No. While experience has led most courts to this assumption, there are certainly circumstances in which a lead driver is found to be at fault for a rear-end collision. If another vehicle turns or merges in front of you too suddenly, does so without signaling, or fails to maintain proper speed and a collision results, they are at fault so long as you can establish that you were not speeding or otherwise violating traffic laws. Also, if the other driver reverses into you in a manner which violates traffic laws, liability rests squarely with them.