Total Horsepower (\( HPt \)):

\[ HPt = HPe + HPl + HPh \]

Where:

• \( HPt \) is the total horsepower, in horsepower (hp).
• \( HPe \) is the power to drive empty, in horsepower (hp).
• \( HPl \) is the power to drive in level, in horsepower (hp).
• \( HPh \) is the power to lift materials, in horsepower (hp).