It depends on what you mean by 'street'.
There are pathway pieces with sidewalks on the edges that are commonly referred to as streets. You can't put cars on them. There are a few vehicles that allow you to drag streets under them (place street piece next to vehicle, extend street under vehicle), but you can't place the vehicles on existing streets.
Then there's Pavement - the pathway pieces without sidewalks. You can put cars on them. You can also put most buildings, decorations, and even plants and trees on them. I use them instead of the street pieces for most of my town because you can do that - plus characters and most invaders (Merrymakers, Bears, Criminals, etc) are attracted to streets, but not Pavement, so by limiting your street area you can contain your characters and invaders.