He goes into the research a bit more in the Google talk and you see where he pulls the magic "15% improvement" from. Also he has a book (which I haven't read) c

He goes into the research a bit more in the Google talk and you see where he pulls the magic "15% improvement" from. Also he has a book (which I haven't read) called Traffic so he might explain it more or cite studies there. I agree though that it doesn't really work in all situations. Tom uses the example of two lanes merging into one for roadworks. Maybe some situations where it doesn't work are an example of poor road design by traffic engineers?