Here is a very informative "close call" written by John S. Allen, Consultant and Expert Witness in Bicycle Accident Lawsuits (the same occupation as John Forester, author of "Effective Cycling"):

www.bikexprt.com/bicycle/helmtrd1.htm

For Mr. Allen's resume (and list of cycling-related achievements):

www.bikexprt.com/witness//bikeres3.htm