Been watching my '
The Last Train' DVD, a 6-part 1999 Brit TV series.
SPOILER- A giant asteroid smacks into Africa wiping out most of the human race worldwide, but a group of train passengers survive because the train was going through a tunnel in England at the time which largely protected them.
They wake up after apparently being being knocked unconscious and climb out of the wreckage and make their way to the mouth of the tunnel and find everywhere is strangely overgrown and the city is in ruins (below).
They realise they've been in suspended animation because a scientist on board was carrying a flask of cryogenic gas which shattered in the crash and put them all to sleep; for how long they don't know at first, weeks, months, years, decades?...