In a footnote to Traffic, MIT’s Moshe Ben-Akiva discusses the varying strategies of dynamic tolling:
“You may want to charge people for time they actually save. That will mean if congestion builds up on the tolled road you reduce the price. On the other hand, you want to maintain a certain level of speed on the toll-road. If congestion builds up you want to increase the toll so as to not have stop-and-go traffic on the tolled road. There is some confusion going on right now as to what strategy is best.”
it seems that confusion is still out there, based on this dispatch from the Miami Herald.
Traffic engineers assumed high tolls would deter drivers from using express lanes. Wrong.
Many drivers, like Perkovich, assume high tolls mean the toll-free lanes are clogged. Could be true, but the tolls rise mainly due to the number of drivers willing to pay a toll.
Perhaps it’s not easy to make these decisions at high speed in a split second. Perhaps there’s some weird signaling effect going on in which higher prices lead to higher demand (for reasons of perceived quality or some other factor). Maybe the tolls aren’t high enough to deter drivers. Maybe the problem would vanish if drivers were given a more precise sense of time savings (as far as I know they are not). But South Florida drivers are not the first to be undeterred by higher tolls.
Before HOT lanes were launched on an I-10 commuter highway serving the Houston area, the Texas Transportation Institute based at Texas A & M University made an extensive study of driver attitudes and beliefs.
As many as 20 percent of the participants in several focus groups incorrectly interpreted the HOT lane toll as an index of traffic congestion in the free lanes, said Susan Chrysler, an institute research psychologist.
“Even after I showed them a video that explained it, they still misunderstood it,” Chrysler said. In Florida, DOT has responded with a crash public information campaign. A prominent message on the Express Lane website, 95express.com, clearly explains the system. And SunPass holders recently received a special mailing with the same message: higher tolls may mean a slower ride.
The market is still working, though perhaps not as rationally as might be hoped.
Despite the misunderstanding, the Express Lanes are easing traffic. Santana says the toll lanes are maintaining a comfortable 16 mile-an-hour speed advantage over the free lanes. A typical $2.50 to $3.00 rush hour toll usually buys a 45-mph drive between South Broward and downtown Miami, according to DOT data.