Track Gauge & Loading Gauge

The loading gauge is a measure of how wide/tall a load can be, and is much more a function of bridge, tunnel and lineside structure clearance than it is of track gauge or weight of lading.

The US and the UK have a common track gauge, 1435mm.  The US loading gauge is so much bigger that normal-size rolling stock would put British lineside structures at considerable risk, not to mention getting stuck like corks in some of the tighter through truss bridges.  OTOH, the South African Railway is 1067mm gauge, but has a loading gauge larger than the railroads in the UK.

Of course, there is one exception in the UK.  Since Brunel built the Great Western with seven foot 1/2 inch gauge (what's with this 1/2 inch thing the Brits seem to have stuck into all of their early track dimensions???) former GW routes have a gigantic horizontal loading gauge by UK standards.  (The former Erie has the same in the US.)

There is also very little correlation between loading gauge and weight of lading.  Pieces of aircraft can be nudging the Plate E loading gauge, but weigh comparatively little.  Those proposed nuclear material carrier casks probably won't even overhang the sides of the multi-wheel flat cars that will carry them.

Of course, if you have a really high, wide, heavy something to move...

You bolt the two ends of a Schnabel car to it, and proceed VERY carefully.

Chuck

Kevin C. Smith wrote:

The question of equipment loading gauge has come up in the D&RG and Narrow Gauge in Ohio threads. I've had a question about this for some time and now seems as good time to trot it out, namely, what is the limit of loading gauge for a given track gauge? About all I can figure is that it's all built around the center of gravity and the lower that is, the better. Assuming a car load of uniform density and a car floor height of-what is the US standard, 48"?-whereabouts do we start maxing out car sizes (assuming that clearances with lineside structures would not be an issue)? In light of observations made on the other two threads, if we had somehow settled on a 3' gauge in North America, I'd guess that we'd would still have COFC freight but not doublestacks-right or wrong? PRB coal would be moving in longer trains of smaller cars-but would they be very much smaller? Conversely, if the Erie had inspired a broad gauge (6') revolution here, would the equipment we use today be that much bigger? Triple stack well cars? Side by side containers? 160 ton coal cars? I've always wondered "what if" but I don't know the science behind the "balancing act" as it were. Any ideas, anyone?

"Loading gauge" is the cross-sectional dimensional envelope that is available to a given railroad line, and is not the same as axle loadings.  (You pretty much said that, but many people mix them together, so I want to make that clarification)  You're really asking about both, and they are not in strict correspondence.  There are railways with a very large loading gauge and a very low maximum axle loading, and vice versa.  A railway with a low maximum axle loading usually dispenses with the cost of obtaining a large loading gauge, but I worked for one sizeable, standard-gauge non-U.S. railway on which all that stood in the way of establishing high-cube double-stack service over a 1,000 mile route was replacing two non-clearing through bridges, whereas the axle loadings were incapable of supporting more than about a 70-ton 4-axle car.  This railway had been engineered with the large loading gauge partly because the railway anticipated future catenary as well as wanted the ability to move oversize loads, but mostly because the topography was open and flat with the population concentrated into a few places, thus the decision incurred no cost penalty.

The absolute upper limit on axle loading is the ability of the rail to accept the axle loading, because the wheel-rail bearing surface is small and the metallurgy has a definite limit.  When that limit is exceeded, plastic deformation of the rail occurs and rail lifetime shrinks dramatically. Bridges can be built to accept virtually any load desired, and because they are limited in number and length the increase in cost to obtain a higher axle loading is usually not prohibitive, when compared to buying new rail every year or two because it's deformed beyond the limits of what can be recovered with grinding.  A narrower track structure than standard-gauge does create challenges in obtaining adequate transfer of the weight between the rail and the subgrade, because the tie is shorter and thus has less bearing surface, but by decreasing tie spacing and improving the quality of the subgrade this can be overcome.  It may require mechanical stabilization of the subgrade, and in wet climates, obtaining adequate drainage is challenging.  But it can be done without extraordinary expenditure.

Loading gauge usually only comes into play on railways that were built long ago in populated settings or difficult topography that have numerous fixed structures such as tunnels, through bridges, overhead grade-separations, and passenger platforms, which in total are fantastically expensive to enlarge in any urbanized or geographically vertical territory, especially if one also needs to keep the line in service during the enlarging process.  In open country or undeveloped country, even a limited choice on loading gauge long ago is rarely an expensive problem to overcome.

I think I can best frame your question by asking, "Was the choice of 4' 8-1/2" as standard gauge in North America a fortunate decision?"  The answer is yes -- it was extremely fortunate, with the caveat that a variation a few inches one way or the other would not have much mattered.  There would be no significant difference had standard gauge been 4' 6" or 5' 0", or anything in between.

Had North America chosen a significantly narrower gauge, say, in the 3' 0" to 3' 6" range, the loading gauge would likely have been much smaller and would have greatly hamstrung the ability to move double-stack or multilevel equipment, as well as resulted in narrower passenger equipment that gave up a lot of useful cubic capacity without proportional savings in cost of equipment acquisition, maintenance, and operation.  North America already has had significant cost issues enlarging its older lines with smaller loading gauges to accommodate double-stacks (including high-cube stacks) and multilevels.  On the other hand, had North America chosen a narrow gauge the axle loadings could have been increased to 286K standards without significant issues, just as they were from the low loadings of the 1850 period incrementally to the present day.

Had North America chosen a significantly wider gauge, in the 6' 0" regime or above, it probably would not have simultaneously implemented a loading gauge significantly larger than it has now, because there would have been no apparent reason to do so a century ago.  But even it if had, it would not have been able to make much advantage of it then or now, as the axle loadings maximums for rail are reached with the bulk materials that railways excel in hauling at a loading gauge smaller than the current North American maximum.  This is amply exemplified by South Africa's Spoornet system, built to Cape Gauge.  Spoornet has very high axle loadings and a relatively small loading gauge.  Conversely, the cost that would have been incurred building the North American system to a 6' 0" or greater gauge would have been so much higher than was spent to obtain 4 8-1/2" that it would have greatly hamstrung the development of the North American rail network, and in turn would have delayed and diminished the economic development of North America.  It would have been a collossal mistake.  Sometimes geniuses like Brunel are best ignored.

RWM 

tomikawaTT wrote:

The US and the UK have a common track gauge, 1435mm.  The US loading gauge is so much bigger that normal-size rolling stock would put British lineside structures at considerable risk, not to mention getting stuck like corks in some of the tighter through truss bridges.  OTOH, the South African Railway is 1067mm gauge, but has a loading gauge larger than the railroads in the UK. Of course, there is one exception in the UK.  Since Brunel built the Great Western with seven foot 1/2 inch gauge (what's with this 1/2 inch thing the Brits seem to have stuck into all of their early track dimensions???) former GW routes have a gigantic horizontal loading gauge by UK standards.  Chuck

 

Brunel's Track Gauge was actually 7 feet and a Quarter of an Inch (84.25") but perversely his Loading Gauge wan't increased proportionately to the Track Gauge.

Next time you're in the UK, look at the layout at a double-line ex Great Western Station. The minimum gap between the outer rails of adjacent parallel tracks in the UK is 6 feet. When the Great Western was undertaking its progressive "narrowing " of its track back to Stephenson's Standard Gauge, it was the outer rail that was removed so as to leave the inner rail as before adjacent to the platform, and the one time broad gauge stations are immediately noticeable by the pronounced gap between the respective running lines.

Hwyl,

Martin

 

British Railways have a considerably smaller loading-gauge than Continental ones, which in turn have smaller loading gauge than USA/CDN. (I do not know how Spain and Portugal are. Sweden and Norway have spacier passenger-cars than Continental Western Europe). However, axle-load in the UK is IIRC 25 metric tons. In Continental Western Europa, many mainlines have a 22,5 tons, but there are still a lot of 20-ton-tracks on mainlines. The former Soviet-Union had wider gauge and loading-gauge than Continental Western Europa, but quite light tracks.

 

Some comparisons I scratched out from around the 'net:

                    Track gauge     Max Width (mult of TG)     Max Height (mult of TG)

Europe (Berne)    1435mm        3150mm       (2.2)              4280mm        (3)

Britian (W9)        1435mm        2296mm       (1.6)              3965mm       (2.7)

Iberia                1668mm         3300mm       (1.9)              4300mm       (2.6)

Scand.              1524mm         3400mm       (2.2)              5500mm       (3.6)

N.A.                  56.5"               128"          (2.3)                242"          (4.3)

It seems that no one wants to (or can) use equipment with a ratio of much more than twice the track width. As for equipment height, there is quite a bit of variation. While I know that, historically, this has to do with lineside structures, is there a ratio at which a car or locomotive-anything-just becomes too tall or too wide and falls over too easily to be of any use?

Some "fun with numbers":

The Erie's 72" track gauge would have us today with a loading gauge of 165"w x 309.6"h. That's over 25 feet high-triple stack boxes, anyone?

Applying Brunel's 84 1/4" track gauge in the proportion of the British Rail loading gauge would yield 134.8"w x 227.5"h for equipment.

Well, if the math (or my transcription of it) is off, it's because it's late and I should be in bed. Think I'll go do that now...

One minor correction. In Scandinavia, 1525 mm (like the former Soviet Union) applies only to Finland, which has been part of the Czar's (i.e. Russian) empire from the early 19th century until 1917, i.e. when railroads were built. Denmark, Norway and Sweden run on standard-gauge. Of course, in all the aforementioned countries, there were narrow-gauge-systems for secondary lines. Iceland, AFAIK, has no railroad.

Ireland has it's own, almost unique gauge of 5' 3". How this came about is quite a story!

The first railway in Ireland, the Dublin and Kingstown (now called Dun Laoghaire - pronounced "Dun Leary") was 4' 8.5". But one or two other lines were built to 6' 2" gauge (dont ask me where the extra 2" came from!). As the question of gauge had already arisen in Britain, any official from the Irish Office (at this time Ireland was part of the UK) rounded the two gauges to 4' 6" and 6' respectively and took the average, which is 5' 3"! This guy must have had the gift of the Blarney as he persuaded all the lines to convert to 5' 3"! Thus it became the standard gauge in Ireland; the only other countries it's found in are certain Australian states (which I believe are gradually converting to 4' 8.5".) and Brazil.

In the last quarter of the 19th century the UK govt gave subsidies to people building narrow gauge lines in Ireland, almost all of which were 3' gauge, and as a result one or two lines converted from 5' 3" to 3', notably the Cork, Blackrock and Passage line which got a subsidy to extend its line from Passage to Crosshaven and as a result of narrow its gauge was able to double track it's existing line!

Railway Man

Had North America chosen a significantly wider gauge, in the 6' 0" regime or above, it probably would not have simultaneously implemented a loading gauge significantly larger than it has now, because there would have been no apparent reason to do so a century ago.  But even it if had, it would not have been able to make much advantage of it then or now, as the axle loadings maximums for rail are reached with the bulk materials that railways excel in hauling at a loading gauge smaller than the current North American maximum.  This is amply exemplified by South Africa's Spoornet system, built to Cape Gauge.  Spoornet has very high axle loadings and a relatively small loading gauge.  Conversely, the cost that would have been incurred building the North American system to a 6' 0" or greater gauge would have been so much higher than was spent to obtain 4 8-1/2" that it would have greatly hamstrung the development of the North American rail network, and in turn would have delayed and diminished the economic development of North America.  It would have been a collossal mistake.  Sometimes geniuses like Brunel are best ignored.

RWM 

Electrifications are less widespread and more delayed, too.