Just as advances in computers and communications technologies are facilitating advances in highway and air traffic control, so are they contributing to a new generation of automatic train control systems. These systems seek to make train schedules, and thus train service, more reliable. There, the blocks used to control train movement may be 50 or more km long, meaning that no train may enter these long blocks while another is within them. The long blocks seriously constrain the movement of trains in a network. Components of an automatic train control system must include a capability to monitor every train in a rail network and, associated with that train, the shipments contained in the railcars, including their expected arrival time at the destination. Vehicle location systems such as satellite-based global positioning systems are an important element in location tracking.
In order to be truly effective, automatic train control must reside within a broader companywide structure aimed at managing operations. The structure includes explicit long-term policy evaluation, which helps to plan resource allocations in support of operations.
The most basic decision that an organization must make is whether to schedule trains at all or whether it is adequate to dispatch a train when sufficient traffic is acquired (i.e., a tonnage operation). This type of operation may be most wise for short-line railroads that feed specialized commodities (e.g., ore or grain) to large railroads. The automatic train control system for the large railroad must be able to accommodate the movement of this train to a yard for subsequent dispatch. The tactical scheduling of trains occurs every two to four weeks, with real-time scheduling of tonnage loads in between. Computer-aided dispatching and automatic train control provide capabilities for real-time management of operations. They also provide evaluation data to use in modifying tactical or schedule policy decisions. The system, in addition to monitoring the location of all trains, must contain information on the status of every section of track and whether trains are complying with automated instructions. The system will thus use train control to improve efficiency but also improve safety by assuring compliance by train crews.