Rail: Guideway
Primary Guidance
- Select at-grade guideway over aerial or underground guideway, if site conditions allow.
- Select ballasted track over embedded or Direct Fixation track if, site conditions allow.
- Guideway should be on a horizontal and vertical tangent whenever possible.
- Standard details should be used in order to minimize the spare parts inventory, simplify maintenance, and eliminate manufacturing costs associated with specially made components.
Discussion
Guideways are an integral component of an overall rail transit system for Metro Subway, Light Rail, and Commuter Rail. Guideways may be at-grade, aerial, or underground. As guideways for rail systems are “fixed,” the guideway’s location must be determined to balance cost with performance and achieve best value.
Underground guideways are typically more expensive to construct than aerial guideways which are typically more expensive to construct than at-grade guideways. Therefore, at-grade guideways must always be the first option considered and cannot be altered unless it fails to:
- Provide for safe and efficient boarding at transit station locations.
- Achieve safe operating speeds for the environment in which they operate while providing efficient travel time.
- Provide adequate and intuitive means for emergency evacuation.
- Provide adequate clearances to ensure safe operations along the entire guideway.
- Avoid prohibitive right-of-way costs and impacts.
Guideways shall be designed to meet NFPA 130 for fire/life safety and ADA for accessibility.
Guideway track section consists of different types that shall be determined based on the following:
- Ballasted Track consists of rails fastened to timber, composite, or concrete ties using a rail clip system on a foundation of ballast, subballast, and prepared subgrade. Ballasted track is preferred for at-grade sections and should be considered for bridges up to 300 feet in length within exclusive right-of-way.
- Direct Fixation track consists of rails fastened to concrete using Direct Dixation fasteners. It is used on non-ballasted aerial structures and in tunnel structures including portal approaches. When bounded by either Direct Fixation or Embedded track, Direct Fixation construction shall also be used on track slab at-grade for sections less than 350 feet in length.
- Embedded Track consists of rails supported on a concrete slab and encased by a concrete slab or other structure. It is required in areas such as roadways where vehicular or pedestrian traffic will be crossing the rails.
Although horizontal and vertical curves will be necessary on any guideway, use horizontal and vertical tangent whenever possible in order to minimize the customization costs for manufacturing and installation. All stations should be located within both horizontal and vertical tangents.
Track geometrics shall be designed to accommodate the capabilities of the design vehicle to prevent excessive wear and poor ride quality.
MTA standard details should be used for all guideway components, in order to minimize the spare parts inventory, simplify maintenance, and eliminate manufacturing costs associated with specially made components.
For MARC, guideway design should conform to the latest requirements of the operating railroad, which owns the track (e.g. Amtrak or CSX). Guideway design on portions of track owned by MTA should conform to the latest requirements of the operating railroad to which the MTA portion connects.
