Maryland is considering a new strategy to reduce congestion on the Baltimore Beltway: putting stoplights on entrance ramps.
Some motorists might not warm to the idea, but state highway officials hope the result -- smoother traffic flow -- will make up for delays of a few seconds per car on the ramps.
If a study being done shows the idea will work -- and early indications suggest it will -- Maryland might install the first such stoplight this spring on the ramp from White Marsh Boulevard (Route 43) onto Interstate 695 in Baltimore County, said Thomas Hicks, director of the State Highway Administration's Office of .. Traffic and Safety.
If that pilot project is successful, more could be installed on the Washington and Baltimore beltways later this year.
Although unfamiliar to many Marylanders, "ramp meters" have been around for decades. California operates more than 1,000, and Minnesota has almost 400 in the Minneapolis-St. Paul area. Northern Virginia has 26 meters on two freeways into Washington.
In a ramp metering system, a stoplight halfway down an entrance ramp allows one car per lane to proceed onto the highway every few seconds. The light turns green for about a second and then red for a few moments.
Some transportation officials regard meters as a relatively inexpensive and environmentally sensitive way to improve traffic flow without resorting to concrete and asphalt. The idea merits ,, serious review because "it's another tool to deal with our biggest challenge, congestion on the Washington and Baltimore beltways," said Maryland Transportation Secretary David L. Winstead.
Engineers say meters reduce congestion and crashes by limiting the flow of cars onto a crowded freeway during peak periods.
"If a whole flock of cars tries to get on the beltway at the same time, there is a tendency for the beltway to break down," Hicks said. "People put on brakes, speed up and make rapid lane changes."
The sight is familiar: A line of cars clogs an entrance ramp as motorists try to muscle their way off the ramp. Traffic on the highway slows down near the ramp, while cars waiting to merge jockey for position and try to avoid ramming each other.
In Seattle, ramp meters reduced the crash rate by more than 38 percent over six years even though traffic increased by up to 100 percent in some areas, said the National Highway Traffic Safety Administration. In Minnesota, ramp meters increased highway speeds by 35 percent and reduced crashes by 40 percent, said its Department of Transportation.
In Northern Virginia, ramp meters have been controlling traffic entering Interstate 395 and Interstate 66 during rush hours since 1985. Still, the idea has not been universally accepted, said Jimmy Chu, manager of the Virginia Transportation Department's traffic control center in Arlington.
"It's controversial," Chu said as he surveyed a bank of television screens and computers that monitor traffic conditions around the region. "You have people who like it, and you have people who hate it. Some people don't understand that if you wait for a few seconds or a couple minutes on the ramp, you make it up on the main line."
Chu said ramp meters have increased highway speeds by 5 percent to 10 percent on the two freeways by reducing bottlenecks at major interchanges. "Every little thing helps," he said.
tTC The benefits were visible at one ramp on traffic-choked I-66 recently. When the ramp meter was off, traffic slowed on the freeway as cars bunched up on the ramp. With the meter on, freeway traffic picked up speed and cars on the ramp merged more easily. The light stayed red for about five seconds, then green for one second. Cars cleared the ramp in less than a minute.
The longest a light will stay red is 12 seconds, so commuters will not have to wait more than about two minutes at the meter. If people have to wait longer, some will begin ignoring the meter, Chu said. On a recent afternoon, all but a few impatient motorists obeyed the meters.
Virginia's system is similar to one Maryland could adopt. The meters can adapt automatically to road conditions, allowing fewer vehicles onto the interstates when traffic is heavy and letting more cars enter when traffic is light.
Meters receive information on traffic volume from sensors embedded in the freeway. The system also relies on other sensors to measure backups on the ramps. If cars are overflowing on the ramp, the meter will be reset to allow more cars on the freeway, or it will be turned off.
Such overrides make the system less effective but occasionally become necessary on shorter ramps, Chu said. "We promised the local jurisdictions we would not interfere with [secondary] roads," he said.
Although the meters can adapt automatically to conditions, employees in his Smart Traffic Center can make adjustments from computers at their posts in Arlington. They receive information from computers, as well as by watching pictures transmitted live from video cameras at key locations on the interstates.
Virginia is not planning to install meters on its portions of the Capital Beltway. Chu said studies are needed before his meter system could be expanded.
Maryland anticipates a less sophisticated design for its pilot meter on White Marsh Boulevard, in which the timing of the red light would be preset. If that is successful, Hicks said, Maryland would adopt an advanced system that allows the meters to adjust rapidly to problems on the road.
Highway engineers are studying the idea and will use a computer simulation to see how a meter will affect traffic, Hicks said.
The meters cost from $50,000 to $100,000 each, Hicks said, and would improve traffic flow by a few percentage points. They would be used only during rush hours, as is the case in Virginia.
Pub Date: 2/01/98
