Rail: Guideway Grade
Primary Guidance
- Guideway should be on a vertical tangent whenever possible.
- Maximum grades are established based on characteristics of each rail mode for typical applications.
- Design grades in excess of those stated below must consider safety, maintenance, power, vehicle, and life-cycle cost.
Discussion
Guideways are more complicated to design, manufacture and install if the guideway is within a vertical curve. Therefore, guideways should be on a vertical tangent wherever possible. Maximum grades are established based on characteristics of each rail mode for typical applications.
Light Rail
Track gradients for guideways on any type of track section (i.e. ballasted or rigid) should conform to the following:
- Mainline: 4.0% Maximum.
- Yard Lead Track: 1.0% Maximum.
- Yard Storage Track: 0.2% Maximum.
- Shop Track: 0.0% Maximum.
- Stations: 1.0% Maximum.
Metro
Track gradients for guideways on any type of track section (i.e. ballasted or rigid) should conform to the following:
- Mainline: 4.0% Maximum.
- Yard Lead Track: 1.0% Maximum.
- Yard Storage Track: 1.0% Maximum.
- Shop Track: 0.0% Maximum.
- Stations: 1.0% Maximum.
MARC
Track gradients for guideways should conform to the latest requirements of the operating railroad, which owns the track (e.g. Amtrak or CSX). Track gradients for guideways on portions of track owned by MTA should conform to the latest requirements of the operating railroad to which the MTA portion connects.
Grades in excess of those stated above may be approved in circumstances where adhering to the maximum grade results in increases to the construction cost of the project because of factors such as the following:
- Excessive grading, impacts to adjacent structures and/or property.
- Increased length and/or height of retaining walls.
- Other difficulties in construction.
In these circumstances, consideration must be given to the following:
- Safety: Grades cannot be increased to the extent of creating unsafe operations for MDOT personnel or the traveling public.
- Maintenance: Steeper grades can result in conditions such as accelerated wearing of the rail as well as the wheels and brakes on vehicles.
- Power: For electrified systems, steeper uphill grades will require more power, and the additional power must be within the power capacity of the system to provide.
- Vehicles: Grades should be governed by vehicle limitations to prevent stalling and wheel-to-rail slip, including when accelerating from a stop while on the grade, in snow and ice weather conditions, and where wet leaves on the rail increase wheel slippage. Grades should also consider vehicle limitations to prevent overheating and excessive wear-and-tear on traction motors.
- Life Cycle Costs: Estimated construction cost savings associated with steeper grades must be compared to life cycle costs considering future rail and vehicle maintenance.
