The department said Thursday the rule takes effect Oct. 1, and it brings railroads into line with rules for companies moving oil by pipeline and by vessel.
Railroads will have to provide Ecology with contingency plans detailing steps the railroad will take if oil spills or a substantial risk of a spill occurs during transport. Officials say they'll review each plan and require that they be tested through appropriate drills.
The state says California and Minnesota have implemented similar laws for railroads.
This fall, Washington is also beginning to require that facilities receiving shipments of crude oil by rail notify Ecology, which will share notice of those plans with local first responders.