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The race between tech and auto giants to release self-driving car is on, but why is Apple opted for a top-secret testing facility while Google and Mercedes Benz test out on the open road?

While Google and Mercedes-Benz had to divulge tech specs on their projects to pass inspection in order to test autonomous cars on public roads, the secrecy of GoMentum helps Apple keep its plans for a driverless car away from prying eyes.

From documents obtained by a public records act request, The Guardian cites correspondence between Apple engineer Frank Fearon and car testing facility GoMentum Station as saying that Apple "Would… like to get an understanding of timing and availability for the space, and how we would need to coordinate around other parties who would be using [it]."

The top-secret GoMentum Station tests driverless car technology at its facility and is described as "an Area 51 for autonomous tech"' – a reference the top-secret facility in the Nevada desert, where the US military test cutting-edge aircraft, allegedly made from UFO technology.

GoMentum Station is a 2,100-acre, disused World war II naval base near San Fransisco, with 20 miles of paved highways and city streets, used to recreate real world scenarios. It is still guarded by the US military and is closed off from the public and paved roads. GoMentum has grown to become the go-to testing ground for auto and tech companies to test their creations in secrecy.

A video of Honda's prototype self-driving car was shot in the facility:

USA Today reports that GoMentum owner Randy Iwasaki remained tight-lipped when asked by the Guardian on whether Apple was a client, "We had to sign a non-disclosure agreement with Apple. We can't tell you anything other than they've come in and they're interested," he said.

Google has already tested prototypes for on the streets of Mountain View, where it is headquartered, and predicts that self-driving cars will be ubiquitous by 2020.

The tech giant has visited GoMentum Station with a view to trialling driverless cars there, but Japanese automaker Honda has been the only one to sign a US $250,000 memorandum of understanding with the facility to begin testing self-driving versions of its RLX saloon.

Uber and robotics-focused institution Carnegie Mellon already had a partnership to work on robotics this past February that would include the creation of the Uber Advanced Technologies Center in Pittsburgh.

Nissan released its futuristic vehicle has part of its "plans to have commercially viable autonomous drive vehicles on the road by 2020," as reported by CNBC.