Nashville now has two tunnel boring machines working underground on the Music City Loop.

One basic construction number remains unavailable: how far they have gone.

The Boring Company's public updates describe Prufrock-MB1 and Prufrock-MB2 as actively tunneling, discuss machine upgrades and show photographs and video from the work. But the company's April, June and August Nashville updates reviewed by LOOP Nashville do not provide a cumulative number of feet or miles excavated by either machine.

The company's Sept. 9 Series D financing announcement likewise says two machines were mining simultaneously by August without giving a Nashville distance figure.

That leaves the public with a clear picture of activity but no current measure of completed tunnel length.

MB1 began mining in late February

The Boring Company says Prufrock-MB1 began tunneling after the TDOT tunnel permit and lease agreement were executed on Feb. 25.

Its April 1 update described the first four weeks as a launch phase, when the machine was being tested, calibrated and advanced far enough to connect trailing support equipment.

The company said that startup period was expected to be slower than full production because of machine setup, rock-removal logistics and calibration.

By June, TBC said MB1 was continuing to tunnel while the team installed performance upgrades.

The August update said MB1 was making "steady progress" with week-over-week performance improvements. No cumulative distance was attached to those descriptions.

MB2 joined the operation this summer

The second machine, Prufrock-MB2, launched from Lot 16 after commissioning, according to the Aug. 1 update.

The company said MB2's first several weeks would similarly focus on testing and upgrades. A second vertical cassette had been placed online to support continuous rock removal from the second machine.

The company's Sept. 9 corporate financing announcement said that by August, two machines were mining simultaneously in Nashville.

Again, the company did not provide a completed distance for MB2.

Why the 25-mile number is different

The Boring Company's current project page describes Music City Loop as an almost 25-mile underground transportation system connecting downtown Nashville, Music City Center and Lower Broadway with West End Avenue and BNA.

The company also says its February TDOT approval authorized 25 miles of tunnel within state right-of-way.

Neither figure represents tunnel already excavated.

Music City Loop is planned around twin, one-way tunnels, and the 25-mile figure describes overall tunnel infrastructure across the authorized or planned system.

Without project-specific progress measurements, it would be inaccurate to estimate completed mileage by multiplying the number of days underground by a generic Prufrock production rate.

Tunneling rates can vary with launch phases, geology, maintenance, machine modifications, logistics and the specific generation of equipment in use.

What TBC does report

The company has published other construction metrics.

Its current FAQ says project geotechnical work includes 49 TBC borings, review of 93 previous boring logs, about 3,550 feet of seismic testing and 187 historical top-of-rock data points compiled from Terracon borings.

The Aug. 1 update says rock compressive-strength testing was consistently around 14,000 pounds per square inch.

The company also publishes performance capabilities for newer Prufrock technology at the corporate level. Those capabilities should not be converted into assumed Nashville production.

A machine's theoretical or demonstrated maximum capability elsewhere is not the same as its actual cumulative advance on this project.

What remains unknown

No official Nashville source reviewed for this article provides current cumulative footage for MB1, MB2 or the two machines combined.

That does not mean the measurement does not exist internally. Tunnel construction is surveyed and tracked for engineering purposes. It means the figure has not been included in the public updates reviewed here.

A project-specific distance would give readers a more useful measure of progress than photographs alone. It would also allow future updates to show production trends without relying on generic machine specifications.

Until such a number is released through company reporting, permit or inspection records, or another authoritative source, LOOP Nashville should avoid estimating it.

The verified construction status is straightforward: MB1 and MB2 are underground and mining; a third machine was in final assembly for shipment as of The Boring Company's Sept. 9 financing announcement; and the public still lacks a cumulative Nashville tunnel-distance figure.

SOURCES