TRANSPORTATION

As part of the I-75/I-4 Systems Interchange Modification Report (SIMR), this SIMR Addendum documents the analysis needed to evaluate the proposed interim roadway improvements needed to enhance traffic conditions within the I-75 at SR 574/Martin Luther King Jr. Boulevard (MLK) area. This addendum is to fulfill the commitment made for the approval of the I-75/I-4 SIMR to revisit this project during the design phase due to concerns with signing. These interim improvements are recommended to improve the operation of the I-75 at MLK Boulevard interchange in the near term and will be designed to require minimal changes when the ultimate improvements are constructed. The ultimate improvements are in the process of being documented in a Project Development & Environment (PD&E) Study along I-75 from US 301 to north of Fletcher Avenue in Hillsborough County.

This document serves as the SIMR addendum between FHWA, FDOT’s Systems Implementation Office (i.e., Central Office) and FDOT’s District Seven Interchange Review Team. The analysis for this SIMR addendum has been performed in accordance with a Methodology Letter of Understanding (MLOU), approved by Systems Implementation Office – Central Office on December 30, 2015. A copy of the MLOU is attached in Appendix A and follows the Interchange Access Request User’s Guide (IARUG).

The addendum to the I-75/I-4 SIMR documents four potential interchange configurations, eventually determining the preferred alternative based on the existing year 2015 and design year 2040 conditions in the study area, the analysis of future conditions, ramps and ingress/egress points between the interstate mainline and the interchange within the project limits including MLK Boulevard northbound and southbound ramps, Falkenburg Road and Williams Road intersections. Safety was also considered in determining the preferred build alternative in regard to reducing the number of conflict points. The alternatives considered are listed below:

• Transportation Systems Management and Operations (TSM&O) Alternative – Evaluation of measures leading to improvement of traffic flows through non-capacity improvements including but not limited to Intelligent Traffic Systems (ITS) deployment, intersection optimization and increased share of alternatives to single occupancy vehicles. It involves optimizing the use of existing facilities. TSM improvements would not adequately accommodate forecasted traffic volumes within the I-75/I-4 SIMR interchange area. Thus, the TSM Alternative is not considered a viable alternative for the addendum to the I-75/I-4 SIMR.

• No Build - Alternative 1 – This is the Build alternative from the original I-75/I-4 SIMR. In this alternative, the I-75 northbound to I-4 eastbound/westbound Ramps create a two-lane exit ramp south of the I-75/MLK Boulevard interchange separating the I-4 traffic on to a new Collector Distributer (C-D) road, retaining the existing I-75 northbound off loop ramp to westbound MLK Boulevard. In this alternative, the loop ramp geometrically will need to be reconstructed to provide a larger radius curve or process a design variation/exception. The proposed two-lane C-D road continues north using a new proposed bridge overpass at MLK Boulevard and a realigned northbound entrance ramp to I-75 from MLK Boulevard.

• Build - Alternative 2 – This alternative begins with an 1800-foot auxiliary lane added to I-75 northbound and is operationally similar to No Build Alternative 1 from the I-75/I-4 SIMR; only the I-75 northbound off loop ramp to westbound MLK Boulevard was removed and the C-D road parallel to I-75 will go under the MLK Boulevard overpass. The traffic exiting I-75 to the northbound off loop ramp is combined with traffic heading to I-4 and will exit south of I- 75/MLK Boulevard interchange via the new auxiliary lane to a two-lane C-D road and then traffic to eastbound and westbound MLK Boulevard will exit off the C-D road. The traffic from northbound I-75 to westbound MLK Boulevard will be handled by triple left-turn lanes at the intersection of the I-75 northbound ramps and MLK Boulevard.

• Build - Alternative 3 – This alternative is operationally similar to Build Alternative 2, with the addition of an 1800-foot deceleration lane on I-75 northbound. The 1800-foot deceleration lane becomes an exit lane to MLK Boulevard and is joined by the first auxiliary lane that splits as a shared through lane at I-75. The traffic from northbound I-75 to westbound MLK Boulevard will be handled by triple left turn lanes at the intersection of the I-75 northbound ramps and MLK Boulevard. The auxiliary lane continues along I-75 northbound and goes under MLK Boulevard and eventually feeds a new two lane C-D road north of MLK Boulevard heading to I-4.

• Build - Alternative 4 – This alternative is operationally similar to Build Alternative 3 with a Diverging Diamond Interchange (DDI) option analyzed at the MLK Boulevard interchange as part of this addendum to the I-75/I-4 SIMR. Figure 2-1 shows a line diagram with all alternatives.

Based upon the analysis, Alternative 4 with the Diverging Diamond Interchange (DDI) configuration is recommended as a preferred build alternative for the I-75 and MLK Boulevard study interchange. Alternative 4 shows the most improved operations at the ramp interchange terminals at MLK Boulevard and simplifies signing for MLK Boulevard northbound off ramps. This alternative also eliminates the conflict with the Florida Gas Transmission (FGT). From a safety perspective, the DDI should reduce both the overall amount of crashes as well as the severity of crashes compared to a diamond interchange. A diamond interchange has twenty-six overall conflict points, with thirteen conflict points concentrated at each of the ramp terminals. The DDI, on the other hand, only has fourteen conflict points. These conflict points are spread out through the interchange, which means that a driver only needs to navigate through one potential conflict at a time. Also, there are only two crossing conflict points in the entire DDI, one at each crossover intersection. This compares to ten crossing conflict points in a diamond interchange. These crossing conflicts provide increased opportunity for severe crashes. This recommended interchange alternative improves signal spacing while eliminating the on and off-ramp conflicts with through lanes by removing the left turns from the main traffic stream.