When things started,there were very strict laws when it comes to lawsuits due to negligence. The courts used a standard called contributory negligence in which a plaintiff must show clean hands before he can sue for damages. If he is found to contribute in any way to his injuries,then he can no longer recover any damages from the defendant. This harsh rule has be repealed in many jurisdictions as lawmakers felt it was impractical and unjust although some states still cling to it.
A new standard was devised to take its place called comparative negligence. What is comparative negligence? Simply put,it acknowledges the likelihood that both parties may have been partially at fault (http://www.clacc.org/suing-for-a-car-crash-caused-by-a-government-vehicle/). A person can still sue despite playing a role in the outcome as long as he has the smaller contribution to the accident. The jury will determine the appropriate percentage of fault and make both parties pay accordingly.
This type of lawsuit works best if there is a wide gap in the contributions of each party. If both were found to be 50% negligent,then the awards will only cancel each other out. If one party is 90% at fault while the other is only 10% at fault,then the court is more likely to award a significant sum. The plaintiff may not recover the full amount that he would like based on the injuries sustained but this is a much better outcome than an outright dismissal with old rule.
Comparative negligence is useful when dealing with car accidents,which is why you want a personal injury lawyer on your side. It is possible for both parties to be breaking traffic laws when the incident occurred. One might be going over the speed limit while the other was driving while distracted by his phone. It would be interesting to see how the jury appreciates the facts of the case.