The middle lane was a passing lane

I remember some that didn't even have a middle, passing lane. If you've ever noticed truckers blinking lights at each other after passing on the Interstates you may wonder what that's all about. In them days they needed to know when they had passed whatever they were passing so they could get back into their regular lane without taking out half a dozen cars. They can't tell easily when they have passed with their long trailers so the passed truck will signal the passing truck when it's safe to cut back in. Some four wheelers will even do it.