Rathole tunnel

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Rathole tunnels are railway tunnels where fumes from locomotives make passage through the tunnel unpleasant[citation needed].

Contents

[edit] Overview

Rathole tunnels are generally

  • long
  • steeply graded
  • single track
  • narrow bores
  • unfavourable winds prevent clearance of smoke
  • type and number of locomotives may have an influence
  • water dripping on rails

In addition, they may

  • be curved, or more rarely, reverse-curved (S-shaped) such that there is a section from which an entrance cannot be seen (e.g. Privett Tunnel, Meon Valley Line, UK)
  • incorporate within them a change of gradient (e.g the tunnel on the Par-Fowey Branch, UK), requiring extra traction at a point hard-to-predict.

[edit] No problem tunnels

  • Box Tunnel on the Great Western Railway, built 1838? was never a problem, even though it is quite long at about 2 km, and has a relatively steep gradient of 1 in 100, because :
    • it is double track.
    • it's dimensions are large compared to the rolling stock gauge of the trains, since the route's conversion from Broad Gauge in the 1890s. Note though that the monumental portals were an act of propaganda when it was built; the tunnel narrows to the proper size inside.
    • there are several air vents along the way, though this is normally the case, there was worry of asphyxiation in the tunnel when it opened so excess were provided.
    • trains rarely enter tunnel from standing start (no station at Box any more)
    • double headed trains rare.

[edit] Avoiding a rathole tunnel

The first Cascade Tunnel, built from 1897 to 1900, had problems with smoke because it was long and steeply graded. The key dimensions are

  • Length = 4228 m
  • Gradient = 1 in 62
  • Rise over length of tunnel = 68 m.

To avoid problems with smoke, the tunnel should be almost level, so that locomotives do not have to work hard while in the tunnel. Depending on the ruling gradient on the rest of the line, the ideal gradient in the tunnel is somewhere between 1 in 62 and level. For example, if the ruling grade elsewhere was 1 in 60, then the preferred grade through the tunnel might only two thirds as steep at say 1 in 90. However, levelling this tunnel would have required substantial construction. While the engineer of this line, John F. Stevens, was experienced, the choice of gradient in the first Cascade tunnel was arguably mistaken.

Note that the tunnel should not be perfectly level as a slight gradient helps water drain away.

[edit] Examples of Tunnels

[edit] Australia

  • Ardglen Tunnel in New South Wales - Garratt locomotives prohibited, because of heat problems in the narrow bore.
  • Coalcliff Tunnel in New South Wales - restricted loads for heavy 57 class engines, so that engine need not work at full blast.
  • The old Otford Tunnel, Otford, New South Wales - notorious for suffocating fumes - at ruling 1 in 40 grade - sea breezes often blew smoke along with train. c1880.
  • The old Lapstone Tunnel that replaced the Lapstone Zig Zag was built too steep and eventually had to be replaced by a gentler alignment.
  • Bylong Tunnel - air intakes for diesel locomotives had to be redesigned to prevent air starvation to the second and third locomotives.
  • The 10 tunnels at Lithgow that replaced the Zig Zag Railway were sometimes considered to be rathole tunnels, but the gradients were fairly gentle at 1 in 90 (1.11%), the tunnels were double track, and the gaps between the tunnels allowed for some intermediate ventilation. The western approaches were graded at 1 in 42 and required use of Bank engine helpers only in the open air. This deviation was opened in 1910.
  • The long tunnel on the Ulan line in New South Wales has a tight profile and train crew must be supplied with respirators before entering the tunnel.
  • The Rhyndaston Tunnel in Tasmania is 955 m long with a small bore, and is graded at 1 in 40.

[edit] Italy

  • In the Balvano train disaster of March 3, 1944, over 500 people who stole a ride on a steam hauled freight train die of carbon monoxide poisoning when the overloaded train stalls in a steeply graded tunnel.

[edit] United Kingdom

[edit] United States

  • The first Cascade Tunnel was built to replace an unsatisfactory quick-to-build section of line with 8 switchbacks, problems with snow, steep grades, train length limits. Unfortunately, the first tunnel was quite long (4.228 km) and had a steep gradient of 1.7%, and had severe problems with smoke, qualifying it as a rathole tunnel.
  • The second longer Cascade tunnel 12.543 km long was built with gradient of 1.7%. It was originally electrified. However when dieselisation came, the fume problem resurfaced, requiring a ventilation system to be installed to clear the air after each train.

[edit] See also

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