The application of elasticity is very useful in evaluating the possible effects that a change in the price of a good or service has on total revenue collected. Consider the use of public transportation in a metropolitan environment. If the subway and bus system decides it needs more revenue, should it raise or lower the price of a ride? How will this affect the demand for other forms of travel such as car traffic and the use of taxis? Make sure to consider the elasticity of demand for the good or service in question as well as the elasticity of demand for close substitutes.