My experience has been limited to a typical 3 and 2 arrangement. However, the BARGAL runs three or four times a week with an additional set of DP, and averages about 11,000 feet. Many stack trains on the UP and BNSF are running 10K feet and more in and out of the LA/LB harbor.

Air problems with DP are ususally limited to electronic/radio issues, not train brake pipe telemetry as each DPU mimics the head end command, and also supplies/depletes the brake pipe simultaneously-unless the 'fence' is put up. With that radio transmission block, the engineer can make seperate commands to each DPU set (A,B or C, etc.), this being useful when making a "bump test": 1. Put up fence. 2. Release the air brakes 3. Command rear DPU to Run 1 and wait for it to 'bump' you forward. This will let one know whether the DP is TRULY functional.

Also, trailing DPU's will relay radio signals so 'in theory on paper' one could have a DPU every mile or so for as many cars and engines as you can provide.

The Mojave Sub employs a Rapid Responder, and exempt Mechanical Dept. employe who is usually summoned at the first sign of trouble and is based out of Tehachapi (not at the yard office or depot!) and is usually helpful, but is not always welcome due to conflicting work agreement interpretations.

I think the real problems will be logistics/dispatching (as pointed out by another contributor) and mechanical defects. And what about the youthful clowns who turn anglecocks 12,000 feet back? There was once a phantom(s) at East Empire who found it amusing to pull our ETD battery out and place it on the coupler while we made our setout there. At least we didn't usually have more than a mile round trip to put it back, but hey...

And what will become of the paramedics/etc. who are blocked while the conductor walks three or four miles?