TRANSPORTATION

Interstate 275 (I-275) is a major interstate highway that connects Pinellas and Hillsborough counties. It runs north-south from I-75 in Manatee County to SR 687 (4th Street North) in Pinellas County, and east-west from SR 687 (4th Street North) to Downtown Tampa. The alignment shifts to a north-south direction from Downtown Tampa to I-75 in Hillsborough County. I-275 is part of the Strategic Intermodal System (SIS) providing connections to two major interstate highways I-75 and I-4, that are also part of the SIS.

Currently, I-275 eastbound between 4th Street on-ramp and SR 60 off-ramp is experiencing significant recurring congestion within the study limits during both AM and PM peak periods due to high traffic volume exiting to SR 60. With the Existing Year (2017) volumes, commuters experience average travel times of 20 minutes and 24 minutes along I-275 eastbound (9.5 miles segment) during AM and PM peak hours. It is anticipated to have longer delays on this segment as demand increases in future years.

The subject I-275 Interchange Operational Analysis Report (IOAR) study explored operational improvements to improve the significant recurring congestion during both peak periods by providing three continuous lanes in the eastbound and westbound directions between Howard Frankland Bridge and Memorial Highway (SR 60). These interim improvements are expected to improve traffic operation along I-275 in the short-term (5-10 years). FDOT is evaluating long-term mobility alternatives to accommodate future travel demand and improve operations along I-275.

The main objective of the I-275 IOAR is to provide a comparison and documentation of the results from no-build and build microsimulation (TSIS/CORSIM 6.3) models. Synchro 10 was used to optimize the intersection signal timings for future year volumes. Traffic and safety analyses were performed in accordance with FDOTs Traffic Analysis Handbook and Interchange Access Request Users Guide (IARUG, January 2018), and FHWA’s Traffic Analysis Toolbox Volume III. Apart from the Existing Year (2017), Three (3) analysis years: Opening Year (2020); Interim Year (2025); and Design Year (2030), were considered to evaluate the traffic conditions with no-build and build alternatives for this study.

Existing traffic counts were collected along I-275 mainline and the ramp terminal intersections within the study area to be utilized for calibration effort. Field travel time data was collected for comparison against the Existing Year (2017) model results to ensure that the models replicate the field conditions. The Existing Year (2017) calibration results indicate that the individual link flows, sum of all link flows, and GEH statistic comply with the FHWA criteria during the AM and PM peak hours. Comparative analysis of travel times for the AM and PM peak hours indicates that 100 percent of the study segments meet the criteria for travel time convergence.

Traffic forecasting was performed using the Tampa Bay Regional Planning Model including Managed Lanes (TBRPM-ML). The methodology used for travel demand forecasting and development of design hourly traffic volume for future conditions comply with the FDOT Project Traffic Forecasting Handbook. The TBRPM-ML model established traffic volumes and area growth rates were used in forecasting future year volumes. The Directional Design Hourly Volumes (DDHVs) were estimated by using approved K and D factors that were identified in the MLOU for this project. Future demand traffic volumes were documented in the Design Traffic Memorandum.