I have an unsubstantiated hunch that the longer traffic lights are on average, the more people text while driving. Why? In cities I've lived in where the traffic lights are shorter, no one gets out their phone because as soon as you do, you'll have to put it away because the light turned green. So you never get into Twitter/Facebook/etc. But if the stop lights are very long, people get engrossed in social media, then when the light turns green, their mental inertia keeps them wanting to read more. So they read while they're driving.

Would be interested to know if anyone has actual research on this.