Let's be honest, running or walking around to catch pokemon in the world is not dangerous. It does become dangerous though whenever they pay more attention to the app then to them actually moving around. Like let's be honest here, if anyone gets injured and killed playing this game then it's just a simple way of thinning the herd.
Sure the game can cause accidents if the gamers are not being careful but that is not the only problem. The players might wander into a place where they are not supposed to be. Examples are private properties and graveyards (imagine a gamer doing that). A good way to fix this however is making sure the search radius is big enough so gamers don't jump any fences that they will regret.
Walking around and staring at a phone is ver dangerous, especially when it involves crossing streets and watching out for cars. Except that's the problem. People would be looking at their phone and not at the car, meaning they could get hit by a car. And besides, what is so fun about that game? Is it really worth your life?