Difficult sentence

Hi everyone,

Can you please help me to understand what the underlined part is referring to in this sentence?

"Consignments intended for the southern (and most heavily populated) parts of Britain had to be heaved onto creaking ox carts and hauled through the docklands and across London Bridge, which had been built in the 12th century and was as cramped and impractical as its early date implied. By 1820, it had become the center of the world’s largest traffic jam.

It was a situation intolerable to a city with London’s pride, and it was clear that if private enterprise could build another crossing closer to the docks, there would be a tidy profit to be made in tolls."

Thank you.