Traffic is seen on Highway 29 as it approaches the Trancas Street over-crossing.

Who are all those people on Napa County highways, and where are they going?

According to a new traffic study, most of those motorists are us — people who live and work in Napa County. Another big group is coming here to work. Only 9 percent of motorists are just passing through.

The Napa County Transportation and Planning Agency (NCTPA) received a new travel behavior study this week from consultants Fehr & Peers.

Officials wanted to not only know how many people are driving on local regional roads, but where they are headed and why.

“One of the shocking things to staff was 55 percent of the travel is caused by people who live and work here,” Napa County Transportation and Planning Agency Executive Director Kate Miller said.

Transportation planners in coming years will try to make the data hit the road. They want the mass of numbers contained in the report to influence the real world, where people deal with the frustrations of rush-hour congestion.

For example, Miller said, knowing where people are going makes it easier to address travel needs through such strategies as transit, carpools and vanpools.

Kevin Johnson of Fehr & Peers talked about the study during Wednesday’s Napa County Transportation and Planning Agency Board of Directors meeting. The firm collected data in a number of ways – from cameras to mobile device tracking systems to surveys – to create a numerical picture of Napa County on the move.

Infrared cameras at 11 locations, including seven gateway sites, counted 181,330 vehicles in a single day. Cameras took photos of 159,389 license plates to help track vehicle movements.

Nine percent of the trips were people passing through the county from one gateway to another. Twenty-five percent were motorists who headed to work in Napa County from another county, given the times they entered and left the county.

Data collected from 206,152 mobile devices, such as cellphones, also showed where people travel. Johnson praised this information source, though he acknowledged that some people might object to their cellphone being tracked.

“There’s a lot of concern with this type of data,” Johnson said. “It is anonymous. They are really recording a unique identification number, which is different than a phone number.”

Consultants can make inferences from cellphone movements. For example, a cellphone that ends up at a certain location for eight hours during the day on a weekday points to a work-related trip.

Of the trips tracked by mobile devices, 55 percent involved motorists who never left Napa County, 36 percent involved motorists who passed through a gateway and 9 percent involved motorists who passed through two gateways.

Given that Napa County is wine country, the study took a look at winery and tourist traffic.

Wineries account for 52,245 vehicle trips on a typical Thursday, 62,217 on Friday and 54,713 on Saturday. Thirty-five percent of wine patrons start their day in Napa County and 23 percent in San Francisco, the study found.

The study also looked at the segment of Highway 12 through Jameson Canyon that links Napa and Solano counties. It estimates that 4,300 more vehicles used Highway 12 on a typical day this October compared to in October 2013, and that 4,600 less vehicles used Highway 29 through American Canyon.

That came as no surprise to board members. They reasoned that some people used Highway 29 in 2013 to avoid the big Highway 12 construction project and have switched back now that construction is finished.

NCTPA spent $219,940 on the travel behavior study, with $50,000 coming from Napa County and $18,400 from the Napa Valley Vintners and Wine Growers of Napa County.

“I think the study is great,” county Supervisor Keith Caldwell said. “It’s the first study we have that really starts to pinpoint where people are going.”

Now, Napa County transportation planners must figure out ways to make the trips that they are documenting easier for travelers.

Subscribe to Daily Headlines

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

Napa County Reporter

Barry Eberling covers Napa County government, transportation, the environment and general assignments. He has worked for the Napa Valley Register since fall 2014 and previously worked 27 years for the Daily Republic of Fairfield.

Comments disabled.