Part of the challenge of these advanced systems (which some regulators think are "available now with 'off the shelf hardware,'") is the complexity of enforcing trains to stop at the limits of their authority without unnecessary false alarms, etc. UP is testing the system in two locations to see how it behaves in different locations in terms of geography and traffic density. Both are "overlay" systems in that the existing traffic control systems (Track Warrant Control or Centralized Traffic Control) remain. An on-board computer calculates braking distance to the end of the train's authority, provides the crew information about the train location and "enforces" if the train is not handled consistent with upcoming requirements. Besides the UP tests, NS and CSX are testing a similiar systems in S. Carolina and BNSF in Illinois. Another system being tested on the UP in Illinois between Joliet and Springfield is being deactivated and moved to a research facility in Colorado for further testing. Finally, ATK has a system in operation in Michigan west of Detroit.

As these pilot projects mature, you may begin to see wayside signals being removed and more and more communication between trains and the Dispatcher using digital radio.