WASHINGTON -- A group of Democratic senators wants to improve the safety of transporting oil by rail in the United States, following a series of high-profile derailments that led to fires and explosions. Sens. Maria Cantwell (D-Wash.), Patty Murray (D-Wash.), Tammy Baldwin (D-Wisc.), and Dianne Feinstein (D-Calif.) on Wednesday introduced the Crude-By-Rail Safety Act, which would direct the Department of Transportation's Pipeline and Hazardous Materials Safety Administration to bar the use of older, riskier types of tankers and ask it to set standards for the volatility of gases in tank cars -- meaning they won't explode as easily.