[aussiesteve]

Cooee BW,
I am scratching me cranium, having chanced upon a facet of modern day train operations here in NSW.
This being the first time that I have encountered this concept.
Anyhoo, many moons ago, in 1990, there was a rear ender prang in the tunnels on Cowan Bank.
Soot belcher 3801 stalled on the 1 in 40, due to a nefarious wagon handbrake discovered later.
The hystericals set back dropping sand in an attempt to get mobile.
But, in doing so, the signal behind them cleared allowing the following interurban emu to slam into it.
It hit the fan, and henceforth all motive power had to have DEsanding apparatus.
Air blowing behind the wheels to remove the sand deposited in front of the wheels for traction.
It became VERBOTEN to use excessive sand to maintain traction.
The sand deposited on the rail head insulating the wheels from the signal track circuits for automatic signals.
AND, should a loco pump out too much sand, Train Control had to be notified.
The sanding gear isolated, or if unable to do so, the train worked under Block Working to prevent a following train.
OK, this was always a bug bear to me in the ensuing yearly accreditation exam.
HOW much sand can you use to maintain traction ?
I'll use as much sand as necessary to keep the thing moving.
WRONG !
OK, to the latest Train Operating Conditions manual scrounged today.
EMU and DMU units here in NSW do not possess sand.
However, today our DMU units must possess a "Track Circuit Assistor"
QUE Mr Fawlty ?
This dingus apparently slings underneath the DMU between the wheel sets to act as an antenna.
This to increase the rail voltage at the wheels to ensure positive track circuit activity.
Have you heard of, or seen this in use in the UK ?

Diesel Multiple Unit trains (DMU) fitted with Track Circuit Assistors (TCA's)
The following DMU trains are approved to operate under track signalling (block working not required), provided that at least one TCA per train is operational:
• Endeavour
• Xplorer
• Hunter RailCar

When both TCA's on any train are offline, failed, or inoperative, block working requirements as shown in Sydney Trains Network Rules, NSY 512 Manual block working, shall apply when operating over the track circuited lines indicated in Figure 4 in section 2.16.2. In this case, Xplorer and Endeavour are exempt from mandatory block working between Kiama and Bomaderry.

E GADs what will the boffins come up with next.
Steve.