Fast-tracking San Diego’s New Light Rail System

How the Trimble GEDO IMS sets a new standard in speed and efficiency for rail construction surveying.

A new method for fast, high-accuracy measurement has enabled San Diego-based CL Surveying and Mapping to transform work on a key task in railway construction and maintenance. The company has put the new technique to work on the Mid Coast Transit Corridor project, a major expansion of San Diego’s regional rail service. CL Rail Survey Manager Josh Draper said the new solution, built on Trimble GEDO technology, is a “night-and-day” improvement that’s boosting performance and opening opportunities for new business.

The Southern California firm is using Trimble GEDO solutions to significantly improve productivity in measurements for tamping—the process in which railway track is adjusted to meet design requirements. In this process, a specialized railcar called a “tamper” lifts and shifts the track and repositions the rock ballast that supports the sleepers; the track then settles into its new position.

To do this, the tamping machine needs precise measurements comparing the existing track to the design. After each pass by the tamping machine, the tracks are remeasured. On new track construction, two or three passes (or “lifts”) are used to gradually bring the track up to the design position. 

Tamper operators have traditionally relied on stakes set by a surveyor using a total station. Typically set at 25-foot intervals, the stakes provide height and position correction information for the tamping process. Then came the Trimble GEDO Vorsys, which eliminated the need for conventional staking at 25-foot intervals. 

The GEDO Vorsys system uses a pair of track-mounted trolleys. One trolley is equipped with a total station while a second trolley carries a prism and other sensors to provide accurate measurements of the track. A companion technology to Vorsys—Trimble GEDO IMS—provides an alternative method for efficient track measurement. 

Mounted on a single trolley, Trimble GEDO IMS combines inertial measurement technology with onboard sensors to produce precise data on track alignment, elevation, gauge and cant (superelevation). Digitally transferred to the tamping machine, the data provides immediate, error-free information for the tamping operator.

Draper has used the Trimble GEDO IMS on more than 20 miles of tamping work. “It’s night-and-day difference as far as how fast we can get things done,” Draper said. “There’s just a single trolley and one person. You measure the first control point, move the trolley on the track to the next control point and get all the core data on the track.” With control points located on catenary foundations roughly 250 feet apart, Draper can closely follow the tamping machine. “I’m right behind them. As soon they are a few feet past a control point, I’ve got the data read and can tell how the track looks.” Draper sees the system becoming the standard for rail construction and maintenance.

CL President Dan Calvillo estimates that his team can support about six miles of track tamping per day with the Trimble GEDO system. In addition to the Trimble GEDO IMS, the company also uses a 3D laser scanner mounted on the GEDO trolley to precisely capture track and surrounding features for clearance analysis, asset documentation and other client-relevant purposes. Calvillo noted that the one-person operation of Trimble GEDO IMS not only speeds up track measurement, it also reduces labor costs or frees up technicians for other tasks.

“The Trimble GEDO system is the only way to meet specs, schedules and requirements on modern rail projects,” Calvillo said. “It has demonstrated its capability and flexibility. We have the equipment and expertise to handle large projects, including high-speed, on ballasted, direct-fixated, and slab track.”