So, in New Leaf, bridges require a bit more space than the average PWP to build, however, after it's built, PWPs can be built next to it normally. So if you were to commision a bridge, build a streetlight near it, demolish the bridge and replace it with a different style, you aren't gonna have enough room.
Normally, the only issue is that you'll need to shell out a lot of bells to demolish and rebuild the adjacent PWP, but in my case, demolition isn't an option since the PWP in question is the cafe.
I'm just gonna crawl in my bed and cry now.