Green Stormwater Approach on Fast-Track Interstate Widening Design

A green approach was just one of the highlights of the Interstate 64 lane additions project.  The project also overcame site constraints and was completed on a fast-track schedule with significant participation by disadvantaged businesses.

The project provided much needed congestion relief to this key corridor in St. Louis County by adding an additional lane along the interstate. The overlay and widening project extends five miles from Interstate 270, West to Route 340 (Clarkson/Olive Boulevard). The design was completed in just seven months and incorporated a project office located at Crawford, Murphy & Tilly (CMT)’s St. Louis downtown office, where team members from CMT and their five sub-consultants worked on design plans in a highly-collaborative fashion. The project team included three local disadvantaged business firms who provided 25% of the workforce to complete this high-profile project.

Providing improvements to the quality of the runoff was important as the project crosses several tributaries to an impaired creek. Providing treatment at every crossing was impractical due to the narrow right-of-way, but through extensive coordination with the Metropolitan St. Louis Sewer District (MSD), CMT was able to mitigate the quality and quantity of runoff to the maximum extent practical. The green infrastructure elements were oversized to limit the project’s impact to the watershed as a whole, despite not treating the runoff at every outfall.

The final design includes detention basins and hybrid ditches for water quality volume and channel protection volume within the interchanges infields along this very tight corridor. In addition to the structures within the project limits, a basin was added at an interchange outside the limits, but within the Creve Coeur Creek watershed. The interchange infield was regraded into a basin and the outlet modified to provide additional channel protection storage. The combination of these elements mitigated the quality and quantity of storm water runoff. CMT’s innovative design made this possible.

This project was delivered on time, under design budget, and was very successful.