This study was conducted to assist the City of Port St. Lucie in making a decision on the appropriate improvements to the interchange of Gatlin Boulevard and State Road 9 (I-95) by providing data and analyses that will aid in evaluating alternative design improvements using SYNCHRO to test different recommended alternatives ranging from revision of signal timings, change phasing and adding lanes. The study provided analysis and recommendations for the projected future years to maintain acceptable Levels of Service (LOS) “E” as adopted by the City and improve operation along the ramps. Several alternatives were recommended, ranked by construction cost and level of service of the roadway and interchange. The pre-existing conditions of Gatlin Boulevard at I-95 consisted of having both the northbound and southbound off ramps operating under stop sign control. This previous condition resulted in failure and severe delay of the northbound and southbound off ramps. Failure of these ramps included vehicles queuing back to I-95, causing severe congestion of the overall interchange operation. Given these conditions, the City of Port St. Lucie received approval from the Florida Department of Transportation to place a temporary traffic signal at the southbound off-ramp intersection until permanent mast arm traffic signals could be installed at both intersections. Since the installation of the temporary traffic signal, the operation of the interchange has been slightly improved, reducing delay time and queuing along the off ramps. Based on the analysis of the current and future conditions, improvements are needed to maintain an acceptable LOS.