The way I have conquered this is to use a small rearview mirror which attached to my glasses. I don't care how dorky some people think it is...they said that about helmets, too. It took a whole 15 minutes to get used to using the mirror. Listen, would you drive a car without a rearview mirror? I don't think so! It is especially helpful when riding alone, which I frequently do. It can mean the difference between bending a wheel in a huge pothole or seeing it's okay in less than a nanosecond to move left.