HS2 needs more than one tunnel
ALTHOUGH it is good news that more tunnels are being created for the HS2, it does question how this will effect the time taken from London to Birmingham.
The picture on the front page of the paper on September 3 shows what I presume is the high speed train leaving a single tunnel.
Some time ago,I did a research on the speed that a train could achieve through a tunnel taking into consideration the problem of air displacement.
I found the fastest trains in the world could achieve up to 220 kph. However, on further research it appeared that two trains entering a tunnel from opposite ends and meeting in the tunnel could not maintain the high speed because of the pressure wave created by the trains.
In putting this to HS2 they agreed that to maintain a high speed of over 300kph not 220 kph, at least two or even three tunnels would need to be built alongside each other. Depending on the length of the tunnel one would be a service tunnel and the other tunnels for trains travelling in opposite directions.
I therefore find it puzzling that the HS2 picture is only showing a single tunnel although it appears to have two tracks. Is it because the tunnel is very short or the speed of the train has been reduced considerably to allow two trains to pass. If the latter is the reason then would the saving in the time from London to Birmingham which was announced in 2009 now have been lost because of the length of tunnel which has been introduced in the past few years to the route.
JAMES JOHNSON Pavilion End Beaconsfield