MDOT MTA Purple Line P3 Light Rail Transit

To improve mobility in the congested Capital Beltway region of Washington D.C. and connect commuters to existing transit, the Maryland Department of Transportation Maryland Transit Administration (MDOT MTA) is constructing the Purple Line, the first direct suburb-to-suburb rail link in the region. The Purple Line is a new 16.2-mile, east-west light rail transit line with 21 stations, providing connectivity between Bethesda and New Carrollton across two of Maryland’s fastest growing counties. The system is expected to begin a 30-year operation and maintenance period in late 2026. We were selected by the Maryland Transit Administration (MTA) to serve as lead designer for the public-private partnership (P3) project.

As lead designer, we assisted MTA by providing design and engineering services for this greenfield project under a design-build subcontract awarded to Maryland Transit Solutions (MTS), a joint venture between Dragados USA Inc. and OHL USA Inc., in April 2022. Our scope of work included the design of the following: 

• Track, a rail yard, an overhead catenary system (OCS) and a low-flow traction power system, including stray current and corrosion control and an energy consumption/management plan for forecasting future usage
• Traffic signal interfaces for more than 50 major intersections, utilizing emergency vehicle preemption and transit signal priority technology
• Lighting, street and wayside signage, including grade crossing warning plans
• Emergency egress, in compliance with the National Fire Protection Association (NFPA) 130 standard
• Train control specifications, including recommended speed modifications through the University of Maryland corridor 
• Solid conductor rail through the Plymouth Tunnel
• Mechanical, electrical and plumbing, including a communications duct bank             
• Roadways, pavement markings, bridges and walls

Our design also featured drainage, erosion and sediment control, landscape architecture, corrosion control, grounding and utility relocations. We worked closely with the utility company to ensure relocations went smoothly, managed environmental permitting, provided geotechnical services, approved the final design to provide service to substations, and coordinated all power drops.

In addition, our team performed a reliability, availability, maintenance and safety (RAMS) and failure modes analysis and developed testing procedures for the system. We undertook electromagnetic interference (EMI), noise and vibration studies and designs focused on minimizing impacts to nearby University of Maryland research facilities housing sensitive laboratory equipment. We also managed pre-energization testing for EMI, oversaw interface management, provided verification and validation services, and ensured technical concerns raised by stakeholders during design development were resolved and incorporated.

Under a separate contract with MTS, we oversaw the selection, design, manufacturing, testing and delivery of 28 extended length (140 foot), 5 module, 85% low floor light rail vehicles (LRV). Combining American and European technology, these extended length LRVs are the first of their kind in the United States. By procuring these vehicles, we were able to reduce the expected fleet by almost 50%, resulting in significant capital and maintenance cost savings. Our team also managed the installation of onboard- to-wayside interfaces, including CCTV, passenger emergency communications, train control, rail worker warning, wheel/rail interface and maintenance facility equipment compatibility.

As part of our commitment to engineer a better future for our planet and its people, we: 

• Coordinated with Washington Metropolitan Area Transit Authority (WMATA) and CSX Corporation to ensure our design minimized impacts to nearby major existing facilities, densely populated residential areas, freight bridges and bridge clearances, parking garages, libraries and more. 
• Made extensive use of 3D modeling to eliminate clashes across engineering disciplines and prepare exhibits for proactive public outreach efforts.
• Eliminated a major overhead bridge replacement through an innovative alignment design.
• Designed a soil nail solution to stabilize a steep embankment at the Rock Creek crossing, which reduced retailing walls and eliminated the need to extend the bridge length.
• Optimized the site plan for the largest maintenance facility, significantly reducing earthmoving and resulting in significant construction savings.
• Incorporated innovations into the rail systems design, including the use of a 1,500V DC traction power system, a hi-low OCS with buried messenger wire, and a traction power system running through the University of Maryland campus to reduce EMI emissions at sensitive research facilities.
• Engaged selected artists to incorporate Art-in-Transit exhibits at all stations.

Because the Purple Line will be powered by an overhead electrical system, emissions will be minimal within its service area. With a projected daily ridership of 69,000 in 2030 and growing to 74,000 by 2040, it is expected to replace an estimated 17,000 cars on the road daily within the next 20 years, saving one million gallons of gas annually. Additionally, the shared use of existing roadways for operation will reduce the Purple Line’s impact on nearby land and water resources.

Once completed, the Purple Line will operate largely at-grade in both dedicated and shared-use lanes and provide rapid and reliable east-west travel, direct transfers to WMATA’s Metrorail Red, Orange and Green Lines, as well as connections to Amtrak and the regional Maryland Area Rail Commuter (MARC) system. It will feature 21 stations, a 1,000-foot tunnel, three aerial sections, two operations and maintenance facilities, 52 grade crossings and over 20 bridge structures that will carry light rail vehicles, street traffic and pedestrians. It will also contain three types of tracks: ballasted, direct fixation and embedded. 

The Purple Line project is the first P3 transit project for the state of Maryland and has received numerous industry awards, including the 2016 Gold Award, Best Transit and Aviation Project from P3 Bulletin, and Infrastructure Journal’s 2016 North American Rail Deal of the Year. The Design-Build Institute of America also named MDOT MTA as its 2017 Transportation Owners of the Year for their efforts on the project.