If you own Tesla's Model S electric car, you can travel for free along well-traveled highways in North America by accessing strategically placed supercharge stations. The trouble is, only 8 of those stations exist today. But that number is going to change rapidly. This summer, Tesla plans to grow that number to 27 stations. This fall, Elon Musk's company plans to cover "most metropolitan areas." Fast froward to 2015, and 98% of the US and Canada will be covered, as depicted in the image above.

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