Project Overview

The Detroit Central Automated Transit System (commonly referred to as the People Mover) is an automated light-rail transit system using an elevated guideway with a continuous loop route configuration. The transit system travels on rails mounted on the top deck surface of the guideway. The superstructure of the guideway consists of precast, pre and post tensioned, concrete segmental box beams supported on a substructure of conventionally reinforced and post tensioned reinforced concrete columns.

The DTC selected NTH to conduct a structure inspection and maintenance assessment to ascertain the current structural condition of the guideway and its components, to provide recommendations for guideway repairs and the methods to complete those repairs, and to provide construction oversight during the repair process. The repair contractor worked as a subcontractor to NTH.

Project Scope

In order to ensure the People Mover remains operational for Detroit residents and visitors, NTH has been conducting bi-annual inspection and maintenance repairs to the concrete structure for 11 years. The Guideway inspections and repairs were accomplished in accordance with Federal Highway Authority (FHWA) National Bridge Inspection Standards (NBIS).

The inspection program included:

  • Inspection of exposed concrete surfaces on support columns and concrete beams to document visible cracks, including the relative crack location, length and width.
  • Documenting locations and size of hollow concrete areas, delaminations and spalling, exposed reinforcing steel, post tensioning tendons or ducts.
  • Identifying areas of leaching, efflorescence, rust stains, water infiltration and scaling which were located on the crack maps.
  • Identifying expansion joints that showed material failure or fatigue, water blockage, water leaking, failure of adhesive or seal, delamination of seal and absence of joint material.
  • Documenting the condition of bearings regarding the presence of rust, bird waste and debris, bent or broken anchor bolts, loose nuts, or abnormal movement of the bearings.
  • Evaluation of the effect and impact of having Power, Electrical and Communications apparatus attached to the guideway.
  • Reporting findings of examinations of bearing devices to ascertain how they are functioning

Once these items were identified, repairs were performed in accordance with the Guideway Maintenance Manual. NTH provided site engineering oversight to identify the repair locations, document the quantities, and ensure repair materials were used and cured properly.

In addition to the inspection and maintenance program, NTH also provided as-needed services for the People Mover including emergency response during multiple events on or around the guideway system, structural analysis of the guideway after critical events to ensure the system could be operated safely, analysis of contractor excavation plans to ensure the Guideway grounding system or foundation systems will not be compromised, providing details for the replacement of track rail anchorage systems to ensure the post tensioned tendons will not be affected, and structural analysis/ repair design for defects at the access stations.

Client Benefit

NTH performed the inspection and repair operations during non-operating hours and regularly adjusted our schedule to accommodate changes in the operating schedule due to special events. In addition, during emergency response events, NTH was readily available via phone 24/7 and responded by sending appropriate personnel to the site immediately. The Detroit People Mover staff were able to relax knowing they had a responsive / knowledgeable partner that was looking out for their best interest.