maybe the paper makes a more compelling case than the summary article.
The authors seem to suggest that demand for roads is infinite, as expanding roads merely increases the number of trips people choose to make, thus infinite expansion will result in infinite trips.
These analyses always appear to me as if they are without any understanding of how humans actually behave, resulting in nonsensical nonsense "laws".
Agree. They literally claim this with “increasing lane kilometers by 1% will increase VKT by 1.03%” but subtly acknowledge that this fundamentally doesn’t make sense with the hand-wavey “any feasible increase in roadways will have no impact on congestion”. Keyword feasible.
The real law doesn’t seem to be that congestion rises to meet capacity but that no one will ever fund enough road expansion to make peak congestion low.
The demand fills capacity is not a good rule of thumb either, from an economist's perspective. Shame on you. Many multi-lane highways are rather empty, why? Many roads are basically never used, why?
Lanes (transit corridors) are a river of money (funnels). When you have populations that are exchanging goods, jevon's paradox fills lanes to increase capital velocity that scales beyond the average value of infrastructure. Infrastructure cost is balanced against a perceived value, which is always skewed toward the larger (poorer) part of the population.
In this case, it's not a paradox at all that capital self-generates demand for this space. This also explains why some corridors are emptied as capital flees a locale.
A driver, besides the cost of the car and fuel, faces a time cost. An extra lane will reduce the time-cost, assuming no new vehicles enter the road. But if time costs fall, it's in effect 'cheaper' to drive. So previous car trips that were not happening, because the time-cost was too high, are now occurring. The amount of extra car-trips is such that we are back to the same time-cost as before the road expansion. That's why VKT ends up growing one for one with road expansion.
To me this says that lane expansion is not the driver of KVT (at at least not the primary one).
The broad question is what would reduce congestion - currently, on the margin, adding a lane will not reduce it. I imagine that hypothetically adding many lanes may reduce congestion, although there may be city driven bottlenecks that don't make this feasible at all.