What happens when the supply of railcars exceeds demand? When there isn’t enough carload traffic to keep all the available cars busy? An oversupply of cars develops -- an excess or surplus of cars that must be dealt with.
The rail network is finite. There is only so much space for the railroads to get their work done and they don’t need extra cars getting in the way. The rail network becomes congested when things get busy. Surplus equipment exacerbates congestion, so railroads want these excess cars to be stored out of the way. The responsibility to store these surplus cars falls to the owner of the cars: either the railroad itself, another railroad, or the shipper/ leasing company that owns the car. Regardless of the reason, a surplus of railcars is an issue that needs to be addressed. Unless the car owners’ answer is to retire and scrap the car, storage will be needed.