The purpose of this Interchange Operational Analysis Report (IOAR) is to evaluate the operational and safety beneit from the interim improvements proposed at the I-10 and SR 121 interchange. The interim improvements are expected to alleviate the traffic operational and safety deficiencies of the study area before the ultimate build improvements, as detailed in an approved Interchange Modification Report (IMR), are implemented at this location.
The following deficiencies have been identified under the Existing Year (2015) conditions that are anticipated to improve as part of this project.
• The I-10 and SR 121 interchange is a partial cloverleaf configuration with nonstandard loops in the southeast and northwest quadrants. Under existing conditions, these loop ramps that were built with lower design speeds, hinder normal traffic operations, especially in the westbound I-10 direction. The westbound I-10 off-ramp is currently a three center radii loop ramp that terminates at a stop-controlled intersection with SR 121. This configuration results in interrupted flow and traffic backups, specifically during the AM and PM peak hours.
• Southbound SR 121 commuters encounter poor sight distance due to the vertical curve over I-10. The I-10 westbound ramp terminal intersection is unsignalized. Hesitation to perform the turning movement to head north on SR 121 due to poor sight distance over the vertical curve leads to high delays for motorists exiting the freeway. Drivers of heavy trucks making this movement have been observed making risky decisions. These conditions result
in unsafe travel conditions and an increase in queue length that backs into mainline I-10 impeding its operations.
• The study area possesses a high volume of heavy truck traffic, which accounts for more than 11 percent of peak hour traffic volumes. The grade differentials and curves of the loop ramps paired with the high truck volumes generate speed differentials that deteriorate operating conditions and safety.
The deficiencies found in the Existing Year (2015) analysis are anticipated to worsen with increased traffic volumes by Design Year (2040). Without adequate improvements to this interchange, the traffic operation and safety within the study area will continue to deteriorate, the queue lengths and delays will increase, and the number of crashes will go up.
This IOAR compares the operational and safety performance for a No-Build Alternative and two Build Alternatives. Two interim improvements: Build Alternative 1 and Build Alternative 2 are analyzed. Build Alternative 1 has the following improvements:
• Add directional ramp for traffic from westbound I-10 off-ramp to northbound SR 121
• Improve SR 121 in the northbound direction
• Install a new traffic signal to control the northbound SR 121 and westbound I-10 off-ramp movements
The Build Alternative 2 is designed to utilize the existing geometry and install a new traffic signal at the intersection of westbound I-10 ramp and SR 121 which is currently stop-controlled.
The design traffic volumes developed through the approved IMR for the ultimate SR 121 interchange improvements are used for this IOAR. The future traffic forecast was performed utilizing the NERPM Version 4.2 with the Base and Design Years of 2005 and 2035, respectively. Additionally, historical growth rates of the study area were used. For the purposes of this study, the analysis years included Existing Year (2015), Opening Year (2020), and Design Year (2040).
Purpose and Need
Download the Purpose and Need (PDF, 138.1KB)
The purpose of this project is to provide interim alternatives to add capacity and improve traffic operations and safety near the SR 121 and I-10 interchange in Baker County while the ultimate build improvements described in the approved Interchange Modification Report (IMR) (May 2016) funds are procured. The approved IMR is provided in Appendix A.
The I-10 and SR 121 interchange is a partial cloverleaf configuration with nonstandard loops in the southeast and northwest quadrants. Under existing conditions, these loop ramps hinder normal traffic operations, especially in the westbound I-10 direction. The westbound I-10 off-ramp is currently a three center radii loop ramp that terminates at a stop-controlled intersection with SR 121. This configuration does not provide efficient operations and results in traffic backups, specifically during the AM and PM peak hours. Additionally, southbound drivers encounter poor sight distance due to the vertical curve over I-10.
In the year 2014, SR 121 carried an Annual Average Daily Traffic (AADT) of 7,500 vehicles to the south and 12,700 vehicles to the north of I-10 on a two-lane facility. The I-10 mainline within the project study area carried an AADT of 25,000 vehicles to the west of SR 121 and 19,300 vehicles to the east of SR 121 on a four-lane facility. If no improvements are made to the interchange, traffic operations and safety within the interchange area will continue to deteriorate as traffic and freight movement to and from the City of Macclenny increases. For this reason, the ultimate build improvements were proposed to address operational and safety deficiencies of the study area. The details of ultimate build improvements are discussed in the approved IMR (May 2016) (Appendix A). However, the Florida Department of Transportation (FDOT) District Two wants to implement interim improvements before ultimate improvements were built out to alleviate traffic operations and safety deficiencies of the study area. This report analyzes two interim alternatives. The Build Alternative 1 includes adding a directional ramp to westbound I-10 to serve traffic heading northbound SR 121, improving SR 121 in the northbound direction, and installing a new traffic signal to control the northbound SR 121 and westbound I-10 off-ramp movements. The Build Alternative 2 is designed to utilize the existing geometry and install a new traffic signal at the westbound I-10 and SR 121 ramp terminal intersection.