The U.S. Department of Transportation’s Federal Railroad Administration (FRA) issued a final rule, extending the amount of time freight rail equipment can be left off-air (meaning parked with its air brake system depressurized) before requiring a new brake inspection, which is expected to reduce the number of idling locomotives. The final rule incorporates longstanding waivers for brake inspections, tests and equipment, while clarifying existing regulations and removing outdated provisions. The final rule extends the period of time "off air" from 4 hours to 24 hours.  You can read the final rule here