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Broken traffic sensors dull Calif. ‘smart’ freeways

Embedded sensors are a key part of “intelligent transportation” systems, but many are proving useless.Reed Saxon/Associated Press

LOS ANGELES — California’s highways aren’t as smart as they used to be.

Buried under thousands of miles of pavement are 27,000 sensors that are supposed to help troubleshoot both daily commutes and long-term maintenance needs on some of the nation’s most heavily used and congested roadways. About 9,000 of them no longer work.

The sensors are a key part of the ‘‘intelligent transportation’’ system designed, for example, to detect the congestion that quickly builds before crews can get out to clear an accident.

A speedy response matters: Every minute a lane is blocked during rush hour means about four extra minutes of traffic. Fewer sensors can mean slower response times, so the fact that 34 percent are offline — up from 26 percent in 2009 — creates an extra headache.


‘‘[It] is not an acceptable number, really,’’ said California’s top transportation official, Brian Kelly.

With limited space and money for new lanes, Kelly said, maximizing flow is critical. To do so, planners rely on cameras, above-road detectors, message boards, and in-road sensors called ‘‘loops,’’ because of their shape. Some loops were cut during construction, others yanked out by copper thieves. Many have died of old age.

The resulting blind spots show up as strings of gray amid the green, yellow, or red on the large map that freeway managers overseeing Los Angeles and Ventura counties monitor.

The outages are significant enough that the sensors alone cannot produce real-time traffic maps that are useful to the public — especially when compared with the many private traffic mapping services that drivers rely on to get around.

So, to post online traffic maps that are ready for public consumption, California and other states are paying the private sector.

The California Department of Transportation gives away data from its loop sensors to Google and other companies; the department also pays Google for a traffic map that incorporates its own data as well as information the tech giant gets from vehicles and cellphones whose owners have agreed to share location data.


California’s tab is not large — the transportation department estimates it at $25,000 per year for its public-facing Quickmap — but other states are giving away data and buying back reliable maps, as well. Michigan’s transportation department pays Inrix Inc. about $400,000 annually for data to populate its Mi Drive map.

An Inrix spokesman said the company has contracts with 25 state transportation departments.

Loops can last decades when properly installed. A bundle of wires under the pavement detects the size, speed, and number of vehicles that pass by, transmitting the information to a roadside box. That data record traffic in real time and help planners who want to know how many of what kinds of vehicles use a road, so they can project when it will start to deteriorate. (More big trucks means more potholes, sooner.)

Drivers may be familiar with loops at intersections, where a circular cut in a turn lane means a loop will detect an idling car and tell the light to change. Replacement materials cost only a few hundred dollars — but installing a loop on a freeway can cost thousands, because to embed the wire crews must close two lanes, probably in the off hours, when labor is more expensive.

In the Fresno and San Francisco Bay areas alone, the state plans to spend $35 million to fix loops sensors — as well as freeway lights, cameras, ramp meters, and other systems — that are down due to metal scavengers or other problems.


The state that pioneered the use of loop sensors is not alone.

In Utah, officials estimated about 20 percent of loops do not work. And 75 percent in the Austin, Texas, area are not working.