APTA STANDARDS DEVELOPMENT PROGRAM APTA STD-ADMIN-GL-001-19 GUIDELINES First Published June 20, 2019 American Public Transportation Association 1300 I Street NW, 12th Floor East, Washington, DC, 20005 Compendium of Definitions and Acronyms for Rail Systems Abstract: This compendium was developed by the Technical Services & Innovation Department and published by the American Public Transportation Association (APTA) to provide a glossary of commonly used definitions and acronyms in documents such as standards, recommended practices, and guidelines, so there is consistency within the rail transportation industry. Summary: APTA, through its subsidiary the North American Transit Services Association (NATSA), develops standards, recommended practices and guidelines for the benefit of public rail transportation. These tasks are accomplished by working groups consisting of members from rail transit agencies, manufacturers, consultants, engineers and other interested groups. Through the development of these documents, working groups have created a wide array of terms and abbreviations, many with varying definitions. This compendium has been developed to standardize the usage of such definitions and acronyms as it relates to rail operations, maintenance practices, designs and specifications. This document is dynamic in nature in that, over time, additional definitions and acronyms will be included. It is APTA’s intention that the document be sufficiently expanded at some point in the future to provide common usage of terms encompassing all rail industry requirements. Scope and purpose: This compendium applies to all rail agencies that operate commuter rail, heavy rail (subway systems), light rail, streetcars, and trolleys. The usage of these definitions and acronyms are voluntary. Nevertheless, it is the desire of APTA that the rail industry apply these terms to all documents such as standards, recommended practices, standard operating practices, standard maintenance practices, rail agency policies and procedures, and agency rule books. © 2019 American Public Transportation Association Compendium of Definitions and Acronyms for Rail Systems June 20, 2019 Introduction The Compendium of Definitions and Acronyms for Rail Systems reflects common terminology used in the rail industry by rail operating and planning agencies, manufacturers, consultants, engineers and general interest groups. The definitions and acronyms have been compiled using existing terms mainly in APTA standards, recommended practices, and guideline documents. This document is dynamic in nature and as such will be updated to accommodate new terminology as new terms emerge. APTA’s goal with this document is to one day be sufficiently broad enough to cover all rail related activities. It is recognized that it is not possible to capture all the definitions and acronyms used in the rail industry. However, the intent of this document is to identify as many as possible, specifically the most commonly used terms so as to standardize their usage. This document can also be useful to those new to the industry who may not be familiar with some of the terms. Some definitions and acronyms referenced in this document may have slightly different explanations or more than one definition. Different explanations are shown as bulleted items. Numbered items all relate to the same definition. Where more than one explanation is shown, the user should use language that best reflects the intent of the rail agency document. References and source material for definitions and acronyms are provided where available. Where none are available, common usage over time as used in the rail industry is the source for such terms. The user is also referred to various other valuable resources such as: • The Association of American Railroads (AAR) • American Railway Engineering and Maintenance-of-Way Association (AREMA) • Institute of Electrical and Electronics Engineers (IEEE) • Federal Railroad Administration (FRA) • Federal Transit Administration (FTA) • National Transit Database (NTD) Each revision to this compendium will show a revision number and date on the front page. This document will not be subjected to the normal APTA standards development process of requiring public comment, CEO or various Policy and Planning Committee approvals prior to publication. The use of any terms contained in this document is voluntary. The distribution and publication of this compendium is provided as a service to the rail industry. Neither APTA nor its employees are responsible for use or misuse of any material contained in this document. If there are errors or new terminologies, please send your comments to APTA at [email protected] quoting the source/s. © 2019 American Public Transportation Association Page 2 of 263 Compendium of Definitions and Acronyms for Rail Systems June 20, 2019 Definitions NOTE: Some article sources and references can be found at the foot appropriate pages. Additional material is at the end of this document. A AAR-Class Bearing Bearings manufactured in accordance with the “AAR Manual of Standards”, Section H, “Journal Bearings and Lubrication,” for use on bearing seat diameters as described. Abandonment • In public transportation operations, a procedure whereby a carrier ceases operation on all or part of its lines and routes with permission from the appropriate regulatory authorities. • With rights-of-way, the relinquishment of the public interest in right-of-way or activity thereon with no intention to reclaim it or use it again for transportation purposes; also known as vacation. Abdominal Compression Criterion Peak x-axis deflection measured at each abdominal sensor, filtered at CFC600. Abdominal Viscous Criterion (VC) A value calculated according to the following formula, using the x-axis data from each abdominal sensor, filtered at CFC600: Abdominal VC = V(t) x C(t), Where V(t) = instantaneous abdominal velocity (m/s) C(t) = instantaneous abdominal compression ratio, C(t)=D(t)/DAB D(t) = instantaneous abdominal compression (mm) DAB = depth of the uncompressed abdomen test device (mm) Absolute Block A block that no train is permitted to enter while it is occupied by another train without appropriate procedure and authorization. Absolute Permissive Block System (APB) A block signal system under which the block is usually from siding to siding for opposing movements an d the fixed signals governing entrance into the block display an aspect indicating Stop when the block is occupied by an opposing train. For following movements, the section between sidings is divided into two or more blocks and train movements into these blocks, except the first one, are governed by intermediate fixed signals, cab signals, or both. The intermediate fixed signals usually display an aspect indicating stop; then proceed at restricted speed, and the cab signal displays an aspect indicating Proceed at Restricted Speed, as its most restrictive indication. Absolute Stop A signal indication which requires a train to stop and not proceed. © 2019 American Public Transportation Association Page 3 of 263 Compendium of Definitions and Acronyms for Rail Systems June 20, 2019 AC Inverter A device for converting direct current (DC) electricity into alternating current (AC) electricity using partial DC voltage rectification to simulate AC current at a specified frequency, usually 60 Hz in North America. AC Track Circuit An ac electrical circuit that makes use of both rails to detect train occupancy of the track and, in response, to actuate signals, train control devices and grade crossing protective equipment. Acceleration Increase in velocity per unit time; in transit, usually measured in feet per second squared (meters per second squared) or, in the United States, sometimes in miles per hour per second. Acceleration Rate Time rate of change of speed of a vehicle. Acceptable Fire Risk • Fire performance characteristics created by combining fire hazard severity information available and fire scenario probability for a given category of equipment and service determined to be in the “no corrective action required” region of the fire risk matrix. • A combination of available fire hazard severity information and fire scenario probability for a given category of equipment and service determined to be inside Category 4 “Acceptable” risk region of the fire risk matrix requiring no corrective action. Access [See also Controlled Access] Permission, liberty, or ability to enter, approach, or make use of. Access, Controlled In transportation, to have entry and exit limited to pre-determined points, as with rail rapid transit or freeways. Access Equipment Any vehicle entryway accessory that deploys to aid the boarding of passengers including steps that deploy when doors are opened. Accessibility • A measure of the ability or ease of all people to travel among various origins and destinations. • In transportation modeling and planning, the sum of the travel times from one zone to all other zones in a region, weighted by the relative attractiveness of the destination zones involved. • In traffic assignment, a measure of the relative access of an area or zone to population, employment opportunities, community services, and utilities. • The extent to which facilities are free of barriers and fully accessible by mobile handicapped people, including wheelchair use. Accessible Transportation Facilities Transportation facilities that are barrier-free, allowing their use by all travelers, including the mobile physically handicapped, elderly,