The Purple Line | USA

Project summary

Service provided:  Development and implementation of monitoring technology during city lightrail construction
Location:  Bethesda, Maryland - USA
See google map
Client:  Maryland Department of Transportation Maryland Transit Administration
Period of the service:  March 2017-Until 2026
Sixense solutions used: 

Images of the project

The Purple Line


The Purple Line is a 16-mile light rail line extending from Bethesda in Montgomery County to New Carrollton in Prince George’s County. It will provide a direct connection to cities in Maryland – Bethesda, Silver Spring, College Park, and New Carrollton.

The Maryland Transit Solutions (MTS) is currently constructing the new city lightrail that will be powered by overhead wires known as a catenary system. Most of the line’s alignment will be at the roadway level (although some short segments will be elevated or underground).

The owner, Maryland Department of Transportation Maryland Transit Administration (MDOT MTA), is the lead agency, working closely with all stakeholders in the project area.


Construction Works

Between stationing’s 270+-50 and 314+00, The Purple Line will run along the existing CSX corridor, where a crash wall will be erected. Also, between stationing’s 306+00 and 306+50, a jack and bore operation will be carried out underneath the WMATA and CSX tracks.

As required by the CSX Public Project Manual 2022, MTS needs to provide survey monitoring to control the work impact on the existing CSX Southern mainline track. Other anticipated construction activites:

  1. Major excavation activities for footings/foundations​
  2. Utility relocations ​
  3. Pile driving ​
  4. Tunnel construction ​
  5. Constructing grade crossings​ and stations
  6. Curb inlet installation​
  7. Backfill and compact drainage structures​
  8. Bridge installation/construction​
  9. Milling and paving temporary/permanent asphalt pavement ​
  10. Retaining wall installation/construction​
  11. Support of excavation installation and removal​


Sixense Monitoring

Sixense was awarded The Purple Line project due to their monitoring and risk management experience from similar projects.  The project was kicked off in several locations: Bethesda Shaft, Manchester Place Tunnel, Silver Spring Metro Station, and CSX Crash Wall.

Five sites were monitored for 8 to 24 months, primarily for track monitoring purposes. Noise and vibration monitoring were scheduled for at least 24 months.

Track monitoring at the construction of the crash wall spanned over 4,000 feet and split into different phases. This monitoring was implemented to survey any movements that could occur on existing tracks during MTS heavy works, such as:

  • Support of Excavation Installation
  • Crash Wall Construction
  • Final Grading between Crash Wall and CSX Railroad
  • Jack and Bore Operations Underneath the Railroads


Noise Control Constraints

One of the main difficulties for a project like The Purple Line is demand continues to increase to improve the quality of life in urban areas. This demand creates restrictive constraints such as noise control, which led Sixense to install real-time noise monitors enhanced by the company’s advanced sound recognition solution – Nora.

Nora is a machine learning model trained by 30,000 labeled acoustic monitoring data samples generated from ongoing Sixense projects around the world that uses artificial intelligence to automatically recognize noise events. Utilizing this technology on the Purple Line allowed users to instantly identify the cause of noise level breaches and monitor events more effectively.


Benefits of The Purple Line

This new transportation development offers numerous benefits to the surrounding community.

  • It is estimated to take 17,000 cars off the road daily
  • Electric power means no air emission
  • The use of existing roadways minimizes effects on land and water resources
  • The job supports community revitalization and connects people to jobs


Sixense is proud to play a key role in this environmentally friendly and transit-oriented development. The monitoring services helped ensure the construction work was conducted as smoothly and safely as possible.


Project Key figures

10 Vibration Sensors
2 Noise Sensors
1 NORA (Noise Recognition Analysis)
250 Prisms
8 Inclinometers
4 MPBX (Extensometers)