London Tram track spacing and minimum radius

[coline33]

On 22/04/2019 at 23:03, jim.snowdon said:

From memory, that was actually a requirement imposed voluntarily by a typically risk-averse operator, rather than in response to any edict from HM Railway Inspectorate or TCL. That said, HMRI were thoroughly appreciative of the need to strike a balance in the standards and guidance for the design and construction of tramway vehicles between the risks to the person/vehicle in the path of the tram and the risks of injury to the passengers, of whom there was generally a greater number.

 

Interesting. A similar, but more passive, approach on my part post opening to provide advance signage of hazards (not specifically in relation to Sandilands) was met with a disinterested response from the Inspectorate and the operators on the grounds that, unlike the common motorist, tram drivers were expected to have sufficient route knowledge to anticipate these hazards.

 

Jim

Now back home this AM.   Jim, your memory is perfect!   Through my past channel of raising issues, I always used the phrase "has this been forced to be done by HMRI or Management?"   Each time it was from 'Management' then from later experience my issue got removed, introduced or changed!!!   I certainly agree with your post-opening approach.   My experience of the San Francisco advance warning of ATC came as our Boeing came off-street on to prw.   About a quarter of a mile ahead I saw a huge white board and exclaimed to the operator "you're got ATC!"   We were already at 50mph when I explained the Sandilands situation and asked for a demo!   Being a PCC enthusiast he agreed as by this time he was already aware that I was not one of his usual passengers!!!   Each of the four boards was large painted white with a big black ATC or numbered 35, 10, and 0.   So just to kindle your mind on your past approaches I attach a view of one of your 'pre-diamond' maximum speed signs on the OLE post.   My apologies to others if I have gone OT!   Colin. 

[coline33]

Tim, I attach a view of my first two sections with the insulator covers and the plough hatch.   These were cut out from Street Level's printed paper conduit sheets and glued in place.   You will see that on the 204mm. radius section the insulators were placed closer together.   Whenever you get to having to do point work let me know as positions varied according to the specific track layout.   Enjoy, Colin.

[roythebus]

Maybe the easiest way to answer the OP is to download one of the large scale maps from the NLS website and scale everything from there.

 

As a guide, if I remember correctly the minimum turning circle for a bus is about 55', radius 27'6". 110mm in 00/EM/P4. The usual railway minimum radius curve is about 1 chain, 66'0". 260mm.

[Hitchin Junction]

Great idea! I hadn't thought about comparing the radius to buses turning circles..  Looks like I should see if I can come up with a bogie chassis that can come somewhere close. I think I'll be gone for a while working on that

 

Cheers

 

Tim

[coline33]

Shapeways have certainly excelled themselves.   I was not expecting my delivery until next month but they arrived today.   So can show you the 204mm./250mm. curves laid out on the board this PM - sorry about the sun's brightness!   The far straight track has only been laid in to represent road space and I am now considering whether to attempt to have a permanent way yard entrance in the top right corner with electrically unconnected track on which to display works cars.  

 

I would be cautious about comparison with modern buses as their axle centre to axle centre dimension is probably greater, despite one set of wheels being able to be turned, than an E/1's bogies' bolster dimension meaning that an E/1 could do a tighter turn as all wheel sets are radial.   Just watch out if the tram has skirts!!!   Colin.      

[Engineer]

Just to compare and contrast, when I was designing various maximum traction bogie chassis [a long time ago] I wanted to begin with design criteria and so worked out some hypothetical module designs using large-scale OS maps, taking assorted London streets and tramway junctions as examples.  I also read as many books as I could obtain at the time that discussed the design of trams, tramway track and overhead.   From the OS work, assuming a pure radius, I found just under 200 mm would be roughly the minimum in 4mm for a scale layout, however I knew that smaller radii would arise in tramway practice even if only in short lengths.  I aimed for the model chassis to cope with around 7 inches radius but run optimally at something larger, say 200-240mm.

[coline33]

15 minutes ago, Engineer said:

Just to compare and contrast, when I was designing various maximum traction bogie chassis [a long time ago] I wanted to begin with design criteria and so worked out some hypothetical module designs using large-scale OS maps, taking assorted London streets and tramway junctions as examples.  I also read as many books as I could obtain at the time that discussed the design of trams, tramway track and overhead.   From the OS work, assuming a pure radius, I found just under 200 mm would be roughly the minimum in 4mm for a scale layout, however I knew that smaller radii would arise in tramway practice even if only in short lengths.  I aimed for the model chassis to cope with around 7 inches radius but run optimally at something larger, say 200-240mm.

I think you are 'spot-on' and certainly confirms the research behind Simon's 'Recreation21' sectional track to arrive at 204mm. inner and 250mm. outer for any first generation British layout.

[roythebus]

The bus turning circle I quoted is for 1950s buses. This has been fairly standard since the early days of buses. Modern buses although longer have a tighter turning circle though the swept area (front and rear overhang) is a lot longer than the typical 27'6 ST/RT/RM.

 

As an aside, I note a lot of London cycleways are about the right width for a standard gauge tramway...

 

[coline33]

Yes, Roy, especially along the Victoria Embankment!!!   But we will never get the 'Subway' cars beyond the kiosk in the south portal!   Colin. 

[Hitchin Junction]

According to my limited drafting skills, I can get two E1's to pass safely on roughly 200 mm and 160 mm radius curves.  I think I'll start going that way. If I have trouble with any larger cars, I can always have some interlocking to avoid both cars being on the same curve at once, I looked at some tracks in Florence and even their modern double track centres in the older streets seem to be a similar distance apart, at least on the striaghts.

 

Tim

[coline33]

Tim, thanks for the data.   How tight are the bogie mechs against the interiors of the sills at these radii?   Do you still have enough room for the body mounted plough carriers?   These are the areas where I have experienced problems even to the extent of having to make cutouts without penetrating and ruining the sill exteriors. 

 

Beware types of second generation trams when comparing.   Basically there are two broad types.   The original articulation type was based on bogies as that was how manufacturing developed in the 1950s.   The German systems that I travelled upon intensively at that time experienced first generation curvature often based on four wheel operation.   Partly to get uniformity they articulated existing four wheelers which I found gave a much inferior ride.   Today mass production to give a basic design from which cars can be tailored to suit most systems, have re-introduced the articulated 'four wheeler'.   In Croydon, we have Bombardier CR4000s principally a bogie type and now the Stadler Variotram which is three four wheelers joined together!   The ride into curves at the end sections is much smoother on the bogies - the four wheelers jerk but being four articulations compared with two of the bogies makes gives less of an overhang so easier to put within the 'swept-path' of existing systems.   Florence like Croydon is a brand new system so the original cars were designed to suit the worst curature.   The Croydon 'bogies' do grind more than the 'four wheelers' but then the distance between bogie centres is greater than between truck centres.   Now you have experienced the problems the LCC faced and went through the E Class to get to the E/1.   Fine in the 1900s but look what happened in the 1930s when the LCC found that 'Bluebird' was the maximum length their system could take as standard.   Both the MET and LPTB found the true limitations of what became the world's largest street tramway under single control with the introduction of the Felthams and their restricted service coverage.   Fortunately in Leeds, built as a four wheel system, the Felthams did not need 'skirt' attention but 'Bluebird' had to have cut-outs.   You might not be able to get model Felthams round without a clash but you know you are OK for the M Class!!!   Colin.        

[rue_d_etropal]

On 25/04/2019 at 18:02, coline33 said:

I think you are 'spot-on' and certainly confirms the research behind Simon's 'Recreation21' sectional track to arrive at 204mm. inner and 250mm. outer for any first generation British layout.

I used these radii simply because that is what the Tilig Luna track system uses and I think the old Hartel system used, so assumed it was the acceptable radii, and most r2r trams would run on it.  It is interesting that Fleischmann also used 250mm radius for its 'industrial' track system. Pity they did not do any points for it.  The track gauge is reconned to be slightly increased to nearer 17mm as well.

[Hitchin Junction]

I dug out some of my limited amount of old Hartel Track and measured their radii approximately with a ruler.  That gave me 180 mm and 225 mm, inner and outer. The turnouts are a little strange as they have a radius curvature "step" and an optional extension piece to allow modellers to create other complex track couble track configurations using just one size of  turnout.

 

Overall, I think I prefer to imitate the prototype track dimensions and appearance as much as possible, even if it means a little extra work.

 

Tim

[Andy Reichert]

I'm still working on making my own tramway track system. Because of my somewhat larger US Pacific Electric interurban cars, I went with 2" track spacing with 8" and 10" radius curves for double track corners and junctions. But I have constructed some  closer 1.5" spacing straight track for use in inner city streets. For that I made some "wide swing" 90 degree corners that use 8" radius on both inner and outer curves.

 

Andy

[roythebus]

I have some Hartel track from an earlier German HO layout. Most RTR artic European trams don't like the very short radius.

 

Going back to bus turning circles, the modern buses may have a longer wheelbase, but with virtual chassisless construction, power steering and the like they are somewhat easier to get round sharp corners than any of the older buses. They were limited by the width of the front of the chassis where the engine used to sit, the danger being the insides of tyres fouling the chassis on full lock. Hence the spec for bus turning circles hasn't changed much if at all over the years.

 

If you want a laugh, watch a stretch limo trying to get round a corner..

Edited December 19, 2019 by roythebus

[alastairq]

The UK Armed Forces have an issue with the turning circle of the [new] MAN 8 wheel [15 Tonne] trucks.....27.5 metres!  Trouble there is both front axles can be driven, hence have UJs to get in the way...plus, a long fixed wheelbase. Army were not happy bunnies when they were first delivered...asked MAN to 'do summat'...MAN ..in simple terms, told Army where to go!  [The price of opting for MAN's cheap knock-off version]..