STB Approves Union Pacific’s New Arizona Branch Line

Published: March 17, 2026

The Surface Transportation Board (STB) has officially approved Union Pacific Railroad’s proposal to construct and operate a new six-mile branch line in Maricopa County, Arizona, marking a significant step forward for rail-served industrial development in the Phoenix metropolitan region. The decision, issued in mid-March 2026, grants the railroad authority to move ahead with the long-discussed project following completion of environmental review and regulatory evaluation.

Union Pacific ES44AC #5295 leads a westbound stack train past the old steam-era water tower on the ex-SP Sunset Route at Gila Bend, Arizona on October 7, 2010. Doug Kroll photo.

Project Overview

The new line—often referred to as the Pecos Industrial Rail Access Train Extension (PIRATE)—will extend approximately six miles from Union Pacific’s existing Phoenix Subdivision. Its primary purpose is to connect the main line with industrial properties located southeast of Phoenix-Mesa Gateway Airport, within the rapidly expanding Pecos Advanced Manufacturing Zone. One notable customer will be the Commercial Metals Company.

This area has emerged as a major hub for advanced manufacturing, with industries ranging from chemicals and metals to plastics and electronics. Until now, these facilities have relied almost entirely on trucking, as the nearest rail transload facility is located roughly 40 miles away.

Union Pacific has argued that the new branch will significantly enhance logistics efficiency, reduce highway congestion, and provide more sustainable transportation options for both inbound raw materials and outbound finished products.

Environmental Review Completed

The STB’s approval follows the completion of a comprehensive environmental review conducted by the agency’s Office of Environmental Analysis (OEA). In late February 2026, the OEA issued a Final Environmental Assessment (EA), concluding that the project would not result in significant environmental impacts provided that recommended mitigation measures are implemented.

The review process addressed a wide range of considerations, including land use, air quality, cultural resources, and potential impacts to surrounding communities. The final assessment incorporated feedback from public comments and outlined specific mitigation strategies to minimize disruption.

Notably, the project had previously faced delays after concerns were raised regarding disturbances to archaeological resources along the proposed right-of-way. Union Pacific worked with regulators to address these issues, including securing the corridor and implementing protective measures before the environmental process resumed.

Economic and Transportation Benefits

Supporters of the project emphasize its potential economic impact. By providing direct rail access to the Pecos manufacturing corridor, the new branch line is expected to:

Reduce reliance on long-haul trucking
Lower transportation costs for regional industries
Improve supply chain efficiency
Encourage further industrial development in the area

Union Pacific estimates the line could remove tens of thousands of truck trips annually from local highways once fully operational, easing congestion and reducing emissions.

Infrastructure Details

Plans for the project include not only the six-mile branch itself but also additional supporting infrastructure. This includes a new wye connection to the Phoenix Subdivision and approximately 2.5 miles of auxiliary track improvements along the existing main line. The line will be constructed as a single-track route designed primarily for freight service, with capacity tailored to meet the needs of large-scale industrial customers.

Looking Ahead

With STB approval now secured, Union Pacific can proceed with final planning and eventual construction of the branch line. The project represents a relatively rare example of new rail line construction by a Class I railroad, underscoring the strategic importance of the Phoenix-area manufacturing sector. As industrial development continues to expand across the Sun Belt, projects like this highlight the growing role of rail in supporting modern supply chains—particularly in regions historically dominated by truck-based logistics.

Facebook X Pinterest Tumblr Reddit WhatsApp Messenger