[aerohead]

Another consideration facing train designers is eardrum protection for the passengers as the non-pressurized cabin higher speed trains enter,or leave a tunnel.
So much can be done with the tunnel ends themselves,building like a muzzle brake,but long,organic shapes help with the pressure spikes.
Also,since the trains run 'forwards' and 'backwards',the 'nose' can make a fine boattail.
Japan's Shinkansen has experimented with nose/tail extensions up to 57-feet in length.
Air-brakes too!