ONE of the United State’s worst passenger rail bottlenecks could soon be unlocked, with plans progressing to construct a $US 4bn twin-bore tunnel to replace the 148-year-old Baltimore & Potomac (B&P) Tunnel on the Northeast Corridor over the next 10 years.

The plans were unveiled by Amtrak and the Maryland Department of Transportation (MDOT) on June 21. The two organisations will, work together on the project. However, the tunnel does not currently have a funding source. Amtrak is still finishing the design and purchasing sections of right-of-way.

The company has earmarked $US 65m for the design and pre-construction phase that will be carried out next year, while it is banking on $US 257m in federal funding for the work. It is hoped the project could be in full swing in 2023.

The new tunnel will be named after the 19th century Maryland-born abolitionist leader, Mr Frederick Douglass, and is the centrepiece of the B&P Tunnel Replacement Program which is planned to modernise a 6.4km section of the Northeast Corridor. Also included in the plans are the replacement of bridges, track and rail systems, and a new accessible West Baltimore Maryland Area Regional Commuter (Marc) station.

The existing tunnel is a safety concern and does not meet the demands of freight and passenger rail. The Federal Railroad Administration (FRA) has marked the tunnel as structurally deficient. Poor soil has caused floor slabs to sink, requiring ongoing maintenance. As recently as last year Amtrak spent $US 71m to install new track in the 2.2km double track tunnel where trains are limited to 48km/h The new twin-bore structure will have a 160km/h maximum speed.

MDOT and Amtrak have agreed on a phased implementation approach for the structure. Two high-capacity bores will be built for electrified passenger trains, and these will be used both by Amtrak and  Marc trains. The latter will be electrified, says Maryland secretary of transportation, Mr Gregory Slater.

“This is a generational project for passenger rail in the State of Maryland and the entire Northeast Corridor,” Slater says. “We are ready to with Amtrak and the federal government to move a new B&P tunnel forward.”

A plan to replace the tunnel with four single-track tunnels was approved by the FRA four years ago. It is believed that revising those designs with  adual bore tunnel that could save as much as $US 1bn and take two years off the expected construction period.

However, the construction of two additional bores for freight trains will be deferred with freight continuing to use the old tunnel.