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Behind The Scenes With The I-59/20 Big Build

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By: Jeff Stephenson, PE, PTOE, Sain Associates

From Sain blog

If you live anywhere close to the Birmingham area or if you have traveled through Birmingham within the past several months, you are certainly aware of the construction taking place on I-59/20 in the Central Business District (CBD) of downtown Birmingham. The emphasis of the project is to replace the aging bridges on I-59/20 between I-65 and the Red Mountain Expressway. Prior to the project, these bridges experienced over 160,000 vehicles per day – twice the amount of daily traffic for which they were designed. As the bridges are being replaced, ramps providing access between the interstate and the surface streets of downtown are being consolidated and reconfigured to reduce traffic congestion and improve safety in the CBD. Construction has been ongoing for a few years now with a few phases of the project being complete, however the work on this project for Sain Associates started several years ago.

In 2012, Sain Associates teamed with the Alabama Department of Transportation to plan and design for the deployment of Intelligent Transportation Systems (ITS) devices such as traffic data collectors, cameras, message boards, and communication networks (both fiber optic and wireless) associated with the project. The intent was to have these ITS in place prior to the bulk of the I-59/20 bridge replacement construction work getting underway. Many of these ITS devices had to be installed several miles outside of the CBD area in order to communicate messages to drivers in time for them to have an opportunity to adjust their routes accordingly, and for ALDOT to be able to measure and monitor traffic patterns and congestion in these same areas. Cameras and traffic data collectors were installed in the project work zone to give ALDOT the ability to monitor construction and detour routes. Additionally, a key fiber optic backbone cable that was attached to the aging I-59/20 bridges had to be addressed. In order to maintain critical communication between ALDOT and most of the traffic monitoring devices in the Birmingham area, a new fiber optic backbone had to be installed to take over the communication prior to the bridge and attached fiber optic cable being removed.

Sain also worked with ALDOT to evaluate projected traffic conditions associated with the 14-month period where I-59/20 will be closed between I-65 and Red Mountain Expressway. The purpose of the evaluation was to identify areas on the detour routes which needed improvements in order to accommodate the projected increases in traffic coming from use of the detour routes. The I-59/20 CBD bridge closure started on the evening of Monday, January 21, 2019, however, Sain’s work with ALDOT on this task started a few years prior to that date. We used travel demand modeling techniques to forecast traffic volumes along the key detour routes as well as the entire north grid of downtown Birmingham. The north grid is defined as the area of downtown Birmingham that is east of I-65, west of the Red Mountain Expressway, south of I-59/20, and north of 1st Avenue North. This area includes over 150 traffic signals that are maintained by the City of Birmingham. Traffic modeling software was used to assess projected traffic operations, identify potential deficiencies, and support recommended improvements to address the anticipated deficiencies. We also used traffic modeling software to establish temporary signal timing plans along the key detour routes and for the entire north grid. This was necessary because all of the signals in the north grid work together in an effort to keep traffic moving efficiently through downtown. The recommended improvements and temporary signal timing plans were all successfully developed and implemented prior to the closure date.

It’s hard to describe the anticipation we had leading up to the I-59/20 closure, having been so involved with ALDOT and the City of Birmingham in the planning stages of traffic management associated with the closure. As the I-59/20 closure transition was being implemented in late January and early February, Sain staff worked closely with ALDOT and the City to monitor traffic and make changes to signal timing as the detour traffic patterns began to settle. Throughout the first week of the closure transition period, Sain supported ALDOT with 24/7 staffing of the ALDOT Traffic Management Center (TMC) along with other members of ALDOT’s project design, maintenance, operations, and construction teams. We monitored traffic using a combination of camera feeds that were being displayed inside of the TMC, the AlgoTraffic app/website and frequent driving of the detour routes during peak periods of traffic congestion. We also assisted ALDOT with responses to calls received on the I-59/20 hotline as needed. We will continue to support ALDOT with monitoring CBD traffic conditions throughout the remaining 10-12 months of the closure.

Our final task associated with this project is development and implementation of permanent signal timing plans for the entire north grid based on projected traffic patterns occurring after completion of the I-59/20 CBD project. We will work closely with ALDOT and the City of Birmingham later this year to complete that task.

Sain Associates has been very intentional on recognizing and stressing the importance of the I-59/20 CBD bridge replacement project with our staff. Being given the opportunity to have such a critical planning and implementation role with this project is a privilege. It is a project we will talk about and revisit our experiences for years to come.

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