What's neat about the tracks is that Mattel had a variety of toy lines compatible with them. They marketed a Hot Wheels variant called Sizzlers that had a tiny motor inside, powered by a small nickel-cadmium battery. You charged it up with a battery-powered charger called the "Juice Machine" (sold separately) and the motor would make the car go. There was also a line of electric trains called "Hotline" that would run on the orange tracks; these were also charged with the Juice Machine.
My nephew ended up getting all my Hot Wheels tracks, and yes, they were forward compatible with new tracks and with all his 1:64 cars. When he was four he would stage elaborate crash scenarios on them, which he called "challenges". I would talk to him in the voice of the Homestar Runner character Stinkoman (an alternate, anime version of Strong Bad), e.g. "That was an exciting challenge! I was excited by the challenge!" Whenever he was playing with his Hot Wheels and I was around, he would exhort me to "do the challenge voice again!"