With the spectre of the Positive Train Control mandate looming over small railroads, it’s not only the short-line railroads impacted. Long-distance rural lines can have considerable dark territory. Such railroads may have substantial cost added to their capital budget by PTC. Without radio contact, such railroads have been limited in dark territory to restricted speed 10-25 mph instead of the 49 mph they might otherwise run in dark territory.
- microwave links - much too expensive for distance, terrain vs. low train count
- leased (dedicated) phone line - same as microwave–too expensive
- PSTN/POTS - use a typical “interconnect” for two-way radio.
The latter option may be much more economically feasible for many rural railroads. This option has not been evaluated for compliance with federal railroad regulations. Railroads in the Rocky Mountains, with vast individual tower coverage areas, have long used DTMF selective calling of dispatch to avoid dispatchers being overwhelmed with constant train chatter.
CONOPS of POTS-linked rural dark territory railroad radio: dispatch has multiple phone lines, all ringing for the same number dedicated to inbound radio calls. Different branches dispatched by distinct dispatchers could obviously have separate phone numbers. The caller ID of the individual interconnect into dispatch identifies the approximate subdivision the train is on (not for legal purposes but for convenience). Cell phones could be used in place of POTS if more economical.
Train to dispatch: train keys up mic, dials dispatch phone number like a standard two-way radio interconnect call. Train engineer uses standard radio message protocol to talk to dispatch, then train hangs up via DTMF. Can use single frequency for network to keep any other trains advised, although dark territory and long distances imply long blocks.
Dispatch to train: dispatch calls phone number of interconnect they believe train is in range of. Train engineer answers via DTMF, uses standard radio protocol to talk. Dispatch hangs up phone, train engineer sends DTMF to close link if phone line hangup not detected.
Besides the typical radio base station tower and antenna, selected with sufficient overlap in 49 mph-desired territory, the Zetron Model 30 is about $600. Cost of power and phone connection trenching might be mitigated by sharing with cellular towers or power utility company where feasible. Naturally, a more advanced interconnect could be used to control and monitor railroad switches and the like, also enhancing railway safety. In regions hauling relatively benign cargo with a single train per day, some in the industry have felt PTC requirements were two stringent. If it’s not too late, some waivers might be obtained for a time at least by using ideas as above, pending compliance with all applicable regulations.