Coded Manual ATP

The BVE sim is fun.

Er yeah, so there's loads of good info here (click). What happens is that the target speed displayed to you is the target speed on entering the next block, which is strictly speaking a smidgen below the maximum safe speed of the next block. So that, by the time you enter the next block, you will be travelling at or below the maximum safe speed for that block. If you are not permitted to enter block 2, the target speed in block 1 will be 0, so you must be doing 0 on entering the next block ----> you must stop before entering the block. The blocks are fixed and the beginning of blocks is marked either by a 2- or 3-aspect colour light signal, or a block marker board (reflectorised white plate with a diagonal red line running through it).

Thus there is SPAD mitigation rather than SPAD prevention. If you pass a BMB/signal with a target speed of 0 you will have entered a block with a maximum safe speed of 0 and so the ATP will put the emergency brakes on and bring the train below the maximum safe speed (which is 0 ----> the train stops).

However, certainly in the sim, and for all I know, this is true of real life, there is an element of SPAD prevention as well. If you wait too long to start braking, especially on the approach to a red signal/MSS of 0 and it doesn't think you're gonna be able to slow down in time, it will intervene. I've noticed on the sim it does this slightly before I believe it's strictly necessary to do so. I think it does also do this for simple straight reductions in maximum safe speed as well. I cannot tell you if this is true to life.

The take home message, though, is you should be doing the target speed before you pass the next block marker board/colour light signal. Before. So you need to start slowing for it. With skill and practise you can start slowing down at a good time - not too early, so as to waste capacity, but not too late either. You don't need to start braking the moment the target speed drops (well, sometimes you do, because of the size of the drop and the lengths of the blocks, but this is not a general rule) (in real life things may be different, perhaps you're expected to, I can't speak to that), but you do need to brake early enough to comfortably reach the target speed before you enter the block (alright, you can enter a little high on the sim, there's that 5 kph leeway there, but you don't wanna take liberties, again, I don't know about real life). In order to prevent overruns and collisions there are circumstances in the sim (the details of which remain mysterious to me) where, if you're approaching a block with a lower maximum safe speed and you're going too fast by a certain point (even if you're within the MSS for the block you're currently in) the ATP will intervene to try and prevent overruns, because it doesn't think you're going to be able to slow down in time. I assume this is true to life, because there are some pretty big drops in target speed.

This is how I thought the system worked. As I understand only the ATO part of the system receives block lengths from the PAC's.
So I'm guessing that say we've got a 109/68 code. AS long as you stay below 109 until the end of the block you'll be fine. It's only when you hit the start of the new block with a 74/68 code you'll get a brake application. This sound correct?

Clive's page also mentiones:


Whereabouts is this button located within the cab? So from the above I would be right in thinking when the ATP system applies the brakes, even if you are now under the MSS, the system won't release emergency braking until this button is reset as well?

Thanks for all for the help. I'm trying to see if I can get in contact with the original develop. Having a coding background myself, hopefully I'll be able to make the ATP & ATO systems even more realistic in the sim!

---

If I might add a few more questions while I'm here!



I had always thought that the CTBC on the 92 stock had a stowed position, then stepless braking, a coast notch or off and release and then stepless motoring arc. I read somewhere from a driver however there are actually a few different notches, anyone know any more? Roughly how many possible power and braking settings are there. I understand its more of a variable system but any guesses?