CTA Green Line Survey

DLZ leveraged the latest technology to perform the CTA Green Line Survey. DLZ provided construction surveying services and static and mobile lidar services for this project, including 14.3 miles of track. With crews working on live tracks during the day and night shifts, zero incidents occurred with over 3,000 staff hours. To further enhance their safety, DLZ subcontracted a security firm to travel with our field crews while working on Chicago’s south side.

DLZ field crews performed traditional control traverse and level loops throughout the entire 14.3 miles of track in preparation for the static and mobile LiDAR capture. DLZ collected over 900GB of survey data, which was used to help align the existing tracks. This data would also aid in the fabrication of new structural members. The use of LiDAR data collection increased the efficiency of the field data collection tenfold vs. traditional methods.

DLZ worked with the CTA to develop a temporary mount for the mobile scanning system. This mount went directly onto the CTA car to capture the mobile lidar data. Thus, the system allowed data capture of existing conditions without interfering with the train schedules.

Static LiDAR of the underside of the elevated CTA structure, as well as control for the Mobile Lidar capture, gave DLZ the ability to analyze the “Whole Picture” vs. individual point locations. The Amberg FRP1000 Trolley was utilized to measure and adjust the track gauge and capture profile data along the track.

The DLZ team is eager to design solutions that meet your infrastructure needs. If you have any questions about the work we do, check out our Services page. We also highlight our diverse experience in our Project profiles. Additionally, feel free to contact us.


Survey, Transportation


Local and State Governments


Chicago, Illinois