Suddenly, as you grind your way through another infuriating rush hour, you find yourself rolling into a real-life economics experiment.
You have cruised into a free-market moment — a classic confrontation of supply and demand that you can decide with a spin of your steering wheel.
On one hand, there’s lane after lane of crawling vehicles. On the other, the promise of a get-there-quick pass.
How much is it worth to slip the surly bonds of traffic? And how is the price calculated?
The past two weeks have seen the 15.5 mile unveiling of an optional toll lane on I-85 in Gwinnett and DeKalb counties. If you have a Peach Pass issued by the State Road and Tollway Authority, you can slip into that lane.
As you do, you are promised that no matter how bad the gridlock on the rest of the road, you will not move slower than 45 mph — a privilege that is yours for a price.
But the price changes frequently. Cameras, lasers and other sensors feed data to computers that calculate how many cars are on the road and how fast they are moving. An algorithm — that is, a set of math-based rules — leads to a recommended price.
Signs tell you how much you’ll pay for using the lane. But for those who come behind you, the cost may shift up or down.
The idea is to set the price just high enough to keep the Peach Pass lane from getting so crowded that it slows below 45 mph. But the price should be low enough so that a lot of drivers think it’s worth it.
That’s not what happened during the first few days. The prices drew howls of outrage from drivers: Pay up to $5.40 for a ride on pavement that taxpayers already paid for?
Most drivers kept on truckin’ down the free lanes. The system meant to improve traffic flow made it worse. Besieged by complaints, the governor quickly ordered the tollsters to ratchet back the price.
So the agency fiddled with the formula, said Christopher Tomlinson, deputy executive director of the authority.
“If there’s gridlock in the other lanes and Peach Pass lane is empty, the price is too high,” Tomlinson said. “It’s too low if the lane is filled up.”
As steep as the peak price seemed those first few days, it came out to 35 cents a mile — not even halfway to the maximum. Prices can range from 10 cents a mile to 90 cents.
But drivers weren’t buying it. So officials put their thumbs on the algorithmic scales.
“We’ve started to vary the parameters and factors to put more emphasis on volume,” Tomlinson said. “So until you have a certain amount of volume, the price should not go up so much. And the volume hasn’t been there.
“Now it’s going up slower and it’s going up lower,” Tomlinson said. “In the past week, we didn’t break $2.”
The price is not supposed to change more often than every five minutes or to rise more than a nickel at a time. The urge to protect drivers from price shock keeps the toll from leaping into the stratosphere.
But that restraint works against the economics. After all, the point is for price to keep the market — that is, the lane — from getting clogged. If price moves too slowly, that may not happen.
“The whole idea is to keep the vehicles from getting too close to each other,” said Randall Guensler, a Georgia Tech engineering professor working on traffic research. “If the flow breaks down, you haven’t provided any benefit.”
The state of Washington has a 10-mile toll lane south of Seattle on SR 167. When that express lane is congested — usually because of an accident — all single-occupancy vehicles are banned until things clear up. Officials decided not to raise the price as a way of discouraging use.
“We do not want to charge people for something we can’t guarantee,” said Patty Michaud, spokeswoman for the state’s Department of Transportation.
The toughest challenges are often more human than technological, said engineer Mark Burris, a professor who studies driver behavior at Texas A&M University.
Demand fluctuates — not just for the whole road, but for each driver, he said.
“People have a different value on each and every trip they make on a daily basis,” Burris said. “The high value may be things like, you need to make it home to catch your kid’s soccer game. Or you need to make it to the airport.”
It’s not a science, but there are working assumptions. Burris said the “rule of thumb” is that a driver will pay half of his or her hourly wage for time. That means, a worker making $20 an hour would pay $10 to save an hour, or about $1 to save six minutes.
But drivers tend to look at toll lanes in overlapping ways, Burris said. The value of saving time is only part of it. Perhaps even more important, he said, is reliability.
One study showed people paying a dollar or two for what was often very little savings in time, he said. “They are not paying for a few seconds. They are paying for the reliability — that they know there won’t be a surprise delay.”
Minnesota, which has 27 miles of tolls on two different highways, sees that kind of decision-making, said Nick Thompson, division director for policy, safety and strategic initiatives at the state’s Department of Transportation.
“People don’t use it every day,” he said. “They just use it days they really need to be somewhere.”
The price averages between $1 and $1.50 for a trip, but it can shoot up quickly when things get crowded.
Drivers are always balancing need and price, Thompson said.
“Four dollars is a price break,” he said. “We see a very sharp drop off when it hits $4. The price may go to $8, but it doesn’t stay there very long.”
Most experts say toll lanes don’t make a dramatic difference. But if done right, they improve the drive a little for a lot of people and a lot for those who pay.
With cars still the preferred transport, “congestion pricing” is likely to increase, they say.
After all, it is possible to have each lane on a highway set for a different speed — and priced to match, said Georgia Tech’s Guensler.
“I think the technology is there,” he said.
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Race to ease traffic
With the new I-85 express lanes in Gwinnett and DeKalb, Georgia joins a growing number of states that are setting up a higher-priced, higher-speed option. Some charge a flat rate. Others – like Georgia – vary the toll based on traffic. The idea is to improve congestion overall by letting some drivers pay electronically for access to a less-crowded lane where travel is faster.
In the first few days of its launch, tolls on the I-85 HOT lanes were peaking at $5.40 – high enough to discourage many people from using them, which only made overall traffic worse. The governor ordered officials to cut the price. After the formula was tweaked, prices did fall dramatically.
Project (miles) --- Length --- Average peak price --- Price range
I-85 Metro Atlanta --- 15.5 --- $1.75-$1.85 --- $1.55 to $13.95
I-15 San Diego --- 12 --- $0.50 - $4.00 --- $0.50 - $8.00
SR 91 Orange County --- 0 --- $3.90 - $9.55 --- $1.25 - $9.95
I-25 Denver --- 7 --- $3.50 --- $0.50 - $3.50
I-394 Minneapolis --- 11 --- $1.00 - $4.00 --- $0.25 - $8.00
SR 167 Seattle --- 9 --- $1.00 - $2.00 --- $0.50 - $9.00
I-10 Houston --- 13 --- $2.00 --- $2.00
I-95 Miami --- 7 --- $1.90 - $2.65 --- $0.25 - $6.20
Georgia State Road and Tollway Authority
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