Tailgating and weaving are caused mostly by frustration due to improper lane usage. It is the law everywhere that on a multi-lane road, the left lanes are for overtaking and slower traffic needs to keep to the right. However it's rarely enforced.

Several states (Indiana being one) have recently enacted new laws that allow ticketing drivers who are driving at the posted speed limit but blocking traffic in the left lane. So even if traffic coming up from behind you is exceeding the speed limit, you are not permitted to block the left lane.