It's not just that cars are closer than they appear, or that the discrepancy 
 increases with distance. The effect makes it nearly impossible to
 accurately judge the other vehicle's speed. Not a problem if I could turn
 my head 180 degrees. If your going close to that vehicle's speed you have
 more reaction time, but when slowed to make a left, they can close on you
 in a heart beat. 
 Don't fret that, I always assume they're out to get me. Let's face it, riding
 a bike in traffic is always dangerous.  Being hit is almost inevitable when 
 you've been on 2 wheels as long as I have,(60 yrs). So tell me me about it,
 son.