Straight ahead or right-turn lane an issue


September 24, 2002|By Jody K. Vilschick | Jody K. Vilschick,SPECIAL TO THE SUN

WE'VE PROBABLY all sat behind someone going straight, while we've waited to make our right turn. So has Mary Ann Fleming, who lives in Ellicott City.

"I don't understand why, at some intersections, there is a left-turn only lane while the other lane is straight ahead and right-turn," Fleming said. "If you have someone in front of you going straight, you cannot turn right on red. Wouldn't it make more sense to have people turning left and those going straight using the same lane? Then when you want to turn right, you wouldn't have to wait for the light to turn green. I am often kept waiting in this circumstance at St. John's Lane [southbound] and Frederick Road, at St. John's Lane [northbound] and U.S. 40, and at Bethany Lane [southbound] and U.S. 40. I think this minor change would keep the traffic moving and make our hectic lives a little easier."

Bill Malone, chief of the Howard County Department of Public Works, Bureau of Highways, Traffic Engineering Division, said that officials looked at the St. John's Lane-Frederick Road intersection not long ago.

"The lane use is the best we can do right now according to our traffic counts," he said. "We do want to revisit the issue when the church school just up the road opens up to its enlarged capacity."

But there is a larger issue here. Diane Schwarzman, a traffic engineer for the Traffic Engineering Division, discussed the situation in detail:

When two travel lanes exist on a side-street approach to a traffic signal, there are two ways of assigning lane use, she said. The first is an exclusive right-turn lane and a shared through/left-turn lane. The second is an exclusive left-turn lane and a shared through/right-turn lane. Each intersection is unique and must be looked at individually, Schwarzman said.

When assigning lane use, a traffic engineer considers traffic volumes and intersection geometrics. If left turns are heavy, usually an exclusive left-turn lane is desired. Likewise, a heavy right-turn use warrants an exclusive right lane. At an intersection with signals, the left-turning and through vehicles must wait for a green signal to proceed. However, the right turns might be able to complete their movement on a red light because of right turn on red.

When developing timing for a signal, a traffic engineer tries to minimize delays for all approaches while favoring the main road to let large groups of vehicles proceed from one intersection to the next, she said. Side roads are given less "green time" because of the smaller number of vehicles.

Usually, it takes less time for the left-turning and through vehicles to clear if they are using two lanes instead of one, according to Schwarzman. If the left-turning and through vehicles are in the same lane, the approach operates as a one-lane approach when the light is green, assuming that most of the right turns were made on red. The use of only one lane may not allow all the vehicles in the queue to clear in one cycle of the green. When right-turning and through vehicles share the same lane, there are times when a vehicle turning right is delayed because the first vehicle wants to go straight through the intersection.

"The few right-turning vehicles delayed add to the total intersection delay, but not to the extent of the other condition," she said.

Schwarzman said that before deciding the lane-use assignment, the engineer studies the intersection at different times under various conditions. Directional traffic volumes are collected for up to 14 continuous hours.

"The lane uses are chosen to provide the most efficient operation of the intersection to minimize delays over the widest period of the day for all users of the intersection," she said.

Lane closures continue

And here is some more bad news for those of you lucky enough to travel Route 32 regularly. Expect continued lane closures in both directions near Route 99 for paving through the end of the month.

If you are driving Interstate 95 north, the lane and shoulder closures will continue for at least another week between the Patapsco River and the Route 100 overpass. Lanes will be closed for construction through Oct. 17 on Interstate 95 south at the Montgomery Road bridge.

Bridge lanes closed

With the summer season over, the Bay Bridge preservation project continues.

Through Oct. 13, construction work will be under way on the westbound span as part of the Bay Bridge deck rehabilitation.

The work does not affect weekend travelers, but weekday travelers should look for a westbound lane to be closed between 9 a.m. Mondays through 6 p.m. Thursdays, and two lanes closed Mondays through Thursdays at night, with all lanes open again by 5 a.m. Fridays.

Information: Bayspan hot line, 877-BAYSPAN (229-7726).

What's your traffic trauma? Contact Jody K. Vilschick at or send faxes to 410-715-2816. Technophobes can mail letters to Traffic Talk, The Sun in Howard County, 5570 Sterrett Place, Suite 300, Columbia 21044.

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