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Operational and Safety Impact Analysis of Implementing Emergency Shoulder Use (ESU) for Hurricane Evacuation

The emergency shoulder use (ESU) was implemented in Florida in September 2017 to facilitate mass evacuation before Hurricane Irma made landfall on the shores of Florida. ESU was implemented on the northbound I-75 for about 39 h and eastbound I-4 for about 6 h when the left shoulders were opened for use as travel lanes. This study discusses the operational and safety effects of ESU. The operational effects of ESU were studied and compared with other alternatives including one-way operation (contraflow) and both left and right shoulder use. The findings showed the left shoulder ESU could be an effective alternative to one-way operation. The one-way operation was not a preferred method as it can only be operated during the day time, requires massive resource allocation, and hampers emergency services reaching to different parts of the state. However, ESU on the left shoulder offers minimal disturbance to traffic and is easy to deploy. The safety impact analysis was performed by conducting a descriptive statistical comparison of crash types, severity, and other relevant factors during ESU operations. The crash analysis showed that the observed number of crashes on an urban I-75 segment during ESU operation is commensurate with normal operation with saturated traffic conditions, in contrast a rural segment experienced a higher observed crash rate than the predicted rate with saturated traffic conditions. The predictive analysis of ESU crashes also showed that ESU implementation helped to reduce the expected number of crashes significantly.