If an investigation determines that the driver was at a bar and drinking heavily prior to the incident, then I would also bet he was drunk.

It would be nice if sworn testimony from people working at a bar, or the passenger, was proof enough of intoxication, sans a timely urine or blood test. Especially in cases like this where the driver has failed to stop, and/or in cases where the driver has a history of driving under the influence.

In other words, under normal circumstances it is a case of innocent until proven guilty. But if the driver does a runner, then it automatically [with regard to driving drunk] becomes guilty until proven innocent.