This paper presents data on the relative frequencies of rear end collisions in comparison to other types of crashes. The severity of rear end impacts is shown to be low, with a mean ETS of about 30 km/hr and 90% of AIS1 injuries occurring below 50 km/hr. The frequency of AIS 3+ injuries in this data set is extremely low at 1%. The results show that plastic yielding of front seat backs is beneficial in that the incidence of AIS 1 neck injuries is lower in comparison to seats which do not yield. Trends in seat design are discussed and it is suggested that the very large number of minor injury, low speed, rear end collisions should not be forgotten in design terms if seat back strength is increased.