According to two individuals that are familiar with the topic, the highly anticipated federal safety rule that will ensure tank cars that are hauling oil and other flammable liquids less prone to rupture is expected to be released on Friday May 1, 2015.The new rule is expected to require, among other things, thicker walls and stronger valves. Safety investigators have long said the older cars, DOT-111s, were prone to rupture in derailments. Recent accidents in both the U.S. and Canada have raised concerns about the newer models, CPC-1232s. Earlier this month the NTSB stated the CPC-1232s can overheat and explode in a fire and recommended they be upgraded or replaced within five years. However, the companies that own the tank cars claim the deadline can't be met.