I don't think it was a cover up and don't think he was on anything. I think he definitely had road rage, due to having his car be blocked in and waiting for some pa to move it making him late for Oprah. Maybe he was also sleep deprived. Road rage can lead to a lot of bad decision making.

If you catch yourself heading down the path to road rage the best thing you can do is to pull over to a safe location and wait, do breathing exercises or meditation until you calm down. You should never drive angry. Obviously Tiger could have asked someone else to drive him and have another person drive the car after if it was needed for the shoot with Oprah. But he was too pissed off to make a rational decision at that point. Honestly I'm not sure how anyone that rich wouldn't have a hired driver available whenever needed.

Tiger suffered a huge personal toll in the accident and since the tests didn't turn up anything drug or alcohol related I don't think he deserves any further punishment. Road rage is a hell of a drug on its own though.