This FDOT Lane Elimination Guidance is a resource for advocates across the state to reference.
Road diets work. West Palm Beach owes much of its downtown revitalization to successful road diets on Clematis Street and Dixie through downtown, and a successful rightsizing of Olive Avenue that stitched back together the campus of Palm Beach Atlantic University and the neighborhoods to its south. (Great video presentation on the history of these projects by Ian Lockwood, City Transportation Engineer at the time).
The FDOT process outlined in this document has been used successfully. Tequesta, a city to the north of West Palm Beach, recently gained approval for a six-to-four lane elimination using this process. Road diets are a proven safety tool to reduce frequency and severity of collisions and make streets more livable, endorsed by the Federal Highway Administration.
This guidance is quite good, and contains an appendix of lane elimination projects in Florida (Appendix A). Appendix C contains existing lane elimination request processes for various FDOT districts.