> relatively cheap This is a surprisingly big factor: we get bitumen from refining crude oil whether we want it or not, and the endless demand for the lighter

> relatively cheap This is a surprisingly big factor: we get bitumen from refining crude oil whether we want it or not, and the endless demand for the lighter fractions of crude means we're gonna do a lot of refining regardless, so the market had to find something to do with the left-over sludge. Also pushing the price down, asphalt is almost completely recyclable: when a worn-out road surface finally gets dug up & replaced, the old asphalt doesn't go to landfill - it can be crushed up, melted down, and re-layed somewhere else. So much of the demand doesn't actually much reduce the amount on the market. Compare to, say, concrete: we don't make concrete unless we want concrete, it's not a byproduct of an otherwise-useful process; and once you dig it up, you can only re-use it as ugly gravel, you can't turn it back into fresh concrete.