City to measure street traffic by tracking cellphones

phone tracking

This story was originally published in the Daily Post on April 9.

Daily Post Correspondent

The city of Palo Alto is implementing a new technology that will track drivers’ cellphones as they move from point to point as a way to study traffic flows.

The technology, from a Santa Ana-based company called Iteris, uses sensors to detect a unique identifier on Bluetooth devices such as smart phones. The identifier is called the media access control, or MAC, address.

The Iteris Velocity system monitors as a Bluetooth device is detected at successive locations, allowing a calculation of average travel times and speeds for a roadway segment. A Bluetooth device’s specific network address remains anonymous, Iteris says on its website.

The city is looking at using the sensors at about 10 intersections, including locations along University Avenue and Middlefield, Embarcadero and San Antonio.

“Deploying several monitors along arterial corridors at various intersections in the road network will provide an efficient means to collect arterial travel times and speeds,” according to a report from the city’s Transportation Division. “All data collected will comply with the city’s privacy policy.”

The report notes that the Iteris Velocity system is already being used by Santa Clara County. Locations the county is monitoring include West Bayshore Road at Oregon Expressway; Middlefield Road at Oregon Expressway; Central Expressway at Mayfield Avenue; and Page Mill Road at Foothill Expressway.

The council on Feb. 26 approved an agreement with Santa Clara County to share traffic data from the systems.

The traffic report was prepared for the City Council’s meeting on April 16. The report recaps recent traffic projects, such as deployment of the Iteris technology and the Middlefield Road “road diet” in north Palo Alto. It also includes data on traffic volumes, delays and collisions.

The council isn’t scheduled to take any action on the report at next week’s meeting. The Planning and Transportation Commission will discuss the report during an upcoming study session.

Road diet’ results

The report contains preliminary data from the “road diet” pilot project in north Palo Alto, in which the previously four-lane road was reduced to two lanes with a center turn lane. It was implemented in response to residents’ concerns about traffic congestion, speeding vehicles, collisions and noise. The road was reconfigured in June for a roughly one-year trial.

After the road diet was implemented, the 85th percentile motor vehicle speed — the speed that 85% of vehicles travel at or below — was measured at three locations on Middlefield Road and decreased by as much as 12.5% as compared to before the road diet.

On Fulton Street, which runs parallel to Middlefield, the speed decreased by about 4% between Lytton and Everett avenues following the road diet, but increased on Fulton between Lytton and University avenues, by about 8.7%.

Near-miss collisions appeared to be up after the road diet reconfiguration, with five observed at Middlefield Road and Everett Avenue.

“This increase in near-miss collisions was representative of an increase in hazardous driving behavior observed during review of traffic camera video and reported by residents through the mid-pilot survey,” the report said.

City transportation planners will ask the council in August whether to make the road diet configuration permanent.

Radar speed signs

In another transportation project, the city over the last several months replaced or repaired its radar speed signs so that 16 are now in operation. The signs start flashing, showing a driver’s speed, if the vehicle is going 1 to 5 mph above the speed limit. If the driver is going more than 5 mph over the speed limit, the signs flash the message, “Slow down.”

The signs operate from 7 a.m. to 9 p.m. Some of the signs collect data including date, time and vehicle speed that can be used to generate reports on speeding.

The transportation report includes data on traffic delays and, perhaps surprisingly, rush-hour delays have decreased at many intersections.

Delays in the morning rush hour were less at 13 out of 22 intersections examined in October 2017 compared to 2013. The greatest improvement was seen at El Camino Real and Page Mill Road, where the delay was 28 seconds less in 2017. Drivers waited 17 seconds less at the intersection of Middlefield and Embarcadero roads in 2017 compared to 2013.
But wait times grew at other intersections. At East Bayshore and Embarcadero roads, for example, the delay increased by 9.2 seconds.

During the evening rush hour, delays were less at 17 out of 22 intersections last year as compared to 2013. The biggest decrease was seen at Middlefield and Embarcadero roads, where drivers waited 16.5 seconds less. Intersections where the delay increased included Middlefield and San Antonio roads, where drivers waited 12.8 seconds longer.

Locations proposed for Bluetooth traffic monitoring:
• University Avenue/Middlefield Road
• University Avenue/ El Camino Real Ramps
• Alma Street /Lytton Avenue
• Embarcadero Road/ Saint Francis Drive
• Embarcadero Road/Middlefield Road
• San Antonio Avenue/Middlefield Road
• San Antonio Road/East Charleston Road
• East Charleston Road/Middlefield Road
• Alma Street/ East Charleston Road
• Arastradero Road/Gunn High School Driveway


  1. This type of tracking seems really inefficient – not all cellphones have bluetooth on. In addition this relies on MAC address and there are ways for phone manufacturers to randomize the MAC ID so now the system is double counting a new MAC address for the same person. Hopefully the city did not pay for a long term contract with tax payer money if cell manufactures choose to update the operating system and manipulate bluetooth tracking 🙁

  2. Most cell phones’ bluetooth signals cannot be tracked because they have to be in discover-able mode to be picked up by most off the shelf scanners. The bluetooth that is being tracked is built into the cars (your bluetooth connected radio, the tire pressure sensors, etc) These are always in discover-able mode and are not easily turned off. These are also a very small percentage of the total vehicle population. It is an averaging system gives the city travel time information. Which then can be translated into better signal timing so that your travels through those areas are improved. You can put away your tin foil hats now.

  3. I’d like to see a policy where the city discards personally identifiable information so that it is not swept up by a super computer and used to track our movements. I’m suspicious that this technology will have a “dual use,” as the government puts it.

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