Weighing over 100,000 pounds per car, traveling on steel wheels over steel rails, and powered by high voltage electrical systems, subway equipment, infrastructure and rolling stock are among the highest maintenance, wear and breakdown prone vehicles in any transportation system. The great mass and weight of subway trains exert extreme forces on every component of the system; from the electrical power required to accelerate and move them, to the mechanical forces necessary to brake and operate the subway vehicles, the forces exerted on track systems, and virtually every moving part of the trains.
Maintenance and repair (including re-grinding of the steel wheels and replacement of the tracks) are constant requirements in the efficient and reliable operation of subway systems; while the long term serviceability and structural integrity of major system components are likely to be foreshortened. Subway vehicles are expected to last only twenty-five years, even with a scheduled maintenance and repair programs including track replacement. This depreciation and accelerated obsolescence may well occur before long-term debt on the system has been retired, while the costs of equipment replacement should be expected to invariably increase.
The accepted fact throughout the rail industry that rail car and train manufacturers realize greater profits maintaining, repairing and replacing rail rolling stock than are realized by the initial sale of rail system equipment offers some indication of the ongoing financial burdens subway and all other forms of steel wheel, steel rail passenger systems place on the budgets and taxpayers of local and state government transportation agencies.