How long does it take for a car to burn?

The other day I saw a car burning on the shoulder. It took 15 minutes for the fire brigade to show up, and when they did, it took them 20 minutes to put off the fire. Also, I have a Siberian friend who told me that in the Siberian winter, if your car breaks down in the middle of the night and you can't fix it or get to a warm place, you should burn your car down if you want to survive. I was wondering how long does it take for a car to burn down completely.