MnPASS pricing algorithm to become a continuous function.

A reporter at the Star Tribune writes: The Drive: MnDOT to tweak MnPass pricing

The Minnesota Department of Transportation charges motorists driving alone anywhere from 25 cents to $8 during peak periods to use the special lanes that are otherwise reserved for carpools of two or more people, buses and motorcycles. But just how much a solo driver is charged is determined by an old complex algorithm operated by an outside vendor. It assesses real-time traffic conditions in the MnPass and the free lanes every 3 minutes and sets the price accordingly. Sometimes that leads to wild price spikes.

That’s about to change. MnDOT has been working with the University of Minnesota Traffic Observatory to develop a new algorithm that will be run in-house and should better set tolls and control how fast prices rise or fall. It’s expected to be in operation by the end of December, said MnDOT freeway engineer Brian Kary.

I am very happy to see this.

Many drivers use the prices posted on overhead signs to judge congestion levels downstream and decide whether to enter the HOT lanes. A sudden burst in traffic can send the MnPass lane price soaring and discourage drivers from entering the HOT lanes, which then become under used. Conversely, MnPass lanes become overcrowded when the price drops too low, thus decreasing the lanes’ efficiency.

Well, actually, when the price spikes, it attracts people, probably because they are using it as a signal of congestion ahead. As this very same reporter in this very same column reported on previously. Our paper on this phenomenon:

The article continues:

How much is too much?

Chicos said $3 is about the point when she would think twice about entering the toll lanes. For others, the cutoff seems to be about $5. Anything above that and drivers are less likely to use the lanes, according to MnDOT research.

Dense rush-hour traffic, a lane-blocking crash or a snowstorm that paralyzes traffic has the ability to instantly send tolls skyrocketing or drop just as fast.

HOT lane pricing has been about as bumpy as the pavement on I-394 was before MnDOT smoothed it out this summer. With the new algorithm, which Kary describes as a tweak to the old one, drivers should less rapid fluctuation as conditions change. The goal is to get more people in the HOT lanes, maximize their use and improve overall traffic flow.

“The old algorithm had a lot of price spikes that weren’t justified, probably because of its complexity,” Kary said. “The continuous pricing algorithm should smooth price transitions.”

More on continuous pricing algorithms in the report: MnPASS Modeling and Pricing Algorithm Enhancement. It is excellent to see research translated into practice.