After a successful six-month trial run, Lisbon's "roundabout" traffic circle should be a permanent fixture by Friday.
Construction crews were to pour concrete this weekend for the center of the traffic circle at Routes 144 and 94 and complete work Friday on four islands that channel vehicles into and out of the roundabout.
If rain pre-empts the concrete work, the project will be delayed by one week.
State Highway Administration officials persuaded skeptical Lisbon residents in April to accept the temporary roundabout, the first of its kind in the state.
Unlike the multilane traffic circles in Washington, the new roundabouts have only one lane and can be used to slow traffic in some cases and to move it more efficiently in others.
The Lisbon intersection was considered an ideal proving ground because of its problems with speeders and its high accident rate.
Motorists using the new, single-lane roundabouts must yield before entering, making the traffic device operate much like a revolving door.
Because all motorists must merge into the same lane that goes around the roundabout, instead of crossing the path of other motorists, the system makes serious broadside collisions highly unlikely, highway engineers say.
State and county highway engineers are also planning or considering roundabouts in Columbia.
One planned for Shaker and Seneca drives near Allview Estates is intended to make the intersection safer.
On Old Montgomery Road in Long Reach village, a proposed roundabout at Oakland Mills Road is intended to speed traffic, while another at Old Montgomery Road is intended to slow it down.
In the Sykesville area, some residents are lobbying for a roundabout at Routes 32 and 99.