## 1 Introduction  
Globally, recent years have witnessed a dramatic increase in the occurrence of emergencies. Emergency situations are often created by natural and man-made disasters, such as the September 11 terrorist attack in New York in 2001, the Indian Ocean tsunami in 2004, the Wenchuan earthquake in 2008, and Hurricane Irma in 2017, all of which caused huge losses of life and property. During a major emergency, an attempt is made to rapidly evacuate a large number of people from the affected area to safer locations. However, the capacity of the evacuation roads may be too small to support the exploding volume of traffic. Strategies for increasing the road capacity in such situations are thus critical. Contraflow, or reversed lanes, in which the traffic flow in some or all of the inbound lanes is reversed, has been widely adopted in emergency response plans to increase the capacity of outbound roads and the overall evacuation speed. According to the Federal Emergency Management Agency [1],reversing one lane of a four-lane dual highway increases the evacuation road capacity by approximately 30%, while [PERSON] [2] observed a 67% increase when all the inbound lanes were reversed. Because contraflow is an important emergency response traffic strategy in many countries, several studies have been conducted on different contraflow strategies and their effectiveness. [PERSON] [2] proposed three types of contraflow schemes, namely, reversing one/some inbound lanes, reversing all inbound lanes, and using the outbound left shoulder as an additional lane with reversed inbound lanes. [PERSON] [3] found that the termination points of contraflow sections usually were characterized by merging conflicts and traffic congestion, therefore proposing to maintain a substantial number of exits along the contraflow section to increase the overall evacuation efficiency. [PERSON] et al. [4] developed a large-scale regional dynamic traffic simulation and assignment model of the contraflow strategy by DynusT, and they demonstrated that the performance of the contraflow strategy could be enhanced when used in conjunction with the phased evacuation strategy, enabling a reduction of nearly 30% in evacuee travel time. [PERSON] et al. [5] modified the design of the contraflow entry-points and exit-points in New Orleans by adding transition sections to avoid congestion. [PERSON] et al. [6] used CORSIM (Corridor Simulation) models to identify the key factors of a contraflow design and recommended the location of a merge zone after a freeway exit instead of before it, and the application of channelization or separation devices to enhance the flow quality near the termination of a merge zone. It has also been suggested that in countries and regions with low levels of private car ownership, buses and coaches provided by the government and organizations should be used as the main transportation medium for human evacuation during an emergency [7]. Hence, to achieve high-efficiency bus and coach shuttling between gathering points and diving points, [PERSON] et al. [8] proposed the implementation of bus-only lanes. These previous studies considered different approaches for improving the efficiency of contraflow lanes under different conditions of emergency evacuation. The proposed methods involved changing road structures at a fundamental level or controlling vehicle movement at a subsidiary level. For further evaluation of the contraflow strategy at a meso-microscopic level, it is necessary to analyze and compare the traffic flow characteristics of contraflow and regular lanes. Despite the long history of contraflow strategy studies, they have been seldom implemented in real emergency evacuations. Incidentally, it is difficult to use the commonly employed methods to duplicate the traffic conditions of a real contraflow lane during an emergency.