Summary:

Street = Has businesses, houses, shops and sidewalks. Designed for humans.

Road = Higher speed limit than streets, generally no businesses or sidewalks, as it's just there to connect areas. Designed for cars.

Stroad = A connection between areas that also has businesses. You have higher speed limits, minimal sidewalks and it's dangerous/impossible to cross on foot. The only way to get around to different businesses along a stroad is by car.