Few guidelines exist on when to shut down roads (AP) - Whether it's a dust storm in Arizona, a whiteout in Maine or wildfire in Florida, the call to shut down a major highway usually rests with local officials, who in some cases have little, if any, written guidelines to follow. In many cases, officials rely on what officers at the scene are seeing - or what they can't see - when they make the decision. In Florida, a foggy, smoke-filled stretch of Interstate 75 in Gainesville was closed in both directions for three hours early Sunday. Shortly after a decision was made to reopen the highway, cars slammed into tractor-trailers on both sides of the interstate in two pileups that killed 10 people. Florida officials said they were willing to review their protocols, but the Highway Patrol was also quick to put the safety onus on drivers, saying conditions can change in an instant and motorists must be prepared to quickly make good decisions. Federal transportation agencies have never issued guidelines on when to close roads due to fog, fires and dust storms. National groups representing insurance companies, the Federal Highway Administration, the National Highway Transportation Safety Administration and the National Transportation Safety Board all said they had not heard of such a policy. The NTSB is investigating the Gainseville crash. Florida, which is vulnerable to smoky roads since it has one of the nation's most active prescribed fire programs, has a 16-item checklist for "smoke/fog incidents" that is part of a larger 28-page policy manual for Florida Highway Patrol shift commanders. Closing a road, which can be costly for tractor-trailers shipping goods, is a decision is made by a supervisor who is consulting with troopers at the scene, although any patrolman can make the call to shut down a road if there is imminent danger, said Capt. Mark Brown, chief of the patrol's media relations. In the I-75 pileup, a district lieutenant based in Gainesville who was the supervisor at the scene made the decision. A day earlier, a different spokesman said a sergeant and lieutenant determined after about three hours that conditions had cleared enough for drivers. We rely on the members on the ground, and their physical presence, people who are actually there - their feedback. The person that can actually see what is going on," Brown said. Troopers also use information and forecasts from the National Weather Service. One key piece of information is an index estimating the humidity and smoke dispersion on a scale of 1 to 10 to help them decide whether to close a road. If the score is 7 or higher, the road should be closed. The index score for early Sunday had been forecast to be 6 in a four-county region that includes the crash area, according to the National Weather Service. The Low Visibility Occurrence Risk Index was introduced to troopers around the state following a deadly crash in 2008 on Interstate 4 between Orlando and Tampa, about 125 miles south of Sunday's pileup. Four people were killed and 38 injured in that crash, which was caused by heavy smoke and fog. "The index was added to get a more scientific approach to decision-making than what was used before," said Sgt. Steve Gaskins, a Florida Highway Patrol spokesman based in the Tampa area. More than anything, troopers rely on the conditions they are seeing. "If I'm a road sergeant and I go to the scene and can't see anything, I call up and I say, `Hey, we're closing the road,'" Gaskins said. In Maine, the nation's most heavily-wooded state, the decision is left up to the trooper on scene. "Every situation is going to be different," said Duane Brunelle, a safety specialist at the Maine Department of Transportation. In Georgia, Department of Transportation engineers work with Georgia State Patrol officers. Their protocol treats smoke more seriously than fog. "Fog is often so widespread that it would be logistically impossible to address," said David Spear, a spokesman for the Georgia Department of Transportation. However, an isolated patch of fog with sufficient density to hamper visibility ... should be treated the same as smoke. Arizona is experimenting with a way to be more proactive, particularly for dust storms. The Arizona Department of Transportation is testing out a new dust warning system that takes field readings on weather conditions, humidity and wind speed. The goal is to detect potential dust storms a few days before they hit and begin posting warnings on signs. Investigators on Tuesday released the name of a seventh person who died in the crashes as they worked to identify three bodies that were so badly burned that dental records and vehicle identification numbers may have to be used to get positive IDs. Christie Nguyen, a 27-year-old college student and dance troupe member was a passenger in a car that crashed on northbound I-75. A former teacher, Gwen Keith, described her as creative, bubbly and smart. "She was very vivacious," Keith said. She was very artistic. Online: Associated Press writers Curt Anderson in Miami; Mark Carlson in Phoenix, Greg Bluestein in Atlanta and David Sharp in Portland, Maine, contributed to this report.