Mistakes, probably. They are also by Americans and Mancs, which are hardly the best examples, I must say.

If you use plural instead of singular, it most likely refers to multiple journeys. But in this case it should be "on" instead of "by".

"I go around the city on trams"
instead of
"I go around the city by trams"
Unless it is in the third person, when "on" or "by" can be used.
"They go around the city by trams"
or
"They go around the city on trams"

Also, "get" is more grammatically correct when using "by".

"Feet" is always wrong, no matter what else is plural in the phrase.

Hmm... I think that there are a few too many rules in the English language...
The one I said earlier is not usually incorrect, so just use that one, I say.