Overview of Microprocessor-Based Controls in Transit and Concerns About Their Introduction David J. Mitchell Battelle Columbus Laboratories Columbus, Ohio Microprocessor-based devices that perform control devices. In time, digital circuitry, based on the and monitoring functions are all around us. They are use of integrated circuits, was employed. Now, be­ being incorporated every day in consumer, automotive, cause of their potential for low cost and design and transit products among others. For example, in flexibility and their ability to perform large num­ consumer products they monitor the operation of bers of complex functions, software-based computers refrigerators. In automobiles they control operations are being used in transit control systems. The pres­ of the engine. In transit vehicles they perform ent trend is clearly in the direction of using com­ functions such as propulsion, braking, and automatic puters (microprocessors in particular) to perform train control. The trend is well established. The ATC functions throughout the entire range of transit benefits of small size, low power consumption, flexi­ controls: central, wayside, and vehicle borne. bility, improved diagnostic capabilities, and low This evolution has spread to other major subsys­ cost are expected to aid transit operators in im­ tems as well. Presented hereafter are several exam­ proving service and reducing cost (both operating ples of how microprocessors are used in controlling and capital). and monitoring rail transit. These are examples With the introduction of any new technology, only; the list is not meant to be all inclusive. transit authority personnel ask themselves three Applications in both heavy and light rail are cited main questions: because much interchangeability of equipment is possible between these two modes, which further • How do I know that the equipment will operate demonstrates the flexibility of such equipment. safely and reliably? • How do I maintain the equipment? • How can I modify the equipment, if needed? Train Control The purpose of this paper is to stimulate discus­ Mi croprocessor s are used throughout train control sion on this subject by acquainting the reader with equipment. The most safety-critical applications present and possible future uses of microprocessors have been in automatic train protection (ATP) equip­ in light rail transit (LRT) and identifying concerns ment. Computer technology has been employed for the associated with such uses. second and third generations of the vehicle-borne ATP equipment (supplied by Westinghouse) at the Sao Paulo, Brazil, Metro. The Atlanta Airport people­ PRESENT USES OF MICROPROCESSORS IN TRANSIT mover system and the Miami downtown component of the Met.1.orail (also Westinghouse systems) use similar The use of microprocessors has evolved in rail tran­ on-board safety equipment. In these systems, a dual sit and has spread to all the major subsystems. This channel configuration with identical hardware in evolution is most evident in automatic train control both channels is used for some functions. Dissimilar (ATC) equipment. ATC functions associated with rail­ software in the two channels is used for indepen­ road and transit control systems have been primarily dence. A fail-safe checker, using discrete component implemented with discrete component technology. Such technology, compares the outputs of both channels circuitry has been commonly based on established de­ dll<l dlluw8 tt:alu mutlun uuly 1( uuth dYH!t! ( 1). signs and, in most cases, has used proven components Standard Elektrik Lorenz AG (SEL) has de;;-eloped a (e.g., relays) in their implementation. Equipment computer-based train control system called SELTRAC, that uses such circuitry has been readily accepted which is now under demonstration on Line 4 of the by the transit industry because it is based on con­ Berlin 0-Bahn. These controls have also been selected cepts and components that have evolved over many by the Urban Transportation Development Corporation years and that have been well proven in actual (UTDC) for their advanced LRT systems to be deployed service. in Vancouver and Toronto and their automated system In recent years the levels of complexity and in Detroit (2). One subsystem of SELTRAC uses three .... ,-. ...... r .... , ... ,,..~ i:"'...... .-:1 ......... ,.., ... .: ... ,.. .:.:1 .......... .: ..... .,,,, .......... ~ ...... .,,, .. o .:n ,...,..,,, ..... h ::SU!,)i1i::s~il.:ctL.iou or Li:aif1 \.,;Ull'-1.U.1. syotcms ua.vc iii­ creased dramatically. Not only is there a trend channel. A two-out-of-three voter allows train motion toward greater levels of automation, but the means if any two of the channels agree. of implementing these systems have changed as well. Computer technology is also being used in Europe Initially, relays were displaced by solid-state and Asia. Ericsson of Sweden has used computer-based 164 Overview of Microprocessor-Based Controls in Transit 165 designs for rail transit interlockings in Gothenburg Microprocessors are also being used in non-safety­ and Malmo, Sweden, and in Denmark (3). The Japanese critical equipment. Here they control train opera­ National Railway has been testing -;ornputer ized in­ tions and assist in transrni tting large amounts of ter lockings on their Joetsu line, as has British data from stations to a central point. Santa Clara Rail at Leamington Spa ( 4-6) • In France, Interelec, is expecting microprocessor-based preemptive signal­ along with Jeurnont Schn;ider, is designing System ing equipment for grade crossings. Aid to Driving Operations and Maintenance (SACEM) (discussion between the author and Marc Genain, Brakes SOFRETU, October 1984). This device will compute safe stopping distances for trains while they are in motion (in essence a moving block system). It is Westinghouse Air Brake Division (WABCO) is providing based on two microprocessors with different hardware a microprocessor-based unit to interface the train­ and software plus extensive cross-checking. Both line electrical signals and the friction brake con­ trol valves for the new Washington Metropolitan Area microprocessors must agree before the safe-to-proceed Transit Authority (WMATA) Breda cars (16). Two com­ signal is given. plete microprocessor units, which use the Intel In the United States microprocessor-based safety 8080A central processing unit (CPU), are provided on controls are now being applied to railroad use. The each car. Each unit controls a separate truck. Union Switch & Signal (US&S) Division of Arner ican Standard, along with the Union Pacific Railroad, tested prototype control systems near Modena, Utah. Vehicle Information Systems This led to their microcode system, which is a micro­ processor-based track circuit system now in service SEL has designed a new vehicle information system on the Norfolk & Western Railroad (2.-~. It provides called Integrated Vehicle Information System or !VIS train detection as well as detection of broken rails for short (17). Its purpose is to receive, process, and failed insulated joints. The device uses a single and transi~supervisory and information data for central processing unit (Motorola 6809). Exhaustive passengers and train operators. SEL has proposed self-checks, such as wrapping the outputs back to that this equipment be used in LRT vehicles for the the input so they can be checked, and interleaving transmission and reception of digital data and voice diagnositc routines in the operating software are information. The unit is based on an Intel 8085 CPU. used to verify proper operation. Figure 1 shows a As many as 32 i terns on board the vehicle can be microcode unit. controlled through one !VIS unit. Propulsio n Westinghouse Transportation Division has supplied microprocessor-based propulsion control logic for several transit systems (18) . These include Rio de Janeiro Metro, Sao Paulo Metro, So u theastern Penns yl­ vania Transportation Authority (SEPTA), Baltimore Metro, Miami Metro, Washington Metropolitan Area Transit Authority (WMATA), Vancouver Transit Author­ ity, Niagara Frontier Transit Authority (NFTA), and Bay Area Rapid Transit System (BART) • These micro­ processor-based control systems operate power switch­ ing devices that in turn apply power or brakes: con­ dition the train-line signal to provide smooth, jerk-free motion, operate the chopper thyristor circuits: and protect against abnormal conditions such as overcurrents. Early Westinghouse equipment was based on the 8-bi t Intel 8080 CPU and later systems have been based on the 16-bit Intel 8086 CPU. Brown Boveri is supplying microprocessor-based FIGURE 1 Microprocessor-based ATP equipment. propulsion control for the Portland light rail system. The General Railway Signal (GRS) Company is also marketing a similar device--the Trakode II. The Fare Collection safety of the device is assured through "safety as­ surance logic," a separate program running in the Microprocessors are being used increasingly in fare same central processing unit as the operating program collection equipment. For example, the fare box (13-15 and General Railway Signal promotional mate­ system manufactured by General Farebox (Figure 2) r ialon safety assurance logic and vital processor uses a microprocessor to count coins or currency, interlocking). The safety assurance logic verifies display this amount, signal when the correct fare that the inputs and outputs of the processor are has been tendered, and allow the motorman to accept correct and that the program is executed correctly.