jim.snowdon

It's the same principle that Brunel espoused when creating the Great Eastern - as you increase the size of a ship the volume available goes up by a cube, whereas the surface area (and hydrodynamic resistance) only goes up by roughly a square.

Mark 1s are a bit like the DC3 - conservatively engineered. As a steel structure, the only real impediments to life are corrosion and wastage of the structural components, and cracking, particularly at the welds. Essentially, much the same sort of considerations as apply to iron and steel railway bridges, some of which, as well all know are still in use with service lives considerably greater than the Mark 1 carriage. In some ways, the Mark 2 carriage may be a greater long term liability, as the body is part of the structure and is affected by corrosion problems.

The Cannon Street accident in 1991 did not involve Mk1 stock at all, but SR designed emu stock, where the principal issue was the absence of any effective means of preventing telescoping of the carriages. The earlier 1961 accident involved an SR emu and a BR Hastings demu, the latter being Mk1 stock. There was relatively little damage to both units, apart from some carriages of the Hastings unit being rolled over and body damage, but no reported separation, to one of the carriages in the latter unit. Critically, BR Mk1 stock remains authorised for use on the National network (unlike pre-Nationalisation coaching stock, which is barred because they do not meet crashworthiness standards).

But, it's all the same technology - a diesel generator set mounted in the car body driving electric traction motors on the bogies. The fact that on the Pullman sets one of the two motor bogies was on the adjacent car has nothing to do with the principles of distributed power, but was the consequence of weight distribution issues with the power cars.

In some ways, they were developed further - the Blue Pullman sets were essentially the same technology. So, in principle, were the Trans Europ Express train sets.

Not technically correct. Unlike most, but not all, pre-BR carriages, the body was inseparable from the underframe - its structural components were all welded directly to the frame. There are still quite a few Mk1s running around on the main line as it is - their issue was the lack of locking on the slam doors.

So am I. It's a pointless exercise in recreating something for the sake of doing so. There's nothing that is either notable or novel in its technology.

Lift over crossings used to be quite common on the first generation tramways, being supplied as castings that fitted either side of the through running rail, which remained continuous.

True, but there is about 5 years between the original class 126 design and the 123s, as well as the enlightening hand of the BR Design Panel, plus the experience of the D10xx locomotives.

Apart from the tramways in the greater Glasgow area, those in and around Portsmouth and the Huddersfield system were also laid to 4' 7 3/4" gauge so as to accommodate railway wagons. Elsewhere, the Cork city tramways were laid to 2' 11 1/2" gauge to accommodate 3' gauge railway stock, and the Dublin tramways were 5' 2 3/16" for 5' 3" railway stock. The Board of Trade (and their successors) were of the view that the width of ordinary railway flangeways was unacceptable for general street use. Tram flanges (and flangeways) have always been narrower than railway standards. They are also shallower, largely to do with coping with tight curves. The flanges on tramway wheels are more rounded and/or tapered on the backs, unlike the straight backs of railway wheels. It is all to do with getting round tight corners, and even then standard practice is to use a wider groove rail on corners to avoid the flanges becoming wedged across the groove. Traditionally, the same grooved rail did for check rails as for plain track, but modern practice is to use a rail profile that is rolled without a groove, the groove then being milled in to precise dimensions as part of the pointwork assembly. A few 2nd generation UK tramways use adjustable horizontal plates as check rails in pointwork, but that is more a consequence of railway designers trying to build tramways. My background has included both tramway maintenance and design (Croydon) and light railways with tramway geometry (Docklands).

BS11 once included a 126 lb/yd grooved rail section specifically for railway wheels.

Going by the Edgar Allen book, which dates from about 1950, 'railway' grooved rail was available and used for some industrial layouts. But, equally common seems to have been the use of 'guarded' rail - flatbottom rail combined with a bulb angle, and double rail. The first is visually difficult to distinguish from grooved rail once it has all been buried in the road paving.

The 123s and 309s, plus the 124s, were designed by Swindon (as I was once informed by the Chief Draftsman in the 1970s when I was often there researching GW wagons).

In 50 years of electrical and mechanical engineering my experience is that it is rare to find any SI units spelled out in full, with the common exception of Ohms when the omega symbol was not available (as now). The abbreviated form of the unit was normal, with the appropriate multiplier and generally no space after the numbers. The meaning was unambiguous with or without the space. I also discovered that it is normal, in engineering large items such as track layouts and structures, to dimension everything in millimetres, avoiding the use (and loss of) the decimal point (or comma, if you are continental European). Decimal points are for things that are machined. Getting back to the subject, in railway traction, it is normal to express the DC traction voltages as full numbers, ie 750V, 1500V, 3000V, but the higher AC voltages are virtually always expressed in kV.

Having been involved in the EMGS at the time, the move to 18.2mm was a consequence of poorer wheel profiles. At the time, the primary source of rolling stock wheels was Jackson, who at the time had been producing both 00 and EM wheels. The latter had a slightly finer flange profile, and ran fine on 18.0mm track. What happened next is that Jackson stopped making the EM wheels, Their 00 wheels, regauged to standard EM back to back, were an uncomfortably tight fit on 18.0mm track, hence the move to 18.2mm gauge. What happened next is that Ultrascale started making wheels for EM, but to the original thinner flange standard, effectively negating the need for 18.2mm. Except, EM, having adopted the 18.2mm standard, stayed with it, with wheels that were now a bit slacker in the gauge than necessary. With all EM point work being hand built of necessity, it left builders some latitude to build track with finer flangeways. I can remember building track with 1mm flangeways then and being complemented every so often on my P4 track (it wasn’t, but you wouldn’t notice). An underlying problem was a failure to appreciate the importance of check gauge, and not back to back. The situation in 0 gauge isn’t much better, in fact possibly worse, through a long standing decision to adopt a gauge for Fine Standard that was wider than the BRMSB’s recommendation, coupled with a woolly wheel standard that allowed for flanges to be anywhere between 0.75 and 1.00mm without adjusting the back to backs. At least Slaters, when they adopted their fine flange profiles increased the back to back to compensate. It also created the opportunity, 20-odd years ago, for the development of the 0-MF and 0-SF track standards. Since then, 0-MF, with its 31.5mm gauge, has become quite common amongst modellers looking for better appearance and running qualities.

Engine hours I presume?

82007 was one such example - there are published pictures.

As I understand it, all that a distant signal tells the driver is that, if On, one or more of the stop signals on the line of route within that signal box’s are of control has to be presumed to be showing a stop aspect. It doesn’t tell the driver which one, so it must always be presumed that it is the next stop signal. If it isn’t that one, it must be the next one, and so on until the driver reaches the section signal. Between those first and last signals, the driver is proceeding under line of sight. The only other certainty with a distant signal is that if it was Off, then all of the stop signals in the line of route were also clear. I’d agree with you as regards ‘block signals’ (or the nonexistence of them in UK civilian practice), but to be fair, the space between signal boxes is termed the block section. From what I can remember, the British Army did refer to block signals / block posts on their military railways.

The GPO made use of both the railways and the canals for trunk routes, essentially because a considerable mileage could be covered under a single wayleave, eliminating the need to negotiate with multiple authorities. On railway routes, there is the added complication of who maintains what. The GPO would not want railway linemen in amongst their circuits, or vice versa, and who would be responsible for the poles. Much easier to keep them separate.

It saved having to install anchor poles in the 'opposite side's' territory, as well as eliminating hazards when one side is isolated and the other isn't.

For all practical purposes the lines used by LU are considered as third rail electrification with an additional traction return rail to allow connection with LU's negative shoes. There is one location where genuine third and fourth rail electrification sit side by side, and that is at Queens Park, on the Watford DC Lines. All four tracks have third and fourth rails, but only on the centre pair and in the carriage shed, used exclusively by LU, are the fourth rails actually at a negative potential. The third/fourth rail section gap is at the country end of the through roads in the carriage shed.

Can't quote you a date, but my understanding is that the original 25kV electrification was confined to the freight route between Primrose Hill and Stratford. The conversion of the routes via Willesden only came about with the later conversion of the North London Line as a whole for TfL's services, when the 378s took over everything.

And that wasn't for very long either, as the North London Line went purely AC except for the last section between Acton Central and Richmond.

Until the 'back door' connection was built between Ruislip Depot and the turnback siding on the Met west of Ruislip, the only route for stock to reach the rest of the system was via White City (reverse) and Ealing Broadway, crossing over onto the District. The westbound Central line was in gauge for surface stock for a long time, only eventually becoming out of gauge through the track being lifted where it passes under the Ealing branch. That was only discovered after an empty stock move involving, I think, a Q stock car revealed that it had scraped the underside of the bridge. I think that was during the 1970s/80s, when I worked for LU, and well after the direct connection to the Metropolitan had been opened, when its importance as a surface stock transfer route had disappeared.

It's worth remembering that although they were wider across the bodies than most stock, they were also shorter, at a tad over 53', which would have reduced the centre and end throws significantly by comparison with, say, a BR Mark 1. They may not have presented as much of a problem as their width might suggest.