I have an idea for possibly making sidewalks from cement. We can currently make asphalt for roads I would think that we would be able to make cement sidewalks. Maybe a cement sidewalk could also increase the walking speed slightly like the running shoes. Just an idea
From a basic building material perspective, a sidewalk is just a reshaped version of the same thing that's put on for vehicles. I've seen plenty of servers create roads made from two materials to delineate road from property. I think the existing road materials already suffice for the game's needs - just that server management (and people's zoning/building habits) need a change.
Believe me when I peeve about how most servers I see have 2-tile wide roads, when any safe operation of a vehicle needs 4, and at least 6 for a two-way street.