But contraflow is difficult to implement and can’t be used in all situations. Careful planning and controls have to be in place to redirect traffic. Authorities will have to determine where the entrances to the newly reversed lanes will be, and driver-awareness plans will be needed to make sure people know the lanes are changing. Additionally, contraflow can involve shutting down certain exits and funneling people toward certain areas; sometimes officials in those locations express concern that they won’t be able to accommodate all of the evacuees.
When contraflow isn’t implemented efficiently, it can be just as bad as not being done at all. Wolshon uses as an example the attempted implementation of contraflow out of New Orleans during Hurricane Ivan. Wolshon says officials built a crossover median to connect the two outside outbound lanes of I-10 with the two inbound lanes, “but it didn’t work as effectively as it could have or should have,” says Wolshon.
Wolshon and other researchers have used trafic simulation models to figure out the best places for the ingress and egress to contraflow lanes. They came up with a specific reloading model for the New Orleans area that was used during Hurricane Katrina. When that was implemented, “traffic flowed much, much better,” says Wolshon. “It wasn’t perfect but it was much better, and they had the data to back it up to show how many more people moved out of the city.”
Merging, which works fine in normal rush-hour commuter traffic, can slow things down too much when so many vehicles are attempting to leave an area, and it can be particularly tricky in contraflow areas. One option is to disallow merging at certain points along a highway. “[W]hen you get to a situation where it may be a life and death, you need to keep people moving, you might say ‘well, look, they might not be able to exit here, they might not be able to get onto this interstate exactly where they want to go, but at least they’re…going to be kept moving,’” Wolshon says.
In the case of the full-on exodus that happened in Texas with Hurricane Rita, the overflow of evacuees was exacerbated by the lack of a contraflow plan in the region, says Henk. Additionally, though people had advance warning, a lot of people waited until the end of the week to evacuate. “Basically, we just had gridlock. The whole system just cratered…people literally sat, and most of the freeways and arterials were parking lots. What usually takes maybe 30 minutes to an hour took the better part of a day in terms of movement and getting people in particular out of the Galveston [and] Houston area,” Henk says.
Fuel. Traffic isn’t the only thing that can stop evacuees in their tracks. An empty tank can have the same effect. With Rita, the gas stations hadn’t ramped up, and everyone had waited until the last minute to fill their tanks. Henk says that now gas stations are advised to get their inventories up to the maximum 96 hours before a storm is expected to hit. There are now agreements between the State of Texas and the private sector petroleum industries to fuel up before a storm. “There’s now a formal countdown starting at four days out where there’s prepositioned fuel, advanced fuel capacity, and that’s just one of the many dynamics that are now in place,” Henk says.