Date of Award
Master of City and Regional Planning (MCRP)
City Planning & Real Estate Development
Dr. Morris, Committee Chair
American roads are becoming increasingly overcrowded as the country continues to grow. Existing urban form is not easily renovated to allow for the necessary expansion of these roads in urban centers. This is especially true in the case of Atlanta, Georgia. Being the largest city in the southeastern U.S., and coming to prominence after the creation of the automobile, Atlanta residents now spend countless hours sitting in traffic on roads not designed for the size the city has grown to and the amount of traffic it generates. To compound this, the growth the city has seen has been sprawling, with large suburban areas stretching out miles from the city center and even incorporating other significant urban areas such as Buckhead. This project seeks to remedy this problem by examining the idea of moving automobile transportation underground (i.e. into a tunnel), under the already developed urban area, in order to attempt to find an alternative to surface road expansion.
Three case studies of similar tunnels were analyzed in order to draw conclusions for this potential project. Tunnel safety, design, construction, cost, construction time, and funding were all reviewed to reach the conclusions found within. Results of this analysis led to the decision to propose an 8.5-mile tunnel that runs under the merged roads of I-75 and I-85 through downtown Atlanta. This project begins where the two roads meet to the north of the city and follows their path to where they diverge again in the south above Hartsfield-Jackson International Airport. This site has been selected for two reasons. The first is because of the significant number of travelers on the existing route; up to 400,000 individual users on a normal work day. Secondly, the geologic conditions of Atlanta make this route viable for tunneling. The rock bed in which the tunnel will be constructed are hard and stable enough to maintain its structure throughout construction, but not so hard as to make tunneling difficult.
To construct this tunnel, a decision has been made based upon analysis to utilize a shield-type tunnel boring machine (TBM), for two reasons. The first and foremost is that a tunnel boring machine causes minimal surface disruption. This is especially relevant for this project as it will run directly beneath one of the busiest sections of highway in the southeastern United States, and limiting disruption to existing traffic flows will be a crucial part of its successful construction and implementation. The second reason for the choice of a TBM is that the rock type being bored through is ideal for a TBM, though it does include softer pockets which may require the shield created by the TBM to help maintain structure and composition during boring.
With the route and tunneling method selected, this analysis then moves into the design stage for the project. The overall design for the tunnel is a single tube, double-deck tunnel with two lanes on each deck running in one direction. This means that the top deck will likely carry southbound users while the lower will handle northbound traffic. The design laid out in the document has enough space for an emergency lane on one side and shoulder on the other in case of breakdowns or non-severe accidents.
For this tunnel to be successful safety will be key. Through analysis, a combination of a mist-style fixed fire fighting system (FFFS) and transverse ventilation system has been determined to be the ideal combination of fire response methods. The effectiveness of these two systems in concert with each other is ideal for this project because of the tunnel’s length; any of the other possible systems studied would likely not be as effective for this reason. The tunnel will have emergency refuge areas for users trying to escape an internal disaster. These will be located every 500 feet along its length, 90 in total, which will be interconnected to escape stairs which lead to the surface placed intermittently every 1,000 feet along the route for a total of 45 escape points, not including the tunnel’s main entry and exit points. To further aid emergency response, dedicated entry and exit points for emergency responders and tow trucks will be located every mile along with route and oriented in the opposite direction of the flow of traffic to discourage users of the tunnel from trying to access them. These will be staffed and operated by the Georgia Department of Transportation (GDOT).
Basic cost and construction time estimates have been made from analysis of the case studies. Based on all review factors, this project is expected to cost $4.24 billion and take anywhere from 5 to 10 years to complete. The accuracy of these figures will depend on a proper and thorough planning phase for this project that ensures it will be efficiently managed and kept on schedule. Any delays could lead to a significant cost escalation factors which will derail the intended positive economic impacts of this project.
With all factors considered and these above estimates, a financing and management structure has been laid out as the final piece of this document. In order to support the significant cost of this project and expedite its construction it has been determined that a public private partnership (PPP) with a company already well-versed in infrastructure construction projects will be necessary. The specialized experience a private company can bring to a tunnel such as this compared to the local entities in Atlanta which have not had as much experience is invaluable to this project’s success. Because of the company’s history of building and managing tunnel projects, Cofiroute has been identified as the ideal partner for this project. This relationship will also make it easier and faster to fund the project, as there are not as many processes to go through to procure the necessary monies. Therefore, it should be expected that Cofiroute plan, construct, and operate the tunnel for a set amount of time. During this time a toll will be placed on the route, for two reasons. First, to finance the PPP Cofiroute must make a return on its investment, and second tolls will to control the number of vehicles in the tunnel at a given time which well help prevent accidents and delays due to overcrowding.
In the end, it has been determined that a project of this scale can be completed with a reasonable cost and timeline if an appropriate and thorough planning period is employed that keeps the project advancing without delays.
Whitmire, Jake, "Metro Atlanta Tunnel Bypass" (2018). Master of City and Regional Planning Terminal Projects. 339.