Nashville's Music City Loop reaches downtown, but a new report warns of sinkholes, flooding and pollution in the rock ahead

The Boring Company's tunnel under Nashville has reached the heart of downtown. This week it was working near the Music City Center, the city's convention centre. At the same time, a new expert report warns that the most difficult ground on the route to the airport is still ahead, WPLN News reported on October 22.

Where the project stands

• The route: the Music City Loop is a pair of parallel one-way tunnels of about 9.5 miles (15 km) between downtown and Nashville International Airport.
• Progress: tunnelling started in February 2026. Based on the machines' location, WPLN estimates that up to 10% of the route has been dug so far.
• Machines: according to the company's October 1 update, Prufrock-MB1 and Prufrock-MB2 are now digging at the same time, MB3 is due to launch in late October and MB4 is being built. The aim is four machines underground by the end of 2026.
• Timeline: the target for opening has moved from late 2026 to early 2027. WPLN says current progress does not appear to match that schedule.

What the report warns about

Nashville sits on limestone, which can dissolve over time and form caves and cavities, a landscape known as karst. The report, written by Western Kentucky University hydrogeology professor Chris Groves, describes four limestone layers along the route. The company plans to stay mostly in the Hermitage Formation, but that layer has eroded away in places. Under Browns Creek, Mill Creek and the Cumberland River the tunnel would have to pass through the Carters Formation, which Groves calls the most intensely karst-developed layer and likely the most problematic.

The risks he lists include sinkholes, sudden inflows of water or mud, flooding of the tunnel and machines getting stuck. Several mapped caves lie within two miles of the route, one with a passage about 30 by 40 feet. Pollution is another concern: the state environment agency has mapped dozens of underground oil tanks and cleanup sites along the corridor. One former industrial site about three miles from the convention centre has documented solvent and heavy-metal contamination.

Critics also question the environmental review. The company's 150-page environmental assessment from late 2025 spent fewer than 10 pages on water, safety and geology, and relied on studies from 1958 to 1990, according to WPLN. Based on that self-funded assessment, the state environment agency did not require a permit. A lawyer for the Southern Environmental Law Center asked what would happen if a machine got stuck under Mill Creek. The Boring Company did not respond to WPLN's questions.

The company's side

The Boring Company says it has all the permits needed to tunnel. The Tennessee Department of Transportation approved a permit and lease in February for up to 25 miles of tunnel in state right-of-way, after more than seven months of technical review. The airport and convention centre authorities each approved connections by 8-0 votes. The company also says it has made more than 300 upgrades to its first machine, often going from design to installation within 48 hours, and that more than 40 stations are in planning or design.

The Tesla link

The Music City Loop uses the same Loop concept as Las Vegas, where Tesla vehicles carry passengers point to point through the tunnels. Nashville, where the machines have to cut through limestone, is the company's most important test outside Las Vegas. If the tunnels open, they would bring Tesla-based transport to a second US city and a major airport; if the geology causes long delays, it would be a warning for Boring Company plans in other cities.

What to watch next

• The launch of Prufrock-MB3 and whether four machines are digging by year-end.
• How the company handles the Carters limestone under the creeks and the river.
• Any response from the company or state regulators to the report.