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New York State Thruway Mainline Interchange 23 & 24

The New York State Thruway mainline between Interchanges 23 and 24 consists of 24 lane miles. Phase V and VI design services for the total reconstruction included the full depth pavement reconstruction of almost 7 miles of mainline on the New York State Thruway between the Normans Kill Bridge (south of Interchange 23) and Interchange 24.


WSP USA developed the design plans for a new full-depth Portland cement concrete replacement pavement along with a new third lane in each direction to alleviate existing and project traffic congestion. As part of the design process, we developed a CORSIM traffic simulation program of the study area to evaluate the mainline transitions to adjacent interchange areas and develop ramp improvements to improve traffic flow. The model was also used in the development of maintenance and protection of traffic schemes and traffic control plans.

A key component of the final design was the implementation of a drainage system that addressed the existing structural and operational deficiencies while conforming to the needs of the projects Stormwater Pollution Prevention Plan (SWPPP), which was prepared in conformance with the latest NYSDEC Phase II guidelines.

The design was further complicated by the extensive wetlands surrounding the area, which were subject to an individual permit, and the stormwater detention basins that were specified in the SWPPP. The wetland permit required that mitigation sites be developed for the areas impacted by the project construction. Other environmental mitigation measures from the Environmental Impact Statement that became part of the final design plans included the construction of more than 2.5 miles of noise barriers and other noise reduction measures, and the cleanup of previous fuel spills. The noise mitigation measures were designed to address both, construction related and post-construction traffic generated noise impacts.