The following are some example: A repaid transit system could increase travel speed (saving time for travelers), reduce accident cost, and reduce private-vehicle operation costs; a water project might reduce flood damage, provide water for residential and other use, and improve effluent dilution for water-quality management: a new fire station may reduce operating costs of an older facility and reduce prospective fire loss in a service area: a word processing system may reduce labor costs, material costs, and filing expenses. It is critical, however, that the analysis focus on the factors that are different in the options under consideration. Nothing can be gained by examination of factors that are not changed by thedecision. The principle seems too simple to matter, except that much policy argument takes place about elements that will not change regardless of the choice selected.