Metering lights at northbound Highway 101 onramps in Sonoma County were switched on today, a month after the traffic were turned on at southbound onramps. The lights at 18 onramps from Gravenstein Highway in Cotati to Shiloh Road in Windsor will be set to solid green for one week to alert drivers to the new driving condition, Caltrans said.

On Oct. 14, onramp meters will cycle through red and green during the morning commute hours, from 6 a.m. to 10 a.m. Onramp metering lights will remain green during afternoon commute hours from 3 p.m. to 7 p.m.

• On Oct. 21, onramp meters during the afternoon commute will also cycle through red and green. Onramp metering lights on northbound 101 will continue to be operational Monday through Friday, from 6 a.m. to 10 a.m. in the morning, and from 3 p.m. to 7 p.m. in the afternoon.

According to Caltrans, ramp metering is intended to improve the safety of vehicle merging and the flow of traffic on the highway. Caltrans staff will monitor the metered locations and make adjustments, and then fine tune the metering operations.

Drivers entering 101 where onramp meters are activated should stop at red and wait until the metering light turns green to enter the freeway.