How does Penelope Fitzgerald use imagery in The Gate of Angels?

Imagery:

"That meant crossing the river, along with a hundred and fifty thousand other Londoners, twice a day. The journey was compared at that time by sociological observers to a great war or catastrophe in a neighboring land from which the fugitives, forbidden to look back, scurried over the river bridges by any means available to them, only checked by fear of falling underfoot .... when the tram lurched round the corner, drawing up sharply, the crowd rolled onto it like a swarm of bees. You had to attack and be among the first."