I have seen many project ideas like this on the web, with not one ever entering prototyping.
First I will point out the obvious flaws.
This kind of game will not work in public, unless the place is reserved.
People will run others over, and get them self hurt by playing this game on the street.
Players who just want to grind score will target people in meetings or at work, who can't get away.
This game will need more than a single player, probably four or five to be fun.
Now looking at the above we can see that this kind of game needs, zoning rules, a suspend mode and will appeal mostly to active groups.
Your best bet for a market is appealing to kids.
My advice is get to prototyping as soon as possible, this is a very new field and there is very little data to be found on doing this.
The faster you prototype, the faster you can find problems and the more interest you can build for this game.
Sharing your findings will allow others to speculate and share there own ideas with you.