The weight of a railroad track depends on its specific classification, but for standard heavy-duty rail in the United States, 1 foot of track weighs between 38 and 47 lbs (based on one rail). Rail is officially measured in pounds per yard. The most common modern standard is 115 RE or 136 RE rail. A "136-pound rail" weighs 136 lbs per 3 feet (one yard), which equates to 45.3 lbs per foot. Since a standard railroad track consists of two parallel rails, the combined weight for one foot of the entire track structure (excluding ties and spikes) is approximately 90.6 lbs. In Europe and Asia, rail is measured in kilograms per meter, with a common standard being 60 kg/m, which translates to roughly 40 lbs per foot per rail. Heavier rails are used for high-speed or heavy freight lines to provide greater stability and durability under extreme stress.