Early Sunday morning, 11 people were killed when numerous car accidents broke out on Interstate 75 just South of Gainesville, Florida. The cause was a deadly combination of fog and smoke from a nearby marsh fire.

In the wake of the tragedy, many people are wondering why drivers were allowed onto the road in the first place. Because of the poor conditions, the same stretch of highway had been shut down just hours before.

However, it was reopened early Sunday morning and within 30 minutes cars on both sides of the highways collided in pileups that left 11 people dead. The National Transportation Safety Board has the incident under investigation.

A recent news report highlighted the fact that the decision to close down busy highways due to unsafe conditions is usually one that's made locally.

In Florida, the decision to close a road is typically made by a Highway Patrol supervisor after consulting with officers at the scene. But any officer can close a highway if there is imminent danger present.

Following a fatal accident on Interstate 4 between Orlando and Tampa in 2008, the Highway Patrol introduced a Low Visibility Occurrence Risk Index, which was intended to give patrolmen a more scientific measure of the amount of smoke or fog in the air.

Additionally, the Highway Patrol uses forecasts and information from the National Weather Service, including an index that rates the humidity and smoke dispersion in the air on a scale of 1 to 10, to monitor road conditions.

Unfortunately, it appears none of these techniques were able to properly forewarn the Highway Patrol about the tragedy that was about to take place on I-75.

Source: CBS News, "Few guidelines exist on when to shut down roads," Feb. 1, 2012