With metro areas becoming denser, gas prices on the rise, and the ever-growing effort to reduce one's environmental footprint, owning and operating a car doesn't carry the weight it once did. As fellow Fool writer Rick Munarriz eloquently put it, "auto ownership is a racket."

The testimony
It was circa summer 2005 when my (now) wife and I scored our first apartment in the heart of the city. With prime real estate, we sought to straddle the precarious line of recent graduates and young professionals. It wasn't long before we learned that the grass, true indeed, turns other shades than green. You'd expect the four-legged neighbors and cabin fever-induced disagreements, but the true excruciating detail about city living is -- without doubt -- parking.

Like a storybook, Zipcar (Nasdaq: ZIP) came to the rescue. The green dots with the big white Z came to represent the big S on the chest: the Superman-like answer to what seemed like a simple parking problem. Within a year after signing up for a Zipcar membership, I donated my old car for the tax deduction.

Zipcar estimates that its members can save up to $7,000 per year by car-sharing with the Zipcar community instead of owning a car. However, that's only a piece to Zipcar's puzzle. It was the ease of hopping online and booking a car whenever convenient that enticed me. It was the cost savings of not owning and operating a car that kept me.

The rub
Zipcar has turned its secret sauce into 33% average year-over-year top-line growth since 2008, and it's only getting started. The company has been at it since 2000, and it wasn't until 2007-2008 that traditional car rental companies got a clue. Hertz's (NYSE: HTZ) Hertz On Demand division is putting up the best fight, but its sweet offering may prove too costly for its own palate.

Predictably, others are following suit, including Enterprise Holdings' WeCar and Amerco's (Nasdaq: UHAL) U Car Share. Car sharing is a global trend. Peugeot has its Mu service, BMW has partnered with Sixt AG, and notably, Daimler AG's car2go initiative recently secured market share in the States.

However, I haven't seen a competitor in my neighborhood yet, while Zipcar has been here for 12 years.

The investment
The Goliath threat is real, but I'm not persuaded. It's been almost four years since Hertz entered the market. Subsequently, Hertz has rebranded and increased its investment. In contrast, Zipcar has increased its community from 258,000 to 650,000 Zipsters, increasing margins along the way and expanding to include 250 colleges and federal and local governments. Furthermore, Zipcar fully integrated its first international acquisition last quarter, Streetcar of the U.K., not to mention its majority stake in Avancar -- Spain's leading car-sharing service.

Zipcar provides a platform of easily accessible cars on demand, including gas and insurance, coupled with effortless reservations. It remedies the frustration of owning a car in the city for less money and more convenience.

It could be one of those classic disruptive American companies that would make Henry Ford blush -- the irony. I'm a believer in the company -- I first bought shares in July 2011. I invite skeptics to watch this story unfold by adding Zipcar to your Watchlist.

Fool contributor Greg Haygood is a shareholder of Zipcar. The Motley Fool owns shares of Hertz Global Holdings and Zipcar. Motley Fool newsletter services have recommended buying shares of Zipcar. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.