What I learned from Professor Per-Olof Gutman about two-loop controls on HOT lanes

On Monday, Metrans hosted Professor Per-Olof Gutman, who discussed some of his work in control engineering for the HOT lane connecting Ben Gurion airport and Haifa (Highway 2).

The HOT lane, like most, is operating under two political mandates. First, those who pay to enter the HOT lane are guaranteed to be allowed to travel 70 kph for the stretch of the HOT lane, and there is also a limit that tolls can go no higher than 30 shekels, which is about $10. Given those constraints, it’s not likely that the franchisee can get to a profit-maximizing strategy–whether there’s a profit at all is the question.

The original automatic control algorithm for setting tolls didn’t function properly: it overestimated the costs and contained a measurable lag: so cars and congestion would be clearing on the tollway and on the free lanes and the automatic control algorithm, responding to previous conditions, would raise the price as congestion was going down. Not what you want with a dynamic pricing model where you want to give people the right price signal when they are confronted with the decision to take the HOT lane or the free lanes.

Professor’s Gutman’s improvement suggested a two-loop control: an interior loop that monitors entry and an exterior loop that monitors changes in flow that cascades back to the interior loop as speeds increase or decline. That enables the company to maintain the floor speed of 70 kph.

The kicker on this–the rickety part of policy–is going to be the 30 shekels, not Professor Gutman’s controls. Because there will be a time, if demand grows, when it’s going to become impossible for the company to attain that speed floor with a $10 toll–if it isn’t there now. One of those performance constraints–the speed floor or the price–have to allowed to vary more once the HOT lane faces higher demand.

I can’t find Professor Gutman’s manuscript online, so he’s probably working on it now. I’ll post a link when we see it. One of my wonderful colleagues, Barak Fishbain, said that there are Youtube videos of some of Professor Gutman’s system control work on robotic motorcycles, but I can’t find those. I’ll post them if I find them.

Aha! edited, thanks to Barak, links to the YouTube of the Unmanned Motorcycle project!