... Human depth perception only works out to a maximum of 10 meters. So it really does not come into play in estimating the speeds of approaching cyclists.....
Wow. Then again our the distance between our eyes is a pretty small component of an isosceles triangle at that depth.
I remember when I ran X-country I was always encouraged to make sure you 'stayed in contact' with the person in front of you as much as possible. Once out of contact, it was hard to motivate yourself to pursue a runner whose distance was hard to judge. Same effect, I imagine.
roughstuff