(Trivia) When does a bridge become a tunnel?

[Metrailway]

In the old days, the correct term for structures over the railway such as the Tesco 'tunnel' at Gerrards Cross or the Metropolitan Railway under Euston Road was Covered Way

 

[Tio Terry]

Using the definition above, those will presumably be ones that have been created without removing the surface. Or are there some listed as under 50m long which have been built by cut and cover methods?

Newmarket is more than 50M but was Cut and Cover because of the racehorses.

 

[Llama]

One that springs to mind would be Pemberton tunnel. 37m long.

 

[lancastrian]

Not always. North Downs Tunnel on HS1 has no airshafts for example. I need to get to my archives to be able to tell you why a particular distance was used to determine when something became a tunnel and I cant do that until tomorrow. The European Railway Agency define a tunnel as being 100m long meaning something of that length or greater must have a full Risk Assessment and Evacuation Plan.

Evacuation procedures do, of course, vary with each site. Modern tunnels that comply with the Interoperability TSI will have clear walkways down one side of the train as per North Downs and Heathrow. Others wont and rely on end cab evacuation, East London line for example. Signalling systems are usually designed such that trains are not stopped in tunnels - at least modern systems are! But there are still some places where this happens. It's all down to the Risk Assessment and how the Local Fire Authority view the situation.

What I was referring to was the need for ZHLS cabling which must be provided in a "Tunnel" as opposed to a long bridge. All Tunnels have to have that kind of cable and from memory the length is 500m.

Many years back when I used to work at Bolton BR. I was told that the Farnworth Tunnel was not officially a tunnel due to its length being less than 400 yards, because of this platelayers and track working didn't "Tunnel Money" for working in it. So although it has always been called a tunnel and has Tunnel Boards at both ends, it was not a tunnel for some official purposes. So I am sure that the length of a tunnel or not tunnel is the defining factor.

Sits back and awaits being proven wrong.