The longest commercial runway in the US is DIA (16,000 ft) followed by LAS (15,000 ft). Hot weather and high elevation are two factors that decrease lift and increase the runway length required to take off and land safely. The longest runways in the US are at Edwards AFB, California (39,000 ft).

The numbers on a runway refer to the compass direction, the runway number is the number of degrees past true north / 10. In other words if you are at the threshold of Runway 18 you are headed due south, and the other end of the runway is numbered 36. If there is more than one runway in the same direction, the leftmost would be numbered, say 18L and the rightmost, 18R. DFW has triple runways in parallel numbered 17L, 17C, and 17R (35L, 35C and 35R at the other end). LAX has 25L and 25R at the south side of the terminal and 24L and 24R at the north.

Which end of the runway is used depends on the prevailing wind direction, since it is preferable to take off and land into the wind.