Jerry writes with a common question. Who sets the HOV time intervals in Marin County and why are they so completely out of sync with the real rush hour crush on 101? Here’s the question (and a similar one from Kristi) and an answer from our archives.

Question:  HOV hours northbound on 101 do not begin until 4:30 pm in Marin and that is obviously well beyond the start of the rush hour north. Check out San Rafael at 4:00 pm if you have any doubts.There’s no advantage in car pooling if you’re northbound out of the city at 3 to 4 p.m. Also, southbound in Marin, HOV hours end at 8:30 a.m., at which time the HOV lane fills and grinds to a near halt just like clock work.

These problems make it very difficult to schedule a rational carpool that minimizes drive time because the hours seem to be out of sync with substantial portions of the actual traffic load. 5 to 9, then 3 to 7 are fair and reflect real road conditions.  — Jerry

Question: I was writing to you regarding the Carpool lane times of 3 to 6:30 p.m. Monday through Friday on Hwy 101 in Sonoma County. Why is it regulated in both directions?? Also the hours are not reasonable, as in Marin County the hours are 4:30 to 7 p.m., so it would be much better if they changed these hours.

Is it possible to change the hours to 4:30 to 7 like Marin County and for the northbound 101 through Petaluma only, which would mean eliminating this restriction in the southbound 101 though Petaluma from 3:00 to 6:30 pm.  — Kristi

Answer: Caltrans spokesperson Allyn Amask said traffic conditions are the key in deciding the hours of operation. There is a significant physical gap — the Marin Sonoma Narrows — between the Sonoma 101 and Marin 101 HOV lanes. There are differences in traffic conditions between the two sections north and south of MSN, so Caltrans treats the two segments as different corridors.

Regular monitoring data indicates that congestion is present in both the morning and evening peak commute times and in both directions within the limits of Sonoma 101 carpool lanes. In fact, within the northbound carpool lane limits, there are more delays on Sonoma 101 in the morning than in the evening peak, and more delays in the southbound evening than the morning peak. In Marin 101, however, the peak congestion is only in the southbound morning hours and in the northbound evening hours.

In January 2012, Road Warrior also asked Caltrans officials that question and got more information from spokesman Bob Haus. In July 1998 Caltrans did an extensive study of traffic congestion along the Highway 101 corridor, in conjunction with the Metropolitan Transportation Commission, CHP and Marin County, Haus said. Then it set hours to coincide with the peak traffic time. On some segments in Sonoma County, congestion happens in both directions at both peaks, but at different hours than Marin. In Marin, southbound traffic is heavy only in the mornings, and northbound only in the evenings.

“Note that once the HOV lanes in Sonoma 101 are connected to the Marin 101, for consistency we will evaluate traffic conditions to come up with the best operational hours throughout the whole corridor in both counties,” Haus said.

We’re still a few years away from completing the last HOV link through the Marin Sonoma Narrows (between Petaluma and Novato). Read more about the timeline for that project here.

Still want more? Read the full 2/1/2012 interview with Haus here.