Which costs more for drivers — per-mile charge or gas tax?

California currently uses gas taxes collected at the pump to pay for road repairs, but as vehicles become more fuel efficient, tax revenues haven't kept pace with the cost of construction.

The state now finds itself in a $59 billion funding hole.

So the California Department of Transportation has been running a pilot program to see if people could be charged not based on the fuel they use but on the miles they drive.

I signed up for the Caltrans pilot in July.

For starters, the state has to figure out how much I'm driving. The program offers six different ways to track the distance I drive, from simply recording odometer readings to high-tech devices that monitor a vehicle's mileage and location.

The state's road charge app shows mock charges for mileage driven and displays information about a driver's car.

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Azuga

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I chose a device that plugs into my car's computer and transmits my miles back to the state automatically. 

It’s been about a month since I installed it, so I called Vanessa Wiseman, a public information officer at Caltrans, to ask what’s next.

"Anyone that signs up is gonna be part of kind of a simulated payment system. Just for the purposes of the pilot, we set a rate of about 1.8 cents per mile," Wiseman said.

To see what mock road charges I’d racked up, I opened a smartphone app that connects to the device. It tells me I’ve driven 81.2 miles this month. So I would have been charged $1.46 under the road charge system. That's about 38 cents more than I probably paid in gas taxes over the same period.

The results aren't unexpected -- I've got a fairly new car with good gas mileage, so it makes sense that the road charge would be more. The opposite might be true for older cars that are less fuel efficient.

The app also tells me some other pretty cool stuff about my car: how fast I’m accelerating and braking, if I’m wasting gas and how much juice my battery’s got left.

Once the state collects information from the nine-month pilot, officials will assess whether the method provides a more stable revenue stream to fund road repairs. The state legislature would then have to vote to institute the program on a permanent basis.

The state is still taking volunteers for its test program. You can sign up on its road charge web page.

If you're already part of the pilot, let us know what you're finding. Submit your comments below or on our Facebook page.

Correction: A previous version of this story read I had driven 463 miles resulting in a road charge of $1.46. The 463 miles denoted in the app actually calculates mileage for the past six months. The $1. 46 charge was for the 81.2 miles driven during August, which was the start date for pilot billing.