Direct traffic control

Direct traffic control (DTC) is a system for authorizing track occupancy used on some railroads instead of or in addition to signals.

In DTC, controlled tracks and sidings (those requiring authority from the train dispatcher to occupy) are divided into pre-specified blocks.

In addition to being listed by milepost in the railroad's timetable, block limits are delineated by conspicuous signs along the tracks.

However, in DTC territory all sidings operate as non-controlled, restricted speed track and there is no safety consideration in a train occupying it without central authority to do so.

Barring human error, this ensures that no two trains are ever authorized on any given piece of track at the same time, thereby preventing collisions.

When this occurs, the authority is marked as "joint," and all movements must be made at restricted speed, which allows stopping within half the range of vision.)

In modern implementations, dispatchers rely on computerized systems to monitor trains that have received authority.

A member of the train crew, usually the conductor, copies the dispatcher's mandatory directive onto a prescribed form.

A mandatory directive cannot take effect until the dispatcher has said, "That is correct," reducing the potential for human error to cause an accident.

Train crew member: "This is a repeat of mandatory directive issued to the forty-three twenty-one, four, three, two, one, with engineer Johnson.

Train crew member: "This is a repeat of mandatory directive issued to the fifty-four thirty-two, five, four, three, two, with engineer Smith.

Train crew member: "This is a repeat of mandatory directive issued to the forty-three twenty-one, four, three, two, one, with engineer Johnson.

"Once train 5432 has fully entered the siding and restored the switch for movement along the main track, they will call the dispatcher and release Anna block, using the following format: Train crew member: "The fifty-four thirty-two, five, four, three, two, would like to release our authority in one block, Anna, over."

Train dispatcher: "Engine fifty-four thirty-two, five, four, three, two, is releasing authority in one block, Anna, over."

This generates additional radio traffic but ensures that there is no confusion as to which train is allowed to enter a given block at any given time.

A DTC authority given under this practice will include a phrase such as "This line is not in effect until after the arrival of train 7940."

Entering a block in which the train is not authorized or releasing a block which the train still occupies is considered a main-line violation by the Federal Railroad Administration and carries stiff penalties for all crew members, which may include time off from work and the suspension or revocation of the engineer's license.

The Alaska Railroad changed its Track Warrant Control territory to DTC and is also implementing CTC in high-traffic areas.

CSX uses DTC on their former Georgia railroad mainline from Scottdale, just east of Atlanta, to Augusta.