Fast and Accurate Railroad Track Measurement - the

Detroit People Mover's New Automated System

Soheil Saadat1, Bernard Schulze2, Steve J. Smith3,

Rickey L. Stratton4, Barbara Hansen5, Richard D. Curtis6, and Jaimy Juliano7

1Soheil Saadat, Project Manager, CTLGroup, Washington D.C. Office, 10480 Little Patuxent Parkway,

Suite 820, Columbia, MD 21044 , Email: ssaadat@ctlgroup.com, Phone: 410-997-0400, Fax: 410-997-

8480

2Bernard Schulze, Principal Engineer & Group Manager, CTLGroup, 5400 Old Orchard Road, Skokie, IL

60077, Email: bschulze@ctlgroup.com, Phone: 847-972-3176, Fax: 847-965-6541

3Steve J. Smith, Principal Engineer & Group Manager, CTLGroup, Washington D.C. Office, 10480 Little

Patuxent Parkway, Suite 820, Columbia, MD 21044, Email: sjsmith@ctlgroup.com, Phone: 410-997-0400,

Fax: 410-997-8480

4Rickey L. Stratton, Transit Electrical Engineer, Detroit Transportation Corporation, The People Mover,

1420 Washington Blvd. (3rd Floor), Detroit, MI 48226, Email: rstratton@thepeoplemover.com, Phone:

313-224-2160, Fax: 313-224-2134

5Barbara Hansen, General Manager, Detroit Transportation Corporation, The People Mover, 1420

Washington Blvd. (3rd Floor), Detroit, MI 48226, Email: bhansen@thepeoplemover.com, Phone: 313-224-

2190, Fax: 313-224-2134

6Richard D. Curtis, Curtis Engineering Consulting Services, Inc., 8731 Crestwood Ave., Munster, IN

46321, Email: curtisengr@aol.com, Phone/Fax: 219-838-2045

7Jaimy Juliano, Piki Technology, 274 Penny Ln., Grayslake, IL, 60030, Email: jjuliano77@gmail.com,

Phone: 847-224-8470

ABSTRACT

Conventional track inspection methods are based on labor intensive visual and manual inspections that

are often either too slow or too inaccurate. Maintenance work on inner-city light rail systems with long

hours of operation and heavy ridership is typically performed during the few hours just before the morning

commute begins. An automated track measurement system that quickly and accurately identifies track

abnormalities is essential to safe and timely operation of inner-city light rail systems.

This paper presents the design, evaluation and implementation of an automated laser-based track

measurement system for the Detroit People Mover (DPM) light rail system by CTLGroup. DPM driverless

vehicles are powered by linear induction motors, with power to the system provided through a pair of

side-mounted conducting rails. The track measurement system utilizes five non-contact scanning lasers in

order to quickly and accurately measure vertical and lateral location of power rails as well as the vertical

location of the linear induction motor (LIM) reaction rail with respect to the running rails.

Sensors and data acquisition hardware are mounted on a lightweight track maintenance cart which is

pulled by a diesel powered maintenance vehicle. The system is run via laptop computer used by the

operator inside the maintenance vehicle, which is connected to the track maintenance cart by an

electrical umbilical cord. Its Graphical User Interface (GUI) allows the operator to start measurement from

any point along the track, adjust measurement increment along the track and automatically generate

detailed work orders for the maintenance crew. Measurements along the track are compared with preset

tolerances to identify locations and make appropriate corrective actions.

INTRODUCTION

The Detroit Transportation Corporation (DTC) of Detroit, Michigan - USA, is owner and operator of the

Detroit People Mover (DPM) system. The DPM system opened in 1987 and is located in the city’s central

business district. It consists of 2.9 miles (4.7 km) of a single-lane elevated concrete guideway loop

(Figure 2), 13 passenger stations, two power substations, and a Maintenance and Control Facility (MCF).

The guideway provides connections between various Downtown Detroit entities, such as:

• Courts

• Governmental administrative offices

• Sports arenas

• Exhibition centers

• Major hotels

• Commercial & personal banking centers

• Retail districts

Table 1 below shows annual vehicle miles from 2004 – 2008 (1).

Guideway & Stations

The elevated guideway offers an advantage over street level traffic: it provides the trains with a distinctive

right of way: clear of automobile and pedestrian traffic. In addition, eight (8) DPM stations are integral with

pre-existing structures (Figure 1). The structure integrated stations link over 9 million square feet where

riders can traverse within, unburdened by outside elements.

Locations around the guideway loop are identified via: surveyor’s chainage markers or local reaction rail

segments. At chainage markers, locations along the guideway begin & end at the same point near the

Bricktown Station (“0+00” to “153+12”). This represents the 15,312 ft (2.9 mi) distance around the

guideway loop. At the local level, it is simply the number reaction rail segments along the guideway and

inside the MCF beginning with segment 000/001 between Michigan Avenue & Times Square stations.

Therefore, any given track location along the guideway can reliably be designated by a chainage marker

and the number of feet past that chainage marker.

DPM track is standard gauge (4 ft. 8.5 in.) using American Railway Engineering Association (AREA)

Standard 115RE rail. Rails are continuously welded in place and secured with elastomeric direct fixation

fasteners.

Vehicles, ATC & Propulsion

The DTC fleet consists of 12 driverless vehicles operated by control operators via the automatic train

control (ATC) induction loop system. The Automatic Train Control (ATC) system conducts all daily

scheduled revenue operations automatically with a minimum of human intervention. The ATC inductive

loop system functions on three-levels:

1. Management (System Management Center - SMC);

2. Operation (Vehicle Control Center - VCC)

3. Activation (Vehicle On-Board Control - VOBC).

DPM vehicles are normally operated in pairs and remotely controlled by an automatic train control (ATC)

system from the central control, which is located at the Maintenance and Control Facility. Trains are

propelled by four linear induction motors (two per vehicle) that are capable of providing a maximum train

speed of 56 mph. However based on the short guideway distance and track curvature, the average train

speed is 12 mph (19 km/hr). Round trip on the system is approximately 15 minutes and headway ranges

from 3 to 4 minutes. The average dwell at each station is 20 seconds. (2)

The LIM produces thrust electromagnetically; therefore, vehicle movement is entirely independent of

traction between the running rails and wheels. The LIM operates in conjunction with the reaction rail,

which is located between the running rails (Figure 2). The nominal air gap between the reaction rail and

bottom of the LIM is 0.43 inches (11 mm). The basic principle of operation is as follows: from the three-

phase AC input supplied by the Power Conversion Unit (PCU), the LIM creates a travelling magnetic field

in the air gap between the LIM and reaction rail. This magnetic field cuts the reaction rail top cap and

induces circulating currents. The interaction between the magnetic field and the induced currents

produces thrust. (2)

The LIM reaction rail forms a continuous electromagnetic conductor throughout the entire length of the

track, Figure 3. The reaction rail is mounted between the running rails with its upper surface at the same

height as the top of the running rails. To maintain proper thrust parameters, the reaction rail and the LIM

are adjusted to maintain a nominal gap. Two opposite polarity power rails, mounted on the concrete

parapet walls of the guideway as shown in Figure 3, transfer power to the vehicles via vehicle mounted

power current collector shoes. To ensure smooth engagement and disengagement of the vehicle power

current collectors, power rail ramps are provided at special locations along the track. The running rails

provide a continuous, non-current carrying ground for the system.

The Problem

DPM hours of operation are 6:30 a.m. to Midnight Monday through Thursday, 6:30 a.m. to 2:00 a.m. on

Friday, 9:00 a.m. to 2 a.m. on Saturday and Noon to Midnight on Sunday. Due to its hours of operation

access to track for inspection, maintenance and repair is primarily limited to early hours of the morning

during the week. Currently, track and guideway inspection is a labor intensive procedure where a trained

technician uses a manual measuring device to inspect track gage point and other critical parameters

(Figure 4). Therefore, it takes considerable time to completely inspect the 2.9 mile long track which is

further hampered by the cold weather during the winter months. This labor and time consuming

inspection process increases the likelihood of not detecting critical problems that can jeopardize safety,

cause damage to LIMs, power collectors, power rails, etc. and loss of revenue service.

In 2008, Detroit Transportation Corporation decided that an automated track inspection system is vital to

its on time operation, safety and lowering track inspection and maintenance costs in the long run. In April

of 2008 DTC issued an invitation for proposals (IFP) to solicit design and delivery of an automated track

measurement system. In response to this IFP, CTLGroup engineers submitted a proposal for design and

integration of an automated, non-contact, laser-based, fast and accurate track measurement system.

CTLGroup system design utilizes commercial-off-the-shelf (COTS) items such as rail road maintenance

carts, electronic data acquisition systems and sensors to measure lateral and vertical distances between

the LIM reaction rail, power rails and running rails for which detail information is provided in the following

sections.

In August of 2009, CTLGroup was awarded the contract by DTC for design and fabrication of the

proposed system. This paper presents the automated track measurement system designed by and

currently being fabricated at CTLGroup. The following sections provide an overview of the currently

available track measurement systems, DTC requirements for an automated track measurement system,

CTLGroup system design, related sensor fusion and data processing.

AN OVERVIEW OF RAILROAD TRACK MEASUREMENT SYSTEMS

Visual inspection was the primary method for track inspection before the advent of modern measurement

techniques, which is inherently slow and highly prone to human errors. Since the 1970’s, both speed and

accuracy of the inspection programs have been improved drastically as a result of technological

advances (3). Although being an integral part of any track inspection program, visual inspections primarily

rely on experience and technical knowledge of individuals who perform them. Since a single segment of a

track may be inspected by different inspectors at different times, visual inspections lack long-term

tractability and cannot be used for comparative studies and trend analyses. In contrast, modern sensing

technologies, electronic data acquisition devices and data processing techniques have made track

inspection process not only more accurate but provided the possibility of performing long-term

comparative and trend analyses.

Current sensing technologies for track inspection include machine vision, light detection and ranging

(LIDAR), non-contact laser transducers and profilers as well as acoustic emission (4, 5). Each of these

technologies has its advantages and disadvantages, therefore, is targeted at measuring or detecting

change in certain track parameters. For example, LIDAR systems provide high cross-sectional resolution

imagery of track and its surrounding area while its longitudinal resolution is affected by the speed of

sensing platform; machine vision systems use high speed video cameras in visible and infrared

spectrums but primarily suffer from having to control and augment lighting.

A variety of systems from semi-automated to fully-automated track measurement systems are available in

the market but, none are directly applicable to this application because of the DPM requirement to

determine the location of the LIM reaction rail and power rails with respect to running rails. In addition, the

custom made system designed by CTLGroup not only addresses all the requirements put forth by the

DTC but also is designed with custom scalability for potential future enhancements that specifically

relates to the DPM track system, such as rail head profiling for the running rails.

DETROIT PEOPLE MOVER REQUIREMENTS - AN AUTOMATED TRACK MEASUREMENT SYSTEM

DPM specifications for the monitoring system are: (a) record these measurements at five foot increments

around the entire guideway loop, (b) identify relative location on each track segment using the DPM

chainage mark system, accurate within six inches, (c) start the measurement at any point around the

guideway loop, (d) automatically detect and alert operator of locations along the track where the LIM

reaction rail and/or the power rails are outside the specified tolerances as well as identifying the amount

adjustments required to bring them back to alignment tolerance, (e) have a graphical user interface (GUI)

that allows the operator to adjust/change tolerances, (f) generate a “work order” type report for use by

field personnel with simple instructions on identifying track segments that require adjustments, (g) export

data, findings and reports to other Microsoft Office software for analysis, print, storage, etc., (h) operate

without an external power source for up to eight hours under environmental conditions present on the

DPM system including temperature ranging from -20°F to 115°F, snow and rain.

Based on these specifications, CTLGroup engineers and scientists proposed an automated, fast and

accurate railroad track measurement system that is presented in the following section.

CTLGROUP AUTOMATED TRACK MEASUREMENT SYSTEM DESIGN

The automated railroad track measurement system proposed by CTLGroup is a non-contact

measurement system that can collect and store track information for both real-time and offline analysis. A

contact-based measurement system is not practical because of the hazard associated with having direct

contact with power rails and, interference with track elements that surround the LIM reaction rail, as well

as the existence of mechanical switches along the track, Figure 5.

Overall, the system uses five non-contact laser sensors to measure the required track parameters. Four

scanCONTROL 2700-100 laser line scanners from Micro-Epsilon™ (6) are used to measure the running

and the power rails. A single beam optoNCDT 1300-200 laser sensor from Micro-Epsilon™ (6) is used to

measure the LIM reaction rail.

Sensors, data acquisition unit, control and computing modules are all installed on a light weight

measurement platform (TS-2) from the Nolan Company (7), as shown in Figure 6. The measurement

platform will be pulled over the track by a track maintenance diesel vehicle that also provides power to the

measurement system. All laser sensors are mounted on a rigid 80/20 aluminum modular frame system

that is mounted on the measurement platform. Figure 7 shows the schematic of laser sensor

configuration and Figure 8 is a picture of setup for initial test and assembly. Each sensor measures

distance of the objects in its field of view and/or range. These measurements are relative distances of the

objects from the rigid frame mounted on the measurement platform. Since all sensors are mounted on a

rigid frame, the vertical and horizontal distances among them are known and fixed. Therefore, one can

easily calculate the absolute vertical and horizontal distances of the power rails, the LIM reaction rail and

one of the running rails with respect to the top of the reference running rail. Either the inner or the outer

running rail can be used as the reference. The reference running rail is the one that is closer to the power

rails and since the power rails switch side around the guideway the reference running rail also switches

from side to side along the track. Presence of power rails are detected from the output of the laser line

scanners, and consequently all of the measurements are referenced to the appropriate running rail.

As shown in Figure 7, there is a global (X,Y) and several local (x,y) Cartesian coordinate systems for

measuring vertical and lateral location of power rails as well as the vertical location of the LIM reaction

rail, with respect to the reference running rail. The global (X,Y) coordinate system is used to reference all

measurements with respect to the reference running rail. The local (x,y) coordinate systems are

associated with direct measurements from individual sensors. For example, the profile obtained from

scanning one of the running rails represents the local (x,y) coordinates of the scanned points with respect

to the location and orientation of the corresponding laser line scanners.

Within the global (X,Y) coordinate system the vertical and lateral distances among all laser line scanners

and the single point laser sensor that measures the LIM reaction rail are known. These are fixed

distances that relate to the location of the sensors on the rigid sensor frame. Therefore, once individual

measurements from each sensor are transferred from corresponding local coordinate systems to the

global coordinate system, all relative vertical and lateral distances can be easily calculated.

In order to identify the relative location of the measurement platform around the guideway loop using the

chainage mark system, a high-resolution, incremental rotary encoder is mounted in line with the platform

rear axel.

Transition points along the guideway such as mechanical switches can create false alarms with regards

to track alignment. Therefore, to better detect passage over mechanical switches and to differentiate

them from actual track misalignment alarms, two single-axis accelerometers are used to measure

acceleration onboard the measurement platform.

Since the measurement platform shall operate under environmental conditions present on the DPM

system including temperature ranging from -20°F to 115°F, an onboard thermocouple is used to measure

ambient temperature during the winter time. The thermocouple output is used to automatically turn on a

series of electric heaters as needed.

An IOtech™ Personal DAQ/3001 data acquisition unit (8) is used to collect data from accelerometers,

thermocouple, encoder and single beam laser sensor. The same unit is also used to trigger laser line

scanners and heaters as needed. A GUI is developed in LabVIEW™ (9) to process sensor data, extract

relevant information, manage data storage and retrieval, generate reports and control the system. The

IOtech™ unit is connected to a laptop running the GUI via a USB connection and the four laser line

scanners are directly connected to the laptop via a USB fire-wire hub. Figure 9 shows the interconnection

of sensors, data acquisition unit and other major electrical/electronic components of the system that are

mounted on the measurement platform. The total power requirement for the system is estimated at 400

Watts and will be provided by the track maintenance diesel vehicle.

SENSOR FUSION, DATA PROCESSING AND SYSTEM OPERATION

The GUI gives the operator options for starting track measurement and managing previously stored data.

If the starting track measurement option is selected, the system then performs a series of self diagnostic

tests. Once it passes these tests successfully, it prompts the operator to select and/or enter certain

measurement settings, and to proceed with data collection. If the data management option is selected,

the system will provide the operator with commands to load, analyze and print previously collected data

and work orders.

The measurement system is periodically checked for dimensional accuracy by utilizing a manually

dimensioned section of the maintenance building track. The cart will be passed over this rail section and

the recorded data will be compared with the manually measured data (previously entered). The system

will allow adjustments to be made so that the system is always calibrated to the reference section of rail.

Once the system successfully passes the self diagnostic test, it prompts the operator to (a) enter the initial

location of the measurement platform according to the chainage mark system, (b) identify if

measurements are taken in the clockwise or counter clockwise direction with clockwise direction defined

as the direction of increasing chainage marks and (c) enter the spatial sampling or the distance between

successive data collections along the track.

At this time, the system is ready to collect data and prompts the operator to move the measurement

platform along the track at a steady and low speed. As the platform moves, the encoder records its

relative location. The system collects (a) the profiles of the running and power rails, (b) the standoff

distance of the LIM reaction rail, (c) the ambient temperature and (d) the accelerometer outputs, at the

user defined spatial intervals.

After each collection, data from all sensors is checked to confirm proper sensors operation. The ambient

temperature is checked to make sure it is within the operating range of laser sensors. If ambient

temperature is lower than the minimum operating temperature of these sensors, heaters will be turned on.

The accelerometer outputs are analyzed in time and frequency domains to identify passage over

mechanical switches and other track components that can introduce false alarms regarding tolerances. If

an out of tolerance alarm is issued while passage over such components is detected, that spatial data

point is discarded. Otherwise, required track parameters for that location are calculated, stored and

prompted to the operator.

Extensive laboratory experiments with profiling the rail head resulted in efficient algorithms for extracting

locations of the gage and top-of-the-rail points on the running rails as well as the reference location on the

power rails. In the case of running rails, the laser line scanners that capture locations of the gage and top-

of-the-rail points are mounted at an angle, as shown previously in Figure 7. A sample of such a profile is

shown in Figure 10 where different segments of the profile associated with the base of the rail head, gage

point and top-of-the-rail are presented in black, red and blue colors respectively.

Similarly, the laser line scanners that capture locations of the power rails are mounted at an angle, as

shown previously in Figure 7 and Figure 8. A sample of such a profile is shown in Figure 11, where

different segments of the profile associated with the face and parts of the upper ledge are presented in

red, blue and black colors respectively.

As mentioned previously, the reference running rail, to which all distances are measured, is the one that

is closest to the power rails. At various locations around the track, the power rails switch sides and so

does the reference running rail. Wherever this happens, there is a transition area where power rails are

present at both sides of the elevated concrete guideway. At these locations, profiles from the two laser

line scanners that are mounted on both sides of the measurement platform are processed to detect

presence of the power rails and to identify which pair to incorporate into the calculations. The elevated

concrete guideway walls are out of laser line scanner range. Therefore, wherever power rails are not

present, the sensor output will be a flat line with all data points having the same standoff distance from

the sensor. When power rails are detected on both sides, a switch from one pair to another happens

when the current power rails go out of sensor range or the other pair comes into the sensor range,

whichever happens first. Finally, the output of the single beam laser looking at the LIM reaction rail is

analyzed and incorporated into calculation of all relative horizontal and vertical distances with respect to

the reference running rail.

A special jig, which represents a small segment of the track, will be fabricated for inspection and

calibration of the system. The horizontal and vertical distances between the running rails, the LIM reaction

rail and the power rails on the jig are known. Whenever it is necessary to check system calibration, the

measurement platform will be moved over this special calibration jig. Through the GUI, the operator

selects the calibration option and then the system will collect a series of data from all laser sensors. All of

the relative horizontal and vertical distances are calculated and compared with preset tolerances. If

deviations from present tolerances are detected, the corresponding sensors are flagged for further

inspection.

CONCLUSION

There are a wide range of track measurement systems currently available. On one end of the spectrum,

there are simple handheld semi-automatic systems that cost a few thousand dollars, which can be used

for limited track inspection tasks. Then, there are fully automated track measurement platforms that can

cost several million dollars, which can inspect long track segments at the track speed. CTLGroup

automated track measurement system is tailored to the DPM specific track monitoring and maintenance

requirements. As such, it provides the DPM with means to monitor, analyze and store relevant track

parameters for immediate and long term trend analysis, with minimum human involvement. At the same

time, its intuitive design makes it easy to operate and the use of commercially-off-the-shelf (COTS)

sensors, data acquisition devices and hardware minimizes the maintenance cost. Finally, the DPM direct

involvement during the conceptual design and development provided them with the opportunity of

purchasing a custom made track measurement system that fits their budget while providing them with the

necessary information to maintain track integrity while also reducing future maintenance costs.

REFERENCES (1) National Transit Database

http://www.ntdprogram.gov/ntdprogram/cs?action=showRegionAgencies&region=5

(2) Maintenance Manual for The Detroit Downtown People Mover, The Urban Transportation

Development Division of Lavlin Technical Publications - Kingston Ontario, Canada – Revision: Dec. 1989

(3) Swadisavi, S., Edwards, J.R., Resendiz, E., Hart, J.M., Barkan, C.P.L. and Ahuja, N., “Machine-Vision

Inspection of Railroad Track,” AREMA 2008 Annual Conference, Salt Lake City, UT, September 21-24,

2008.

http://www.arema.org/eseries/scriptcontent/custom/e_arema/library/2008_Conference_Proceedings/Mach

ine-Vision_Inspection_of_Railroad_Track_2008.pdf (accessed June 2, 2010)

(4) Clouse, A. and Kesler, K., “Advancements in Track Inspection,” AREMA 2003 Annual Conference,

Chicago, IL, October 5-8, 2003.

http://www.arema.org/eseries/scriptcontent/custom/e_arema/library/2003_Conference_Proceedings/0002

.pdf (accessed June 2, 2010)

(5) Clouse, A.L., Bloom, J. and Cook, S., “Track Inspection into the 21st Century,” Proceedings of the

AREMA 2006 Annual Conference, Louisville, KY, September 17020, 2006.

http://www.arema.org/eseries/scriptcontent/custom/e_arema/library/2006_Conference_Proceedings/053.

pdf (accessed June 2, 2010)

(6) Micro-Epsilon America, 8120 Brownleigh Drive, Raleigh, NC 27617. http://www.me-sensor.com

(accessed June 2, 2010)

(7) The Nolan Company, 1016 Ninth Street SW, Canton, Oh 44707. http://www.nolancompany.com

(accessed June 2, 2010)

(8) Measurement Computing Corporation, 10 Commerce Way, Norton, MA 02766.

http://www.mccdaq.com/index.aspx (accessed June 2, 2010)

(9) National Instruments Corporation, 11500 N Mopac Expwy, Austin, TX 78759. http://www.ni.com/

(accessed June 2, 2010)

FIGURES

1. Times Square Station 2. Grand Circus Park Station *

3. Broadway Station 4. Cadillac Center Station *

5. Greektown Station * 6. Bricktown Station

7. Renaissance Center Station * 8. Millender Center Station *

9. Financial District Station * 10. Joe Louis Arena Station *

11. Cobo Hall Station * 12. Fort Cass Station

13. Michigan Ave Station

Figure 1 Map of DPM

Figure 2 DPM Guideway Cross-section & Pictoral View

Figure 3 Linear Induction Motor (LIM) reaction rail configuration

Figure 4 Manual measurement device

(a) (b)

Figure 5 (a) Mechanical switch inside maintenance shop, (b) Location of the power rails and LIM reaction rail with respect to the running rails

Figure 6 Nolan Company, model TS-2 Cart

Figure 7 Laser sensors configuration schematic

Running Rail LIM reaction rail

Power Rails Laser Profilers Sensor Platform Single Point Laser

X

Y

x

y

y

x y

Figure 8 Picture of setup for initial test and assembly

Figure 9 Sensors, data acquisition unit, and major electrical/electronic components of the system

Figure 10 Typical Running Rail profile captured by the laser line scanner

Figure 11 Typical Power Rail profile captured by the laser line scanner

LIST OF FIGURES

Figure 1: Map of DPM

Figure 2: DPM Guideway Cross-section & Pictoral View

Figure 3: Linear Induction Motor (LIM) reaction rail configuration

Figure 4; Manual measurement device

Figure 5: (a) Mechanical switch inside maintenance shop, (b) Location of the power rails and

LIM reaction rail with respect to the running rails

Figure 6: Nolan Company, model TS-2 Cart

Figure 7: Laser sensors configuration schematic

Figure 8: Picture of setup for initial test and assembly

Figure 9: Sensors, data acquisition unit, and major electrical/electronic components of the

system

Figure 10: Typical Running Rail profile captured by the laser line scanner

Figure 11: Typical Power Rail profile captured by the laser line scanner