If it's not feasible to just stop using the old DOT-111's in favor of a tank car that can survive common crashes, then degassing is an appropriate secondary measure. Given what's happened in several cases with untreated Bakken oil, it clearly falls into my 4th category (see [www.altamontpress.com]) and is ripe for regulation - which the state is doing. Source treatment to reduce or eliminate release is a common approach for hazardous materials and pollutants in general.

The thing to be careful about is to not apply the OH NO IT'S AN OIL TRAIN panic to all forms of transported crude. Bakken and similarly-sourced oils are unusually volatile. Other crude oils are not, and some (the heavy Canadian bitumens) are almost solid at normal temperatures and basically can't explode (or even burn easily). There's a tendency in the Press and the "advocacy" organizations to apply the most spectacular worst case everywhere; that doesn't work in the real world, but does get eyeballs on the web site ads (hardly anybody actually reads dead-tree newspapers any more). When politicians do that, bad things happen for both business and the end user.