Replacing signals when a train is approaching

" said:

Waterbeach doesn't have a TRTS plunger but a seperate set of 'treadles' which become active when 'stopping' is selected. Once the train departs the station and activates this treadle the barrier sequence starts and the signal clears after about 15 seconds.

Are you sure about that? My understanding was that it is triggered by occupation of the platform track circuit for 30 seconds (possibly with a treadle as backup). I'm sure I've seen the signal clear before the train departs.

When we do annual tests on these crossings all the timers have to be checked very closely. There is only a ten per cent tolerance in the standards, which does not leave any room for variation at all on some of them, which can be as little as three or four seconds.

Where you have crossings close to stations and stop/non-stop controls such as Bradford-on-Avon, the protecting signal will generally be allowed to clear once the barriers themselves have started to lower.

(it's I think it's a horribly dangerous crossing for other reasons - at rush hour it regularly has road traffic backed up across it)

Anyone who stops on a crossing should't retain their driving licence. Incredibly dangerous.

Whilst I have no sympathy whatsoever for those who blindly drive onto a crossing when their exit is clearly blocked (and even less sympathy for those who drive with a mobile phone pressed against their ear!), there are some locations where the road layout means that it's inevitable that even well-driven vehicles will block the crossing at some point. One of the crossings (CCTV, in this case - at Luffenham, if anyone wants to look at it in Streetview) on our patch has a right turn into an industrial unit immediately after the crossing, close enough that an HGV waiting (for oncoming traffic) to turn into the unit will be foul of the crossing - even if the driver stopped short of the crossing to wait for a gap in traffic, there's no guarantee that he'll be able to make the turn by the time he's negotiated the crossing and reached the junction! Another example is somewhere on the Southern (possibly Wokingham?) where the crossing is immediately followed by a roundabout - any long-ish vehicle stopped waiting for an opportunity to enter the roundabout will, again, be foul of the crossing. That's exactly why AHBs are only permitted where the road layout (and other factors) meet strict criteria!

I am intrigued with the minimum 27 second time, because I'm sure that an AHB I used to drive my car across regularly violates it.

The crossing is at Great Coates station, and on the Down line the crossing is immediately off the platform end - the signal is also at the platform end, only a few feet from the crossing.

The sequence I've witnessed several times is: train draws to a stand in the station with the barriers up, sequence starts and barriers lower, then train starts as soon as the barriers are down and is on the crossing almost immediately. Being a car driver I can't tell you the signal aspect, but I really don't think there is 27 seconds from the amber road light coming on to the train being on the crossing.

(it's entirely possible my subjective timing memory is wrong of course. I think it's a horribly dangerous crossing for other reasons - at rush hour it regularly has road traffic backed up across it)

I'd imagine the signal won't clear until the barriers are proved down which gets rid of the risk of a train appearing with little warning.

In the US and probably elsewhere they have traffic light preemption. This is an early warning from a level crossing (grade crossing) that a train is approaching and alters the traffic light sequence to release any trapped vehicles on the crossing. Not sure if that's done in the UK.

Bradford-on-Avon town council did a good one at Greenland Mills AHB. They narrowed the road in such a way that a car waiting on one side of the crossing would block the exit of a car coming the other way. It didn't last long.

" said:

In the US and probably elsewhere they have traffic light preemption. This is an early warning from a level crossing (grade crossing) that a train is approaching and alters the traffic light sequence to release any trapped vehicles on the crossing. Not sure if that's done in the UK.

Bradford-on-Avon town council did a good one at Greenland Mills AHB. They narrowed the road in such a way that a car waiting on one side of the crossing would block the exit of a car coming the other way. It didn't last long.

It's called phased advanced. We have a hurry button on Crawley High Street CCTV on our panel 7 which when pressed causes the road traffic lights at the road junction immediately beyond the crossing to advance though the sequence to give the traffic coming over the crossing a green road traffic signal to clear the crossing. We also have a sealed key release to turn the road traffic lights off, only to be used in extreme circumstances of which we've never had to do that in the 13 years I've been at TBASC. I also believe Lancing has one for one of their CCTV crossings.

Getting back to N/S selectors we have one for Parsonage Road AHBs for trains calling at Littlehaven or not, set on "N" and the signal clears straight away set on "S" and there is a delayed clearance based on TC occupation.

" said:

" said:

In the US and probably elsewhere they have traffic light preemption. This is an early warning from a level crossing (grade crossing) that a train is approaching and alters the traffic light sequence to release any trapped vehicles on the crossing. Not sure if that's done in the UK.

Bradford-on-Avon town council did a good one at Greenland Mills AHB. They narrowed the road in such a way that a car waiting on one side of the crossing would block the exit of a car coming the other way. It didn't last long.

It's called phased advanced. We have a hurry button on Crawley High Street CCTV on our panel 7 which when pressed causes the road traffic lights at the road junction immediately beyond the crossing to advance though the sequence to give the traffic coming over the crossing a green road traffic signal to clear the crossing. We also have a sealed key release to turn the road traffic lights off, only to be used in extreme circumstances of which we've never had to do that in the 13 years I've been at TBASC. I also believe Lancing has one for one of their CCTV crossings.

Getting back to N/S selectors we have one for Parsonage Road AHBs for trains calling at Littlehaven or not, set on "N" and the signal clears straight away set on "S" and there is a delayed clearance based on TC occupation.

Turn them off? What good would that do?

" said:

" said:

Waterbeach doesn't have a TRTS plunger but a seperate set of 'treadles' which become active when 'stopping' is selected. Once the train departs the station and activates this treadle the barrier sequence starts and the signal clears after about 15 seconds.

Are you sure about that? My understanding was that it is triggered by occupation of the platform track circuit for 30 seconds (possibly with a treadle as backup). I'm sure I've seen the signal clear before the train departs.

Hi Clive, yes im pretty sure although you've planted the seed of doubt now! Some of the PM peak services are extremely busy from Cambridge and we stop at Waterbeach for a lot longer than 30 seconds and the signal never clears.

If you depart and accelerate to quicker than about 15/20mph you'll be stopped at the protecting signal whilst the barriers are lowering. Im driving up there twice this afternoon so i'll do a little investigation!

With AHBs there is usually a pair of strike in treadles at the extreme end of one track circuit, and either track occupied or one of the treadles down will initiate the sequence. Is there a block joint by your treadles?

TomF, I don't think any AHBs are allowed to be commissioned any more, irrespective of the intricacies in road and railway layouts.

" said:

With AHBs there is usually a pair of strike in treadles at the extreme end of one track circuit, and either track occupied or one of the treadles down will initiate the sequence. Is there a block joint by your treadles?

TomF, I don't think any AHBs are allowed to be commissioned any more, irrespective of the intricacies in road and railway layouts.

I think instead you have to install an ABCL (basically the same thing but with Obstacle Detection and ERTMS capable).

Hope this helps,
Jamie.

" said:

(I think it's a horribly dangerous crossing for other reasons - at rush hour it regularly has road traffic backed up across it)

It would be mitigated by the fact that a train is starting from a stop and presumably wouldn't proceed if a car is straddling the crossing right in front of it. In the case of stopping trains I'd imagine the signal won't clear until the barriers are proved down which gets rid of the risk of a train appearing with little warning. I grew up in the area and at the time the crossing was modernised in the late 80's the housing estate on the up side of the line wasn't there, Neither was Europarc and in general I don't think traffic was so heavy.


I suspect it wouldn't get commissioned as an AHB today.

Quote:

I'd imagine the signal won't clear until the barriers are proved down which gets rid of the risk of a train appearing with little warning.

Tom, as has been said that's not the case with AHB's. The signal will clear when the sequence has been initiated for long enough to prevent the train arriving before 27 seconds. If starting from a stand this is very likely to be around 10 seconds after the crossing sequence has initiated. (As Clive said actual timings depend on the distance from signal to crossing.)

FF

Rather wide of the mark there, I'm afraid - an ABCL is rather a different beast, in operation, to an AHB, and only really suitable for relatively quiet roads

There are two further treadles, one of which is slightly beyond the car stop and the other is level with the platform ramp of the down platform at the Grimsby end.