When you go on a trip via airplane, chances are good that your car sits at home or in an expensive airport parking lot while you are away.

Wouldn't it be great if that car could earn money while you are gone, or at least not generate parking expenses?

Now, it can. Car-sharing services FlightCar and RelayRides have jumped into one of the rental car industry's hottest markets: the nation's airports.

FlightCar bills itself as the first car-sharing company to "help consumers deal with the high expense and hassles of getting to and from the airport and figuring out what to do with their cars while they're away on a trip." Instead of renting a new car from a traditional rental agency, travelers can rent a someone else's car in what's known as "peer-to-peer" renting.

FlightCar currently operates near San Francisco International Airport and Boston's Logan Airport.

Car owners can drive to FlightCar's parking lot in Millbrae and leave the car there -- for free. If your car is a 2001 model or newer, you can earn money from its rental; the newer the car, the better the chances of it being rented. You don't make a lot of money, but if your car is a 2008 model or older, you get $10 per rental. If it's a 2009 or newer, you earn $10 each day it is rented. Luxury brands, like a BMW or Lexus, will earn you $20 a day.

"If your most valuable asset is your house, your second most valuable asset is your car," said Rajul Zaparde, one of FlightCar's founders. "When are you not using your car? When you are traveling."

Robert Cortlandt, a photographer and filmmaker, lives in San Francisco and regularly travels out of SFO. He recently went to Florida for 11 days, and left his 2001 Lexus SUV at FlightCar's lot near SFO while he was gone.

"I had to drop my car off at 4 a.m. in order to make my flight on time, but FlightCar was there," said Cortlandt. "A couple of days later I got an email that said my car had been rented. When I arrived back at SFO, my car was clean and they handed me a check for $110. I got a check, free parking, a free car wash, and a free ride to and from the airport from their lot. It also eliminated the need to worry about street cleaning in San Francisco while I was gone."

Cortlandt plans to go to Los Angeles over the Labor Day weekend and says he'll leave his car with FlightCar again.

FlightCar, based in Cambridge, Mass., hopes to eventually disrupt the $11 billion airport car rental market dominated by Enterprise, Avis/Budget and Hertz. FlightCar provides insurance coverage to vehicles while they are being rented out, including $1 million for bodily injury and property damage to third parties.

But airport authorities are crying fowl.

The city of San Francisco, which has jurisdiction over SFO, has filed a lawsuit against FlightCar, arguing that the startup is flouting car rental agency rules by skirting fees that other car rental agencies pay to the airport.

In 2012, more than 44 million passengers traveled through SFO. Car rental agencies pay 10 percent of their gross profits to SFO for the cars rented out of the airport, but FlightCar currently does not pay those fees.

In the 2011-12 fiscal year, SFO collected $94 million in fees from the 12 rental car companies that operate on or near the airport, including from Alamo, Dollar, Hertz, Advantage and Payless.

"Twelve rental car companies are licensed to do business at the airport, including three that are off airport property," said SFO spokesman Doug Yakel. "FlightCar is catering to an airport clientele. They just appeared and said 'we're open for business' without ever engaging with the airport staff."

John Penny, left, and Marty Puranik load their luggage into a rental Prius at FlightCar in Millbrae, Calif. on Wednesday, Aug. 7, 2013. They just arrived
John Penny, left, and Marty Puranik load their luggage into a rental Prius at FlightCar in Millbrae, Calif. on Wednesday, Aug. 7, 2013. They just arrived on a business trip from Florida. FlightCar is a car-sharing service that allows travelers to leave their cars in a parking lot so that others can rent it while they are gone. (Gary Reyes/Bay Area News Group)

But despite the lawsuit, FlightCar is growing, largely by word-of-mouth. On a typical day, FlightCar rents out 30 cars at SFO.

RelayRides, which operates car-sharing services in several cities, has also introduced a new service near SFO, but it's slightly different. Car owners don't make any money. In exchange for letting RelayRides rent out the car, owners receive free parking at the RelayRides lot.

"Airport parking can be expensive, so that's a big motivation for people," said Steven Webb of RelayRides. "Within a year we expect airports to be 50 percent of our revenue. We're cooperating with airport authorities and expect to pay some kind of fee."

Doug Yakel, of SFO, said the airport is in active discussion with RelayRides, but not FlightCar. He warns that both startups need to be aware of another issue: rules that govern vehicle emissions near the terminals, which both companies are violating.

SFO has heavily invested in the AirTrain, a light-rail system that connects all airport terminals to garages, the BART station and the rental car center. FlightCar currently picks and drops people off curbside via a third-party limo service; RelayRides uses a shuttle service.

"One issue is that we expect car rental companies to use the AirTrain system to ferry passengers to the airport terminal," said Yakel. "We are trying to reduce the amount of vehicular traffic, and greenhouse gas emissions, near the airport."


FlightCar is a new ride-sharing service currently operating near San Francisco International Airport. Here's how it works:

For car owners: You can park for free by renting out your car to approved travelers. FlightCar will wash and clean your car before returning it to you and protect the vehicle with a $1 million insurance policy. You'll get free parking even if your car isn't rented.

For travelers: Enter your trip information on FlightCar's website and book a vehicle type that you like. When your plane lands, call FlightCar and a black car will pick you up at the curb and take you to the FlightCar parking facility. When the rental is over, return the car to the FlightCar lot.


RelayRides is another ride-sharing service that operates near SFO. Here's how it works:

For car owners: You can park for free, but you get no compensation, by allowing RelayRides to rent out your car to approved travelers. The car is protected by a $1 million insurance policy. RelayRides will transport you to the airport terminal via a shuttle.

For travelers: You can search the RelayRides website for cars that are available to rent out of SFO. Return the car to the lot where you picked it up for the checkout process.