On 5 Nov, 21:55, Tom Anderson wrote:
As in the train behind comes forward and does a push-out or sends over a
new driver or something. Is it possible to couple two trains in the tunnel
and have the relieving driver drive the double train from the front?

The procedure is known as "leap-frogging" which involves the train
operator of the train behind stopping short of the rear of the first
train, going forward to investigate and, if nescessary, moving the
first train forward. Subsequent trains repeat this, until a relief
operator is on-site.