Reader Sandy Yates wanted to know why the Caltrans street sweeps block traffic on Highway 101 during the morning commute:

What is the reason for street sweepers on the freeway during commute time the last two weeks?  I have twice encountered lane closures for this seemingly ridiculous activity at 9:00 a.m. on Northbound 101 at the Cotati grade.  Last week it had 101 backed up to the Petaluma River.

The answer comes from Allyn Amsk, spokesman for Caltrans:

On this portion of U.S. 101 Caltrans Maintenance sweeps the median across the Petaluma River and the Highway 116 Lakeville bridges in Petaluma, and the new median wall from North Petaluma Blvd to Highway 116 in Cotati. Caltrans also sweeps all the shoulder of the freeway from Petaluma to Cotati. Maintenance sweeps northbound U.S. 101 in the early morning hours from about 8 a.m. to noon. In this manner they can complete work before the afternoon commute on northbound U.S. 101. After the morning commute passes, maintenance sweeps in the southbound direction in late morning, early afternoon, from about 10:30 a.m. to 3 p.m. The Petaluma Maintenance crew borrows a sweeper out of Marin County to complete this work, so they sweep as much roadway as they can in each day. Maintenance tries to sweep this area about every two to three months. To complete this operation takes about four days for median and shoulders.