When the traffic on Timothy Connor's quiet Maryland street suddenly jumped by several hundred cars an hour, he knew who was partly to blame: the disembodied female voice he could hear through the occasional open window saying, "Continue on Elm Avenue . ..."
The marked detour around a months-long road repair was several blocks away. But plenty of drivers were finding a shortcut past Connor's house in the suburb of Takoma Park, Maryland, slaloming around dog walkers and curbside basketball hoops, thanks to Waze and other navigation apps.
"I could see them looking down at their phones," said Connor, a water engineer at a federal agency. "We had traffic jams, people were honking. It was pretty harrowing."
And so Connor borrowed a tactic he read about from the car wars of Southern California and other traffic-weary regions: He became a Waze imposter.
Every rush hour, he went on the Google-owned social-media app and posted false reports of a wreck, speed trap or other blockage on his street, hoping to deflect some of the flow.
He continued his guerilla counterattack for two weeks before the app booted him off, apparently detecting a saboteur in its ranks.
That made Connor a casualty in the social-media skirmishes erupting across the US as neighbourhoods try to contend with suddenly savvy drivers finding their way on routes that were once all but secret.
"It used to be that only locals knew all the cut-through routes, but Google Maps and Waze are letting everyone know," said Bates Mattison, a city councillor in the Atlanta suburb of Brookhaven, Georgia. "In some extreme cases, we have to address it to preserve the sanctity of a residential neighbourhood."
When population growth began to overwhelm a set of major intersections in his district, there was an increase of 45,000 cars a day on some residential streets, as app-armed commuters fought their way to nearby Interstate 85. In response, the city is posting signs to restrict left or right turns at key intersections.
The apps didn't create the traffic, Mattison said, but they gave drivers options they wouldn't have known about otherwise.
Waze, with 50 million users worldwide, provides navigation guidance by combining its map database with data it collects in real time from every logged-on driver. Average speed, backups, and fleeting hazards such a car pulled over to change a flat appear almost instantly on the app's cartoonish interface. When the first Waze-enabled car finds its way to a promising shortcut, thousands can follow.
In Portland, Oregon, for example, when drivers trying to avoid local construction began flooding a street that had been redesigned as a "greenway" bike route, city officials had to put up barrels on some stretches to filter out the vehicular through-traffic. It worked.
"The apps reacted pretty quickly to that," said Jonathan Maus, publisher of Bikeportland.org.
In California, where navigation apps are as common to drivers as sunglasses, several communities are contending with overwhelmed local streets that residents blame at least in part on the programmes. In the Los Angeles region, Waze's biggest US market, the Sherman Oaks City Council is considering a motion asking the programmes to exclude some small residential streets from their algorithms.
It was here that Connor learned that some Waze warriors had launched concerted campaigns to fool the app. Neighbours filed false reports of blockages, sometimes with multiple users reporting the same issue to boost their credibility. But Waze was way ahead of them.
It's not possible to fool the system for long, according to Waze officials. For one thing, the system knows if you're not actually in motion. More importantly, it constantly self-corrects, based on data from other drivers.
"The nature of crowdsourcing is that if you put in a fake accident, the next 10 people are going to report that it's not there," said Julie Mossler, Waze's head of communications. The company will suspend users they suspect of "tampering with the map," she said.
Waze's mission is to distribute traffic more efficiently across the grid of public streets, Mossler said, not to create traffic jams.
"That said, the traffic has to go somewhere," she said. Although the app will continue to route drivers down any legal street, Waze programmers are working to build in alerts about school zones and other slow-speed zones, Mossler said.
Traffic engineers say the side street flare-ups are a downside to the otherwise positive effect that navigation apps can have on vehicle flow. They have proved to be a powerful force in moving cars past bottlenecks, and in many jurisdictions, including Maryland and the District, officials have begun working directly with Waze to glean information about potholes, backups and other real-time data.
The cut-through disputes "are an unintended consequence of this great technology that is supposed to help people avoid sitting in traffic," said Paul Silberman, a traffic engineer with Sabra, Wang & Associates in Columbia, Maryland. Those who live on side streets have been complaining for years about becoming through routes, but now it's happening at Internet speed.
"These great shortcuts used to spread by word of mouth, but now they just spread like wildfire," Silberman said.
In Maryland, Connor complained to the city's public works and police departments, but nothing stemmed the flow. He put out two plastic watch-for-children figures, but one was hit by a car and the other was stolen.
Connor and his neighbours put up "No Through Traffic" signs. And their city councillor, Tim Male, tried to get Google Maps to take note of the official detour, by calling the company and flagging it through the apps' feedback feature.
But still they came. One afternoon, Connor counted a vehicle every two seconds on a street with a single lane available between parked cars. One morning, neighbors awoke to a cacophony of honks and went out to find a backup dozens of cars deep, two drivers in the middle about to come to blows.
The traffic flow began to wane when the road construction ended, Connor said, but remains three or four times higher than before it began. For some drivers, their app-inspired shortcut became a permanent route.