4.4.3.1 Contraflow Lane Reversal

Evacuating impacted individuals prior to or immediately following a disaster can be difficult due to limited transportation infrastructure. Under certain conditions, contraflow lane reversal may provide additional capacity to an existing roadway system to expedite the evacuation process.

Contraflow lane reversal modifies the normal flow of traffic to aid in increasing the flow of outbound vehicle traffic during an evacuation (Figure 4.4.3.1.1). Typically, one or more lanes in the opposing direction of a controlled-access highway are used to increase capacity during the evacuation/displacement phase.

Contraflow operations require considerable planning to avoid any interference with response operations since necessary resources will likely be mobilizing into the area while evacuations are taking place. Contraflow may also create issues if the transition from contraflow reversed lanes back to normal lanes is not properly planned. This transition can create bottlenecks and confusion for drivers and significantly slow the evacuation. Contraflow operations also require a significant amount of time and resources to be safely implemented and are therefore most beneficial during large-scale evacuations. Permanently installed traffic control devices and signage will expedite the activation of contraflow plans and free up valuable resources ahead of a disaster (Figure 4.4.3.1.2).

Contraflow procedures almost always occur on controlled-access highways. Most contraflow plans operate on divided four-lane controlled-access highways. Traffic in all four lanes is traveling away from the disaster location toward destinations where the dangers posed by the approaching hazard are significantly reduced. Contraflow can also be implemented such that one lane remains in normal operation, carrying disaster response traffic toward the impacted area.

An important consideration in contraflow is the termination point. The inbound traffic is twice the normal flow and must be distributed to minimize congestion. This can be accomplished by locating the terminus at a freeway interchange with direct-connect ramps with a crossover just past the interchange for through traffic. Another method is to use multiple termini directing each lane of contra-flow to a separate exit. Based on infrastructure and traffic needs, the termini should be selected to minimize congestion and driver confusion.