At least Google maps usually makes it easy to compare 2 or 3 different route options and let you choose which makes the most sense. But I agree it should more heavily discount "dangerous" manoeuvres, or at least ones that could potentially take far longer than the average time. As far as whether such directions contribute to gridlock, I'm not so sure - in principle if everyone followed directions generated by the same algorithm with access to "live data", it should significantly help reduce it. It'll be interesting once all cars are self-driving/self-navigating whether that proves to be true, and whether there might end up being fundamental conflicts between different algorithms used by different makes of vehicle.