Re: why do tyres burst when vehicles are going at very high speeds on roads?

Without more specific information about the tires (their speed rating, age, tread condition, etc), it is impossible to say. But I can offer you a few hypotheses:

1) speed exceeded tire rating: tires are rated to perform up to a certain speed. If you drive faster than the rated max, you run the risk of damaging the tire because of heat build-up (could cause tread to come off, weakening the tire) and overinflation (could cause tire to burst).

2) hot outside temperature: tire pressure is dependent on temperature. Check your tire pressure in the morning when the outside temperature is cooler, and then again in the afternoon when the outside temperature is at its peak. You will notice that the tire pressure has increased. Overinflation can cause tires to burst.

3) poor tire condition: weak tires are more susceptible to failure for obvious reasons. It is important for safety that you regularly check your tires for wear, pressure, and other damage.

So, while I can't answer your question with any accuracy, I hope I've given you a few things to think about. If you'd like more information, How Stuff Works has some great explanations about tires and pressure gauges, and the Tire Rack has a good description of speed ratings

Drive safely!

Kieran