A federal safety rule to make railroad tank cars that haul oil and other flammable liquids less prone to rupture will be released Friday, according to two people familiar with the issue.

The highly anticipated rule probably will require that tank cars have thicker walls and stronger valves, along with other safety features. The Obama administration is issuing the regulation after a series of fiery accidents, including a July 2013 wreck in Lac-Megantic, Quebec, that killed 47 people.

The U.S. Transportation Department has taken some steps, including on April 17 announcing that trains must travel at 40 miles per hour (64 kilometers per hour) or slower in densely populated areas. U.S. lawmakers have pressed regulators to take further steps.

Reuters reported on plans to release the tank-car rule earlier Wednesday. The people familiar requested anonymity because the timetable hadn’t yet been announced.

Safety investigators have for years said older cars used to haul oil, known as DOT-111s, are prone to rupture in derailments. Recent accidents and spills in the U.S. and Canada also raised concern about newer, stronger models called CPC-1232s that the industry voluntarily agreed to build in 2011.

The National Transportation Safety Board said earlier this month that CPC-1232s can overheat and explode in a fire. The NTSB recommended oil tank cars be upgraded or replaced within five years.

Industry groups, including the Railway Supply Institute, which represents companies that own the tank cars, have said that deadline can’t be met.