It has long been a nightmare scenario for privacy advocates: Every time you get in your car, a computer relays your location and tracks your trip from start to finish. It can track how far you go, where you drive, how long the trip is, and even how much traffic you encounter.

Technology has made that scenario a reality—one drivers seem widely willing to embrace. Urbanites are flocking to ride-sharing programs such as Zipcar or Car2Go, even though both services can see where their cars and users are. Even private-vehicle drivers have adopted E-ZPasses, which speed them through tolls but also create an electronic record of their tollway trips.

Now, urban planners hope public acceptance of tracking will allow them to address one of transportation policy's most pressing problems: how to fund roads and highways.

For decades, highway and road maintenance was funded by a gas tax. But that revenue has dropped as cars have grown more fuel-efficient and the tax has stayed stagnant, leaving highways short on funding. A tax on use, rather than gas consumed, could close that shortfall, advocates say.

Under such a system, drivers would simply be charged for every mile driven (or some equivalent). The tax would charge roads' biggest users the most, leveling the playing field between fuel-efficient cars and gas guzzlers. It's also an easy way to account for use by the hybrid and electric cars that are passing up gas pumps—and it could even alleviate congestion by charging drivers extra fees for driving into congestion.

A vehicle-miles traveled (VMT) fee, however, would require tracking drivers' movements, and the associated privacy concerns have been enough to kill any such proposals.

When Ray LaHood, President Obama's first-term Transportation secretary, floated the proposal in early 2009, the administration hastily walked it back, saying it was off the table. And congressional support has been mild—even a proposal to research a VMT system didn't make the final version of the 2012 transportation reauthorization bill.

But VMT proponents say the privacy concerns are unfounded, especially in the era of big data.

"Logic has not really entered into that discussion," said Joshua Schank, president of the Eno Center for Transportation. "People have had cell phones and private cell companies knowing where they travel for years, but somehow that doesn't give them any more comfort if the federal government is going to track their driving."

And location tracking has moved beyond the smartphone to the dashboard.

Private companies have done plenty to allow their drivers to be located, especially as car-sharing models have disrupted traditional family car ownership. Take, for instance, the popular Car2Go car-sharing system, which offers Smart cars in 26 cities worldwide. Rides are tracked with connections to internal systems for location, speed, travel times, and other information for use on invoices, checking to keep cars within a reservation area and prevent fraud, according to the service's privacy policy. The start and finish of each trip is also stored on invoices.

Zipcar similarly has on-board monitoring for its customers—according to its privacy policy, the latitude and longitude of Zipcars is "transmitted to Zipcar and temporarily stored (including while it is hired to you)" so that employees can provide roadside assistance, ensure it is restored to the right place, and locate lost cars. The policy says Zipcar does "not actively track or monitor vehicle location, and we do not story historical GPS data regarding vehicle location."

Uber, the rideshare and taxi service, likewise uses GPS and geolocation through its mobile app to see where users and drivers are, but its privacy policy says the data is not shared with third parties and is used only for purposes like customizing services, promotions, and data analytics.

"There's really a lot less privacy with those systems because they know at least where you are picked up and dropped off and someone's keeping track of that," said Rob Atkinson, president of the Information Technology and Innovation Foundation. "I have no reason to doubt that these companies are trustworthy and it's possible that as people become more comfortable with that, they'll see that there are less privacy concerns."

Even the private cars that those companies are looking to replace have a degree of monitoring. Electric cars like the Nissan Leaf and the Chevrolet Volt have become data sources for car companies and others looking for stats on how clean cars are used. The EV Project—backed by the Energy Department, Nissan, Chevrolet, and others—offers up free chargers in exchange for permission to collect data on vehicle use, charging patterns, and energy use.

They've even become a badge of honor for some drivers—the website Volt Stats lets drivers upload their engine use data, enabling a not-so-subtle competition to see who can drive the farthest with the least gasoline.

Democratic Rep. Earl Blumenauer of Oregon, a longtime VMT supporter, has even pointed to E-ZPass toll systems and traffic cameras as proof that the privacy concerns are overblown.

"I don't think that means we should be any less concerned about the government doing something like this," said Gautum Hans, an attorney with the Center for Democracy and Technology.

Hans said that individuals may be more comfortable with a private company using location tracking for business or research use—"as we like to say, a private company can't put you in jail," he said—but even that may be lessening amid the outcry over research projects done by Facebook and OK Cupid. And there are particular concerns that come with the potential for the government to watch where and when citizens are driving.

"Research is understood by individuals. You can understand why a ride-sharing app would want to do research as long as its aggregated and takes steps to protect your privacy," Hans said. "With the government, there are reasons you would be concerned, whether it's the First Amendment and the freedom of association or how the information is kept and how."

"It seems odd to me that there would be a solution that is so expensive and carries so many questions," he added.

It's still an open question what sort of technology would be employed with a VMT. A pilot program in Oregon offers the 5,000 volunteer participants a variety of options, including a smartphone app, self-bought GPS systems, or even a flat fee that would require no tracking at all. Experts say a "black box" is unlikely—it's expected that, at most, the system would rely on a one-way GPS system that simply relayed the distance traveled to alleviate the bigger driving concerns.

For Atkinson, who chaired a federal commission that recommended a VMT system in 2009, said that he sees "movement" toward a VMT, with support growing among conservatives and environmentalists alike for a more equitable transportation funding system.

"A full-steam-ahead effort to develop a standard, mandating every car comes equipped with an on-board GPS, that's going to be a while," he said. "As cars become smarter, you'll end up with more that have the capability to do this. I think if you start with a voluntary system, you'll see it grow."

(Image via Denys Prykhodov/Shutterstock.com)