I was driving along a divided highway (the QEW, a 400-series highway just west of Toronto, here in Ontario). There were two lanes going in my direction. Since I don't know the road very well, I was paying attention to the overhead signs. In Britain, this had always allowed me to change lanes well in advance and be ready to exit the highway where I wanted.
At one point the overhead sign showed one lane continuing and the other lane turning off, and it gave the name of the exit. Since I did not want to exit, I signalled and changed lanes into the left lane (the 'fast' lane). As I passed the sign, I saw that the road widened to three lanes, right at that point. The sign, which showed one lane going off and one staying on, was referring to the new lane and the former right-hand lane. Since the new lane was not visible when I first saw the sign, it was natural to mistake the lanes. Fortunately, there was not much traffic, or somebody could have caused an accident by suddenly performing what is, in fact, an unnecessary lane change.
When designing the roads, and especially when deciding what signs to erect, somebody should think about the drivers who have to respond to them. In this case, the sign had at least two mistakes. First, it was placed where the lane it showed was not visible (and there was no indication that a new lane was coming). Second, it was wrong. It showed two lanes, with one being forced to exit. The road at the point of exit had three lanes, with one being forced to exit. If the sign had shown three lanes, then it would have been natural to read it as saying that the existing two lanes both continued, and a new lane would exit.
A friend of mine says that a good writer always considers the audience; who will be reading the book. If the people who planned the road signs could try to think about their audience when they put up signs, maybe it would be a little easier to drive these roads. After all, not everybody is familiar with the roads, and those who are don't really need the signs. Meanwhile, until they start putting more thought into the signs, all we can do as drivers is realize the problem, and be kind to anybody who gets confused by these signs.