NPS | Stephanie Spencer – C&O Canal National Historical Park
The park plans to repair three public vehicular tunnels at Carderock Recreation Area (mile 10.4), Four Locks (mile 108.5), and McCoys Ferry (mile 110.2). The historic stone masonry tunnels at Four Locks and McCoys Ferry are showing signs of deterioration and drainage issues. The modern concrete box culvert tunnel at Carderock is showing signs of erosional issues and needs concrete repairs. What is the P.L.A.N. ?Purpose? [Why are we undertaking this project?]To repair three existing vehicular tunnels in order to establish a safer and more reliable method to carry pedestrians and vehicles under the C&O Canal in order gain access to the Carderock Recreation Area, Four Locks Boat Ramp, and McCoys Ferry Campground and Boat Ramp.Length? [When are we closing, and how long?]The project is anticipated to begin mobilization in Winter 2026 and extend through Spring 2026, weather dependent. This webpage will be updated periodically to reflect the timeline for work at each specific site.Alternative Activities? [What can I do instead?]During construction, the Carderock Recreation Area will remain open with a single-lane closure, while the tunnel repairs are underway. Work on the Four Locks Tunnel and McCoys Ferry Tunnel will be sequenced so that only one tunnel is closed at a given time. During construction at the Four Locks Tunnel, the Four Locks Boat Ramp will be inaccessible by vehicles. During construction at the McCoys Ferry Tunnel, the McCoys Ferry Campground and Boat Ramp will be closed. Through traffic on the towpath for pedestrians and cyclists will be maintained.Throughout construction and while the recreation areas at Mile Markers 108.5 and 110.2 are closed, you can still bike, walk, run, and fish along the towpath in all areas outside of the work zone. The towpath will still be accessible. There are many sections of the towpath to be explored! Next Step? [What are the future benefits?]The repair of the Carderock, Four Locks, and McCoys Ferry tunnels will improve safety, preserve historic resources, and result in a more sustainable method for accessing the park’s recreational areas.
NPS | Professional Services Division – C&O Canal National Historical Park 
NPS | Professional Services Division – C&O Canal National Historical Park 
NPS | Professional Services Division – C&O Canal National Historical Park CURRENT DETOURS AND CLOSURES
Above are maps showing the project areas and the closures that are in place. All portions of the towpath will remain open for the duration of the project. FREQUENTLY ASKED QUESTIONS (FAQs)What is the need for the project?The existing tunnels at Carderock, Four Locks, and McCoys Ferry are showing signs of deterioration and are in need of repairs in order to preserve the structures. To prevent larger future repair needs and ensure the safety of visitors and NPS staff, it is critical that this project is undertaken.What does the project include?At the Carderock Tunnel, the work consists of repairing deteriorated concrete, vegetation removal, restoring earthwork, repairing the stone masonry wingwalls, repaving the asphalt approaches, and installing new traffic signage.At the Four Locks and McCoys Ferry tunnels, the work consists of replacing the existing concrete slabs within the tunnels, repairing and repointing stone masonry, improving drainage, removing vegetation, and repaving the asphalt approaches. Additionally, the existing drainage channel downstream of the Four Locks Tunnel will be regraded and stabilized in order for the tunnel to better convey water out to the Potomac River. Where will the project take place?This project will take place at Carderock Recreation Area (mile 10.4), Four Locks (mile 108.5), and McCoys Ferry (mile 110.2).When will the project begin and end?The project is anticipated to begin Winter 2026 and continue through Spring 2026, weather dependent.
NPS | Stephanie Spencer – C&O Canal National Historical Park How will this project impact park visitors?To facilitate the work, the Four Locks Boat Ramp (mile 30.8) will be CLOSED to vehicles while work is being conducted at the Four Locks Tunnel. The McCoys Ferry Campground and Boat Ramp (mile 110.2) will be CLOSED while work is being conducted at the McCoys Ferry Tunnel. The work at Four Locks and McCoys Ferry will be sequenced so one tunnel remains open to visitors at all times.The Carderock Recreation Area (mile 10.4) will remain OPEN for the duration of the project. A single-lane closure will be in effect while work is active. Through traffic on the towpath will remain possible for pedestrians and cyclists throughout the project. How will this project benefit park visitors?Once the project is complete, the repaired tunnels will improve visitor safety by providing a more sustainable method of accessing these recreational areas of the park. The historic structures within and adjacent to the project areas will be protected and preserved for the enjoyment of future generations.How will this project impact natural and cultural resources?Every project the NPS executes undergoes review by a multidisciplinary team to ensure compliance with Section 106 of the National Historic Preservation Act (NHPA), National Environmental Policy Act (NEPA), and other federal, state, and local laws.What is the park doing to protect those resources during the project?NPS resource protection experts, engineers, and the contractor’s team will be monitoring the tunnel and stone work in these recreation areas, along with contractor’s operations and visitor safety during the project with the goal of safely protecting the environment surrounding the project. Every project undertaken by the NPS is conducted in compliance with the National Environmental Protection Act (NEPA), the National Historic Preservation Act (NHPA), and other regulations.How much does the project cost?The contract for the repair of the Carderock, Four Locks, and McCoys Ferry tunnels is funded from the National Park Service’s Federal Lands Transportation Program.Who can I contact if I have further questions regarding the project?Additional questions are to be directed to the park headquarters at 301-739-4200.
NPS | Stephanie Spencer – C&O Canal National Historical Park |
Last updated: February 20, 2026