The Traction, Tread wear and Temperature ratings on tyres come from a US Federally mandated test regime. If the tyres are to be sold in the US, they must have them. Traction is an artificial WET traction test where the tyre is run through basically a large puddle (cant remember the speed though). It is a measure of resistance to aquaplaning. Temperature is a measure of the tyres resistance to damage caused by continuous high speed running. It is tested by mounting on a machine which spins the tyre at various speeds and internal pressures against a rough roller which varies in surface temperature. The force of the roller vs tyre can be changed too. Therefore a 2000kg car doing 160kmh for 6 hours in the Arizona desert at 85* road temp with a slightly underinflated tyre can be simulated if required. Of course the test is actually standardised. The tread wear is also from an artificial testing method using computer driven machines. It is used more as a measure of tread hardness rather than mileage.