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Driving
Lessons
Why most of what you think you know about
traffic is wrong
By Charles Montgomery
LON LACLAIRE IS A CAREFUL MAN, not given
to running red lights or making snap left turns. He
knows that in Vancouver, most traffic signals cycle
from green to green every 65 seconds, so he generally
brakes when he sees an amber. As the City of Vancouver’s
strategic transportation planner, he has faith in the
logic of our street grid, the wisdom of the Highway
Capacity Manual and the million tiny decisions the good
drivers of Vancouver make to maximize the efficiency
of their journeys. But at 5:20 p.m. on this Monday we’re
cruising north on Seymour, and the Don’t Walk
hand at Nelson has stopped flashing. The green is about
to change. We could stop, but LaClaire tightens his
grip on the wheel of the city’s SmartCar and floors
it.
LaClaire is not a floor-it kind of guy. It’s just
that he’s kind of distracted. He’s remembering
the moment the secret was imparted to him. Please pay
attention here. I want to share the secret with you
as well. It may not set you free, but it could bring
you peace on your daily commute. And once you accept
this first secret, you’ll be ready for more.
In 1968, the German mathematician, Dietrich Braess,
was modelling the response of traffic to different road
networks. Braess assumed that drivers keep adjusting
their trips until they find the quickest commute possible.
This is one of the premises of EMME/2, the computer
program used to predict traffic flows in every big city
around the world. The EMME/2 models assume that, like
water molecules in braided streams, cars will distribute
themselves until all roads are pretty much flowing equally.
This is why the Alex Fraser Bridge was jammed within
a few months of opening. It’s also why your shortcut
to work never stays a shortcut for long. Braess discovered
a curious wrinkle in the traffic universe. His math
showed that adding new capacity to an existing network
of roads can actually lengthen peoples’ commute
time. This fact is fueled by human selfishness: We all
try to choose the fastest route home. But when ten thousand
of us make that same choice in isolation, we all just
might arrive home later.
LaClaire heard about Braess’ Paradox from a visiting
traffic scholar in a Wall Centre conference room back
in 2000. He remembers the equation, and the epiphany
it brought. His blue eyes twinkle as he recalls the
moment he raised his hand.
“I said, ‘Hey, maybe these paradoxes, these
problem roads, already exist in our city. If they did,
we’d just need to take them out to improve the
flow!’ I thought it was a brilliant idea. I mean,
these problem roads must be out there.”
In the engineering world, it has long been heresy to
suggest that less concrete and asphalt might be preferable
to more. LaClaire had crossed the line. “The guy
looked at me like I was a freak. He laughed, like I
was joking, and then he just went on teaching.”
LaClaire furrows his brow as we cruise through another
amber. “But I was right.”
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"Vancouver
never succumbed to the freeway trap. For every
blocked arterial, drivers have two or three alternatives
a few blocks away."
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LaClaire’s victory paradox is just one of many
ways that the streets of our city do not behave as we
expect them to. New pavement will not always move more
cars. Bus lanes will not always move buses more quickly.
A straight line is not always the shortest distance
between A and B. These quirks of physics and geometry
have a special urgency in the Lower Mainland, where
the car inventory is growing faster than the population.
There are 36,000 new vehicles registered here every
year: one every 15 minutes. Line ’em all up and
you’d have a traffic jam from Kitsilano to Hope.
The problem for folks who spend their
lives trying to move us around is that human psychology
is as important to traffic flow as ample road space.
“Inside every car or truck is a human, and you
know the problem with humans, right?” says Clark
Lim, the manager for transportation research at TransLink,
the Greater Vancouver Transportation Authority. “We’re
irrational.”
Lim is a numbers guy. He sees drivers as machines whose
function is to gather, process and react to information—though,
as machines go, we perform abominably behind the wheel.
We’re easily distracted, prone to daydreaming
and fiddling with our iPods. A 1986 study found that
the average driver pays only 30 to 50 percent of the
attention needed to move efficiently and avoid crashing.
It’s bad enough that our inattention bends fenders;
because of our propensity to slow down and look, every
minute an accident blocks a lane adds five to seven
minutes of congestion behind it.
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