News and Events

Mass Transit Rail Inspection Improves Safety

posted 03.11.2020

Terracon mass transit rail inspection

A Terracon employee inspects a mass-transit rail.

Did you know that Terracon helps the traveling public stay safe by performing quality assurance inspection on rail for mass transit projects? Rail construction integrity is vital to the mass transit industry because rail flaws and defects can lead to broken rails or possible derailments. When you consider that the commuter rail network in the United States has an approximate rail service line of over 12,000 miles, it’s paramount that the rail gets tested and inspected properly during construction and placement.

Understanding Specialized Railway Inspections

The process of joining rail together typically occurs by using flash butt welding or thermite welding- which is not the same as welding that occurs with structural steel. Flash butt welding is a resistance welding process that produces a weld at the closely-fit surfaces of a butt joint by a flashing action followed by the application of pressure after heating. Thermite welding is a process that joins rail ends by melting them with superheated liquid metal from a chemical reaction between finely divided aluminum and iron oxide.  There are a variety of visual and non-destructive tests required to be performed on flash butt welded connections and thermite welded connections of rail according to the American Railway Engineering and Maintenance-of-Way Association (AREMA). These tests can include:

  • Visual alignment
  • Ultrasonic testing
  • Magnetic particle testing
  • Brinell hardness testing
  • Macroetch examination and testing
  • Slow bend testing

Flash butt weld

A flash butt weld cools from a temperature of about 1600 F.

It’s important to note rail welding inspection and structural welding inspection are not the same thing! Some of the equipment, techniques, and procedures used are different and a lot can go wrong during construction if you don’t have specific experience in rail inspection.

Terracon’s experienced team has performed quality assurance testing on some of the newest segments of light rail construction in the Phoenix metro area. One of these recent projects includes the Gilbert Light Rail Extension in Mesa, Ariz. This project for Valley Metro consisted of a 1.9-mile extension to the light rail line that started in October 2016 and was opened to the public on May 18, 2019. Our role on the $186 million project included preparing non-destructive testing procedures and plans in accordance with requirements from Valley Metro and AREMA. Terracon’s Phoenix office inspectors observed and tested flash butt, thermite, and insulated joint welded connections that occurred over the course of construction. Upon completion, 17,050 linear feet of rail was installed by the contractor and tested by Terracon.

Verifying Rail Construction Quality Across the Country

Based on our performance and expertise on the Gilbert Light Rail Extension, the team was asked to perform similar services for the 3-mile, $192 million Tempe Street Car Mass Transit project in downtown Tempe, Ariz. Terracon prepared the appropriate non-destructive testing procedures and assigned experienced Certified Welding Inspectors with the required non-destructive testing experience and certifications to witness and test the welded connections for the rail.

Visual testing of continuous welded rail strings

Visual and non-destructive testing of continuous welded rail strings.

Recently, Terracon’s Phoenix team was designated as subject matter experts and provided consulting and training for another mass transit project in the Boston, Mass. area, where our team performed similar services on light rail construction to support the construction team.

Rail construction and maintenance will continue as the public looks for additional sustainable transportation options.  It’s important to understand that rail welding inspection, ultrasonic testing and non-destructive testing of welds on rail is not the same as structural steel welding inspection. Terracon’s experienced team can help you to verify the safety and quality of your next rail project.


Tracy Grover headshotTracy Grover is a principal and assistant service line director for materials services based in Terracon’s Phoenix office. He serves as a regional resource in the western United States on transportation projects involving materials testing and inspection He has 15 years of experience consulting on light rail construction in the United States.