At the Hartsfield–Jackson Atlanta International Airport, the automated people mover system was extended and the terminal was renovated at the baggage claim station as part of the Atlanta Plane Train Tunnel West Extension (PTTWE) progressive design-build project. The City of Atlanta is the project owner, and Delve Underground is the lead designer for the Clark/Atkinson/Technique design-build joint venture.
The project added a switch and tail track west of the current western end of the Plane Train system to enable a reduced headway and to increase capacity for future ridership. The existing tunnels have been extended westward about 660 feet to a 30-foot-diameter construction and emergency egress shaft. Approximately 408 feet east of this shaft connection, a twin tube bifurcation was constructed, and the tunnel divides into a north tunnel and a south tunnel to connect to the existing automated people mover mainline tunnels. The typical tunnel section is horseshoe-shaped with finished dimensions of approximately 12 feet wide at springline and 17.5 feet tall. The finished dimensions of the bifurcation include a span up to 40 feet wide and a height of 17.5 feet with up to 25 feet of flat roof in the span’s middle. The project included the design and construction of a ventilation system for the tunnel extension, which involved the construction of a ventilation pathway at the egress shaft, a cut-and-cover ventilation tunnel, and a utility building housing two new 120 kilo-cubic feet per minute (kcfm) fans.
Reconfigured emergency ventilation shafts and cut-and-cover tunnel
Ventilation Newcomb & Boyd and Stacey Agnew provided ventilation design as subconsultants to Delve Underground. The ventilation in the existing Plane Train system used fans at the ends of the tunnels and in the middle of the tunnels for supply and exhaust based on the desired airflow direction. This allows the system to be operated in discrete ventilation zones to respond to fires. With this configuration, the ventilation for the West Extension could be designed such that there are no performance or operational changes to the existing system.
The flexibility of the progressive design-build model allowed the team to develop alternative design and construction approaches to present to the City of Atlanta for consideration during the predesign and design phases of the work. This resulted in several improvements to the project, including relocating the existing ventilation pathway from the west end of the existing tunnel into the tunnel extension, resulting in a more favorable ventilation pathway by eliminating an existing plenum with sharp transitions. This also allowed for the ventilation shafts to be located closer to the existing ventilation fans. Shifting the ventilation pathway involved constructing large penetrations in the crown of the north and south tunnels, just east of the large bifurcation. Also, a shallow cut-and-cover tunnel was constructed to connect the ventilation shafts, and a bump-out of the existing ventilation plenum was constructed to connect the new ventilation pathway to the existing plenum, with fans positioned directly above on the roof.
Measurements were taken in the ventilation system three times prior to the final testing and commissioning:
Prior to the start of construction to establish baseline performance of the existing system.
After the switchover to the temporary ventilation ducting to confirm no adverse construction impacts.
Before the switchover to the final ventilation configuration, again to confirm no adverse construction impacts
Testing & Commissioning
Between June 24 and June 28, 2024, the City of Atlanta’s commissioning consultant, Total Systems Commissioning, performed final testing and commissioning of the new ventilation system. During this period, airflow, air velocity, and pressure measurements were taken at critical points in the system to confirm that the performance of the existing system at the baggage claim station was not impacted and that the new system performed as designed.
For this testing to be completed, the Plane Train system had to be shut down and trains positioned within the tunnel to simulate how they would be positioned in a fire event. However, because of the very busy nature of the airport, and flight departure and arrival times, testing could only be completed between 1 a.m. and 5 a.m. each night.
Representatives of our design team were on site during this period to observe the testing and assist with troubleshooting. At the completion of the testing, the project team was able to confirm that the ventilation system operated as designed by providing the required performance in the West Extension without adversely impacting the operation of the existing ventilation system.
Tunnel ventilation fan
North emergency ventilation shaft and connecting cut-and-cover tunnel