During Saturday’s long slog north in holiday traffic, the rain got heavier and heavier and then, after dark, it turned to sleet. The wiper-washers on our Infiniti QX70 kept the front and rear windscreens clear, but the radar eye in the car’s nose was getting plastered with sand, salt and slush. Finally the adaptive cruise control gave a despairing, high-pitched beep and simply switched itself off. “I give up,” it seemed to say. “I can’t see a thing. You’re on your own, captain.”