It’s always easy to say people don’t make mistakes but the reality is they do. They will drive the speed the road is designed for. They will lose focus. They will be distracted. Similarly road maintenance will be skipped or delayed and there will be times with no paint on the road or missing signs.

We can’t afford to build roads for people’s ideal behavior but need to account for their actual behavior, and need roads work safely despite human failures.

A clear line of sight makes it look like there’s no reason they can’t go straight ahead. A straight approach makes it look like there’s no reason they can’t go straight ahead. A dirty windshield or excessive headlight glare makes it look like there’s no reason they can’t go straight ahead. An unfamiliar road or a couple seconds of inattentiveness is all it takes before they figure it out too late. Meanwhile something as cheap and simple as shrubs interrupts their line of sight from way back to alert them that something is different