Austin, Texas has the perhaps-dubious distinction of being the largest city in the nation served by only a single Interstate. Loop 1 — the MoPac — runs more or less parallel to I-35, a few miles to the west, and it becomes a toll road north of Parmer Lane. TxDOT’s latest idea to relieve congestion on the MoPac is to add two lanes to the existing six between Parmer and the river, a distance of about 11 miles, which will have variable tolls, and I do mean “variable”:
[T]he added northbound and southbound lanes would be open only to those willing to pay a toll, to transit buses, to registered van pools and to emergency vehicles.
But the real departure would be the nature of the tolls themselves, which would change minute by minute depending on the level of traffic in the lane. The point … would be to keep the toll at a level calibrated to keep speeds in the lane at 50 mph or more.
If traffic gets too thick and traffic begins to slow, the toll would instantly increase in an effort to discourage some people from choosing to use the express lane. Signs well upstream of the express lane entrances would alert people to the current toll rate.
Since traffic on MoPac is occasionally moving a lot slower than 50 mph — sometimes it’s not moving at all — people might be willing to pay quite a bit to get up some speed. Chris Bradford thinks it’s a swell idea:
This is how we ought to add new capacity. It will make everyone better off. The people who choose to pay the toll will be better off because they value the time savings more than the cost of the toll. Bus commuters will be better off — they might be the biggest beneficiaries, in fact — because they will get a suddenly much shorter commute for (I presume) the same bus fare. Drivers who continue to use the free lanes will endure slightly less congestion, even if it’s just a narrower period of peak congestion. Finally, taxpayers, if not better off, will be no worse off because they won’t have to pay for the extra capacity. The capacity will be paid by those who value and use it.
Wilbur Smith Associates, which has been doing traffic and revenue studies on the project for the [Central Texas Regional] Mobility Authority, has indicated to officials that the project would be financially feasible with a top rate initially of $2.57 in 2011 dollars. Since the road wouldn’t open until 2016, that would equate to about $3 on opening day. Officials emphasized that the actual toll rates have not been set yet and that Wilbur Smith later will produce a more rigorous “investment-grade” study.
During periods of low or no congestion — I am told that such exist — the toll might be as low as 50 cents.
So drivers will be faced with a choice. Bradford explains:
[T]he congestion cost each driver imposes on his fellow drivers will be approximately equal to the price of driving in the congestion-free lane. That’s one of the quirks of the economics of congestion — it turns out that the cost of congestion a driver imposes is equal to the congestion-clearing price.
Which seems counterintuitive, but it seems to work in real life.