Hi-rail Mobile LiDAR operations began utilizing a MBTA pilot who was in continuous communications with dispatcher to integrate the hi-rail vehicle track movements across revenue and non-revenue tracks, and through each yard facility. The hi-rail Mobile LiDAR data acquisition was completed in 4 weeks by the two crews and the MBTA pilots assigned to the task. The 3D feature extraction work started with extracting all the individual tracks at 1-foot intervals, including the “switch and frog” points. Point files for each track were created so that the design engineers could perform linear regression to define the track alignments and identify all the track “cardinal” points. Upon completion of the track work extraction 3D extraction work began on all other planimetric features to complete the base mapping. Features including guard rail, restraining rail, trip stops, impedance bonds and signals included in the project’s geospatial data base. The geospatial data base was utilized the existing track alignment data and the track feature locations to populate station and offsets for all track side features. During the creation of the track charts the database was populated with all the alignment geometry and feature locations labeled with station and offsets.

MBTA – Transit System Track Charts, Boston, MA

The MBTA Transit System project covered all the revenue and non-revenue tracks within the Red, Blue, Green and Orange Lines, and included more than 160 miles of track infrastructure.

The SSI Solution

Mobile LiDAR was required to capture all visible features to develop the existing track alignments and to create the planimetric base mapping for the project. Conventional surveying services were utilized to develop the primary and secondary survey control networks. Conventional surveying operations also set and tied multiple survey control points set at every underground station. Field crews with Flagman protection created the survey control network using static GPS and robotic total station observations to establish the horizontal coordinate values and ran differential level loops through the network points to establish the control point elevations. All conventional survey operations were completed during day and night hours using multiple crews for 5 weeks.