HS2 needs more than one tun­nel

Buckinghamshire Advertiser - - OPINION -

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

ONL

INE

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