Accidents do happen anytime, but if you can prevent it then you need to do something about it. It is true that it is unpredictable as no one can predict when it could happen and where. But, there is an old saying that prevention is better than cure and this could be applied on the road too. If there is someone or some signs that could guide the driver then it could lower the occurrence of such accidents. Sure, it won't guarantee no accidents on the road, but it could surely lessen road accident as there is something that the driver could follow. In a small town, where accidents happen all the time, you got assign as the new traffic police and you need to do your job to get a promotion.
The game is played with a mouse and the objective here is to make sure that no one gets hurt on the road. You would get some stars depending of the number of people you prevented from getting an accident. As you make some progress, you would get more signs to be use on the road and expect that there would be more cars on the road.