Marco della Cava

USA TODAY

SAN FRANCISCO — Google's self-driving cars are getting some attitude.

Company engineers have been working on teaching their autonomous vehicles the subtle — and often obnoxious — art of honking, according to Google's May self-driving car report.

The innovation makes sense. While Google's 24 self-driving Lexus SUV fleet are hybrid machines with a modicum of engine noise, Google's growing gaggle of 34 pod-like prototypes are all-electric machines that barely whisper their presence. Sometimes, a tap of the horn is required to let folks know they're coming.

In its report, Google notes that for the past months engineers have programmed the car's computer brain to understand which road situations might require a toot, sometimes discreet and sometimes determined.

"Our self-driving cars aim to be polite, considerate, and only honk when it makes driving safer for everyone," says the report. "During testing, we taught our vehicles to distinguish between potentially tricky situations and false positives, i.e. the difference between a car facing the wrong way during a three-point turn, and one that’s about to drive down the wrong side of the road."

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At first, the car played its horn — either two short blips for a friendly warning, or a long blast for an urgent one — inside the vehicles, so engineers riding on board could note whether the sound was made appropriately. Then the cars were given the green light to honk away at the world, or at least motorists in its testing grounds of Mountain View, Calif., Austin, Kirkland, Wash., and Phoenix.

"Our goal is to teach our cars to honk like a patient, seasoned driver," says the report. "As we become more experienced honkers, we hope our cars will also be able to predict how other drivers respond to a beep in different situations."

No word on how motorists in other cars might react to a honk coming from a car carrying a passenger with a nose buried in a book. Road rage enters uncharted territory when there's technically no driver to get mad at.

Other news in the report includes the fact that on May 4, a Google self-driving prototype ran into a median at 9 mph and sustained minor damage. The car was not at fault, however, because at the time it was being manually driven by a Google employee.

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Perhaps the biggest Google auto news of the month didn't come out of Mountain View, but rather Detroit. Also on May 4, Google announced a partnership with Fiat Chrysler to have the automaker build 100 Pacifica mini-vans to specifications that will accommodate Google's array of autonomous car tech, such as radar, laser and cameras.

The program will allow Google to more rapidly expand its testing program beyond those existing four cities. To date, Google Lexus SUVs and prototypes have logged 1.6 million miles over the past seven years, with a current testing pace of 10,000 to 15,000 miles a week.

A few weeks after the Fiat Chrysler news, Google said it would be opening a 53,000 development center outside Detroit to use as a base of operations for its growing partnerships with automakers.

Google has always said it wanted existing auto manufacturers to build out the self-driving vehicles of the future, leveraging its technology as a platform.

Follow USA TODAY tech reporter Marco della Cava on Twitter: @marcodellacava