What did one car say to the other car? If you make that turn I'll hit you!

You're driving through town with your mind half on work, half on the traffic around you. You come to the two-way intersection you've crossed a thousand times before, stop, look around and start to turn left.

And then your car sounds a warning bell, loudly and insistently. It's telling you, "WAIT -- the pickup truck barreling straight at you can't stop in time."

Got your attention, no?

It works because your car and that pickup are exchanging their location, speed, acceleration, direction and steering faster than we can blink. Many consider this conversation -- called vehicle-to-vehicle, or V2V -- the most important lifesaving technology to hit the auto industry in the past 10 years.

If V2V did nothing more than warn you not to turn left or enter an intersection, it could prevent about half a million crashes and save around 1,100 lives a year, according to the National Highway Traffic Safety Administration.

But automakers, universities and government organizations are exploring V2V for more than just intersection safety. They're also developing the technology to see around blind spots, warn when a pickup five cars ahead has suddenly braked, and tell you, "Whoa, don't pass that horse trailer, because there's oncoming traffic you can't see." Because of benefits like these, the US Department of Transportation is pushing automakers to adopt V2V within the next few years.

"Connected, automated vehicles...have the potential to revolutionize road safety and save thousands of lives," Transportation Secretary Anthony Foxx said in a statement last year. "The department wants to speed the nation toward an era when vehicle safety isn't just about surviving crashes; it's about avoiding them."

In other words, there's an excellent chance that five years from now, V2V will be standard in every new car people buy.

Catch-22

Without that government mandate, automakers can decide when, or even if, to add the technology. And that's an issue because the promise of V2V depends on nearly universal adoption.

"If I've got a talking car and there's no one else to talk to, that would be a problem," explains Gordon Trowbridge, NHTSA's communications director.

So far, General Motors is the only automaker to announce production plans for the US market, saying V2V will be on its 2017 Cadillac CTS luxury sedan. Toyota last year added the technology to three models sold in Japan.

Further complicating V2V's critical mass: We don't seem to be in any hurry to buy that new car or truck. The average age of cars driven on US roads is now a record 11.5 years. And that means it will take almost 30 years for 95 percent of the nation's cars and trucks to talk to each other, says Russ Rader, senior vice president of the Insurance Institute for Highway Safety.

Who's there?

Last July, car security experts Charlie Miller and Chris Valasek hacked into a Jeep Cherokee and drove it into a ditch. A month later, Chrysler recalled 1.4 million Jeeps.

It shows what can go wrong with the connected-car and wireless infotainment systems that automakers already offer in their high-end models. But that vulnerability is especially worrisome for a technology like V2V, which aims to touch nearly every vehicle on the road, says Jeff Williams, co-founder of Contrast Security. "You're connecting your car to any random person out there," Williams says. "It's likely to save tons of lives, but people might misuse the system."

For its part, the NHTSA claims its V2V design already meets "a very high level of security" and says the agency is "actively engaged with security experts" to make the system safe, secure and private.

In the meantime, automakers like Ford, GM and Honda are working on V2V because it's a good idea -- not just the law.

"The root cause of people dying in car crashes is drivers. It's not the vehicle, and it's not the environment," says Mike Shulman, Ford's V2V technical leader. "Like polio vaccines, if we have technology that could prevent thousands of deaths each year, why not use it?" 

Talking traffic lights

If your car talks to other vehicles on the road, shouldn't it talk to the city, too?

That's the idea behind vehicle-to-infrastructure (V2I) technology, an important complement to V2V. With V2I, your car can have fruitful chats with traffic signals, road signs, streetlights, and sensors embedded in pedestrian walkways.

Imagine, for example, that your car is having a nice conversation with the string of traffic lights that dot your city's major artery. Using V2I, those traffic signals could advise you, through the car's dashboard, that driving 31 miles per hour would let you sail through every green light.

Other situations include dashboard alerts for road construction, lane shifts and traffic advisories. And advocates for the blind envision beacons attached to light poles that would help the vision-impaired cross busy streets.

The downside depends on how states and cities use the data they glean from your driving habits. It would be fairly easy -- and lucrative, for example -- for them to automatically issue traffic tickets every time you exceed the speed limit.

And then there's the issue of timing. Unlike V2V, which the federal government can mandate for new vehicles, the Department of Transportation can only offer city and state governments incentives, guidance and support to install the intelligent infrastructure.

The DOT is currently drafting detailed guidelines to make sure V2I works the same everywhere, but it will be up to cities and states to implement it. And that means it's anyone's guess when your car and Mr. Traffic Light can have their chat.

Paula Vasan (@paulavasan) is a multimedia reporter writing about business and technology. She lives in New York. CNET's Wayne Cunningham contributed to this report.

This story appears in the spring 2016 edition of CNET Magazine.