As part of a study to gauge traffic behavior, a consulting firm working with Napa County will be collecting license plate images and hundreds of thousands of anonymous records of cell phone location data from residents, commuters and visitors.
The county is collaborating with the Napa County Transportation and Planning Agency in producing the $198,000 study, which aims to answer long-standing questions about where the traffic clogging county highways is coming from, and thus help land-use planners and elected officials figure out what to do about it.
They’ll need massive amounts of data, which needs to be refined and analyzed for patterns. Transportation consulting firm Fehr & Peers has been hired to collect it, county Planning Director Hillary Gitelman told the Napa County Planning Commission on Wednesday. The goal is to have the study finished by April or May of next year.
“We need more data about who’s driving in their cars, where and when,” Gitelman said. “This is a good prerequisite to having thoughtful planning.”
Getting that data will need methods that would be considered unheard of a decade ago, but are quickly becoming normal in the smartphone and GPS era.
Kevin Johnson, a senior transportation planner at Fehr & Peers, told the commissioners that throughout Napa County, his firm will be setting up infrared cameras and computer systems that can record drivers’ license plates.
The cameras will be located at 12 locations inside the county and in gateways outside its boundaries to capture images of the license plates. The plates can be read through the computer software.
The plates will be used to look up the drivers’ home addresses through the Department of Motor Vehicles database, and Fehr & Peers will send surveys asking questions about the drivers’ trips — where they were going, how often they make those trips, and which roads they travel on, among other queries, Johnson said.
Fehr & Peers will also contract with a company called Air Sage, which collects anonymous GPS data from cellphones and provides it to the firm. Air Sage computers watch as the cell phones move around on a map, and classifies the location based on the length of time spent there.
If a cellphone remains at a location overnight, for example, Air Sage labels that “home,” Johnson said. Time spent at one location between 9 a.m. and 5 p.m. is assumed to be a resident’s work. The cellphone data also shows how the residents traveled between those points.
“Essentially they watch millions and millions of points move around the network,” Johnson said. “Basically all cell phones that are active ... will make a point.”
Neither Air Sage nor Fehr & Peers can tell any personal information about who owns the cell phone — aside from locations — and what data is on the cell phone or how it’s used, Johnson said.
Fehr & Peers did a similar survey of cellphones’ travel patterns in Monterey, and collected 1.4 million cellphone records, Johnson said. How much will be collected in Napa County is anyone’s guess.
“I have no idea how many we’re going to get,” Johnson said. “It’s going to be a lot, though.”
Examining the results of initial data collection, Johnson said a lot of trips to Napa County were originating in San Francisco, Alameda County, Contra Costa County, Solano County and from Sacramento.
The firm will also have traffic counters set up in the driveways of 30 wineries throughout Napa County, gauging the traffic volumes in and out of the wineries and when it’s heaviest. People will also go to those wineries and ask visitors if they would like to participate in a survey about how they got there, where they’re going next, if they’re staying in Napa Valley, or if they’ve been to multiple wineries.
An online survey will be issued to major schools and employers in Napa County, asking questions about students’ and employees’ commuting patterns.
All four of these methods should provide enough data for the study, Johnson concluded. The goal is to have all of the data assembled by February.
The vehicle license plate recording will take place Oct. 4, while the cell phone data will be collected in three one-week periods, which won’t run consecutively.
Commissioners Matt Pope and Heather Phillips noted how seasonal shifts in traffic volumes in Napa Valley can affect the data collected. With schools back in session and harvest and crush under way, traffic is now quite different than it was in mid-summer, Pope said.
“Just empirically there’s a huge difference between the middle of the summer and the start of the fall,” Pope said.
Gitelman said the efforts put into the study will be worth it, providing the most accurate information about how traffic originates, and how it moves through Napa County roadways.
“We’re going to be able to use these tools to analyze the projects the commission sees,” Gitelman said.
Napa County is contributing $50,000, the Napa County Transportation and Planning Agency the rest.