Northbound Highway 101 during the afternoon carpool-lane hours. Click to enlarge. Road Warrior photo.

With more carpool lanes being built along Highway 101 in Sonoma County, we’ve been wondering how many people carpool and use the lanes. Here are some facts and figures we’ve come across:

Carpooling remains at historic lows

The Census Bureau’s 2010 American Community Survey found 10.3 percent of  workers living in Sonoma County carpool. That’s 22,622 carpoolers out of 219,015 workers.

The 2010 stats are lower from 2009, when 11.1 percent, or 24,713, of 222,386 workers carpooled.

Percentage-wise, 2008 was the recent historic low at 10.1 percent.  That compares to 12.6 percent in 2000, 13 percent in 1990 and 16.3 percent in 1980, according to Census Bureau data.

For 2010, the Census Bureau data showed the highest percentage of carpoolers was  among those 25 to 44 years old with 44.2 percent, those earning $15,000 to $24,999 a year at 22.2 percent, those in service occupations at 26.4 percent and those who described their industry as educational services and health care and social assistance,t 17.8 percent. Carpoolers also were  mostly male at  58 percent.

As for getting to work, the highest percentage, 18.7 percent, said it took 10 to 14 minutes but the next highest percentage, 14.5 percent, said it took an hour or longer. As for the place of work, 75.8 percent of carpoolers said they worked in Sonoma County.

 How many people use carpool lanes

A 2010 Caltrans report showed that almost twice as many people used Sonoma County’s carpool lanes in the evening peak hour than in the morning’s peak hour.

A total of 974 vehicles used the carpool lanes from 8 to 9 a.m. while 1,888 used them from 5 to 6 p.m.

For the morning peak hour, the southbound lane from Windsor to Highway 12 recorded the lowest carpoolers at 108 vehicles, then northbound from Highway 12 to Windsor at 244, northbound from Wilfred Avenue in Rohnert Park to Highway 12 at 308 and southbound Highway 12 to Wilfred at 314. It seems likely that some were counted twice if their commute was in both of Caltrans’ counting zones, either northbound or southbound.

Transportation officials have said that a highway lane has a capacity of 2,000 vehicles an hour.

The carpoolers made up a small percentage of total vehicles on Highway 101 during those peak hours.

For the morning commute, Caltrans found 5 percent of the vehicles on the road were in the carpool lane from Windsor southbound to Highway 12,  7 percent from Highway 12 south to Wilfred, 8 percent from Wilfred northbound to Highway 12 and 7 percent from Highway 12 north to Windsor. The evening commute was  higher, with 7 percent in the carpool lane from Windsor south to Highway 12, 14 percent from Highway 12 south to Wilfred, 13 percent from Wilfred north to Highway 12 and 11 percent from Highway 12 north to Windsor.

The percentage of carpool violators during the two peak hours was among the lowest for Bay Area carpool lanes, ranging from 0.9 percent for the evening southbound commute from Highway 12 to Wilfred to 4.3 percent for the morning northbound commute from Wilfred to 12.

To see the report, 200 pages of all kinds of carpool stats for highways throughout the Bay Area, CLICK HERE.

In the past, in spite of low use of carpool lanes, public officials have said carpool lanes are a good idea for Sonoma County because they help ease traffic congestion and environmental problems.

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