What happens when Route 340 between Harpers Ferry and the Potomac River Bridge is closed? We’re about to find out. On September 12, the West Virginia Department of Highways (WVDOH) will close the road between the intersection of Chestnut Hill Road (to the east of the Shenandoah River bridge) and the traffic signal at Harpers Ferry Road (by the Exxon station) for a project that will stabilize the rock cliff along the highway. The project schedule indicates the road will be closed 24 hours a day, 7 days a week from September 12 through December 11 (90 calendar days). The complete project may extend beyond 90 days, but WVDOH has emphasized repeatedly that the contractor has committed to the 90 day window to finish the work that will require the road to be closed.
The falling rocks at this location have been a concern for years and WVDOH announced its intent to schedule this project a couple of years ago. Local leaders and businesses requested alternatives to the 24×7 closure, but ultimately, the concern that the work would be dislodging a large amount of rocks that could fall on the road at any time led WVDOH to pursue the full closure for the duration of the project.
The Detour Takes Shape
For drivers heading from Harpers Ferry to Maryland (or the reverse), WVDOH estimates the full 22 mile detour route (in gold on the map above) will take 35 minutes. For drivers starting from Charles Town and heading to Maryland (or the reverse), WVDOH estimates that the detour route will add approximately 6 miles and 10 minutes of travel time. A big caveat to these numbers — they are a best case scenario with clear skies and light traffic on the roads.
The unstable rock above this stretch of road poses a persistent danger along this heavily-traveled route. 
Route 340 normally sees a significant amount of truck traffic. 
For traffic heading from Charles Town towards Maryland, the official detour signs will start at the interchange of Routes 340 and 9 (just outside of Charles Town, near the casino). 
All traffic crossing from Maryland on Route 340 will be routed south onto Harpers Ferry Road (Route 671) at the traffic signal. 
Harpers Ferry Road (Route 671) is a scenic route through Loudoun Heights. 
Traffic heading east along the detour will make a left turn from Route 9 onto Harpers Ferry Road (Route 671) in Loudoun County. The traffic signals at this intersection will be adjusted to accomodate the left turn traffic. 
Harpers Ferry Road (Route 671) between Route 9 and Route 340 is a single traffic lane in each direction.
WVDOH reports that an average of 21,800 vehicles pass through the project area every day (this number is an average of all traffic across the entire year). Unofficial published information from 2022 reported that peak westbound evening traffic at the intersection of Route 9 and Harpers Ferry Road (Route 671) was approximately 1,700 vehicles per hour. The peak evening traffic at the intersection of Route 340 and Harpers Ferry road was approximately 2,100 vehicles per hour (and 10 to 13 percent of the Route 340 traffic was heavy trucks). If all of the Route 340 traffic follows the detour through the Routes 9 & 671 intersection, that would be a doubling of the traffic heading over the mountain and coming down the hill on Route 9.
The traffic control signals at the north and south ends of Harpers Ferry Road (Route 671) in Loudoun County are controlled by the Virginia Department of Transportation (VDOT). A VDOT spokesperson reported that the traffic signal at Routes 340 and 671 (by the Exxon station) will be retimed as needed. The signal at Routes 9 and 671 will have a temporary signal installed and VDOT plans to also adjust the stop line markings on the pavement to allow more room for large vehicles to make turns.
WVDOH reports that it has alerted online mapping services about the Route 340 Rockfall Remediation project detour and detour signage is already in place.
For drivers traveling westbound/southbound from Maryland along Route 340, the detour will begin after crossing the Potomac River bridge. As an added complication for traffic heading in the other direction (north across the bridge), drivers will see detour signs for the National Park Service construction project currently underway on Harpers Ferry Road (also Route 671).
Drivers traveling eastbound along Route 9 will see the detour signs starting at the intersection of Route 340 and Route 9 just outside of Charles Town. If you are using an online mapping service and set a destination in Maryland, the services currently suggest several alternatives (Cattail Run Road, Chestnut Hill Road) as you drive on Route 9 to go over the mountain into Loudoun County, but neither of these routes will get you past the detour and both are very narrow and twisty roads.
[Read More: Alternative Routes Have Bottlenecks]
The project website (US340HarpersFerry.com) will not provide traffic updates. WVDOH representatives suggested the WV511.org website as a resource for drivers looking for current traffic information during the project. The Observer will post any project updates we receive from WVDOH on our website at WeAreTheObserver.com. You can sign up for The Observer’s email updates here.
Updated September 11 2023 to reflect WVDOH confirmation of 90 calendar day window for road closure.
Updated August 31 2023 to include additonal information provided by West Virginia Department of Highways and Virginia Department of Transportation.
By Steve Pearson