But clearance time does not account for traffic backups. Baker explains that commute time is a measure of how long the folks will be spending on the road. And that’s important too. “The average time that people in Charleston spent commuting [from Floyd] was about ten hours. So if you’re sitting in the road for that long, especially if it’s the interstate where you can’t get off very often, then you have bathroom problems and medical problems and food problems and water problems and people running out of gasoline, and it’s just a helpless feeling for people to be sitting there and not moving at all,” says Baker. Additionally, if the backup lasts long enough, people might not be out of the area they needed to evacuate from when the storm hits.
Contraflow. One possible solution that has been tried is called contraflow. It is a method of reversing the direction of certain lanes of traffic during an evacuation or other events to make the flow out of an area more efficient. For example, if you have several lanes on a highway coming into an area that’s being evacuated, contraflow plans would appropriate some of those lanes to give people more lanes for driving out of the area.
Contraflow is being used more often in evacuation planning and has been implemented in several evacuations, including many hurricanes. There are contraflow lanes of all different lengths, according to Transportation’s Role in Emergency Evacuation and Reentry, written by Brian Wolshon, a professor in the Department of Civil and Environmental Engineering at Louisiana State University and director of the Gulf Coast Center for Evacuation and Transportation Resiliency. He has spent years studying hurricane-evacuation traffic patterns and trying to develop computer models that could predict future patterns to aid in evacuation planning. According to that book, the shortest contraflow lanes are about 25 miles long out of New Orleans, but there have been lanes of more than a hundred miles in other areas.
The data indicate that contraflow can make a major difference in evacuations. Contraflow was not implemented on a certain stretch of I-55 during Hurricane Ivan evacuations in 2004, but it was implemented on that same stretch a year later for Katrina. While only about 61,000 vehicles were able to evacuate on a northbound stretch of highway in the 48-hour evacuation period during Ivan, contraflow allowed 85,000 to get out over that same road and timeframe during Katrina, according to Wolshon’s book.