A pedestrian tunnel at the intersection of Manchester Road and Mary Avenue is one of the enhancements included in the Manchester Road Improvements project.
The tunnel will be 14’ wide and 9’4” tall at the highest point. The walking surface inside the tunnel is approximately 12 feet below the ground level of Manchester Road. To accommodate the addition of the pedestrian tunnel, Manchester Road has been raised approximately 5 feet from its previous ground elevation.
LED light fixtures will extend the length of the tunnel on both sides and will be lit 24 hours a day. Outside lighting will lead into the tunnel at both entrances. Safety features in the tunnel also include at least one camera at the east entrance of the tunnel (closest to the new Brentwood Park); consultants and staff continue to discuss a way to add a second camera at the tunnel access closest to Manchester Road. The tunnel will be closed for use during any significant rain/flood event.
Keeping Water Out
The tunnel will be kept as dry as possible through a combination of stormwater management, raingardens/bioswales, and pervious pavers in the shoulder area of the tunnel. The stormwater management involves grading slopes to capture storm water runoff before it gets to the tunnel and redirecting it to the raingardens or to storm drains that pipe water under Manchester Road. Additionally, the trail pavement has ADA-compliant trench drains on both ends of the tunnel that will help capture stormwater before it enters the tunnel/underpass.
While one of the objectives of the Brentwood Bound Plan is to mitigate the base flood event (1% annual chance) along Deer Creek south of Manchester Road, the pedestrian tunnel will be approximately 12 feet lower than Manchester Road at the point of crossing, and it is possible for a flood event to exceed project design constraints. Check valves have been incorporated into the flood mitigation design to prevent storm sewer backups from the flood mitigation area into the pedestrian tunnel; however, a significant area tributary to Deer Creek resides north of Manchester Road. Storm sewers are typically designed to convey more frequent events, and when larger events occur, flood waters can sometimes be conveyed overland to their downstream most point. Because of the low elevation of the tunnel, it may accumulate some of this water during large storm events. Flooding can be extremely unpredictable, and because the pedestrian tunnel is connected to the new Brentwood Park and the flood mitigation area of the trail system – which will be subject to more frequent flooding – the tunnel will be closed off during any significant storm event.
More than 70% of the $4.8 million tunnel is being funded through grants from MoDOT, Great Rivers Greenway and the East-West Gateway Council of Governments.
Pedestrian Tunnel FAQs