LTK Engineering Services, Atlanta, Georgia USA

Laser profile survey delivers fast, comprehensive measurement of MARTA's tunnel network to investigate planned changes to existing passenger trains.

Business Challenge
LTK Engineering Services is a US based engineering consultancy that specialises in rail systems engineering.

The Metropolitan Atlanta Rapid Transit Authority (MARTA) engaged LTK to prepare a feasibility study for the construction of a new ‘heavy rail’ rapid transit line. The MARTA network is a third rail system and consists of 48 miles of track of which 20 miles are underground. The new transit line was to consider a catenary (overhead wire) system rather than a third rail system.

So that MARTA’s existing passenger fleet could traverse the entire MARTA network including the new transit line, LTK needed to quickly understand what minimum vertical clearance would be available in underground sections should existing passenger trains be retrofitted with pantographs.

As an experienced provider of laser-based clearance surveys to North American railroads and mass transits, Geomatic Technologies (GT) was asked to locate, measure and document the minimum vertical clearances throughout all tangent and curved track within the MARTA tunnel network.

Services Overview
To record laser data through the MARTA network, GT mobilised its GT Asset Inspection Mapping System (GT AIMS) on a MARTA hyrail truck. GT AIMS has over many years performed numerous laser-based clearance surveys on railroad networks and mass transits in North America, Australia and New Zealand. With processes honed over many years recording on rail networks, GT was able to quickly mobilise GT AIMS in preparation for the night time recording windows.

Once recording was completed the field sessions were processed to obtain positional information relating to the track (curvature, cant, and grade). This track information along with the raw laser data was combined to produce a geo-referenced 3D point cloud of the MARTA tunnel network.

Kinematic parameters supplied by LTK allowed GT to model the actual sway and loading of MARTA’s passenger trains to ensure that vertical clearances were accurately modelled. GT passed the kinematic envelope of the existing passenger trains through the laser data to establish the vertical clearance available within the tunnels for the proposed pantographs.

CAD drawings were created from the laser data to enable LTK to accurately assess the feasibility of modifying either MARTA’s vehicles and/or discrete tunnel sections in order to accommodate the proposed pantographs. In total GT delivered 148 CAD drawings along with driver’s view imagery detailing start point, end point and minimum clearance point of each tunnel section.


  • Using GT’s services, LTK was able to obtain detailed survey information on MARTA’s tunnels in a much quicker and cost effective way than using conventional survey teams on-site.
  • Delays to revenue services were minimised as data was collected at ‘line speed’ over 4 nights.
  • LTK could focus on its core business activities rather than on non-core data acquisition and processing.