[WEC-All] good article about traffic light timing as traffic mitigation
mark at oilempire.us
Mon May 19 23:57:42 PDT 2008
Posted on Tuesday, May 13, 2008
There is something that can be done about the traffic
By Frank Greve
WASHINGTON — Fine-tuning controls on the nation's traffic signals
would cut U.S. road congestion by as much as 10 percent,
transportation experts estimate.
It would also reduce air pollution from vehicles by as much as a
fifth, cut accidents at intersections and save about five tanks of gas
annually per household, according to the National Transportation
Operations Coalition, an alliance of federal, state and local traffic
departments and equipment-makers.
That's the good news. The bad news is that the average local traffic
department earned an overall grade of D on the alliance's latest
report card. Streamlining intersections is happening in only some
cities and states, even though it's eminently doable.
"People who say we can't do anything about congestion are wrong. We
can do lots," said Joel Marcuson, a specialist in urban intersections
who's with the Jacobs Engineering Group Inc. in Phoenix.
Right now, however, three out of four of the nation's 300,000 traffic
signals need replacement or timing adjustments for optimum
performance, according to the U.S. Department of Transportation.
Among the obstacles are a nationwide shortage of skilled traffic
engineers, unfocused local political leaders with tight budgets and
stodgy local traffic departments. For that matter, federal aid that
could ease congestion goes mainly to building and maintaining roads.
Nonetheless, lots of cities and at least seven states — California,
Florida, Washington, Minnesota, Maryland, Georgia and Texas — are
finding ways to move traffic through intersections faster, according
to the transportation engineers group.
And where does your metropolitan area stand?
It could need improvement, traffic engineers say, if your answer is no
to any of these questions:
• Can you sometimes make it through six to eight consecutive
intersections on green lights?
• Is there useful traffic information on the radio and on roadside
• Is it rare that there's no cross traffic when you're stopped at a
• Can you drive into the next jurisdiction without encountering
congestion at the border?
• Are predictable traffic jams, such as the post-game exits from
stadium parking lots, handled adroitly?
Most traffic departments can do better at each of three levels of
traffic management, Marcuson and other experts said: individual
signals, coordinated signals and regional traffic management.
Technologically, most U.S. traffic signals remain very 20th century,
said Philip Tarnoff, director of the Center for Advanced
Transportation Technology at the University of Maryland in College Park.
Roadside or centralized timers drive most of them by changing lights
at scripted intervals, he explained. "They tell the signals: `It's 6
a.m. Use timing schedule A until 9 a.m. Then use timing schedule B
until 4 p.m.'"
If timers are accurate, and the prescribed signal intervals are based
on accurate and recent traffic surveys, these systems can do as well
as fancier ones in typical traffic situations.
That's a big if, however. Most timed systems aren't refreshed and
adjusted at the three-year intervals recommended for busy
intersections or ones that see big changes in traffic due to new homes
or businesses. In the industry self-report card issued last year,
traffic departments nationwide earned a collective F for traffic
monitoring and data collection, which are key to well-timed
"As a result, signals may not operate based on actual traffic
conditions, resulting in delays," the National Transportation
Operations Coalition's report concluded. The 417 departments in 47
states on whose data the grade was based control nearly half of all
Even perfectly tuned timer-dependent signal systems can't adapt to
unpredictable roadway events such as accidents, construction and bad
weather. Together, those factors cause half of U.S. traffic
congestion, according to Transportation Department statistics.
For all these reasons, Tarnoff and many other traffic engineers favor
adaptive signal-timing systems first adopted 30 years ago in the
United Kingdom and Australia. They measure traffic minute-to-minute
with cameras or in-pavement sensors and automatically adjust signal
times to maximize flow for existing conditions, including accidents,
construction and bad weather.
These adaptive signals haven't caught on with local U.S. traffic
departments, however. They're costly and challenging to program, and
initial local U.S. experiments with foreign-made systems failed. So
did efforts to come up with home-grown ones.
Samuel Staley, director of urban and land use policy at the Reason
Foundation and a specialist in transportation, said traffic
departments often lack the money, skill and local political power to
innovate with adaptive technology.
"They're resistant to change, particularly if it involves learning a
new technology," Staley said. "The small cities don't have the depth
of technical knowledge, and the big cities, while they have depth of
knowledge, also have a lot more politics that resists innovation."
Whatever the reason, more than 95 percent of U.S. traffic signals
today are still timer-driven, Tarnoff estimates.
That makes more difficult the next step in signal streamlining:
synchronizing a succession of lights so that motorists flow through
them smoothly at the posted speed.
Timer-based signals at intersections typically gain or lose a few
seconds a year, Marcuson said. Over two or three years, he continued,
the drift can make synchronized traffic stop-and-go.
So can adjacent jurisdictions, such as municipalities and counties,
whose traffic departments don't work together. That's commonplace. A
third of the traffic departments responding to the report card said
they did no signal coordination across their boundaries.
Regionalized traffic management is the secret in U.S. metropolitan
areas that move traffic best. They include Las Vegas, Milwaukee,
Minneapolis-St. Paul, Los Angeles, Seattle, Kansas City, Denver,
Houston, Miami-Dade County and the Washington, D.C., metropolitan area.
Among the most resourceful is Portland, Ore., which installed carbon
dioxide emissions monitors at intersections before it improved their
flow. The lower pollution that the monitors recorded enabled Portland
to claim pollution-reduction credits that it sold for $560,000 on the
carbon offset market. The money helped pay for Portland's intersection
Lakewood, Colo., another community that closely tracked before-and-
after conditions, found that synchronizing lights at just 16 of its
intersections delivered huge benefits. They included a daily savings
of 635 hours in driving time, 172 gallons of gas and 758 pounds of
pollution emissions, according to Denver's regional traffic authority.
Richard Plastino, Lakewood's director of public works, described the
gains from improved intersections as "one of the few low-cost
alternatives...to physical reconstruction of intersections and streets."
Then there's the real-life gain. Seattle, for example, retimed and
synchronized more than 500 intersections between 1998 and 2002. The
clearest result was a 20 percent drop in congestion on three of the
city's major arteries.
As then-Seattle Mayor Paul Schell, the effort's leading proponent,
argued at the time: "It's the one investment we can make in the near
term that will make a difference in people's lives every day."
ON THE WEB
For a primer on optimized traffic signals, go tohttp://www.its.dot.gov/jpodocs/repts_te/14321.htm
To view a 13-minute Transportation Department video on improving
intersection flow, titled "It's About Time," go to:http://ops.fhwa.dot.gov/arterial_mgmt/outreach.htm
To read the latest transportation industry report card on local
traffic department performance, go to: http://www.ite.org/reportcard/
A LOOK AT SOME STATES' TRAFFIC SOLUTIONS
Texas, a U.S. leader in traffic signal efficiency since the mid-90s,
adjusts its state-operated signals every two or three years to reflect
changes in traffic volume. Once in three years is a national goal
unmet in many states. Austin, the capital, earned a rare grade of A on
its National Traffic Signal Report Card for providing proactive annual
maintenance to all the city's lights at no added cost to taxpayers.
Washington state coordinates the timing of half the 1,000 traffic
signals that the state is responsible for. It checks the timing of
signals on busy arteries every two-and-a-half years. That compares
with a three-year standard unmet in many states. In addition, the
transportation department now reports directly to the governor rather
than to a transportation commission.
Minnesota, which is among the nation's leaders in traffic control,
retimes signals on the state's main arteries every two years, said
Steve Misgen, a Twin Cities metro traffic engineer. Most states and
communities struggle to adjust their traffic signals every three
years. Most signals can be adjusted from a central control center in
Roseville, he added. The state's ratio of benefits to costs is well
above 60 to 1, Misgen said, counting only gas savings from less
waiting time at intersections.
Maryland is a leader in coordinating traffic corridors; about half of
the 2,700 signals that the state controls are linked to other signals
to optimize traffic flow, said Eric Tabacek, the division chief of the
state office of traffic and safety. Maryland adjusts signal timing
every three years — and has done so since the mid-1990s. It's a
standard that many states are struggling to meet. In addition,
Maryland is experimenting with intersection video monitors that
continuously adjust traffic light timing to maximize traffic flow.
Florida, which is among the nation's leaders in traffic control, gets
credit for its success in linking city, county and municipal systems
to improve traffic flow, most recently in the Sarasota-Bradenton area
and around Tallahassee. It's also a leader in managing lights from
regional command centers. Mark Wilson, deputy state traffic operations
engineer, said that checking the timing of Florida's signals every
three years or less is a key goal.
Georgia focuses much of its energy on the 20-county area around
Atlanta when it comes to traffic signal improvements. Since 2005, it's
cut travel time in Atlanta's traffic corridors by 18 percent and time
stopped by 39 percent, said Yancy Bachmann, assistant state traffic
engineer. Macon and Columbus have also seen traffic signal
improvements, he said.
California has new money for traffic signal improvements, unlike most
states. A 2006 bond issue yielded $150 million for the Los Angeles
area. Top priority there and elsewhere goes to intersection
improvements that improve driving time, cut accidents and reduce air
pollution. Those that involve multiple jurisdictions working together
also are favored under the traffic signal initiative whose first
grants are expected later this month.
(Researcher Tish Wells contributed to this story.)
McClatchy Newspapers 2008
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