Interlockings: From crossing over to starting over

By Jeff Stagl, Managing Editor

Interlockings and control points serve the same purpose: to prevent trains from colliding at intersecting tracks.

Used to control traffic at a junction of two or more railroads, an interlocking includes signals and signal appliances that provide a clear signal to a train if a route is deemed safe, then lock in position until the train passes.

A control point functions similarly at intersecting tracks on a railroad, such as electric switches at the end of sidings or crossover locations on a double mainline.

Since the late 1970s, Class Is have installed more microprocessor-based or solid-state interlockings controlled by software logic than electrical relay-based interlockings controlled by wired networks because the equipment’s operational commands can be changed by reprogramming software instead of rewiring equipment.

Large roads are specifying solid-state interlockings for all new installations and continue to replace a number of electro-mechanical interlockings with microprocessor-based units.

Not that there’s any safety concerns about the electrical variety, which date back more than 70 years. Of the 72 interlockings spread system-wide at CSX Transportation — which also has 2,850 control points — several are electro-mechanical units.

“We have interlockings from the 1950s that still are robust and safe,” says CSXT Chief Engineer-Communication and Signals Craig King.

Although the solid-state changeover is a gradual one, electrical models likely will vanish from Class I networks within the next two decades.

Solidly behind solid state

In the meantime, communication & signals (C&S) department officials are seeking solid-state interlockings that offer remote diagnostics, can be tested automatically and provide optimal software logic for each specific location.

“It’s all about configuration management and software management,” says BNSF Railway Co. Assistant Vice President-Signals Jim LeVere.

Officials also believe it’s about time the Federal Railroad Administration (FRA) revise two-year signal locking test requirements on microprocessor-based interlockings and control points. The equipments’ programmed logic doesn’t change after installation unless a railroad reprograms the software — meaning any significant changes are unlikely in two years’ time, C&S managers says.

They’re keeping an eye on BNSF’s petition to the FRA requesting that tests on microprocessor-based interlockings/control points be required every four years after initial testing or a program logic change.

Currently, Title 49 Code of Federal Regulations part 236’s sections on approach, time, route, indication and traffic locking require signal locking tests every two years.

“The testing requirement dates back more than 30 years to pre-microprocessor, electronic applications,” says LeVere.

In their September 2006 petition to the FRA, BNSF officials argue that the two-year signal locking tests “place an undue burden on the railroad” because each route must be tested individually with “complex control points having 20 to 30 routes.”

In addition, some of the tests require track time between control points on either side of a location, tying up 20 miles or more of track during tests, BNSF officials claim.

“Due to train traffic, some large control points can take a month or more to complete the two-year locking tests,” the petition states.

BNSF officials recommend the following be required every four years:

• verification of the cyclic redundancy check (CRC), check sum and universal control network (UCN) of the existing location-specific application logic to the previously tested version;
• verification of tests on equipment outside the processor (such as switch, track and searchlight signal indication) to the processor’s inputs, and tests on switch locking from the processor’s output to the switch machine; and
• tests on the duration of any timers with variable settings.

“Once a processor-based system has been tested and locking tests documented on installation, since the operation does not change, retesting should not be required,” BNSF officials said in the petition.

Under consideration

As of late March, an FRA safety board continued to review the petition. The board plans to meet on the topic again in the near future, says FRA spokesman Warren Flatau.

CSXT also plans to seek an FRA waiver on two-year signal locking test requirements governing certain microprocessor-based units.

“It’s an opportunity to extend the test period and have no effect on safety,” says CSXT’s King.

For now, the Class I is working with interlocking suppliers GE – Transportation, Safetran Systems Corp. and Union Switch & Signal Inc. to implement remote diagnostics in the field.

The interlockings would feature communication connectivity — via cellular or other phone service — to link with CSXT’s central dispatching center to improve self-diagnosing capabilities and field servicing. CSXT plans to implement remote diagnostics at several interlockings later this year.

Automation at first location

Also by 2008’s end, Norfolk Southern Railway plans to launch an automatic testing system on a small interlocking. The Class I — which will monitor the outcome of BNSF’s FRA petition — is working with Ultra-Tech Enterprises Inc. to implement the InterTest® automated interlocking test system.

Featuring permanently installed and portable hardware and two software programs, InterTest is designed to create a detailed, computerized model of interlockings and associated wayside signal locations, and automatically generate test scripts for both two-year and in- service tests.

“We’ll get a consistent test, done the same way every time,” says NS Assistant Vice President-Communications & Signals Ray Rumsey, adding that the system will be specified for every new interlocking.

InterTest can be used on any interlocking expect Safetran’s, says Brian Sykes, NS’ chief engineer-C&S engineering, adding that NS is working with Safetran to develop an automated testing system for the supplier’s GEO^® Geographic Signaling System. Next year, the Class I plans to implement InterTest at large interlocking locations.

Boxed in

Canadian National Railway Co. also is interested in remote diagnostics and automated testing, but the Class I is awaiting controller boxes that can be installed at each interlocking location, says Chief Engineer-Signals & Communications Dwight Tays.

In addition, CN is seeking better software tools. Young software designers are more familiar with programmable logic than long-time designers and, over time, should help develop optimal software, says Tays.

Also on CN’s wish list: voice over data, Internet protocol and more cellular capabilities to improve wayside data management. However, cellular coverage is spotty in remote locations and the cost of satellite service is prohibitive, says Tays.

Getting timely, accurate diagnostic data into the hands of central office staff will help CN — and all Class Is — conserve manpower and service interlockings before they break down.

“You can send a maintainer out in advance,” says Tays. “That way, you’re not getting a call in the middle of the night.”