Items that can be placed on streets

Manholes
Crosswalks
Barriers

anything else?

Nessie and the street sweeper go on the dirt roads.

Can't be anything big the characters walk on the road so you can't hardly anything block there path

@rockyb2006
Do you mean Roads (Road, Dirt Road, Cobblestone Road - which have sidewalks) or streets (Pavement & Dirt - which do not).
There's not much you can put on Roads, but there's a lot of stuff you can put on streets. I have cars on my streets, as well as other things.

Manhole Station.

I'm specifically wondering about dirt roads. I just tested it, and only the barrier and crosswalk can go on it. The manhole won't, but goes on the regular street. I'm using the dirt road to create the abandoned aquaduct from the SF map. It looks good, except when the regular street crosses over top of the dirt road. I have the crosswalk placed as a sort of "grate" to make it seem like a bridge, but I'm not really happy with it.

Parking Meters go on the side of regular roads.

I don't know the proper names but there are junctions that you can place at crossroads. Of late there are also buildings designed to be placed over roads. Then there are some signs that you can place across a road too.

I have a saint Patrick's day banner. I believe a black month banner also. Simpsons did a African event about black people before the major BLM movement.