Why does gravel around railroad ties smell bad?

Also, many passenger trains flush the toilet waste right onto the tracks. Combine that with creosote and yes, it will smell.

Railroad ties are soaked in an oily substance called creosote to keep them from rotting. I suspect that is what you smell. There is a desert bush called creosote bush that smells the same way, especially when it is hot.

I've never noticed but what you are likely smelling would be the creosote in the ties, there is nothing in the ballast (gravel) itself that would smell bad unless you may be near an industrial location with chemicals spilled. Passenger trains do NOT flush their waste onto the tracks, that has been outlawed for years and years, it goes into chemical holding tanks, somewhat like the tanks in RVs. There would be no methane in the ballast, methane is caused by organic compounds breaking down.

I have to say, I am one who loves the smell of creosote.

dead animals, chemicals etc.