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Seeing
the (Traffic) Light
Synchronizing
traffic lights is an indispensable tool for coping
with traffic congestion. There are limits to what
it can accomplish, but the return on investment is
better than for most alternatives.
By
Bob Burke
It’s
barely dawn on a weekday morning, and the
northbound lanes of Interstate 95 in Prince
William County are already jammed with commuters
trekking to work. Then it happens: a fender-bender
near the Dale City exit blocks a couple of lanes
and wrecks the morning rush hour. Suddenly, a
highway network that can barely handle the traffic
on a good day is approaching system failure.
But
the response from traffic engineers is quick. At
the Smart Traffic Center 20 miles away in
Arlington, controllers monitoring the highways can
see the accident on TV screen via a traffic
camera. One controller posts a warning on one of
the giant message signs that hang over the
interstate, letting drivers approaching the scene
from the south know what’s ahead.
A
second controller determines which alternate
routes will be affected and changes the timing of traffic
lights there to make room for the extra traffic.
An hour or so later the worst is over, and
controllers can go back to the round-the-clock job
of managing traffic flow in one of the country’s
most congested regions.
That
kind of event plays out here dozens of times every
year, and it underscores one of the most appealing
parts of this technology. In a region where
road-building money is tight and demand is rising
fast, signal synchronization is a faster and
cheaper way to get the most out of what’s there.
Second to building new roads or adding more lanes, it’s
the best tool that traffic engineers have.
“We’re
constantly looking at the efficiency that we can
squeeze out,” says Ling Li, traffic operations
director for the Virginia Department of
Transportation’s Northern Virginia traffic
center.
Northern
Virginia has come a long way in management of
traffic demand in the past decade. In 1997 VDOT
spent $26 million to install 15,000 vehicle
detectors to help coordinate the timing of traffic
lights at about 1,200 intersections, but before
that there was little system wide control. Today
the flow of vehicles on many roads can be measured
in real time, and the timing of lights changed to
adjust to anything from special events, traffic
accidents, even holiday shoppers at 13 shopping
malls.
While
the ongoing fight for more transportation funding
focuses largely on new roads, there are also
proponents of expanding the use of these kinds of
system-management technologies. “Here’s
something that uses technology, is not that
expensive to operate and has tremendous
returns,” says Philip Shucet, a former VDOT
commissioner who is now president of the Virginia
Beach-based Dragas Companies.
The
Northern Virginia center, on Columbia Pike in
Arlington, covers Fairfax, Prince William and
Loudoun counties. About 30 controllers work there,
using the network of cameras and road sensors to
gauge traffic volume. To manage the system traffic
engineers have divided the region into about 20
localized networks, each with its own formula for
moving traffic.
In
2003 a web-based system was installed that shows
real-time traffic flow, letting controllers adjust
the system based on the data. In 2004, Shucet made
system operations - which cover areas such as
signal timing, congestion management and dealing
with accidents - one of VDOT’s core functions.
There are two other smart traffic centers, in
Richmond and Hampton Roads.
According
to VDOT data, the technology has proved itself.
After the first region-wide round of signal
optimization was completed in Northern Virginia in
the late 1990s the total annual savings were
estimated at $265 million, from reductions in
stops, travel delays for commuters and fuel
consumption. But a second round of re-timing the
lights produced far less savings – about $93
million, according to VDOT estimates.
That’s
still a substantial sum but it suggests that
there's a limit to what you can squeeze out of a stressed
road network. “Capacity isn’t changing, but
the volume is rising,” Li says. “We do not
control the land use. Developers build shopping
centers and residential everywhere. But we can
only do so much.”
Supporters,
though, point to the savings that can be gained by
expanding the program. This fall Shucet urged a
senate panel to support matching funds to
encourage localities to join, and to require them
to join if necessary. The Northern Virginia
center, for example, serves three counties but
doesn’t handle traffic light synchronization in
adjacent Arlington County or the city of
Alexandria. “Those are things where we would be
wise to do them across jurisdictions,” he says.
“I think it’s a darn good use of
transportation dollars.”
There
are also technological advances that could help.
Li says she’s studying the use of “adaptive
signal” systems, in which signal light timing is
automatically adjusted based on real-time traffic
data. There have been hitches, though. A new
adaptive signal system installed earlier this year
at 22 intersections along Route 7 in Northern
Virginia was supposed to use cameras to detect
traffic and automatically adjust the lights, but
sunlight effectively blinded the cameras and the
system flopped.
Even
when the hardware works, managing a transportation
network is complicated, says Brian Park, associate
director for research at the University of
Virginia’s Center for Transportation Studies
(CTS). In fact, the more information you have, the
harder it is: As demand rises, traffic patterns
change and the system needs to as well. “It’s
a big challenge, because there are hundreds of
parameters that you can play around with,” says
Park, who helped VDOT set up the Web-based light
synchronization system in Northern Virginia.
The
next evolution in traffic management will be even
more complex. Engineers are looking at ways to
send information about traffic conditions directly
to vehicles equipped with global positioning
systems and short-range transceivers, and receive
data in return. The Federal Highway Administration
is pushing the concept and is joined by
automakers.
Park
says having all that data creates new challenges.
After all, it doesn’t help to tell everyone
which route is the quickest because they’ll all
take it and shift the congestion to a new location.
The goal is a network “where we are not giving
the information to everybody,” he says. “We
distribute it in such a way that everybody
benefits. That’s what we are hoping for.”
While
the technology changes, the main mission
doesn’t, Li says. “We have to think about the
ways that we can move traffic.”
Bacon's
Rebellion News Service
December
13, 2005
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