I caged it the last few days, up and down the Monash. While doing that, I tested myself. I set out to keep a solid vigile for bikes - more than I normally would, even being a biker! Every 10-15 secs I would look back down the lines of traffic behind me, searching for that ellusive headlight(s), coming up from behind. Nothing - nothing - nothing - vroom!...a bike cruises past. Not racing or doing anything stupid...just a gixxer thou, splitting through the evely spaced cars and going just a little faster than the cars, as we all do. WHAAA!...Why did'nt I see him!?...I was really looking out for bikes!...He was doing the same thing "i" do every day heading to work and back.... Obviously, his extra bit of speed coming up through the traffic put him upon me in that 10-15 sec I was using as a reasonable scan period. I flat out had no idea he was coming! So...maybe even theose cars that ARE looking out for us, simply don't see us either, all of the time. It points to the speed differential. If you are behind a car long enough, chances are they might see you back there...but if your speed is 10-15k's more than the traffic speed at the time, there is a good chance that you will be missed by most drivers. In the rear-view mirror, cars remain pretty static. See a white ford back there, and chances are it will still be there in the same position 10-15secs later. as will all the other cars - NOT SO with bikes, if you are making your way through the traffic. Just bear all that in mind when you are commuting...you may 'think' they should have seen you, but in fact, they easily might not have. Safest is to assume they have'nt - you'll live longer.