The ponchatrain bridge is a 16 mile toll bridge that crosses Lake Ponchatrain. 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 15 per minute. In the exact change lanes with employees, the service time is essentially constant at 3 seconds for each driver.

With machines, the average service time would still be 3 seconds, but it would be exponential rather than constant, because it takes time for t he coins to rattle in the machine.