This Interchange Modification Report (IMR) for the Interstate 4 (I-4) and SR 557 interchange in Polk County covers the documentation requirements agreed upon in the Methodology Letter of Understanding (MLOU). This was utilized to update previous analysis and to accommodate the future I-4 Beyond the Ultimate Improvements.
The purpose for conducting the IMR study is to document the impacts and evaluation of the operational traffic conditions for the proposed modifications. This is to determine if the diamond interchange configuration, as originally approved by FHWA in 2010, and modified with roundabout ramp termini as proposed by FDOT District One, remains viable as the preferred interchange alternative design.
This IMR study aims to improve the safety, Operational and Engineering acceptability, Level of Service (LOS), and traffic operations at the Interstate 4 (I-4) and SR 557 interchange. This study documents the analyses of three (3) potential interchange configurations, eventually determining the recommended preferred Build Alternative based on traffic operations. The alternatives evaluated as part of this study are listed below:
- No Build Alternative: This alternative represents the existing partial cloverleaf (2 quadrant) interchange configuration with the Polk TPO and FDOT committed roadway improvements. Note that per discussions with FDOT District One and Polk TPO, the year 2044 No Build shall include the
Managed Express Lanes with the I-4 Beyond Ultimate improvements and the SR 557 and CR 557 widening from 2 lanes to 4 lanes from US 17/92 to I-4.
- Build Alternative 1 (Diamond Interchange): This alternative represents the configuration approved in the original 2010 IMR study. This build condition represents a diamond interchange configuration with traffic signals at both ramp terminal intersections.
- Build Alternative 2 (Diamond Interchange Configuration with Teardrop Roundabouts): This alternative is similar to the Diamond Interchange Build Alternative 1 configuration but features roundabout ramp termini using a teardrop configuration instead of utilizing traditional traffic signals at both the ramp terminal intersections. Build Alternative 2 with the roundabout ramp termini is the recommended Build Alternative.
Traffic operational analysis was performed for all previously mentioned alternatives for the opening year 2024 and design year 2044. The No-Build condition alternative is projected to operate at or below the adopted LOS Targets whereas the two proposed Build Alternatives are projected to operate within the adopted LOS Targets. The Build Alternative interchange will have no adverse impacts to the operations of I-4 and SR 557 based on the operational analysis performed for this study. For Build Alternative 1, all ramps, mainline freeway segments, roadway segments and intersections are anticipated to operate at or above the acceptable LOS Targets, except for the westbound off ramp intersection that was found to operate at a LOS E condition for the design year 2044. Based on the queuing analysis, queues from the ramp terminal intersections will not impact the mainline I-4 freeway traffic operations in both Build Alternative scenarios. No additional roadway capacity improvements are necessary to mitigate conditions
based on the proposed geometry for both Build Alternatives assuming that both ramp terminal intersections are either signalized or designed with teardrop roundabout intersections within a diamond interchange configuration. The analysis contained in this Interchange Modification Report indicates similar design year traffic operations for the two Build Alternatives. Based on traffic evaluations and comparing the results, it is recommended that Build Alternative 2 be selected as the preferred alternative for final design.
Purpose and Need
Download the Purpose and Need (PDF, 51.3KB)
Intestate 4 (I-4) is an integral part of the Strategic Intermodal System (SIS) providing for high speed high volume traffic movements within the State of Florida. The purpose for conducting the IMR study is to document the impacts and evaluation of the operational traffic conditions that the proposed modifications to determine if the diamond interchange configuration as originally approved by FHWA in 2010 and modified with roundabout ramp termini as proposed by FDOT District One remains viable as the preferred interchange Build Alternative.
The need for this IMR study was primarily originated to replace the existing SR 557 bridge structure and facilitate the mainline realignment to accommodate the future I-4 Beyond the Ultimate configuration. The existing exit loop ramps providing access from I-4 eastbound to SR 557 and from I-4 westbound to SR 557 feature a tight turning radius posted at 25 mph speed with no mainline deceleration lanes and are determined to not meet safety and design standards. In addition to the exit loop ramps, the entrance ramp connections were also considered for replacement. The IMR approved in 2010, proposed a diamond interchange configuration with spread out eastbound and westbound mainline travel lanes to accommodate the proposed HSR corridor (which has been replaced by the future I-4 Beyond the Ultimate configuration). The design year 2035 analysis presented in the 2010 IMR showed the freeway segments operating at LOS D or better, ramps operating at LOS D or better, and ramp terminal intersections with signalization operating at LOS C or better conditions.