[canucker2016]

For two-lanes-or-less-each-way streets, buses don't offer much benefit if the streets are busy since the chance of being able to get enough space for a very heavy, long bus to switch lanes is low/impossible.

Streets cars/trams weakness include breakdowns - trailing streetcars/trams are blocked if a streetcar breaks down on the track. But, they can also carry more passengers than buses. I think many modern versions are about 3-4 bus-lengths long.