Sanibel Causeway Improvements Study

PBS&J conducted a PD&E for Lee County that evaluated improvement alternatives for the Sanibel Bridge and three causeway bridges.

PBS&J was selected by Lee County to conduct a project development and environment (PD&E) study for improvements to the Sanibel Causeway and three causeway bridges located in Lee County, Florida.  The analyses considered the removal of the entire causeway, as well as rehabilitation and replacement alternatives for the three bridges.

Traffic was evaluated and simulated for three alternatives: a 26-foot drawbridge with one lane onto and two lanes exiting the island; a 50-foot mid-level drawbridge with one lane onto and two lanes exiting the island; and a 70-foot fixed-span bridge with only one lane exiting the island. Each bascule bridge alternative considered the need for an additional lane on the Sanibel Causeway for traffic exiting the island.

VISSIM traffic simulation models were developed for each of the alternatives based on existing PM peak-hour traffic conditions. The alternatives were compared based on measures of effectiveness (MOEs), for example, travel time, driver delay, levels of service (LOS), queue lengths, and average vehicle speed. The videos clearly showed significant differences in traffic congestion between the alternatives. Video clips of the VISSIM 3D traffic simulations were created for each alternative and were shown to the public at community meetings and a public hearing.

These traffic evaluations revealed that a fixed-span bridge, with one lane exiting the island, would provide the best capacity off the island, yielding a free-flow situation. The fixed-bridge alternative also offered uninterrupted flow for shipping traffic, providing improved safety conditions in a channel known for strong currents.