TRANSPORTATION

A Project Development and Environment (PD&E) study was conducted between April 2016 and July 2018, evaluating a new interchange at NW 170th Street on the Florida’s Turnpike Extension. The Interchange Justification Report (IJR) submitted as part of this PD&E study was approved in August 2018 by FDOT Systems Implementation Office on a condition of a re-evaluation submittal, evaluating enhanced local street connections at the interchange, requested by Miami-Dade County. This document provides the requested re-evaluation.

The approved Turnpike Extension interchange is to be located in northern Miami-Dade County at the proposed west side construction of NW 170th Street (Milepost 37). The interchange is midway between the US 27 (Okeechobee Road) interchange (MP 35) and the I-75 interchange (MP 39). A programmed project to widen the Turnpike Extension from three to five lanes in each direction was recently let for construction and Miami-Dade has plans for the construction of NW 170th Street. The purpose of the interchange at NW 170th Street is to adequately serve the future access needs and travel demands of the existing and approved land uses in the area, which include two recently approved Miami-Dade Comprehensive Development Master Plan (CDMP) amendments for the land east of the Turnpike Extension and north of NW 170th Street.

Extensive project coordination efforts between Florida’s Turnpike Enterprise (FTE), Miami-Dade County, and area stakeholders resulted in the desire for the interchange to be constructed concurrently with the Turnpike’s programmed widening and to include a flyover from NW 107th Avenue, south of NW 170th Street, over NW 170th Street to connect to the Turnpike Extension northbound on-ramp and a connection from the northbound off-ramp directly to southbound NW 107th Avenue. Miami-Dade County requested these additions in a resolution, with the intent to better serve NW 107th Avenue and planned future development south of NW 170th Street and improve traffic operations in the region. This IJR re-evaluation documents the traffic analysis conducted according to the Methodology Letter of Understanding (MLOU, April 2019) prepared for the re-evaluation. The interchange alternatives include a No-Build, Build without 107th Avenue enhanced connections, and Build with enhanced connections.

The traffic analysis considered operations, safety, and access within the Area of Influence (AOI). The AOI includes the Turnpike Extension between US 27 and I-75, and NW 170th Street at the Turnpike Extension and at the intersection of NW 102nd Avenue. The evaluation demonstrates an acceptable level of service (LOS) with the enhanced access and no adverse operational impact to the interchange. Analysis indicates the existing interchanges cannot accommodate future traffic at an acceptable LOS, and the local roadway network will not be adequate to serve the traffic growth envisioned for the project area. The enhanced local connections to NW 107th Avenue supplement the access provided within the vicinity of the approved interchange at NW 170th Street. As outlined in the IJR, while the interchange adds traffic to Florida’s Turnpike, most mainline segments and local intersections will operate at LOS D in year 2040. LOS E is considered acceptable with planned managed lanes. Five years of crash data show increasing crash frequency with decreasing crash severity, which is indicative of a roadway with worsening congestion. The planned Turnpike Extension improvement project will help alleviate congestion. The planned Diverging Diamond Interchange (DDI) at Florida’s Turnpike and NW 170th Street, also known as a double crossover diamond, is safer than conventional interchange designs since it reduces conflict points and has been demonstrated to reduce crashes.

The configuration crosses traffic to the opposite side between the ramp terminals, allowing left turns to flow unopposed. This innovative design is more efficient when an interchange has heavy left turns, and significantly reduces the number of vehicle conflict points compared to a conventional diamond interchange. Plans for NW 170th Street also include bike lanes and sidewalks to enhance multimodal safety.

The maximum queue length analysis of the IJR Build with enhanced connection to NW 107th Avenue shows similar queues at ramp terminal intersections and reduced queues at NW 102nd Avenue compared to the previous IJR Build. The enhanced access facilitates truck traffic from the adjacent industrial areas along NW 107th Avenue and provides more direct access to/from NW 107th Avenue.

The proposed interchange design accommodates access for each directional movement between the Turnpike Extension and NW 170th Street. The enhanced local access evaluated within this document will not result in changes to the movements provided at the interchange. The west side of Turnpike Extension is outside Miami-Dade’s urban development boundary, and traffic demand to or from the west of the interchange is minimal. The interchange has been designed to allow for potential future extension needs of NW 170th Street.