Although violating a speed limit is likely to get you a large ticket (and potentially other penalties), compliance with speed limits alone will not dictate who is at fault for an accident. It seems intuitive that relying on the posted speed limit to dictate how fast you travel should be a valid defence, but this is not always the case.
Ultimately what it comes down to is whether there was negligence. The courts will decide if the drivers involved have driven “with the skill and care expected of a reasonable driver at the time and place in issue”:
What this means is, even if you are complying with the posted speed limit, you can still be found to have caused an accident by driving too fast if there are other conditions that require you to slow below the speed limit. An easy example of a condition that might cause the reasonable driver to slow down is weather. Wet, cold, snowy, and icy conditions can all cause roads to be less safe. The reasonable driver should react to this by slowing down.
Other examples of conditions that might make the courts decide that a driver should have slowed below the posted speed limit include lighting conditions, hills, and road obstructions. For example, the courts have held drivers who were traveling at the speed limits liable, because they did not slow down for another accident up ahead. In certain circumstances drivers should be aware that there are likely to be pedestrians who have exited their cars and adjust their speed accordingly.
This just shows that even seemingly straight forward applications of what appears to be the law can lead to complex legal argument and fact investigation. As always, I recommend that anyone involved in a motor vehicle accident consult with a lawyer as quickly as possible.