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How to mine cell phone data to plan transit

September 06, 2017

24 million people visited Lake Tahoe in 2015—and only 1.4% used transit. Planners want 20% and a better way of studying travel patterns is helping.

Lake Tahoe is a natural playground for millions of Americans. But the lake’s famously blue, crystal-clear waters are under threat. Regional government agencies have built infrastructure to reduce the amount of sediment entering Lake Tahoe from construction and storm runoff. But there are still water-quality impacts from vehicles to consider. Residents believe the visitors are the problem. Our team supported the Tahoe Transportation District and Tahoe Regional Planning Agency in developing a comprehensive multimodal transportation plan.

To create our plan, we need to understand where Lake Tahoe visitors come from, how they travel, how often they visit, and where they visit. But how would we identify these travel patterns to the majestic lake that straddles the border of California and Nevada?

It’s all about the phone.

Historically, tracking visitors relied in large part on transient occupancy tax collections, license plate surveys, and state-implemented traffic counts. These methods of data collection require a great deal of time, financial resources, and extrapolation.

We wanted better information. And we wanted it faster. How could we get it?

With cell phone data.

Today, cell phones are ubiquitous. Cell phone data enabled us to develop an innovative transportation management plan using the newest information technology and sophisticated ArcGIS tools to visualize the results. Our team purchased cell phone activity data (anonymized to protect cell phone users’ privacy) from AirSage Analytics, and used spatial software and Excel to analyze and illustrate travel through Lake Tahoe’s main traffic corridors. Basically, the data shows the locations of cell phones, allowing us to know when and where the phones entered the Lake Tahoe region and how long they stayed.

We also integrated this data against other information like as land use, transit ridership, transit stops, bicycle and pedestrian infrastructure, U.S. Census data for employment and housing, and traffic counts.

Third party vendors such as AirSage, in partnership with wireless carriers, aggregate and anonymize the locations of cell phones. These companies process tens of billions of data points each day and turn them into meaningful information. Stantec acquired a vendor’s complete menu of variables for three months for the entire Tahoe Basin for a very reasonable amount.

The data included February and July to analyze the variance between winter and summer travel patterns. We also included August to confirm the peak summer month in Lake Tahoe. This seemingly straightforward data acquisition process required careful and strategic thinking to fully comprehend the questions we needed the data to answer before engaging the vendor. If you do not think it through beforehand and ask for additional data after the vendor has aggregated it to your study area, the cost is potentially double.

Purpose of the plan

Like many popular resort destinations, the steady increase in visitors to Lake Tahoe worsens traffic congestion—compromising the quality of experience and impacting air quality. Degrading air quality directly correlates to degrading water quality. Lake Tahoe agencies and non-profits have collectively spent over $1billion to protect the clarity of Lake Tahoe’s famous blue water.

Countless installations reduced sediment flowing into the lake from construction activities and stormwater runoff. Additionally, bike lanes have been striped and shared-use paths have been paved. However, transit remains disconnected with long headways and few rider amenities. The purpose of our multimodal transportation plan was to fully understand the travel patterns of the various travel groups and integrate those findings with transit routes, stops and boardings; locations of sidewalks, bike lanes and shared use paths; development patterns and zoning; and popular Basin destinations. The outcome was a bold, yet achievable, action plan based on a far more comprehensive dataset than previously collected.

What we learned

With this much information about the population movement patterns, it was difficult to stop conducting query-analysis-ArcGIS mapping exercises. The data is gloriously robust!

And what did we learn? The number of annual visitors entering the Lake Tahoe Basin is 24 million people. That’s about twice as many annual visitors than the busiest national park in the United States—Great Smoky Mountains National Park. It’s also double the number of visitors the client thought were coming to Lake Tahoe.

Lake Tahoe isn’t a national park. But it is clearly a popular recreation destination.

The home location data identified California as the source for over 60 percent of all visitors. Even small growth forecasts in a state of 37 million people has huge implications for the increasing number of visitors to Lake Tahoe. Figure 1 (at the top of the blog) highlights the magnitude of visitor trips compared to resident trips in the Basin.

The Tahoe Transportation District established a goal of achieving “20 in 20”—20 percent transit mode share in 20 years. Transit ridership totaled 1.1 million in 2015. Using the cell phone data, we estimated the total number of internal trips made throughout the Lake Tahoe basin annually exceeded 79 million. Since only 1.4 percent of all trips were made on transit, the District has a long way to go to reach its goal. Figure 3 shows that 1.6 million vehicle trips were counted at the popular Emerald Bay State Park/Eagle Falls areas, while the seasonal transit shuttle carried just 7,500 people. Knowing this allows for better alignment of transit services and mobility infrastructure with population movements and locations.

Using the data to change patterns

The Linking Tahoe: Multimodal Transportation Management Plan included detailed recommendations for transit services and routes, prioritized gaps in bikeways, proposed sidewalks and, most importantly, identified numerous mobility hub locations throughout the Lake Tahoe Basin and at key interception points. Mobility Hubs are not park-n-ride lots. Instead, they offer additional services such as bike rentals, bike lockers, car parking, and a transit shelter. The intent is to intercept visitors and shift the transportation form from passive to active and from single car to transit use. 

Converting vehicle trips to transit rides will require significant human and financial resources. After several high-traffic summers and a debilitating winter, the basin agencies are motivated. Lake Tahoe successfully demonstrated that, when all five counties, two state agencies, and three federal land management agencies come together to pool resources, they achieve tremendously successful outcomes.

Our experience with the cell phone data and the popular Lake Tahoe region has taught us to look beyond a pure “vehicle count” and to look at each trip. Using this data, we can help the Lake Tahoe region prepare for its current and future transportation needs. And we’re better prepared to help other communities mine the wealth of data that our cellphones can share.

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