Billionaire investor Warren Buffett is set to be a chief beneficiary of a bid by Senate Republicans to weaken new regulations to improve train safety in the $2.8 billion crude-by-rail industry, a key cog in the development of the vast North American shale oil fields. A series of oil train accidents, including the July 2013 explosion of a train carrying crude in Lac-Megantic, Quebec, that killed 47 people, led U.S. and Canadian regulators to announce sweeping safety rules in May. Among other things, U.S. oil trains are required to install new electronically controlled pneumatic (ECP) brakes.