Edwin_m

This was recognised as an issue with the BR ATP systems back in the 90s. In some places "infill loops" were provided to act as a continuous balise. There was also a "release speed" which drivers could accelerate to if they could see the signal had cleared, but if was still red the system would still be able to stop the train, beyond the signal but within the overlap so not at risk of collision. With continuous transmission, ETCS Level 2 avoids this issue completely.

I'd guess that it's because the haul roads are slow speed and they want to do the minimum of earthworks for them (to reduce time, cost and impact). So they may have to zigzag to get a reasonable gradient over even minor undulations in the terrain.

Reminds me of the Simpsons episode where the family car is T-boned and pushed along in front of an Amtrak train, and Homer climbs out to get some food from the lounge car.

The selfie stick question relates to the clearance to platforms. For clearance to bridges which is the issue here, as far as I can see there's no hazard to people if it's too tight, just a risk of arcing which may cause some wire degradation and a power outage that can immediately be reset.

Usual practice would be to provide electrification clearances where practicable, but not to re-build structures if the only reason to do so would be to provide those clearances. Are there any arched bridges that are being left largely alone, with both tracks continuing to pass through the same arch? If so these are likely to need work as part of any future wiring (unless electrification cost saving initiatives find ways to avoid this in the meantime).

Moorgate and the ECML will be Level 2, which is already running on Thameslink. It produces some capacity benefit from being able to optimise block sections without the constraint of lineside signals, and the absence of those signals also reduces costs somewhat. But it remains fixed block with lineside train detection equipment. Moving block under ETCS doesn't happen until Level 3, which isn't in service anywhere.

Arguably all signalling is digital, as it works with binary states (signal off or on, point normal or reverse). A mechanical interlocking does the same job as a digital logic controller, just using a different technology.

Not sure this timeline could have worked. The ECML was finished in 1991, by which time all the Regional Railways Sprinter fleets had been ordered and most of them delivered. The timescale for TPE would probably have been similar to the 7 years from approval to completion of the ECML, meaning that the only possible saving would be to soldier on with DMUs for longer on Thames and Chiltern and replace them with cascaded Sprinters instead of building the Turbos.

Reminds me of a cat called Moses we had when I was a child. My mother decided he didn't get enough exercise and he was put in the car and dropped off half a mile away to find his way home. General consternation when he wasn't seen for some hours, until we realised he'd managed to sneak in unnoticed and take up his usual position on top of the boiler.

Resembling in name only the sort of bank activity that most of us come across, but traders in merchant banks need access to data within milliseconds in order to carry out transactions at exactly the right time to maximise their profits. Time lags of 1 to 2 seconds are typical for railway signalling.

I wasn't trying to suggest that railway signalling was particularly comparable to bank systems, rather the narrow point that card readers employ coding that ensures they can work securely over a communications channel that isn't in itself secure against tapping or other interference. Potential fraudsters would have a big incentive to crack that coding, but as far as I know nobody ever has. The vital communication between computer-based interlockings and the trackside employs similar principles to make it extremely difficult for anyone to hack into it even if they have access to the communications channel.

Looks like the two side pieces would have to be placed at exactly the correct spacing and exactly vertical, otherwise the top piece won't fit.

I'd say they can be trained if the incentive is significant and immediate, whereas dogs don't need that sort of motivation or at least not to the same degree. Having said that Gizmo knows he shouldn't be in the kitchen and will leave if I point this out to him without me needing to shout (except when there's something good cooking). He clearly knows what is expected of him but chooses to ignore it.

I don't think the new station site is chosen to avoid the old one - it's the logical place to put it particularly so the main entrance is alongside Moor Street and as close as possible to New Street without demolishing the Bullring or going underground. If the old building had been in the way of this site then I guess they would have considered moving it, but I suspect we would have ended up with a station somewhere a bit less convenient instead.

That would be consistent with the behaviour of governments over the past decade or two, but they seem to be taking a different line now. Possibly some spin doctor has decided it's counter-productive to announce something that won't be completed for some years, or to announce it multiple times, or to announce something that isn't in the "north".

Many places ban dogs but make an exception for guide dogs, which will be specially trained and can probably be relied on to behave. Cats are well known to be untrainable.

There will be an entrance to the station at that end, but the alignment means the old building is actually a short distance away from it, so it's difficult to see how it could have been incorporated as part of the operational station. To do so would probably have required drastic changes in the historic structure in any case.

The Sheffield-Rotherham tram-trains have the ability to run on 25kV as well as 750V, but it isn't used. The overhead line on the Network Rail section is designed to be convertible to 25kV with minimum modification, although someone at NR later said it would have been better to provide standard 750V equipment and replace it if that section was ever energised at 25kV. I understand that there is a risk of damage if a system configured for 25kV is fed with 750V (too much voltage) or vice versa (too much current), so if the tram-trains lose power for more than a certain length of time a voltage detector circuit is employed to ensure closing of the circuit breakers to send the power to the correct set of traction equipment. This requires a longer neutral section (measured in running time) than typical on a 25kV system. I believe the old 25kV/6.25kV system did something similar, with spectacular results on a couple of occasions when it didn't. Lost track somewhat of where we got into this bit of discussion, but in an attempt to get back onto topic will point out that TfGM has been looking at ideas for tram-trains for at least 20 years, and these would require dual-voltage vehicles. The tram-trains now being delivered for Cardiff Valleys will be 25kV or battery only.

Indeed so, but my point is about how the rails got from the end of the existing track to where they are needed. For a normal renewal a rail train will drop rails at the trackside, and I believe this is done by anchoring one end of the rail and slowly drawing the train away so the rail comes off (I think it sits on rollers on the train). But that can only be done if there is a track there already.

My understanding is that they hacked the TV guides that appear on smart TVs to show their own message instead of the programme information. These will almost certainly have a gateway to the internet so programme providers can log in and provide the details that are to be broadcast. Such systems are able to be hacked, most likely by someone getting hold of the password. The are also not "vital" systems in the engineering sense - it's unlikely anyone will die if the TV programme fails. Railway signalling systems are built to much higher integrity and separated from public access in the ways described by others. They are also protected by interlockings which only respond to requested actions if safe to do so, so even if someone got access to the control system it would be extremely unlikely that they could cause a derailment or collision.

I'm not familiar with the details for ETCS, but I know the SSI systems from the late 1980s employed digital coding of the data streams to ensure that controls and indications wouldn't be acted on if they were corrupted or, for example, the cable to the trackside was inadvertently connected to the wrong interlocking cabinet. That's a much higher level of protection than the older relay interlockings, where most of the trackside cables just carry simple unencoded currents (although the short tail cables from the trackside modules to the actual equipment still do this). It's similar in principle to the sort of coding that ensures that credit card transactions can be securely processed when the reader is only connected by non-secure wifi and landlines.

Down is towards Bletchley. This was previously Up, presumably because the line was originally built as a branch from Bletchley to Oxford so the LNWR's trains from London would use it in that direction. So it's a rare example of Up and Down being reversed, which wouldn't have caused any of the usual problems because in most respects it's a totally new line. On the tracklaying question, how are the rails positioned with no tracks to bring them in on? Does some suitable off-road vehicle have to drag a long string of rail along the ballast?

You also need to be aware of the heat dissipation in the diodes or resistor, which is equal to the voltage dropped multiplied by the current passing through. The power rating of the device needs to be greater than that figure, or it will burn out.

That might depend on whether aerodynamic and other resistance forces have been considered. I seem to recall Dionysius Lardner ignoring these and predicting an improbably high exit speed if a the brakes of a train were to fail in Box Tunnel. I make the speed without resistance to be around 170mph, in a lot less than three pages, so I assume the calculation allowed for these resistances.

Puts my own little faux pas into the shade - needing 10 battery holders for some kit I was building as a placement student in an electronics workshop, and ending up with 10 packs of 10. I found an empty drawer in one of those metal cabinets those workshops always seemed to have, labelled it "battery holders", and for all I know they're probably still there 35 years later.