Apparently a number of posters on here don't agree with the grand jury's decision.
The grand jury had access to way more information than any of us. They watched two videos of of the incident in real-time, slow-motion and frame-by-frame. The heard testimony from about 20 eyewitnesses as well as sprint car racing experts and an accident reconstruction expert.
While Ward's being under the influence of marijuana certainly was a major factor in their decision, it's important to note that they found no fault with Stewart's actions behind the wheel.