Interesting comment from an AOL message board from an air traffic controller with over 30 years experience, currently employed at one of the nation's busiest airports:
"For several years now the air traffic controllers, that work the system from the front lines every day, have told the FAA and Administrator Blakey that a system called ASDE-X is a necessary component to safe operations of ground traffic in the air traffic control towers. This system allows the controller to see and track via radar, all aircraft and vehicle movement on the airport surface area. It allows the controller to see if an aircraft is entering a area where it should not be such a crossing an active runway or taking a taxi route to the wrong runway. This system is especially helpful to the controller during times of bad weather or night time operations when normal visibility is restricted. This may have been the case in Lexington where reports state that the pilot, in the early morning darkness, may have taxied to the wrong runway. Most of the 35 busiest airports do not have this equipment. Those that have been scheduled such as my location are on waiting lists that stretch for several years from now. The FAA Administrators rule is if the airport has had several ground errors during a specific time period they will be more likely to receive the equipment rather than those with a safer operating record."
More info about the ASDE-X:
http://www.sensis.com/docs/128/