The Pontchartrain Bridge is a 16-mile toll bridge that crosses Lake Pontchartrain in New Orleans. Currently, there are 7 toll booths, each staffed by an employee.

Since Hurricane Katrina, the Port Authority has been considering replacing the employees with machines. Many factors must be considered because the employees are unionized. However, one of the Port Authority's concerns is the effect that replacing the employees with machines will have on the times that drivers spend in the system.

Customers arrive to any one toll booth at a rate of 10 per minute. In the exact change lanes with employees, the service time is essentially constant at 5 seconds for each driver.

With machines, the average service time would still be 5 seconds, but it would be negative exponential rather than constant, because it takes time for the coins to rattle around in the machine. Contrast the two systems for a single lane.