Chief executives from the world’s leading car makers will be competing for headlines next week at Beijing’s biannual international auto show, many claiming new innovations in low-emission vehicles, in-car connectivity and automated driving systems.

On the streets of China’s capital and in many other Chinese cities, the daily toll of accidents and fatalities will continue. Pollution is likely to be high and will only get worse: 35 cities in China have more than one million cars on the road; 10 cities have more than two million....