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Glossary

Power to weight ratio (P/W)
A ratio that measures the amount of power per weight unit, thus expressing the ability of a train to gain speed and to get over grades. In the U.S. hp/hon (horsepower per ton) unit is used.
Tons per Operative Brake (TOB)
A ratio that measures the amount of weight per train vehicle with operative brakes, thus expressing the ability of the train to stop, especially on downgrade.