I'm not sure your north and south are right there - but I see now that there is no dashed line on the west because the pavement is wider, so no need for an arrow and words from the south to warn you not to drive on he pavement. From the north there is little time after the roundabout to see and react to the dashed line on the east side before you go into shadow, so the arrow would certainly help. And that asymmetry is even worse than that - if you drove north without having to move over, you would be preconditioned to come back south without doing so too.

Never eat the stuff.

There doesn't seem to be any simple way of finding out where signs are mandatory, but the form they should take if present is prescribed (the word used) in The Traffic Signs Regulations and General Directions 2016. The Traffic Signs Manual generally repeats this in something resembling comprehensible English (which the TSRGD 2016 are not), but are all older than 2016 so may no longer be correct.

In the case of units on bridge signage, I found a Sunday Times report that a 2014 DfT^» (Department for Transport - about) consultation proposed making dual units compulsory on new signs but let old ones stay. That's consistent with the 2013 TSM^▸ (Track Section Manager) saying metric is optional, and the TSRGD 2016 only showing the signs with both - but I wouldn't put it any stronger than that. Distances (along the road) are of course still to be given in miles.

I guess they might want prove to buyers there is no established right of way?

For arch bridges the meaning of "advance" is a bit puzzling, since they are doing two things. At the bridge, the main concern is getting vehicles into the right bit of the road. At the last turning, or in advance, the concern is to prevent overheight vehicles going that way and diverting them. So the inserts within advance direction signs are the same as other low bridges, while the markings and the "final warning sign" (use middle of road) are specific to arches. But then, for some reason, single triangular signs at the last turning (with no "route avoiding" message) or further away have a little arch in them. Since that last turn can be miles back (needing a distance label) or right up close (as in Hatchet Lane), they may or may not be "in advance". Anyway, what I meant was something at least half a mile away.

The rules - Traffic Signs Manual: Chapter 4 - say this about composite bridges:

The signage it specifies for an arch bridge of this width includes a single chord (as on the north side) plus the roadside signs at the bridge which look right. There should also be advance signs and "route avoiding" arrows on other signs; I din't know if they are present here.

How often do you see an arch-shaped dangly thing under a bridge? Not often! The manual has more to say about them (straight ones are also used):

And finally, road markings, which are in TSM^▸ (Track Section Manager) Chapter 5:

Note: the current chapter 5 is dated 2003, so its references to chapter 4 are out to date - that is now the 2013 edition.

From what I've seen, Tp (it was T(p)) is Hitachi's functional type code, which defines what can go where in a unit and it still work, but TPS is painted on its end. The same apples to the 'e' meaning "has engine", and some of the numbers in functional types also appear in paint (along with S, C, or F) - but not necessarily in the same order.

As to where bits like the power converters and APS go, I only have a scruffy little diagram showing them as part of the combined "Traction/APS system" on motor vehicles. That looks logical, given that they do have to operate powered solely by the on-board GUs on 800/802s. How intermediate power is routed from transformer to APS is less clear to me - and is it AC (up to 1800 V) or DC^▸ (Direct Current) (up to 3000 V)? Either way it's one of the reasons for all those big cables between the carriages!

Churchward PLC was part of Carillion, and a winding up order was granted to the Official Receiver in June. So what has happened now? All it seems to have done was own and manage property, so I guess this property has been sold. But to whom?

That's true - and I'm sure there should be. But look left from the initial Street View and there's a roadside sign, plus a dashed line on the road. However, given that the first bridge hides the second, I'd expect words and arrows on the road too (plus those width lines). Note that from the other side there is no line on the road, though there is the same roadside sign.

I went to look at the thing last year, as I was in Caen anyway (but with no time to try it out). Certainly the service wasn't very reliable - even the not-very-exisitent Sunday one, being 30 minutes late.

But it's hard to draw conclusions about such systems generically from the issues at Caen, and at Nancy (though they haven't decided to scrap theirs - yet). Bombardier had so little success selling them they gave up supporting them some time ago, so if some quite feasible design changes would have made a big difference we don't know - they were never tried.

PS: that view is the back end - you can only drive them from the front, so they need a turning loop.

As it stands, that doesn't make a lot of sense to me. It's not comparing like with like - the real alternative is a few more 9-cars; a "completely standard fleet of nine cars" is no more realistic than a mix of the existing nines and only sevens. And operationally it would be a mess, surely? But we don't now the actual question it might have been an answer to.

I thought there was some information from Hitachi that even-length trains would have half their vehicles motored, with one trailer more if odd-length - but that may have been my/our inference instead. In any case this idea breaks that "rule", at a cost in performance. The original designs included an eight-car variant, which was like a nine with the central MES2 taken out. If adding TS2s (38.1 t tare) is as easy as that post suggests, you could take one of those out of an 8-car, and then the two vehicles added to a 5-car would be an MEC3 (or MES3 - 49.4 t I think) and a TPS (41.0 t). More weight, obviously, but more power too.

Incidentally, that TPS looks an odd code - there certainly isn't a pantograph on it is there? However, there is a 25 kV insulator on the corner to feed power downwards, so obviously it has a transformer (though as I said earlier that should have a code letter X). That suggests that each transformer weighs 2.9 t and can supply 2.5 MW but nor 3 MW.

(Sorry about the dark picture, but they stop in the stygian underdeck at Reading - hence no picture from above either.)

That's misleading about the original Bowden and Tabor insight (as in the original 1939 Royal Society paper). I meant the basis of what's now called the adhesion theory of friction:

• all real surfaces are rough at the atomic scale, even if they look smooth and flat
• when placed together, they touch at only a few tiny high points
• when pressed together, the tips are squashed, and so meet at a larger (but still tiny) area
• at the same time more new tiny points meet
• this squashing is plastic yield, and the force is proportional to the yield strength x real contact area
• when you slide them, these minuscule areas of contact shear, with a force = area x yield strength
• which is Coulomb friction

Obviously that's the starting point for adding extra bits of reality, some of which fit well and others don't -  that's why it's an explanatory fairy tale. But it does give a new picture of what, basically, is going on, which for example has helped with explaining rolling friction and the related wear. So while this may look like an area where experience and engineering "cookery" are the only guides, there is a lot more scientific contribution hidden away behind the scenes.

Wikipedia has surprisingly little on the subject, so presumably the profession (or tribe?) of tribologists isn't very interested in proselytising. As an applied science, it was pretty much created by those two people - Phillip Bowden and David Tabor - working together in Cambridge before and after the war and in Melbourne during it. They were both experimental physicists, but the teams they set up always interdisciplinary and included everyone from theoreticians (some effects can be traced to quantum theory) across to engineers with lubrication problems within industry. That was unusual for the time, though obviously fitted with wartime attitudes. Both have detailed biographies at the Royal Society (Bowden, Tabor).

True - I did start adding something about WSP, but took it out as the post was getting too long and detailed (of course it still was). Perhaps I should have put back something to expand the point about friction, though. The simple model assumes that friction is uniform, so even if it is unknown then at least the division of traction force between wheels is optimal. In reality friction (or adhesion, the preferred railway terminology) often varies within the length of a train so to be optimal the traction per wheel has to be made proportional to that too.

Which is what the WSP does. If it's good enough, the damage or excess wear to wheel and rail is low enough that drivers don't even need to be told to avoid WSP activation, and it becomes just part of the train's traction control system. Of course nobody puts one motor per wheel, so friction imbalance between the rails is something no current system can fully cope with.

The Adhesion Working Group is where the railway industry looks at all of this, and it has produced "Managing low adhesion - AWG manual Issue 6". It's probably where to look if you really want to know more - and I do mean more, as it's 351 pages long. It does include several mentions of "a good WSP", and names names (e.g. the worst tree species) and numbers, like this table:

Adhesion Level	Typically	Description
High	>15%	Clean rails wet or dry
Medium	10-15%	Damp rails with some contamination
Low	5-9%	Typical autumn mornings due to dew / dampness
		often combined with light overnight rust
Exceptionally low	<5%	Severe rail contamination often due to leaves
		but sometimes other pollution

I'm not sure I'd go that far, but I do remember being very struck whenever it was (probably 28th November 1968) I first heard the Bowden and Tabor explanation of Coulomb friction. One of the best "explanatory fairy tales".

The full quote is "An initial inspection of any impact damage to the bridge revealed the bridge came through the experience unscathed - a huge steel barrier at the entrance to the bridge took the full force of the bus's roof, and protected the bridge as intended."

Well, they are still running trains over that "barrier" - it's the the northern, steel, bridge put there some time after the Severn Tunnel and the line from Wootton Bassett were built. That is 15'2" up, which is plenty to take a double-decker under - so it didn't hit it. It hit the brick arch, having failed to move out to the middle of the road, which is why the roof in the picture on Bristol Live lies under the steel bridge. Draw your own conclusions about the reporting!

Aha! I was going to ask if the idea was to run buses over the rail route - and why. The roads may be congested, but £40M ought to buy a few bits of bus lane and bus-only access road, without the hazard of meeting a goods train.

STRAIL are a German company, though that name (they prefer capitals) appears in their product names. If you go your local level crossing, the chances are you'll see some of their road panels between and beside the rails. I think their big advantage is that you can just lift them to get access to the track and then as quickly put them back, without any pneumatic drill or tar boiler.

Well, IETs^▸ (Intercity Express Train) (a fraction of them anyway) have:
 Pantograph Camera System
 Unattended Overhead Line Measurement System (UOMS) (provison for future fit only)
 Unattended Track Geometry Measurement System (UGMS).

So in the sense that there are branches IETs won't venture down, maybe it answers more to that.