MINUTES OF MEETING
IEEE GUIDE FOR THE CALUCLATION OF BRAKING DISTANCES FOR RAIL TRANSIT VEHICLES STANDARDS COMMITTEE (WG #25)
Meeting Date: October 17th, 2005
Meeting Location: SYSTRA Consulting Office
1601 Market Street, 17th Floor
Philadelphia, PA
Attendees:
Jim Dietz / Kamel MokhtechJohn Ewing / Dave Phelps
Jim Hoelscher / Jack Ronalter
Geoff Hubbs / Donald Sandala
Paul Jamieson / David Thurston
John LaForce / Tony Zakel
Attachments: A. Agenda for IEEE WG25 Braking Distance Standard Committee
B. Safe Braking Distance Calculation Proposal
C. Signaling and Capacity Through Computer Modeling (David Thurston paper, February 26th 2004)
Conventions used in these minutes: Action items are shown in bold italics.
1.0 Agenda
A detailed agenda was provided in advance of the meeting to aid the discussions. These minutes are modified from the agenda.
2.0 Housekeeping
2.1 Minutes of Previous Meeting
As this is the first meeting of Working Group #25, there are no previous minutes.
2.3 Next Meeting
The next meeting will be at Parsons Transportation Group offices in Baltimore, MD on December 12th at 9AM. The office is located in downtown Baltimore at 10 East Baltimore Street, Suite 801, Baltimore MD.
3.0 Committee Issues
3.1 Policies and Procedures
A. Per the attachment, this Working Group is to develop a guide, not a standard, for the calculation of braking distances for rail transit vehicles. Consensus was reached that this included airport people movers, light rail, heavy rail, commuter rail and freight applications. The guide will be written so that different entities can develop braking models to suit their needs and infrastructure. It was noted that if the rail transit vehicle was traveling on a shared-usage track (i.e., typical commuter rail practice), then the guide should also address braking distances for both types of vehicles traveling on the shared track.
B. It is anticipated that the guide will be developed within 1 year. Due to this schedule, it is envisioned that a Working Group meeting will be conducted every other month.
C. It was noted that this Working Group is not a balloting group since this Group is development a guide, not a standard.
D. Dave T. provided a brief presentation on IEEE rules for proprietary and anti-trust discussions at the Working Group. These rules will be presented at the start of every meeting.
3.2 Funding Status
J. Dietz noted that at this time that it was not yet clear if this Working Group would be developing a guide for the IEEE, or ATPA, or a combination of both. This should be clarified at the next Working Group meeting.
4. Standard Development Actions
4.1 Overview and Definitions
A. It was noted that definitions from other Working Groups can be used for our Working Group so that definitions and abbreviations are consistent. Paul J. has maintained a compilation of definitions and abbreviations for all the IEEE Working Groups, and these are provided on the RSTVIC website (http://grouper.ieee.org/groups/railtransit/).
B. The overview of the guide should define that the term “braking distance” takes into account all aspects of the vehicle and wayside upon entry into more restrictive territory, including propulsion, braking, vehicle overhang, safety factors, etc.
C. Jim H. noted that braking models for Airport People Mover’s have already been developed as part of the IEEE standardization process. It was anticipated that there would be minimal difference between these braking models and the braking model developed by this Working Group. ACTION: Dave T. to investigate and determine the standard which outlines braking models for people movers.
D. Dave P. volunteered to provide the IEEE standard style manual which the guide will follow when text is developed. The format/style for a guide is the same as for an IEEE standard.
E. Definitions to be addressed in the guide:
§ MAS – maximum authorized speed
§ Buffer distance
§ Preceding train overhang
§ Brake assurance
§ Reducing – this is a request for braking to reduce speed in advance of a curve, etc.
§ Grades and Curvature.
F. Consensus was reached that the guide should include typical examples of Braking Models in the body of the document, not in the annex.
4.2 Braking Model Components
A simplified illustration of the proposed Braking Model guide is provided for reference.
A. Maximum Entry Speed at Entry Point. The Maximum Entry Speed is also the Maximum Attainable Speed, which is the MAS plus a tolerance (usually 2-3 mph) to prevent a train from applying brakes instantaneously upon exceeding the MAS. It also should take into account equipment tolerances (i.e., wheel diameter, speed sensor error, etc.).
B. Entry Point. Entry Point is defined as the point where a train enters more restrictive territory. An Entry Point can be defined as a signal, impedance bond or insulated joint, or a transponder.
C. Reaction Time. This component of the Braking Model may consist of two parts:
§ Equipment Reaction Times. The maximum reaction time of the carborne equipment to detect a more restrictive condition is typically the time allowed for the train to travel at the less-restrictive condition past the entry point in the absence of signal information. This time can also include the latency of the communications system transmitting signal information to the train from the wayside, and processing time on the wayside to determine the more-restrictive condition based upon train location. The Equipment Reaction Time also typically includes the time for the carborne equipment relay to drop due to the overspeed condition.
§ Operator Reaction Time. This is the reaction time provided for action by the operator to suppress the overspeed condition, usually by either acknowledgement of the overspeed condition or through a manual application of brakes.
D. Runaway Acceleration. This is assumed to be the maximum acceleration rate available at the Maximum Entry Speed based upon the optimal vehicle performance characteristics. This component starts at the end of the Reaction Time. If Runaway Acceleration were to occur earlier, then the Braking Model would begin at the less-restrictive Maximum Entry Speed from territory prior to the Entry Point. Thus, the worst-case occurs when Runaway Acceleration occurs at the conclusion of the Reaction Time. Runaway Acceleration is typically included in Braking Models which feature ATO and microprocessor-based propulsion control logic. An interrelated failure analysis may also be performed. This component of the Model is grade compensated.
E. Jerk-Rate Limiting (Propulsion Removal). This component of the Braking Model involves the removal of propulsion simultaneously with the application of brakes. From a worst-case perspective, this is typically assumed to be half the acceleration rate of the vehicle at the train speed achieved at the end of the Runaway Acceleration period. This component should be verified by test, and defined in the vehicle technical specifications.
F. Dead Time. This component is after removal of propulsion, and prior to a 10% application of the braking system after command by the carborne signal equipment. The train is typically assumed to be in coast during this time. Again, this component should be verified by test, and defined in the vehicle technical specifications.
G. Brake Build-Up. Brake Build-Up is the time for the train to “build-up” to the Braking Rate of a train from 10% (i.e., this is not the time to “build-up” to the full performance braking characteristic of the train). The train is typically assumed to have achieved half the deceleration rate of the Braking Rate during this period. Again, this component should be verified by test, and defined in the vehicle technical specifications.
H. Braking Rate. The Braking Rate is a de-rated deceleration rate defined by a railroad or transit authority, and can either be a service brake or emergency brake application based upon the railroad or authority. It is based upon the application of friction brakes only, and is typically applied through fail-safe or safety-critical circuits. In some instances, allowance is provided here for brake assurance.
I. Safety Factor. The Safety Factor is typically used to capture a range of issues that may not be addressed in other components of the Braking Model. These include the following:
§ Adhesion levels
§ The percentage of failed brakes on a train, both the percentage of brakes on a train in which the train can continue service and then additional brakes that may fail upon brake application due to the more restrictive condition at the Entry Point
§ Operating Rules and Procedures
§ Equipment tolerances (vehicle braking systems, etc.)
§ Slip/slide systems
§ Load weigh failures
§ Magnitude of the Braking Rate used.
J. Vehicle Overhang. This is the distance between the front coupler face of a train and the device which is used to detect the more-restrictive condition. This can be an antenna on the lead truck, a magnetic transponder, etc.
4.3 Sub-Committee Assignments
The following actions were taken by the various Working Group individuals to be completed prior to the next meeting:
A. Tony Z. and Don S. to develop preliminary language for the Braking Model components A through C defined in 4.2 above.
B. John E., Paul J. and Jack R. to develop preliminary language for Braking Model components D through G defined in 4.2 above.
C. Dave T. to develop preliminary language for Braking Model components H, I and J defined in 4.2 above.
D. Jim H. to submit to Dave T. an electronic version of P679.1 dated May 1982 of an IEEE Proposed Recommended Practice for the Determination of Safe Braking Distance in Fixed Guideway Land Transportation Systems (this Practice was never published).
E. Dave P. to provide the electronic template of an IEEE standard.