Advanced Sensors and Applications: 

Commercial Motor Vehicle Tire Pressure 

Monitoring and Maintenance

February 2014
FOREWORD

This project was completed as a follow-on to several projects performed under the provisions of 

Section 5117 of the Transportation Equity Act for the 21st Century (TEA-21). The primary 

objectives of this project were to provide vital cost and benefit information for the 

implementation of tire pressure monitoring systems (TPMSs) and automatic tire inflation 

systems (ATISs) to improve tire performance and safety and to influence maintenance intervals 

and practices. The work performed under the project included:

• Updating and expanding the Federal Motor Carrier Safety Administration’s (FMCSA’s) 

past market research studies on tire inflation maintenance and monitoring systems.

• Selecting TPMSs that were representative of currently available products in the 

marketplace.

• Arranging for field testing of these systems with a commercial fleet, in a normal 

“everyday” service environment.

• Developing data collection and analysis plans.

• Installing systems on test vehicles.

• Preparing for and conducting the field test.

• Analyzing the data and observations collected during the field test.

• Developing a report that summarizes the results of the analysis including observations 

and conclusions.

NOTICE

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

in the interest of information exchange. The U.S. Government assumes no liability for its 

contents or the use thereof.

The contents of this report reflect the views of the contractor, who is responsible for the accuracy 

of the data presented herein. The contents do not necessarily reflect the official policy of the U.S. 

Department of Transportation.

This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers named herein. Trade or 

manufacturers’ names appear herein solely because they are considered essential to the objective

of this report.
Technical Report Documentation Page

1. Report No.

FMCSA-RRT-13-021

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

Advanced Sensors and Applications: Commercial Motor Vehicle Tire 

Pressure Monitoring and Maintenance

5. Report Date

February 2014

6. Performing Organization Code

7. Author(s)

Brady, Stephen; Van Order, Deborah; Sharp, Asa

8. Performing Organization Report No.

9. Performing Organization Name and Address

Booz Allen Hamilton Inc., McLean, Virginia

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

U.S. Department of Transportation

Federal Motor Carrier Safety Administration

Office of Analysis, Research, and Technology

1200 New Jersey Ave., SE

Washington, DC 20590

13. Type of Report and Period Covered

Final Report

14. Sponsoring Agency Code

FMCSA

15. Supplementary Notes

Contracting Officer’s Technical Representative: Chris Flanigan

16. Abstract

This study evaluated the costs and benefits of tire pressure monitoring and maintenance systems for commercial 

fleets by conducting a yearlong field test. Specifically, the study’s goal was to determine whether these systems 

could influence maintenance intervals and practices and improve performance and safety.

The team evaluated tire pressure monitoring systems (TPMSs) and automatic tire inflation systems (ATISs) on two 

private fleets. The first fleet, CLI Transport, monitored 24 married tractor-tanker pairs at their maintenance 

terminal in Altoona, PA. The team installed Wabco’s Integrated Vehicle Tire Monitoring (IVTM) System on 12 

tractors and Meritor’s Tire Inflation System by Pressure Systems, Inc. (PSI) on 12 tankers. The second fleet, 

Gordon Food Service (GFS), monitored 24 tractors, 30 standard 50-foot trailers, and 20 refrigerated pup trailers

(reefer pups). The team installed HCI Corporation’s (HCI’s) Tire-SafeGuard on 12 tractors and 15 standard 50-

foot trailers. GFS ensured the equipment would operate together during the entire field test. In addition, the team 

installed Meritor’s Tire Inflation System by PSI on 20 reefer pups.

The team used fuel logs, maintenance records, and technician failure/inspection reports to analyze the impact of the 

equipment on maintenance practices, performance, and safety. The field test results showed the use of TPMS/ATIS

equipment reduced the operational costs of the fleet and improved the driver’s awareness of the tractor-trailer 

tires. The test fleets experienced a 1.4-percent improvement in fuel economy over the control fleet. The test fleet 

equipped with TPMS/ATIS equipment exhibited an increase in the life of the drive tires by 19 percent compared to 

the control fleet. Using the analysis results, the team estimated the equipment costs would be recovered in less than 

18 months. The return on investment (ROI) dropped to less than 6 months as the cost of fuel and tires increased. 

The findings from the field test and the ROI calculations confirm that the use of TPMS/ATIS equipment will 

reduce fleet operating costs. 

17. Key Words

Commercial motor vehicle, field test, fuel, monitor, 

monitoring, mi/gal, tire pressure, tires, TPMS

18. Distribution Statement

No restrictions

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

94

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.
ii

SI* (MODERN METRIC) CONVERSION FACTORS

TABLE OF APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

in inches 25.4 millimeters mm

ft feet 0.305 meters m

yd yards 0.914 meters m

mi miles 1.61 kilometers km

AREA

in2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yards 0.836 square meters m2

Ac acres 0.405 hectares ha

mi2 square miles 2.59 square kilometers km2

VOLUME 1,000 L shall be shown in m3

fl oz fluid ounces 29.57 milliliters mL

gal gallons 3.785 Liters L

ft3 cubic feet 0.028 cubic meters m3

yd3 cubic yards 0.765 cubic meters m3

MASS

oz ounces 28.35 grams g

lb pounds 0.454 kilograms kg

T short tons (2,000 lb) 0.907 megagrams (or “metric ton”) Mg (or “t”)

TEMPERATURE Temperature is in exact degrees

°F Fahrenheit 5 × (F-32) ÷ 9

or (F-32) ÷ 1.8

Celsius °C

ILLUMINATION

fc foot-candles 10.76 lux lx

fL foot-Lamberts 3.426 candela/m2 cd/m2

Force and Pressure or Stress

lbf poundforce 4.45 Newtons N

lbf/in2 poundforce per square inch 6.89 kilopascals kPa

TABLE OF APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

Mm millimeters 0.039 inches in

M meters 3.28 feet ft

M meters 1.09 yards yd

Km kilometers 0.621 miles mi

AREA

mm2 square millimeters 0.0016 square inches in2

m2 square meters 10.764 square feet ft2

m2 square meters 1.195 square yards yd2

Ha hectares 2.47 acres ac

km2 square kilometers 0.386 square miles mi2

VOLUME

mL milliliters 0.034 fluid ounces fl oz

L Liters 0.264 gallons gal

m3 cubic meters 35.314 cubic feet ft3

m3 cubic meters 1.307 cubic yards yd3

MASS

G grams 0.035 ounces oz

Kg kilograms 2.202 pounds lb

Mg (or “t”) megagrams (or “metric ton”) 1.103 short tons (2,000 lb) T

TEMPERATURE Temperature is in exact degrees

°C Celsius 1.8C + 32 Fahrenheit °F

ILLUMINATION

Lx lux 0.0929 foot-candles fc

cd/m2 candela/m2 0.2919 foot-Lamberts fL

Force & Pressure Or Stress

N Newtons 0.225 poundforce lbf

kPa kilopascals 0.145 poundforce per square inch lbf/in2

* SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of 

ASTM E380. (Revised March 2003, Section 508-accessible version September 2009).
iii

TABLE OF CONTENTS

EXECUTIVE SUMMARY ......................................................................................................... ix

1. INTRODUCTION AND BACKGROUND.........................................................................1

1.1 BACKGROUND ...........................................................................................................1

1.2 RATIONALE AND RESEARCH OBJECTIVES.........................................................2

1.3 OVERVIEW OF APPROACH......................................................................................3

2. DESCRIPTION OF THE FIELD TEST ............................................................................5

2.1 HOST FLEETS..............................................................................................................5

2.1.1 CLI Fleet ........................................................................................................... 6

2.1.2 GFS Fleet .......................................................................................................... 7

2.2 TECHNOLOGIES UNDER EVALUATION ...............................................................8

2.2.1 Wabco Integrated Vehicle Monitoring System................................................. 9

2.2.2 HCI’s Tire-SafeGuard..................................................................................... 12

2.2.3 MTIS System by Pressure Systems, Inc. ........................................................ 15

2.3 TEST PLAN.................................................................................................................19

2.3.1 Objectives ....................................................................................................... 19

2.3.2 Roles and Responsibilities.............................................................................. 20

2.3.3 Equipment....................................................................................................... 21

2.3.4 Schedule.......................................................................................................... 21

3. DATA COLLECTION.......................................................................................................23

3.1 PERIODIC MAINTENANCE INSPECTIONS ..........................................................23

3.2 MAINTENANCE RECORDS.....................................................................................24

3.3 FUEL RECORDS ........................................................................................................24

3.4 MAINTENANCE STAFF AND DRIVER INTERVIEWS ........................................24

3.5 MAINTENANCE STAFF AND DRIVER QUESTIONNAIRES ..............................24

4. FIELD TEST DATA ANALYSIS......................................................................................27

4.1 CLI...............................................................................................................................27

4.1.1 Fuel ................................................................................................................. 27

4.1.2 Tires ................................................................................................................ 29

4.1.3 System Accuracy ............................................................................................ 36

4.1.4 System Reliability........................................................................................... 37

4.1.5 Driver Feedback.............................................................................................. 43
iv

4.2 GFS ..............................................................................................................................49

4.2.1 Fuel ................................................................................................................. 49

4.2.2 Tires ................................................................................................................ 50

4.2.3 System Reliability........................................................................................... 55

4.2.4 Technician Feedback ...................................................................................... 59

5. CONCLUSIONS .................................................................................................................63

5.1 HYPOTHESIS ANALYSIS ........................................................................................63

5.2 COST-BENEFIT ANALYSIS.....................................................................................69

REFERENCES.............................................................................................................................77
v

LIST OF FIGURES

Figure 1. Grid. Example of data collection schedule.......................................................................x

Figure 2. Chart. Annual savings on road calls, tires, and fuel per TPMS/ATIS-equipped tractortrailer. ............................................................................................................................ xii

Figure 3. Graph. Accumulated monthly savings per TPMS/ATIS-equipped tractor-trailer......... xii

Figure 4. Map. GFS distribution network........................................................................................7

Figure 5. Grouped photo. Wabco tire pressure sensor wheel module (left), display unit (center), 

and electronic control unit (right).....................................................................................9

Figure 6. Photo. Wabco IVTM sensor unit mounting system. ........................................................9

Figure 7. Photo. Wabco IVTM system indicating tire location and low pressure reading............10

Figure 8. Grouped photo. Module installation of steer wheel (left) and drive wheel (right) with 

steer tire counterweight location. ...................................................................................11

Figure 9. Grouped photo. ECU (left) and display unit (right) installations...................................11

Figure 10. Grouped photo. HCI Tire-SafeGuard components.......................................................12

Figure 11. Grouped photo. HCI Tire-SafeGuard TPMS: DDU displaying tire position (left) and 

the wheel-mounted sensor (right). .................................................................................13

Figure 12. Grouped photo. HCI Tire-SafeGuard antennas............................................................14

Figure 13. Grouped photo. DDU installation: coaxial cables connecting DDU (left) and the DDU 

displaying tire location and pressure data (right). ..........................................................15

Figure 15. Photo. Pressure protection valve (CLI). .......................................................................16

Figure 16. Grouped photo. MTIS, rotary units on wheel ends. .....................................................17

Figure 17. Grouped photo. Wheel end assembly with press plug and stator (left) and through-tee 

(right)..............................................................................................................................18

Figure 18. Grouped photo. CLI and GFS control box installation between taillights (right) and on 

tanker’s crossbeam (left). ...............................................................................................18

Figure 19. Grouped photo. CLI and GFS indicator light installation on the fender (left) and 

underside of the reefer pup (right)..................................................................................19

Figure 20. Graph. Monthly average fuel economy (CLI) for control and test fleets.....................28

Figure 21. Graph. Monthly average fuel economy, original tractors (CLI). .................................29

Figure 22. Graph. Tread wear of control fleet tires (CLI). ............................................................34

Figure 23. Graph. Tread wear of test fleet tires (CLI). ..................................................................34

Figure 24. Graph. Tread wear per mile, steer, drive, and trailer axles: control versus test tires 

(CLI)...............................................................................................................................35

Figure 25. Graph. Regression analysis of tread wear per mile (CLI): control versus test tires.....36

Figure 26. Diagram. Wheel module failure locations and number (CLI)......................................38

Figure 27. Grouped photo. Wabco wheel modules, side-by-side comparison of first-generation 

and second-generation modules. ....................................................................................39

Figure 28. Grouped photo. Second-generation wheel module (fill valve) failure.........................40

Figure 29. Photo. IVTM wheel module installation. .....................................................................41

Figure 30. Photo. PSI equipment on tire: oil leaks at the output port and air leaks at the valve 

stem. ...............................................................................................................................43
vi

Figure 32. Pie charts. Driver survey results: TPMS tractor display experience (CLI)..................45

Figure 33. Pie charts. Driver survey results: ATIS tanker display experience (CLI)....................46

Figure 34. Pie charts. Driver survey results: tire failure experiences (CLI). .................................47

Figure 35. Pie charts. Driver survey results: system failures experience (CLI). ...........................48

Figure 36. Graph. Monthly average fuel economy (GFS) for control and test fleets....................50

Figure 37. Graph. Analysis of tractor tire wear for control and test tractors (GFS)......................55

Figure 38. Photo. GFS reefer pups in yard. ...................................................................................56

Figure 39. Photo. Tire-SafeGuard reliability, displaying tractor tire data only (GFS)..................57

Figure 40. Photo. Tire-SafeGuard reliability; display missing left inside tire data (GFS). ...........58

Figure 41. Photo Tire-SafeGuard reliability; failed wire harness..................................................59

Figure 42. Graph. Hypothesis #1—comparison of tire wear per mile (CLI).................................64

Figure 43. Graph. Hypothesis #1—comparison of tire wear (GFS)..............................................65

Figure 44. Hypothesis #2—fuel economy analysis (CLI). ............................................................66

Figure 45. Graph. Hypothesis #2—fuel economy analysis (GFS). ...............................................66

Figure 46. Chart. Annual savings per TPMS/ATIS-equipped tractor-trailer.................................74

Figure 47. Graph. Accumulated monthly savings per TPMS/ATIS-equipped tractor-trailer........75

LIST OF TABLES

Table 1. Analysis of field test hypotheses. .................................................................................... xi

Table 2. CLI tractor and tanker specifications.................................................................................6

Table 3. CLI tractor and tanker tire specifications. .........................................................................7

Table 4. GFS tractor specifications..................................................................................................8

Table 5. GFS trailer specifications...................................................................................................8

Table 6. GFS tractor and trailer tire specifications. .........................................................................8

Table 7. Test objectives/methods...................................................................................................20

Table 8. Technologies under evaluation. .......................................................................................21

Table 9. Total field test mileage (CLI). .........................................................................................27

Table 10. Fleet fuel consumption (CLI). .......................................................................................28

Table 11. Tire maintenance actions (CLI). ....................................................................................30

Table 12. Maintenance actions per million miles, by axle (CLI). .................................................30

Table 13. Control fleet failure reports (CLI). ................................................................................31

Table 14. Test fleet failure reports (CLI).......................................................................................32

Table 15. Number of tire wear measurements (CLI).....................................................................33

Table 16. IVTM system failure reports (CLI). ..............................................................................37

Table 17. Wheel module replacement by tractor and location (CLI). ...........................................38

Table 18. PSI failure reports (CLI)................................................................................................41

Table 19. Total field test mileage (GFS). ......................................................................................49

Table 20. Fleet fuel consumption (GFS)........................................................................................49

Table 21. Tire maintenance actions (GFS). ...................................................................................51
vii

Table 22. Maintenance actions per million miles, by axle (GFS). ................................................51

Table 23. Test fleet tire failures (GFS). .........................................................................................52

Table 24. Control fleet tire failures (GFS).....................................................................................53

Table 25. Tire maintenance actions (GFS). ...................................................................................54

Table 26. Analysis of field test hypotheses. ..................................................................................63

Table 27. Hypothesis #3—road calls per million miles, by axle...................................................67

Table 28. Assumptions for ROI calculations.................................................................................69

Table 29. Cost of TPMS equipment. .............................................................................................70

Table 30. ROI calculation for fuel savings (fuel at $3.976 per gallon). ........................................71

Table 31. ROI calculation for fuel savings (fuel at $3.000 per gallon). ........................................71

Table 32. ROI calculation for fuel savings (fuel at $5.000 per gallon). ........................................72

Table 33. ROI calculations for tire replacements due to wear.......................................................72

Table 34. ROI calculations for road calls eliminated. ...................................................................73
viii

LIST OF ABBREVIATIONS, ACRONYMS, AND SYMBOLS

ABS antilock braking system

ATIS automatic tire inflation system

CLI CLI Transport 

CMV commercial motor vehicle

DDU driver display and tractor ECU

ECU electronic control unit

FMCSA Federal Motor Carrier Safety Administration

FOT field operational test

GFS Gordon Food Service

HCI HCI Corporation

IVTM Integrated Vehicle Tire Monitoring 

MHz megahertz

mi/gal miles per gallon

MTIS Meritor Tire Inflation System 

psi pounds per square inch

PSI Pressure Systems Inc.

reefer pup refrigerated pup trailer

RF radio frequency

ROI return on investment

TPMS tire pressure monitoring system
ix

EXECUTIVE SUMMARY

OBJECTIVES

The Federal Motor Carrier Safety Administration’s (FMCSA’s) Research and Technology 

program, defined by 49 U.S.C. 31108, includes activities that improve “...the safety and 

efficiency of commercial motor vehicles (CMVs) through technological innovation and

improvement.” Within that context, this project assesses the value of tire monitoring and 

automatic inflation systems. This study consisted of a yearlong field test on two tire pressure 

monitoring systems (TPMSs) and an automatic tire inflation system (ATIS). The study’s goal 

was to determine whether these systems could influence maintenance intervals/practices and 

improve performance and safety.

Prior to this field test, preliminary studies were conducted on the following: 

• The impacts of tire inflation practices.

• The equipment reliability of the TPMS and the ATIS on a controlled test track.

• The performance and reliability of TPMS equipment in revenue service.

FIELD TEST PLAN

The outline for the field test included the following five hypotheses:

• TPMS or ATIS use will increase the tire life.

• TPMS or ATIS use will reduce fuel consumption of tractors.

• TPMS or ATIS use will reduce road calls for damaged/flat tires of tractor-trailers.

• TPMS or ATIS will accurately measure the tire pressure of tractor-trailers.

• TPMS or ATIS use will not introduce unscheduled maintenance that adversely affects 

day-to-day fleet operations.

The authors developed a data collection plan to minimize the impact of the field test on the 

technicians’ daily maintenance responsibilities. The plan, outlined in Figure 1, identified the 

collection cycle for each data source.
x

Figure 1. Grid. Example of data collection schedule.

FIELD TEST FINDINGS

Overview

Two private fleets participated in the field test. The first fleet, CLI Transport (CLI), monitored 

24 married tractor-tanker pairs. The research team installed Wabco’s Integrated Vehicle Tire 

Monitoring (IVTM) System on 12 tractors and Meritor’s Tire Inflation System by Pressure 

Systems, Inc. (PSI) on 12 tankers. The second fleet, Gordon Food Service (GFS), monitored 24 

tractors, 30 standard 50-foot trailers, and 20 refrigerated pup trailers (reefer pups). The team 

installed HCI Corporation’s (HCI’s) Tire-SafeGuard on 12 tractors and 15 standard 50-foot 

trailers. GFS ensured the equipment would operate together during the entire field test. In 

addition, the team installed Meritor’s Tire Inflation System by PSI on 20 reefer pups.

CLI conducted the field test for 13 months. During the test period, the fleet traveled more than

3.8 million miles and consumed more than 600,000 gallons of diesel fuel. Each tractor-tanker 

married pair averaged 14,000 miles per month. The technicians conducted 324 inspections to 

measure tread depth and verify system operation. Between the test fleet and the control fleet, CLI

replaced 160 tires for wear and identified 38 tire incidents.

During the 18-month test with GFS, the tractors traveled approximately 3.4 million miles and 

consumed more than 500,000 gallons of diesel fuel. The tractors averaged 7,900 miles per 

month. The trailers traveled approximately 5.5 million miles and averaged 4,300 miles per 

month. The technicians replaced 278 tires for wear and identified 77 tire incidents.

Findings from the field test for each fleet were thoroughly analyzed for fuel consumption, tire 

maintenance actions, tire wear, system accuracy, system reliability, and user feedback. Each of 

the 5 hypotheses was analyzed independently for the 2 fleets under test (resulting in a total of 10 

hypotheses). 
xi

HYPOTHESIS ANALYSIS

The field test validated the assumptions outlined in 6 of the 10 hypotheses. No hypotheses were

proven invalid. Previous experience and subjective data gleaned during the field test suggest that 

an extended field test might have provided sufficient data to prove the inconclusive hypotheses 

valid. Table 1 presents the results. 

Table 1. Analysis of field test hypotheses. 

No. Hypothesis Analysis CLI GFS

1 The use of TPMS and ATIS 

will increase the life of 

TPMS/ATIS-equipped tires. 

Analyze tread wear per 

mile. Analyze based on tire 

location (steer, drive, 

trailer). 

Valid Inconclusive

2 The use of TPMS and ATIS 

will reduce the fuel 

consumption of equipped 

tractor-trailers.

Analyze average miles per 

gallon (mi/gal). 

Valid Valid

3 The use of TPMS and ATIS 

will reduce road calls for 

damaged/flat tires for 

equipped tractor-trailers.

Analyze overall road calls. 

Analyze tire failures. 

Inconclusive Valid

4 TPMS and ATIS will 

accurately display the tire 

pressure of equipped 

tractor-trailers at the driver 

interface.

Analyze accuracy of 

equipment.

Inconclusive Inconclusive

5 TPMS and ATIS will not 

introduce unscheduled 

maintenance that will affect 

the day-to-day fleet 

operations.

Analyze unscheduled 

maintenance actions.

Valid Valid

COST-BENEFIT ANALYSIS

The findings from this report may encourage fleets to use TPMS or ATIS equipment due to their 

potential to reduce CMV operating costs. Researchers conducted a cost-benefit analysis to 

estimate the fleets’ expected return on investment (ROI). The cost of fuel, the cost of tires, and 

the average mileage traveled influenced the ROI for the TPMS and ATIS equipment. For 

example, CLI operates a high-mileage fleet with wide-based single tires (a high-cost consumable 

supply). As shown in Figure 2, CLI would recover the costs of the TPMS and ATIS equipment 

in less than a year. Although fuel savings offer the highest incentive for TPMS and ATIS use, the 

high cost of wide-based tires further shortens CLI’s expected ROI. In comparison, GFS operates 

a lower-mileage fleet with standard tires. In addition, the size of GFS’s fleet reduces the need to 

dispatch the entire trailer fleet daily. The annual savings for GFS are less than half of the savings 

for CLI. At the mid-2011 cost of $3.98 per gallon of diesel fuel, CLI would save $3,160 per year 

for each tractor-trailer, compared to $1,327 per year at GFS. 
xii

Figure 2. Chart. Annual savings on road calls, tires, and fuel per TPMS/ATIS-equipped tractor-trailer.

While CLI would recover the cost of the TPMS and ATIS equipment in less than 6 months with 

the cost of fuel at $3.98 per gallon, GFS’s cost recovery period would be twice as long. GFS

would recover the TPMS and ATIS purchase cost within 14 months with fuel priced at $3.98 per 

gallon (as shown in Figure 3). 

Figure 3. Graph. Accumulated monthly savings per TPMS/ATIS-equipped tractor-trailer.

The findings from the field test and ROI calculations confirm that the use of TPMS/ATIS

equipment is very likely to reduce the operating costs of a fleet. The time required for the ROI 

decreases as the cost of diesel fuel increases. Fleets that use TPMS and/or ATIS equipment will
xiii

not only reduce their operating costs, but will improve their tire pressure maintenance programs. 

The use of such equipment encourages mechanics and drivers to monitor tire pressures and 

report abnormal tire conditions. Interviews with drivers confirmed their acceptance of the 

equipment and a desire to expand use to the entire fleet.
xiv

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1

1. INTRODUCTION AND BACKGROUND

This section is organized as follows:

• Background on the Commercial Vehicle Safety Technology Diagnostics and 

Performance Enhancement Program.

• Rationale and objectives for this research project.

• Overview of approach.

1.1 BACKGROUND

A study conducted by the Federal Motor Carrier Safety Administration (FMCSA) in 2003(1)

identified potential safety benefits for properly inflated tires, identified and validated the 

equipment available to the industry, and identified the durability of selected systems. The study 

found that a significant portion of fleet operators do not regularly perform tire pressure 

maintenance to the standards recommended by tire manufacturers, and suggested that improper 

inflation increases total tire-related costs, including lifecycle cost of individual tires, and 

unscheduled service calls on tractor-trailer combinations. As a result of these findings, FMCSA 

also performed a cost-benefit analysis of tire pressure maintenance systems (TPMSs). The 

analysis found that the cost of many of the TPMSs on the market at that time averaged between 

$1,000 and $1,500 per tractor-trailer. Conservative assumptions about the effectiveness of such 

systems in motivating changes in tire pressure maintenance practices assume that the payback 

period for many fleets is less than 2 years. Further, the 2003 report found that the market 

penetration of tire pressure maintenance equipment has remained low due to the lack of 

objective, accurate, real-world test data concerning the effectiveness of current and emerging 

technologies. Most of the cost and benefit data on such systems are not well documented, lack 

proper baseline testing, and/or are anecdotal in nature.

From the findings of the first study, FMCSA sponsored two additional studies to expand on the 

cost and benefit of TPMSs and automatic tire inflation system (ATIS) equipment—a track test 

and a field test. The second study, published in 2006,

(2)

evaluated dual-tire equalizers, TPMSs

and ATIS equipment for overall performance. The study tested vehicles under controlled 

conditions on a test track at the Transportation Research Center (TRC) in Columbus, Ohio. The 

study examined the accuracy, responsiveness, resolution, and reliability of the various tire 

pressure inflation and monitoring systems on a tractor-trailer and a motorcoach. The majority of 

the equipment performed as advertised by the manufacturer. No catastrophic equipment failures 

were introduced during the track testing. 

In the third study,

(3)

researchers conducted a field test of a TPMS on commercial heavy-duty 

buses operating under real-world conditions. The transit bus platform provided a severe urban 

stop/start duty cycle—an environment that accelerates tire wear, thus allowing the sensor 

systems to be heavily “exercised” over the study period. After testing identified a limited number 

of manufacturing flaws, the systems held up to the rigors of an urban city environment. Key 

challenges associated with the introduction of the sensor systems included implementation of 
2

proper training for maintenance staff and disciplined tracking of the installed sensors to ensure 

that equipment was not lost during routine and non-routine maintenance.

From the results of these three studies, FMCSA sponsored an additional field operational test

(FOT) to further explore the technologies using over-the-road commercial tractors/trailers. The 

goal of the FOT was twofold: to provide solid, credible evidence of the utility and costeffectiveness of the tested tire pressure monitoring system (TPMS) and ATIS, and to highlight 

the potential operational, safety, and productivity benefits associated with the two systems. The 

findings from this FOT are reported here.

1.2 RATIONALE AND RESEARCH OBJECTIVES

TPMS and ATIS technologies show significant promise for improving safety and reducing costs 

in the commercial vehicle industry. Improved tire pressure management directly relates to 

improved vehicle stability, reduced tire wear and damage, better braking, improved fuel 

efficiency, and fewer roadside breakdowns—and thus, enhanced safety and cost effectiveness. 

Improved tire pressure maintenance and general tire management can have a direct and 

substantial impact on carrier productivity as it relates to downtime and road calls.

FMCSA contracted the authors to perform an FOT to determine whether the systems could

influence tire maintenance practices and reduce the need for frequent tire maintenance. The test 

was also conducted to help determine system costs and benefits, as well as system reliability and 

accuracy.

Researchers originally planned to collect test data for 1 year. However, due to minor issues with 

the equipment and the installation process, data collection ended up lasting 13 months for CLI 

Transport (CLI) and 18 months for Gordon Food Service (GFS). Researchers designed the field 

test to have minimal impact on routine operations and maintenance performed by the selected 

fleets; researchers also designed the field test so that it would not alter established fleet practices 

related to reporting road calls and tire failures. Fleet technicians continued regular maintenance 

practices as outlined in the company’s standard operating procedures. Additionally, fleet drivers 

continued to perform U.S. Department of Transportation (USDOT) pre-trip condition 

assessments and post-trip inspections without demonstrating further vigilance on non-equipped 

vehicles. 
3

1.3 OVERVIEW OF APPROACH

The study team’s approach to implementing a comprehensive FOT included the following tasks:

• Conduct a market research study to supplement the study completed in 2003 through the 

following steps:

– Identify all current and future (within 2 years) TPMS and ATIS technologies offered 

to the industry. Outline the changes to the TPMS/ATIS market from the previous 

market study.

– Conduct a detailed analysis of each system to determine application, installation 

requirements, maintenance requirements, unit and installation costs, system 

performance factors, system operational characteristics, and other general knowledge 

on system operation and industry penetration.

– Outline findings from previous track and field tests to highlight potential hurdles and 

lessons learned.

– Evaluate identified systems for use in the FOT using an evaluation matrix to rank 

each system. 

• Select candidate TPMS/ATIS technologies based on the evaluation matrix, commercial 

availability, willingness to participate in a sponsored field test, and FMCSA approval.

• Identify a commercial fleet operator (or “host” fleet) with characteristics that would allow 

for effective and fair evaluation of systems and technologies, including: 

– An operating environment and duty cycle that are representative of the industry in 

terms of tire wear and annual mileage.

– Homogeneity of the fleet in terms of vehicle type, make, and model to eliminate the 

potential for the vehicles to influence the evaluation.

• Perform a field test, including test plan development, system installation, test monitoring, 

and data collection.

• Conduct a data analysis and present the findings in a final report.
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5

2. DESCRIPTION OF THE FIELD TEST

This section provides additional information on the following:

• Host fleets.

• Technologies under evaluation.

• Fleet test plan.

2.1 HOST FLEETS

Based on experience with previous research, several criteria were established for selecting the 

host fleet(s) for the FOT. The selection criteria included:

• Private Fleet: In previous field tests, the use of a privately-owned fleet ensured a close, 

direct relationship with fleet management. This relationship is essential to ensure the 

timely exchange of collected data and support for the installation of equipment, etc.

• Matched Tractor-trailer Pairs: In previous FOTs, the use of non-matched tractor-trailer 

sets proved to be cumbersome. Fleet operators were not able to consistently return the 

fleet to a facility for data collection. In particular, fleets that operated a “drop-trailer” 

could not guarantee when the trailer would return to the maintenance facility and could 

not track the location of the trailer throughout the field test.

• Daily Return to Central Facility: Ideally, the equipment would return to the same 

maintenance facility daily. This would ensure that the FOT-trained maintenance 

personnel would track all maintenance and equipment failures. The fleet could also 

operate from various depots, but all maintenance would be performed at a single facility

to ensure no data loss. 

• Interest in Innovative Technologies: Although not essential, the fleet’s interest in tire 

pressure maintenance technologies would enhance participation. With management buyin, the field test would run more smoothly, as management would encourage staff to 

collect accurate data, communicate failures to the project team, and install equipment in a 

timely manner. 

• Single Company/Single Site: To ensure reliable data, the test fleet should operate from a 

single maintenance facility. Training a single facility to collect data would ensure a 

consistent collection method and accurate analysis. Although ideal, it would not be 

essential to use a single company. If multiple companies were used, the data from each 

fleet would be analyzed separately to ensure that the analyses accurately reflected the 

fleet operation.

Using these criteria, two commercial motor vehicle (CMV) fleets were identified—CLI and 

GFS. Each fleet brings unique characteristics to enhance industry acceptance of the test results. 

CLI offers tanker trucks that operate on wide-based single tires. As the industry gradually adopts 

the use of these tires, results from this FOT will provide information for fleet operators 
6 

considering the adoption of these technologies and will confirm the basic reliability, durability, 

and inflation monitoring features of the tested TPMS and ATIS technologies. GFS offers 

accelerated-wear tires with inner-city distribution networks and highway operations. 

Additionally, the use of 50-foot refrigerated trailers in the field test offers information on the 

adaptability of TPMS technologies during the connection and disconnection of trailers.

2.1.1 CLI Fleet

CLI is a dedicated transportation company for a large, privately-owned gas and convenience 

store chain based in Altoona, PA. CLI operates 90 state-of-the-art petroleum tanker trucks out of 

7 major terminals. 

The field test was conducted at CLI’s Altoona terminal. The facility has 26 domiciled, married 

pairs that return to the facility daily. The tanker pairs operate an average of 450 miles per day. 

The vehicles are outfitted with wide-base single tires on tractors’ drive axles and on the tankers.

The fleet provided a unique operating environment as tires were exposed to maximum and 

minimum load thresholds during a single shift. 

CLI manages the drivers. The drivers operate in two shifts with three drivers assigned to each 

tractor. A separate maintenance contractor provides full-time maintenance technicians who are 

responsible for periodic and unscheduled maintenance. In addition, they conduct service calls 

when a vehicle breaks down while in service. 

Table 2. CLI tractor and tanker specifications. 

Specification Details

Tractor Model Freightliner Columbia

Tractor Model Year Test: 2007 (9), 2008 (1), 2009 (1)

Control: 2006 (5), 2007 (3), 2008 (1), 2009 

(5)

Tractor Engine Mercedes-Benz 4000

Tractor Transmission Eaton FRO-15210C

Tractor Wheelbase 170 inches

Tractor GVWR 80,000 pounds

Trailer Model Heil

Trailer Model Year Test: 2004 (1), 2006 (1), 2007 (3), 2008 (5)

Control: 2004 (4), 2005 (1), 2006 (3), 2008 

(1)

Trailer Type 406 Tanker

Trailer Length 44 feet 5 inches

Trailer Wheelbase 49 inches

Trailer GVWR 80,000 pounds
7 

Table 3. CLI tractor and tanker tire specifications. 

Specification Steer Tire Details Drive Tire Details Tanker Tire Details

Tire Manufacturer Michelin Michelin Michelin

Tire Make/Type XZE2, XZA (1, 2, & 3) XDA-HT, MD400 XTE

Tire Size 275/80R22.5 445/50R225 445/50R225

Tire Pressure (in 

pounds per square 

inch [psi])

110 110 110

2.1.2 GFS Fleet 

GFS is the largest family-owned food service distributor in the U.S. It provides a wide variety of 

food, beverage, and paper products to restaurants, hotels, and other institutions. Headquartered in 

Grand Rapids, MI, GFS operates 9 distribution centers and 132 stores in 14 States, including 

most of the Midwest and Florida, as shown in Figure 4. 

Figure 4. Map. GFS distribution network. 

The maintenance terminals operate 28-foot reefer pups and 50-foot refrigerated trailers. The 

trucks under test exclusively pull the 50-foot trailers. The reefer pups operate over highway and 

local roads, delivering to areas with limited maneuverability (e.g., loading docks, alleys). The 

tires experience highway wear, local wear, and scuffing due to the operation of the trailers. The 

standard trailers primarily operate on highway routes. 
8 

The Grand Rapids maintenance facility conducted the field test. It employs a full maintenance 

crew to perform periodic and unscheduled maintenance. The facility maintains 233 tractors and 

324 trailers. The facility employs a tire service company for changing and repairing tires. The 

tire service company is also responsible for service calls. 

Table 4. GFS tractor specifications. 

Specification Tractor 1 Details Tractor 2 Details

Model Volvo VNM42T200 IHC 8600A 6X4

Model Year Test—2005 (1), 2008 (9)

Control—2008 (12)

Test—2007 (2)

Engine Volvo D-11 Cummins ISM

Transmission Eaton FR13210B Meritor M14G104A

Table 5. GFS trailer specifications. 

Specification Standard Trailer Details Pup Trailer Details

Model Great Dane Great Dane

Model Year Test—2006 (15)

Control—2006 (5), 2007 (6), 2008 (4)

Test—2006 (14), 2007 (6)

Control—1998 (13), 2006 (7)

Trailer Type Straight Straight

Length 50 feet 28 feet

Wheelbase N/A 265 inches

GVWR 39,000 pounds 39,000 pounds

Table 6. GFS tractor and trailer tire specifications. 

Specification Steer Tire Details Drive Tire Details Trailer Tire Details

Tire Manufacturer Michelin Michelin Michelin

Tire Make/Type XZE, XZE2 XDA, XZE, XDN2 XZE, XZE2

Tire Size 295/75R22.5 295/75R22.5 295/75R22.5

Tire Pressure (psi) 95 95 95

2.2 TECHNOLOGIES UNDER EVALUATION

The team used two main criteria to select the TPMS and ATIS for this study: documented 

successful performance under controlled testing and commercial availability. The systems 

selected were: 

• Wabco’s IVTM System. 

• HCI’s Tire-SafeGuard. 

• Meritor Tire Inflation System (MTIS) by Pressure Systems Inc. (PSI). 
9

2.2.1 Wabco Integrated Vehicle Monitoring System 

2.2.1.1 General Description

Wabco (in conjunction with Michelin) developed and launched the IVTM system in 2003. The 

IVTM system consists of three main components, shown in Figure 5:

Figure 5. Grouped photo. Wabco tire pressure sensor wheel module (left), display unit (center), and 

electronic control unit (right).

In the IVTM system, each tire and wheel assembly is equipped with a sensor unit, which

contains a pressure transducer and a transmitter. A built-in lithium battery with a 5-year service 

life supplies power for the sensor unit. The sensor unit is secured to the wheel rim at a location 

adjacent to the valve stem using the two closest lug nuts. A pneumatic hose runs between the 

sensor and valve stem (as shown in Figure 6).

Figure 6. Photo. Wabco IVTM sensor unit mounting system.

The valve-stem-mounted sensors continually check tire pressure and transmit a pressure reading 

to an electronic control unit (ECU) via a radio frequency (RF) signal every 15 minutes. The ECU 

is generally mounted on the tractor (or vehicle) chassis halfway between the front and rear axles. 

It contains a built-in antenna to receive the pressure data from the tire pressure sensor units. If 

the sensor detects a loss of pressure (below a predetermined level), the system increases the 
10

transmission frequency to once every 30 seconds. The operating frequency is 433 megahertz 

(MHz). The ECU is hardwired into the vehicle’s 24-volt power supply circuit.

The centralized location of the ECU between the monitored tires (roughly equidistant from the 

six wheel locations on the tractor) eliminates the need for additional antennas housed within the 

sensors. If the vehicle is equipped with a trailer, a second (separate) ECU, located at a 

centralized point between the tires on the trailer chassis, collects inflation pressure data from the 

trailer tires. This data is then re-transmitted to the “main” ECU on the tractor.

The main ECU is hardwired to a display unit that is designed to mount on the dashboard. The 

display unit warns the driver visually and acoustically of low tire pressures. A yellow lamp 

indicates a slow rate of pressure loss or slight decrease in pressure, and a red lamp indicates 

extremely low pressure. The yellow and red lights are located at the lower edge of the display. 

Using an on-screen menu, the driver can select the position of any instrumented tire and can 

query its inflation pressure. If all tires are within an appropriate inflation pressure range, the 

display is blank. If a tire has low pressure, the display screen shows the location of the tire and 

its pressure. For example, Figure 7 shows a low-pressure reading of 5.9 bar (85 psi) on the right

rear tag-axle tire.

Figure 7. Photo. Wabco IVTM system indicating tire location and low pressure reading.

2.2.1.2 Installation

The Wabco IVTM system was installed on 10 tractors at CLI. Installation was led by a Wabco 

service engineer.

The tractors used in this field test had six tires (standard-width tires on the steer axle and widebase single tires on each drive axle); thus, six sensor units had to be installed.

To install the sensor unit, the pneumatic hose was first connected to the sensor module and then 

connected to the tire’s valve stem. With the hose connected to the valve stem, the sensor unit was

slipped over the wheel lugs and secured in place with the cap nuts. The quickest way to mount 

the wheel module to the steer tires was to attach the sensor unit to the valve stem with the short 

hose before securing it to the wheel. Figure 8 illustrates the wheel-module installation process on 
11

a steer tire. As shown in the photos, the steer tires required mounting a counterweight onto the 

tire, opposite the sensor. The weight countered the effect the sensor had on the rotation of the 

wheel. Because the sensors were installed near the wide-base single tires’ center of gravity, the 

drive and trailer tires did not require a counterweight. 

Figure 8. Grouped photo. Module installation of steer wheel (left) and drive wheel (right) with steer tire 

counterweight location.

The ECU must be mounted in a centralized location relative to the tire sensors. The ECU was 

bracket-mounted to the rear cross-member of the cab, equidistant from each of the six sensor 

locations. The display unit, hardwired to the ECU, was mounted within reach of the driver on the 

cab’s dashboard, as shown in Figure 9. The display was electrically protected by mounting an 

inline 5-ampere fuse in the glove box.

Figure 9. Grouped photo. ECU (left) and display unit (right) installations.

After installation of the IVTM hardware components, the system was programmed in accordance 

with the manufacturer’s instructions. The IVTM ECU was equipped with a diagnostic data port 

that could be accessed with a laptop so that technicians could communicate with the ECU via 

Wabco’s IVTM diagnostic software. The diagnostic software shows tire pressure readings and 

system messages. During installation, the software was used to monitor the tire pressures at each 

wheel location.
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2.2.2 HCI’s Tire-SafeGuard 

2.2.2.1 General Description

HCI manufactures the Tire-SafeGuard TPMS. For the FOT, the team installed the internal rimmounted model, which consisted of the following components:

• Wheel Module—Monitors internal tire pressure and temperature.

• Driver Display and Tractor ECU (DDU)—Establishes communication with the 

connected trailer’s ECU. Processes RF signals transmitted from the tractor and trailer 

wheel modules. Displays the condition of tires at all wheel locations.

• Trailer ECU—Performs wireless “handshaking” with the DDU to establish 

communication. Relays RF signals transmitted from the trailer’s wheel modules to the 

DDU via the tractor antenna.

• Tractor Antenna—Relays the RF signals transmitted from the tractor’s wheel modules 

and the trailer ECU to the DDU.

Figure 10 shows a wheel module secured to a wheel by a steel band (top left), the dash-mounted 

DDU (top right), the trailer’s chassis-mounted ECU (bottom left), and the tractor’s chassismounted antenna (bottom right).

Figure 10. Grouped photo. HCI Tire-SafeGuard components.

The wheel module includes an integrated pressure-temperature transducer, an RF transmitter, 

and an internal battery to supply power to the unit for more than 5 years. The wheel module (or 

sensor) is strapped to the hub of the wheel inside the tire. It continuously transmits the tire’s

pressure, temperature, wheel position, and tire status to the trailer ECU using RF signals. The 
13

wheel modules transmit the tire condition based on several factors, including vehicle movement. 

If the vehicle is stationary, the module will revert to transmitting the tire condition every 2 hours

to maximize battery life. If a tire pressure change has been detected, an immediate RF signal is 

transmitted to the ECU.

The DDU processes the RF signals received via coaxial cable from the tractor-mounted antenna, 

which is mounted at a location equidistant between the front and rear axles. The DDU alerts the 

driver of low-pressure situations by providing the location, temperature, and pressure readings 

via display icons and an audible signal. Figure 11 shows the wheel-mounted sensor (right) and 

the DDU (left). The default display screen shows the tire pressures of all “located” tires. (A tire 

is “located” when the DDU has successfully received communication from the wheel sensor at a 

specific tire location.) The user can cycle through the display modes to view the tire pressure and 

temperature at a single tire location. The display automatically returns to the default mode after 8 

seconds. The system uses two 12-volt power sources for operation. A keyed source provides 

power to the display. A second, non-keyed source provides power to the ECU. As a result, the 

cab display is only active while the vehicle is keyed, but the ECU operates continuously. 

Figure 11. Grouped photo. HCI Tire-SafeGuard TPMS: DDU displaying tire position (left) and the wheelmounted sensor (right).

The trailer ECU includes a receiver and a transmitter. It receives the RF signals from the trailer 

wheel modules and wirelessly transmits the signals to the DDU via the tractor-mounted antenna. 

Unlike previous versions of the equipment, the version used in the FOT automatically detected 

equipped trailers. It did not require the tractor to be married to a specific trailer. A handshake 

signal from the DDU (when the tractor is keyed-up and trailer power is restored) initiates the 

linkage between the DDU and the trailer ECU. The DDU links to the appropriate trailer through 

one of two processes—a keying sequence at startup or an elimination process after key-up. In the 

first case, the driver initiates a key-up/key-down sequence, which resets the internal clock of the 

DDU and the trailer ECU. After the third power-up cycle, the DDU links to the trailer ECU with 

an identical clock cycle. In the second case, if the operator does not initiate a keying cycle, the 

DDU monitors the surrounding RF signals to identify ECUs with similar startup clock cycles.

The DDU links to the trailer ECU with a similar clock cycle, since both were reset during the 

key-up. The linkage period for the second scenario could take up to 5 minutes. In both cases, 

after establishment of the initial link, the DDU stores the trailer ECU information and eliminates 

the need for future initiation cycles.
14

2.2.2.2 Installation

A team of engineers and GFS technicians installed the Tire-SafeGuard TPMS on 13 tractors and 

15 trailers. The team followed the instruction manual provided by HCI. For ease of installation, 

HCI provided installation kits for tractors and trailers. The kits included wheel modules with preassigned locations and a programmed DDU or ECU to recognize the supplied wheel modules.

Engineers installed a wheel module on the tractor and trailer at each assigned location. With the 

tire removed from the wheel, engineers strapped the sensor to the wheel at the lowest point of the 

drop-center well using metal strapping. Once the sensor was secured, the tire was remounted to 

the wheel and inflated. The right photo in Figure 11 shows a tire pressure sensor strapped to a 

wheel. The team mounted the wheel sensor near the wheel’s valve stem port to prevent damage 

to the sensor unit when changing the tire. If the paddle arm of the tire-changing machine were to 

contact the wheel module, it could damage it. By placing the module in a specific location (at the 

valve stem in this case), the tire changers had a reference point for the module when removing 

the tire casing from the rim and avoided contact with the paddle arm.

Engineers installed two receivers for the system (shown in Figure 12). An antenna was mounted 

in front of the rear axles on the truck frame using a magnetic base, and a coaxial cable was used 

to connect the antenna to the dash-mounted DDU. The trailer ECU was mounted to the trailer’s 

cross beam (between the trailer tires). Using an antilock braking system (ABS) connector,

engineers connected the ECU to the trailer’s 12-volt power source. 

Figure 12. Grouped photo. HCI Tire-SafeGuard antennas.

The DDU (as shown in Figure 13) was installed on the dashboard of the tractor. A coaxial cable 

connected the DDU and the antenna by routing the cable through an existing access port in the 

dashboard. HCI programmed the DDU to assign each wheel module to a specific location and set 

the warning threshold for the tire pressure to 103 psi (approximately 10 percent below the 115 

psi set tire pressure). Upon powering the DDU, the team tested the system to ensure that each of 

the wheel modules was communicating with the DDU and properly reading the tire pressures. 

The DDU was also used to verify operation of the trailer unit. When the DDU was within range 

of the trailer, it would detect and display the trailer’s wheel module data. With the DDU 

preprogrammed for the tire locations, the team did not have to program the location of each 

wheel module. The DDU has the capability to recognize the location of wheel modules after a 
15

tire rotation or tire change-out. The wheel modules do not have to remain in the preprogrammed 

location.

Figure 13. Grouped photo. DDU installation: coaxial cables connecting DDU (left) and the DDU displaying 

tire location and pressure data (right).

2.2.3 MTIS System by Pressure Systems, Inc. 

2.2.3.1 General Description

The MTIS distributed by Pressure Systems, Inc. (PSI) consists of the following six components:

• Pressure Protection Valve—Maintains trailer air system at 80 psi in the event of a tire 

or inflation system failure (Figure 15).

• Control Unit—Controls the pressure distributed to each axle end and illuminates 

indicator light.

• Press Plug—Used with hollow axles to seal pressurized axle interior from wheel end

(shown in Figure 16).

• Stator and Through-tee—Rotary union assembly delivers air from the pressurized axle 

to the wheel end. 

• Indicator Light—Illuminates when airflow within the system has been detected.
16

Figure 14. Graphic. Components of the MTIS.

The inflation system (shown in Figure 14) uses compressed air from the trailer’s air system to 

inflate any tire that falls below the predefined target pressure. Air for the inflation system is 

routed from the existing trailer supply tank to the control box. A pressure protection valve (see 

Figure 15) regulates the air supplied to the inflation system. If the supply pressure falls below 80 

psi, the pressure protection valve inhibits the flow of air to the inflation system.

Figure 15. Photo. Pressure protection valve (CLI).

The control unit includes a system filter, a shut-off valve, and a control box. The filter prevents 

contaminants from entering the system. The shut-off valve isolates the inflation system from the 

air system. The control box regulates the air pressure to the wheel ends and illuminates the 

indicator light when airflow is detected. Inside the control box, a regulator valve is factory set 

according to a fleet’s recommended tire pressure, which can be adjusted in the field. In addition, 

the control box has a flow-detection switch. If airflow is moving through the system, the switch 

illuminates the indicator light to alert the driver of a tire issue. 

The hollow, pressurized trailer axle carries air from the control box to a rotary union at each 

wheel end (Figure 16). A hose connected to the rotary union routes the air to the wheel. A one-
17

way check valve located in the hose protects each tire against air pressure loss. If a puncture

results in the loss of air pressure, the check valve prevents loss of pressure in the other tires.

Figure 16. Grouped photo. MTIS, rotary units on wheel ends.

2.2.3.2 Installation

The installation procedure for the inflation system was similar at both test sites. The only 

differences were in the location of the control box and the use of two hoses on the GFS fleet 

(because CLI uses wide-base tires on the tanker, only one hose is needed). PSI provided a field 

technician to demonstrate and assist in the installation of the inflation systems. The team 

installed 30 inflation systems—10 systems on CLI’s tankers and 20 systems on GFS’s reefer 

pups.

The installation began with preparation of the axles and wheel ends. A hole was drilled and 

tapped at the center point of each axle, and the axle air fitting was installed. The hubcaps and 

Welsh plugs were removed to provide access to the interior of the axle. Using compressed air, a 

cleaning wand removed debris and metal shavings from the axle. After clearing the debris from 

the axle, a press plug was inserted into each wheel end to seal the axle. The stator was threaded 

into the press plug (as shown in Figure 17, left) and a hubcap designed for use with the MTIS

was bolted onto the wheel end.

The through-tee assembly was attached to each trailer hubcap. For the CLI fleet, the through-tee 

included a single output port (as shown in Figure 17, right). For the GFS fleet, the through-tee 

included two output ports. A hose was connected between the output port and the wheel valve 

stem to deliver the pressurized air from the axle to each wheel.
18

Figure 17. Grouped photo. Wheel end assembly with press plug and stator (left) and through-tee (right).

The installation of the system air components included installing the pressure protection valve, 

mounting the control box, and routing the hose. The pressure protection valve was installed on 

the spare port of the trailer’s air tank. A hose was routed from the valve to the input of the 

control box. The GFS control box was mounted on the trailer’s crossbeam, forward of the rear 

axles (as shown in Figure 18, right). The CLI tanker did not have crossbeams under the tanker. 

For this reason, the CLI control box was mounted at the rear of the tanker in a recessed area 

between the taillights (as shown in Figure 18, left). From the control box output, a tee split the 

hosing to deliver air to each of the axle fittings.

Figure 18. Grouped photo. CLI and GFS control box installation between taillights (right) and on tanker’s 

crossbeam (left).

The final component of the PSI inflation system is the indicator light. The indicator light was 

installed in a location that allowed the driver to see the light through the driver’s side mirror. On 

the CLI fleet, the light was mounted on the fender of the tanker (as shown in Figure 19, left). On 

the GFS fleet, a mounting bracket was fabricated to allow the light to be mounted on the 

underside of the reefer pup, forward of the axles (as shown in Figure 19, right). The operation of 

the indicator light required a constant supply of 12-volt power. The CLI fleet used the tanker’s 

seven-way box, and the GFS fleet accessed the ABS wiring via a pigtail connector. Electrical 

wiring was routed from the indicator light through the identified power source to the electrical 

contacts of the flow-sensing switch in the control box.
19

Figure 19. Grouped photo. CLI and GFS indicator light installation on the fender (left) and underside of the 

reefer pup (right).

2.3 TEST PLAN

The study team developed a test plan to address the requirements of the field test. The test plan 

was divided into the following sections:

• Objectives.

• Team members’ roles and responsibilities.

• Equipment.

• Schedule.

2.3.1 Objectives

FMCSA identified a list of important factors to consider in the development of the test plan. 

Chief among the factors was the capability of the field test to generate the data, observations, and 

insights needed to validate or refute key questions and hypotheses regarding the efficacy and 

performance of TPMS and ATIS devices and systems. FMCSA’s factors included:

• Scheduled Maintenance—Frequency of scheduled TPMS and ATIS maintenance.

• Reliability Measures—Frequency of unscheduled TPMS and ATIS maintenance; 

accuracy of TPMS and ATIS units.

• Maintenance Considerations—Interference with routine truck maintenance (e.g., tire 

changes, tire rotations, brake inspections and repair, RF data links); influence on tire 

inventory management (increased predictability of tire life).

• Lifecycle Costs—Cost savings for implementing a TPMS and an ATIS (e.g., tire 

inspection costs, tire life, retread life, fuel, road calls).

• Driver Impact—Improved driver productivity; improved driver satisfaction.

• TPMS and ATIS Perception—Viewed favorably by drivers and technicians; improved 

image with shippers/customers.
20 

• Safety Benefits—Impact on braking performance, vehicle stability, and vehicle handling; 

tire maintenance (e.g., decreased blowouts, less roadside tire debris); and CMV crashes, 

injuries, and fatalities. 

From these factors, the study team identified five key test objectives, as shown in Table 7. The 

study team broke down each hypothesis to identify the required sources to conduct a thorough 

analysis to prove/disprove the hypothesis. Because of the relative infrequency of catastrophic tire 

failures, a hypothesis of the impact these systems would have on braking performance, vehicle 

stability, and vehicle handling and the resultant crashes, injuries, and fatalities was not included. 

Section 3 describes the data collection process.

Table 7. Test objectives/methods. 

Hypothesis Description Analysis Source(s)

The use of TPMS and ATIS 

will increase the life of 

TPMS/ATIS-equipped tires. 

Prove the tires on equipped vehicles will 

experience less tread wear per mile as 

compared to non-equipped vehicles.

Analyze tread wear 

per mile. Analyze 

based on tire location 

(steer, drive, trailer). 

Vehicle mileage, 

periodic 

inspections, and 

maintenance 

records.

The use of TPMS and ATIS 

will reduce the fuel 

consumption of equipped 

tractors.

Prove the equipped vehicles will 

experience improved fuel mileage as 

compared to non-equipped vehicles.

Analyze average 

mi/gal. 

Vehicle mileage, 

fuel records. 

The use of TPMS and ATIS 

will reduce road calls for 

damaged/flat tires for equipped 

tractor-trailers.

Prove road calls and tire failures for 

equipped vehicles will be reduced as 

compared to the control vehicles.

Analyze overall road 

calls. Analyze tire 

failures. 

Failure reports, 

maintenance 

records. 

TPMS and ATIS will 

accurately display the tire 

pressure of equipped tractortrailers at the driver interface.

Prove the monitoring systems provide 

accurate tire pressure values at the 

display. Prove the inflation system 

maintains the tire pressure at the proper 

setting.

Analyze accuracy of 

equipment. 

Maintenance 

records, 

questionnaire. 

TPMS and ATIS will not 

introduce unscheduled 

maintenance that will affect the 

day-to-day fleet operations.

Prove the equipped vehicles will not 

introduce additional unscheduled 

maintenance as compared to the control 

vehicles. Prove the equipped vehicles 

experience few unscheduled maintenance 

calls due to tire failures.

Analyze unscheduled 

maintenance actions. 

Failure reports, 

questionnaire. 

2.3.2 Roles and Responsibilities

The success of the field test depended on a clear understanding of the roles and responsibilities

for each of the participating parties—the study team, the host fleets, and the vendors. 

The test coordinators, in conjunction with FMCSA, identified the host fleets and secured a fleet 

agreement. They developed the field test plan, procured the TPMS equipment and spares, and 

oversaw the system installations. The test coordinators also developed and maintained a test 

database for storing all data collected during the field test. In addition, the test coordinators 

conducted educational sessions for the maintenance technicians and the drivers participating in 

the field test. The presentations used in these educational sessions described the purpose of the 

field test, the systems being tested, and the responsibilities of the personnel. 
21 

The test coordinators worked with the host fleets to develop a memorandum of understanding. 

The document outlined the responsibilities of the host fleet during the field test. The 

responsibilities included providing use of the tractor-trailers for 1 year; providing maintenance 

support for system installation, data collection, and system monitoring; and providing 

maintenance data on vehicle mileage, tire repairs, equipment failures, and fuel logs. 

The vendors supported the field test by providing system documentation, overseeing initial 

system installations, and demonstrating proper installation, maintenance, and operation. Each 

vendor provided ongoing engineering support and component spares as necessary. 

2.3.3 Equipment

Table 8 shows the distribution of the technologies between the host fleets. The MTIS was 

installed on 10 tanker trailers and 20 reefer pups. The IVTM system was installed on 10 tractors. 

The Tire-SafeGuard system was installed on 12 tractors and 15 standard trailers.

Table 8. Technologies under evaluation. 

Vehicle Type Total 

Fleet 

Size

Control 

Fleet

IVTM TireSafeGuardMTIS

CLI Tractor 25 14 11 – –

CLI Tanker 19 9 – – 10

GFS Tractor 240 12 – 12 –

GFS Trailer 400 15 – 15 –

GFS Reefer Pup 263 20 – – 20

Each host fleet identified tractors and trailers that would be used for the control fleet. For CLI, 

the entire fleet was tracked during the field test. GFS personnel identified the control fleet based 

on tractors and trailers that would experience driving conditions and mileage similar to the test 

fleet. 

2.3.4 Schedule

The field tests operated for a period of approximately 1 year from the installation of the 

equipment on the fleet. The length of the field test permitted operation of the equipment in 

various weather conditions and operating environments. 

The study team visited the CLI facility on March 3, 2008 to assist in equipment installation, 

provide presentations to drivers and technicians on the test expectations, and meet with vendor 

representatives. The maintenance technicians continued to install the equipment through April 

2008. The technicians also collected baseline readings on the control fleets’ mileage and tire 

depth in April 2008. The field test began in May 2008 and continued for a period of 13 months. 

An extra month was added to the field test to account for the data variability experienced during 

the initial data collection period (May 2008). 

The study team visited GFS on November 5, 2008 to present an overview of the field test to the 

maintenance technicians. This included data collection requirements, a system overview, and 

GFS’s roles and responsibilities. PSI and the study team installed the inflation system on 
22

December 2 and 3, 2008. The study team visited GFS on February 17, 2009 to demonstrate the 

installation of the Tire-SafeGuard equipment. The maintenance technicians installed most of the 

systems by June 2009. The field test began in May 2009 and continued through November 2010.
23

3. DATA COLLECTION

The study team identified the sources of data necessary for a successful field test. Based on the 

five hypotheses outlined in the previous section, the study team determined that the following 

five parameters were required to address the objective of the field test:

• Tire wear.

• System reliability.

• Tire failures.

• Fuel consumption.

• System functionality/usability.

The information was obtained from periodic maintenance inspections, tractor and trailer 

maintenance records, fuel logs, staff interviews, and wrap-up surveys. 

3.1 PERIODIC MAINTENANCE INSPECTIONS

At the beginning of the field test, every control and test unit was baselined by recording unit

mileage, tread depth, and tire make and model. In addition, the technicians recorded the serial 

numbers of the TPMS sensors installed on the test vehicles.

During the field test, the technicians regularly collected unit data according to an inspection 

schedule established at the beginning of the field test. CLI conducted test inspections during the 

scheduled periodic maintenance. CLI’s periodic maintenance occurs every 9,000 miles 

(approximately every 3 weeks). GFS conducted test inspections either when the units were on

site for maintenance/storage or every 6 weeks, whichever occurred first. GFS’s periodic 

maintenance schedule could not be used to track the field test accurately, as periodic 

maintenance did not occur regularly at the test facility and could have extended beyond a 2-

month cycle.

The technicians recorded vital statistics on the tractors, tankers, and trailers used in the FOT. 

They used a single form to record the periodic inspection and failure data. A form unique to their 

operation was provided to each fleet. The forms recorded:

• Date.

• Tractor and tanker/trailer number.

• Tractor and tanker/trailer mileage.

• Vehicle type (test or control).

• System-displayed tire pressures.

• Gauged tire pressures.
24

• Tire condition (damaged, scuffed, etc.).

• Mounting/physical condition of sensors.

• Tire changes.

The data collection forms also recorded infrequent tire maintenance activities, including tire 

replacement, TPMS or ATIS system failure, and tire failure. For system and component failures, 

the technicians reported the unit mileage, component failure, failure location, and detailed failure 

data (e.g., component failed, action taken to resolve discrepancy). For tire replacement, the 

technicians reported the unit mileage, tread depth, and location of the tire removed, as well as the 

tread depth, tire model, and location of the tire installed. For the GFS operation, the data 

collection form also noted whether the tire installed was a retread, and if possible, the number of 

times the tire casing had been retreaded.

3.2 MAINTENANCE RECORDS

The maintenance records provided oversight on the data collected by the technicians during the 

field test and ensured that all tire actions were recorded. The study team inspected the fleet’s 

vehicle maintenance system at the completion of the field test to collect data on tire maintenance 

incurred by the fleet throughout the test period. The team identified tire replacements, tire 

changes, tire failures, and road calls that occurred. 

3.3 FUEL RECORDS

The host fleets provided monthly fuel logs for the test and control tractors. The logs included 

vehicle usage and fuel consumption during a monthly period. At CLI, the drivers recorded the 

vehicle mileage and fuel consumed to the tractor’s log. The terminal manager assembled the data 

and submitted the findings to the fleet manager. CLI provided the study team with a monthly 

summary of mileage traveled and fuel consumed. At GFS, the study team downloaded fuel logs 

from the maintenance database.

3.4 MAINTENANCE STAFF AND DRIVER INTERVIEWS

Maintenance technicians and supervisors were interviewed informally throughout the test period. 

The intent of these interviews was to gather information about the technicians’ and supervisors’

experiences with maintaining the systems, the ease of the data presentation, and the usefulness of 

the equipment.

3.5 MAINTENANCE STAFF AND DRIVER QUESTIONNAIRES

Questionnaires were distributed to the technicians and the drivers at the completion of the field 

test. The questionnaires collected subjective feedback on the use of TPMS and ATIS equipment. 

The questions addressed a number of issues, including:
25

• Driver Time Savings—Did the addition of the equipment reduce the need for tire 

inspections during a pre-trip inspection?

• Driver Satisfaction—Did the addition of the equipment provide the driver with valuable 

information (during driving) that was not previously available? Was the driver 

comfortable with the operation and intent of the equipped systems?

• Fleet Image—Did the addition of the systems improve the image of the fleet with 

shippers, customers, or fellow truck drivers?

• Maintenance Requirements—Did the systems require additional maintenance beyond 

verifying that the components were secure?

• Unscheduled Maintenance—Did the systems have a high number of failures during the 

test? 

• Ease of Failure Diagnosis—Were the system/tire failures difficult to diagnose? With 

identified failures, were technicians able to quickly repair the failure and return the 

vehicle to service?

• Accuracy—Did the systems provide false information to the drivers or technicians? Did 

the drivers and technicians rely on the data reported by the system?

• Impact on Normal Maintenance—Did the systems decrease the amount of work 

required during tire inspections? Did the systems result in increased maintenance times 

during tire rotations, tire replacement, brake system maintenance, and brake inspections?

• Driver/Technician Perception—Did the systems improve tire life? Did the systems 

reduce road calls? Did a failure occur that would not have been found without the 

system?

• Overall Perception—What is the user’s overall perception of the system, including the 

effect on operations, confidence in the system, preferred features, and likes/dislikes of 

installed systems?
26

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27 

4. FIELD TEST DATA ANALYSIS 

This section analyzes the data collected during the field test, including vehicle total miles 

traveled, total maintenance actions performed, and fuel consumed. Specifically, the section 

analyzes the following: 

• Fuel consumed. 

• Tire maintenance actions, including tire failures and road calls. 

• Tire wear. 

• System accuracy. 

• System reliability. 

• Driver/technician feedback. 

4.1 CLI

As stated previously, the field test at CLI took place from May 2008 through June 2009. During 

this time, CLI operated two delivery shifts per day, averaging 450 miles per day per truck. The 

25 trucks under test operated a total of 3,856,337 miles during the field test (Table 9). The 

technicians completed 324 inspections, with the vehicles averaging 12,831 miles between 

inspections. 

Table 9. Total field test mileage (CLI). 

Fleet Mileage Under 

Test

Number of 

Inspections

Miles Per

Inspection

Test Fleet 2,028,631 197 10,360

Control Fleet 1,827,706 127 14,772

Total 3,856,337 324 12,831 (Average)

4.1.1 Fuel

The study team tracked fleet fuel consumption using monthly fuel logs distributed by the 

terminal manager. The fuel logs tracked monthly mileage and fuel consumed. The fuel logs were 

generated using an automated fuel tracker system that recorded the fuel added to the tractor at the 

beginning of each shift.

The fleet consumed a total of 632,870 gallons of fuel during the 13-month field test, with an 

average fuel economy of 6.10 mi/gal. As shown in Table 10, the test fleet averaged 6.19 mi/gal, 

and the control fleet averaged 6.04 mi/gal. The test fleet had a 3.06-percent improvement in fuel 

economy above the control fleet. 
28 

Table 10. Fleet fuel consumption (CLI). 

Tractors Mileage Under Test Fuel Consumed Average mi/gal

Test Tractors 2,028,631 327,774 6.19

Control Tractors 1,827,706 305,096 6.00

Total 3,856,337 632,870 6.10 (Average)

The monthly fuel logs were used to track the fuel economy of the test fleet and the control fleet, 

with the fuel economy of the test fleet consistently surpassing the control fleet. As shown in 

Figure 20, the test fleet averaged a 3.2-percent improvement in fuel economy, with the largest 

improvement occurring in December 2008. 

Figure 20. Graph. Monthly average fuel economy (CLI) for control and test fleets.

The control fleet’s fuel economy dropped by approximately 0.53 mi/gal between November 

2008 and December 2008 (as shown in Figure 20). Although decreases in fuel economy are 

expected during the winter months, the 8.8-percent drop in fuel economy between November and 

December cannot be associated with adverse weather conditions during the month. CLI noted 

that six of the oldest vehicles in its fleet were replaced with new 2009 Freightliners. New 

vehicles require an engine break-in period prior to obtaining their optimal fuel economy and may 

have had differing engine and emission control packages, which could have affected their fuel 

economy. 

Removing the new tractors from the analysis eliminated the drop in fuel economy due to new 

equipment. Without the new tractors, the test fleet demonstrated a 1.39-percent improvement in 

fuel economy over the control fleet (as shown in Figure 21). As shown in the chart, when the 

new tractors were removed from the analysis, the fuel economy dropped by only 1.7 percent 

between November 2008 and December 2008. Thus, it appears that the large drop in fuel 

economy shown in Figure 20 can be attributed to the new tractors.
29

Figure 21. Graph. Monthly average fuel economy, original tractors (CLI).

4.1.2 Tires

During the periodic maintenance inspections, technicians recorded the tire depth at each of the 

10 tire locations on the tractor-tanker. Technicians measured the tire depth from the center tread 

of the tire, ensuring that the measurement was not taken on a wear bar. 

CLI’s tire replacement policy did not allow the retreading of any tires in the fleet. The steer tires 

and drive tires were usually replaced with new tires. The tanker tires were replaced with either 

used drive tires or new tires. New steer tires had an average depth of 18/32nds of an inch. New 

wide-base single tires had an average depth of 27/32nds of an inch. CLI moved drive tires to the 

tanker axles to obtain the maximum life of the tire. If a tire was moved from the drive axle to the 

tanker axle, the average tire depth was 16/32nds of an inch.

The following sections discuss maintenance actions (the replacement of tires due to wear or 

failure) and tire wear (the analysis of tire depth measurements as a function of miles traveled).

4.1.2.1 Tire Maintenance Actions

A “tire maintenance action” was the act of replacing or repairing a tire. The actions included

replacing a tire due to wear or failure, repairing a tire due to penetration of a foreign object, or 

conducting a road call due to a catastrophic failure during service. The host fleet submitted 198

reports of tire actions during the field test, as shown in Table 11. Tire action reports included

failure reports submitted by drivers, failure reports submitted by technicians, and periodic 

inspections that included a tire change-out. During the field test, CLI completed 160 tire wear 

replacements, 16 tire failure replacements, 16 tire repairs, and 6 road calls. 
30 

Table 11. Tire maintenance actions (CLI). 

Fleet Tire Wear Tire Failure Repair Only Road Call Total Tire Actions

Test Fleet 102 11 12 4 129

Control Fleet 58 5 4 2 69

Total Tire Actions 160 16 16 6 198

Percent 81% 8% 8% 3% N/A

The largest contributor to tire maintenance actions was the replacement of tires due to tire wear

(81 percent). The technicians replaced 160 tires due to wear during the field test. Table 12 breaks 

down the distribution of the tire replacements per million miles. Tankers had the highest number 

of tires replaced. The tanker tires did not necessarily experience more wear, but they were 

routinely replaced with used drive tires. Therefore, the tires were replaced more frequently due to 

the lower starting tire depth. The following section provides more detail on tire wear patterns.

Table 12. Maintenance actions per million miles, by axle (CLI). 

CLI Tire 

Wear

Tire 

Failure

Repair 

Only

Road 

Call

Total

Tire 

Actions

Test Fleet Steer Axle 12.3 0.5 0.5 0.0 13.3

Test Fleet Drive Axle 13.8 2.0 3.5 1.5 20.7

Test Fleet Tanker Axle 24.2 3.0 2.0 0.5 29.6

Total (Test Fleet) 50.3 5.4 5.9 2.0 63.6

Control Fleet Steer Axle 6.0 0.0 0.0 1.1 7.1

Control Fleet Drive Axle 10.9 1.6 0.5 0.0 13.1

Control Fleet Tanker Axle 14.8 1.1 1.6 0.0 17.5

Total (Control Fleet) 31.7 2.7 2.2 1.1 37.8

Average Maintenance Actions between Fleets 41.5 4.1 4.1 1.6 51.3

Tire failures, tire repairs, and road calls accounted for the remainder of the tire maintenance 

actions. Drivers and mechanics submitted 38 failure reports during the field test. Table 13

provides a breakdown of the control fleet’s failure reports. The technicians and drivers submitted 

11 failure reports on the control fleet. 
31 

Table 13. Control fleet failure reports (CLI). 

Incident Number of 

Events

System 

Warning

Drove to 

Garage

Road 

Call

Comment

Tractor Foreign Object 

Detected 

2 N/A Yes No Drivers identified a bolt in the 

tread.

Tractor Pre-trip 

Inspection

2 N/A No No Drivers identified a tire bulge 

and a tire leak (due to a slice on 

the inner sidewall).

Tractor Tire Failure 2 N/A No Yes Report of tire blowout and nail 

in tire.

Total Tractor Events 6 – – – –

Tanker Low Air 2 N/A Yes No Drivers identified low air.

Tanker Foreign Object 

Detected

2 N/A Yes No Drivers identified a nail and a 

bolt in the tread.

Tanker Pre-trip 

Inspection

1 N/A No No Driver identified a slice in the

sidewall.

Total Tanker Events 5 – – – –

Grand Total 11 – – – –

In one instance, two drivers submitted reports for low pressure in a tanker tire. The drivers added 

air to the tires and continued their shift. After the second report, the technicians inspected and 

pulled a bolt from the tire. The tire was repaired, and the tractor-tanker unit returned to service. 

(If this were a test unit, the light would have illuminated, the tire pressure would have been 

maintained, and maintenance would have been notified of the impending tire failure at the start 

of a shift.) 

In two instances, the tanker tires had significantly low tire pressures (more than 30-percent loss 

in recommended pressure) during service. In both instances, drivers observed the low pressure 

due to the significant loss in tire pressure. (If this were a test unit, the tire pressure would have 

been maintained, but the driver would have been notified of the system refilling the tires. A 

driver would not have had to add air to the tires during service.)

Table 14 provides a breakdown of the test fleet’s failure reports. The technicians and the drivers 

submitted 27 failure reports. The test fleet had a significantly higher number of failure reports. 

The test fleet may not necessarily have had more failures, but the systems increased the visibility 

of the failures.
32 

Table 14. Test fleet failure reports (CLI). 

Incident Number of 

Events 

System 

Warning 

Drove to 

Garage 

Road 

Call 

Comment

Tractor Low Air 3 Yes Yes No –

Tractor Leaking Valve 

Stem 

2 Yes Yes No –

Tractor Foreign Object 

Detected 

5 Yes Yes No Drivers identified screwdriver, 

bolts, and nails. 

Tractor Pre-trip Inspection 3 Yes No No Identified prior to trip. Included a 

broken belt, an air leak, and torn 

tread.

Tractor Tire Failure 3 Yes No Yes Reports on only 2 incidents: 

at service station, nail in tire; 

at truck scale, faulty tire valve.

Total Tractor Events 16 – – – –

Tanker Foreign Object 

Detected 

8 Yes Yes No Drivers identified screws, nails, 

and bolts. System maintained air. 

Tanker Pre-trip Inspection 2 No No No Drivers identified tire separation 

and nail during pre-trip inspection. 

Identified prior to failure. Fixed 

prior to shift. 

Tanker Tire Failure 1 No No Yes Tire blowout. System could not 

maintain air. 

Total Tanker Events 11 – – – –

Grand Total 27 – – – –

In three instances, the IVTM system warned the driver of low pressure in the tractor tires. The 

driver continued the service deliveries while monitoring the tire pressures on the in-cab display. 

In two instances, the driver specifically noted that the system warned of the low tire pressure at 

95 psi. No low-pressure warnings were issued for the tanker tires. It is likely that low pressures 

were not noted for the tanker tires because the inflation system properly maintained the tire 

pressures. The failure reports noted four instances in which the inflation system was adding air to 

the tires. In each of these instances, the technician identified a foreign object in the tire and 

serviced the tire accordingly.

The IVTM system warned the driver of a low tire pressure problem with a tractor tire in four of 

the five foreign object events. The driver was able to continue servicing his route, while 

monitoring the tire pressure. Upon returning to the terminal, the driver reported the warning to 

the technicians, who then serviced the tire accordingly. 

In one instance, a tire on the front drive axle picked up a nail in the tread while the driver was 

pulling into a station for delivery. Before continuing the delivery route, the IVTM system issued 

a STOP warning to the driver, indicating that the tire pressure was dangerously low. The driver 

was able to request a service call prior to returning to service and potentially causing a 

catastrophic failure while driving.

The MTIS maintained the tire pressure in all eight foreign object events. The system light 

warned the driver or technician of a potential failure at the tire and provided supplemental air to 
33 

maintain the tire pressure. When the vehicle returned to the terminal, the driver or technician 

identified a foreign object in the tire. The system maintained the tire pressure during the shift, 

and all tires were replaced at the terminal. None of the tire events on the trailer resulted in a road 

call.

The tire failures on the test vehicles were either catastrophic failures or failures of the tire casing. 

One failure required an out-of-State road service to replace the tire. Failure information on this 

tire was not available. The remaining failures were the result of a broken belt, a sidewall bulge, 

and the tread separating from the tire. The systems did not warn of these instances, as the tires 

had not experienced loss of air prior to discovery. 

Finally, faulty tire valves accounted for two of the failure reports. Each system identified leaks at 

the valve stems due to the loss of air in the affected tire. In one case, the driver identified the leak 

while at the scale house. The tire pressure dropped to 55 psi in a drive tire and required the 

replacement of a bad valve stem while in service. In the other cases, the driver identified and 

corrected the leaking valve stem without removing the vehicle from service. The control vehicles 

did not identify any tire valve failures.

4.1.2.2 Tire Wear

The technicians collected 362 tire depths as part of the field test through tire replacement actions 

or end-of-test measurements. The test tractors had 193 tire depth measurements, and the control 

tractors had 169 tire depth measurements. Table 15 breaks down the distribution of the tire 

depths by vehicle type and axle location. The analysis measured tire wear between initial tire 

installation and tire removal. Due to the low tire wear between inspection intervals, tire wear was 

difficult to track throughout the life of the tire.

Table 15. Number of tire wear measurements (CLI). 

CLI Steer Axle Drive Axle Tanker Axle Total

Test Fleet 44 72 77 193

Control Fleet 39 75 55 169

Total 83 147 132 362

Figure 22 and Figure 23 show tire wear per mile for the control vehicles and the test vehicles, 

respectively. The data points chart axle location (steer, drive, or tanker), and the trend lines show 

the average rate of wear for each axle location. As the slope of the trend line decreases (i.e., 

becomes “shallower”), the life of the tire increases (more miles per 32nd-inch of wear). Each 

exhibit shows consistency in tire wear by location. The drive tires for the control and test 

vehicles had the highest wear rates and were replaced more frequently. The tanker tires had the 

lowest wear rates. 
34

Figure 22. Graph. Tread wear of control fleet tires (CLI).

Figure 23. Graph. Tread wear of test fleet tires (CLI).

Figure 24 presents trend lines from the test and control vehicles in a single chart to compare the 

tire wear between the two datasets. The solid lines represent the test vehicles, and the dashed 

lines represent the control vehicles. TPMS and ATIS improved the tire wear for tires installed on 

the test fleet’s drive and tanker axles. 
35

Figure 24. Graph. Tread wear per mile, steer, drive, and trailer axles: control versus test tires (CLI).

The use of TPMS resulted in a 19-percent improvement in the wear rate of the tires on the test 

vehicles’ drive axles. The drive tires had a wear rate of 125/32nds of an inch of wear per million 

miles on the test tires and 154.5/32nds of an inch of wear per million miles on the control tires. 

The use of ATIS resulted in a 5-percent improvement in the wear rate of the tires on the test 

vehicles’ tanker axles. The tanker tires had a wear rate of 59.1/32nds of an inch of wear per 

million miles on the test tires and 61.9/32nds of an inch of wear per million miles on the control 

tires. Due to the wear patterns of tanker tires, the small improvement is expected. CLI routinely 

installed worn drive tires onto the tanker axles, limiting the overall wear rate at this tire location. 

As stated earlier, worn drive tires that were moved to the tanker axles averaged 16/32nds of an 

inch of tread depth remaining.

The use of TPMS did not improve the wear rate of the tires on the test vehicles’ steer axles. 

According to the trend lines, the control vehicles actually had a 5-percent improvement over the 

test vehicles, but the data analysis showed that this result was not statistically significant. A 

review of tire maintenance practices concludes that the tire wear at the steer axles is very similar

among the test and control vehicles. Maintenance technicians closely monitor the wear and tire 

inflation at the steer tires due to the belief that steer tire failures will result in higher damage 

liability to the fleet. 

The authors conducted a regression analysis of the scatter plots to determine the statistical 

significance of the data (as shown in Figure 25). The findings for the drive and steer axles are 

nearly identical to the trend lines plotted as part of the scatter plot. According to the analysis, the 

tanker tires on the control vehicles had a lower wear rate as compared to the test vehicles, but the 

result of the analysis showed that this difference was not statistically significant. The team 

attributes this discrepancy to the minimal difference in wear rates between the test and control 

fleets. The trend lines for the tire wear rate validated that the test fleet’s drive tires experienced a 
36

slower rate of wear than the control fleet’s drive tires. In addition, the wear rate calculations 

further validate the rate of wear identified for the drive and steer axles. Statistical analysis

confirmed the wear rate of the drive tires to be statistically significant at the 95-percent 

confidence level (t = 38.4 [Mileage] and 5.8 [Variable A]). Note: Variable A = Tractor Mileage 

(x-axis) * (1 if test, 0 if control).

Figure 25. Graph. Regression analysis of tread wear per mile (CLI): control versus test tires.

4.1.3 System Accuracy

During the analysis, the team identified two conditions that resulted in inaccurate tire pressure 

readings—technicians recorded system tire pressure readings after adjusting pressure at the tire,

and the monitoring system sensors inaccurately displayed tire pressures. A review of the data 

shows that when a technician measured a lower tire pressure, he frequently added air to the tires 

before recording the pressures at the in-cab display. As a result, the data analysis inaccurately 

represents the valid tire pressure measurements. The team could not determine whether the 

discrepancy between the measured tire pressure and the in-cab display’s tire pressure readings

was due to inaccuracy of the in-cab display or to the data collection procedure. In addition, the 

technicians continuously reported reliability issues with the wheel sensors. When the wheel 

sensor failed, the in-cab display would display an incorrect tire pressure. The technicians 

identified tire pressure differentials of up to 30 psi. In these situations, the technicians verified 

that the tire pressures were correct using a manual tire pressure gauge. The technicians reported 

the tire sensor failure, but continued to complete periodic inspections with the invalid wheel 

sensor. The team conducted a review of the data, discarding any readings that appeared to meet 

these conditions, and identified consistent tire pressure measurements between the manual 

measurement and the system measurement with minor tire pressure differentials of no more than 

2 psi.
37 

4.1.4 System Reliability

CLI submitted 99 failure reports concerning the operation of the tested systems. The failure 

reports included 38 driver reports and 61 technician reports. The drivers and the technicians 

submitted failure reports to document abnormalities in the operation of the systems under test. 

Failures included loss of communication with the cab display, pressure warnings, oil leaks at the 

wheel ends, and abnormal operation of the system. This section divides the analysis of the 

system reliability into two parts: the monitoring system and the inflation system.

4.1.4.1 Monitoring System

The monitoring system accounted for all of the driver failure reports and 85 percent of the 

technician failure reports. As shown in Table 16, the majority of the failure reports were due to 

failed wheel modules. 

Table 16. IVTM system failure reports (CLI). 

System Failures Driver Report Technician Report

Wheel Module Failure 15 39

Air Leak 8 6

Operator Error 1 0

Communication Failure 3 0

Hardware Failure 0 4

Unknown 11 3

Total 38 52

Wheel Module Failures

At the beginning of the field test, technicians installed 121 wheel modules. Of those original 

modules, all but 14 were replaced. An additional 52 wheel modules had to be replaced during the 

field test. According to the driver and technician failure reports, the wheel modules were 

removed for one of two reasons: loss of communication with the in-cab display, or invalid tire 

pressure shown on the in-cab display. 

During the field test, the authors and Wabco worked together to identify the cause of the wheel 

module failures. The team identified four possible scenarios for the failures: wheel module-toantenna separation, specific tractor influences, external electromagnetic interference, or 

equipment failure. 

As shown in Figure 26, the team could not identify a failure pattern based on the distance 

between the wheel module and the antenna. The wheel module failures were evenly distributed 

among the six wheel locations. A failure pattern could not be determined based on axle or wheel 

location. The data showed that the failures were not the result of an installation issue, the 

location of the antenna was not inhibiting communications, and the drive wheels did not block 

RF communications. 
38 

Figure 26. Diagram. Wheel module failure locations and number (CLI). 

Similarly, the failure analysis did not show failures grouped to any particular tractor or group of 

tractors (as shown in Table 17). The tractors averaged 5.2 wheel module failures during the test 

period. One tractor, 7495, only had a single wheel module failure, caused by operator error. 

Table 17. Wheel module replacement by tractor and location (CLI). 

Tractor Tire 

Location 1

Tire 

Location 2 

Tire 

Location 3 

Tire 

Location 4 

Tire 

Location 5 

Tire 

Location 6 

Total

7375 1 0 0 1 2 2 6

7376 2 1 2 1 1 1 8

7377 1 2 1 2 1 2 9

7378/75 1 1 1 1 1 0 5

7379 0 2 0 0 0 2 4

7380 1 1 1 2 0 0 5

7381 1 1 0 0 1 1 4

7385 1 1 0 1 1 2 6

7386 1 1 1 0 1 0 4

7495 0 0 0 1 0 0 1

Total 9 10 6 9 8 10 52

Wabco, CLI, and a representative for the authors met at the Altoona terminal in January 2009 to 

review the sensor failures to date, to discuss failure scenarios, and to review Wabco’s proposal to 

correct the wheel sensor failures. By January 2009, CLI had replaced 16 wheel modules; 11 of 

the modules were replaced between October 2008 and January 2009. During the meeting, Wabco

presented the next version of the IVTM equipment, which included a second-generation wheel 

module (as shown in Figure 27). The new equipment, when paired with the new in-cab display, 
39

would enhance the driver’s interface with the IVTM system. Wabco requested that the team 

replace the first-generation modules to improve the communication within the system. The 

second-generation modules were 100-percent compatible with the original IVTM equipment

installed for the field test.

The second-generation modules included notable modifications. First, the modules “stood off” 

the mounting brackets. As shown in Figure 27, the new modules were not installed between the 

tire lugs, as they were in the previous generation. Instead, the mounting bracket incorporated an 

extended metal standoff to prevent the module from lying between the tire lugs, possibly 

improving the system communications. Second, the technician determined the length of the air 

tubing during installation, instead of using a predetermined single length during manufacture. 

The technician identified the required length of tubing and trimmed the excess prior to 

completing the installation. The technician inserted and locked the trimmed end into the wheel 

module. The new design permitted the air hose to be adjusted and allowed the use of longer air 

hoses to ease removal and installation of wheel modules during tire changes. 

Figure 27. Grouped photo. Wabco wheel modules, side-by-side comparison of first-generation and secondgeneration modules.

Wabco provided 30 second-generation wheel modules to equip 5 tractors with new equipment. 

CLI retrofitted two tractors by replacing all the first-generation wheel modules on each tractor.

CLI used the remaining second-generation wheel modules as spares to replace failed wheel 
40

modules. The spare wheel modules replaced an additional 26 first-generation wheel modules that 

failed between January and July. At the end of the field test, the failure rate for the firstgeneration wheel modules equaled 47 percent, with only 14 of the original modules functioning 

throughout the entire field test. The failed wheel modules were returned to Wabco for failure 

analysis. At the time of the report, Wabco had preliminary failure reports identifying three

potential issues: no failure found, premature battery failure, and failure under investigation. 

Wabco did not provide a summary on the final analysis of the equipment. At the time this report 

was prepared, the team was unable to discern whether the high failure rate was directly 

attributable to premature battery failure.

The second-generation wheel modules experienced a lower failure rate (27 percent). Of the seven 

modules that were replaced, one failure was due to improper maintenance. The fill valve of the 

wheel module (as shown in Figure 28) did not allow users to add air to the tire using traditional 

methods. A low-clearance tire chuck had to be used in order to access the fill valve properly. 

When this particular module required additional air, the user did not use a low-clearance tire 

chuck. Instead, a stick tire chuck was used to fill the tire, and the stick chuck likely was used as a 

lever: when the stick could not fully engage the fill valve, a large force was applied as a lever, 

breaking the fill valve on the wheel module. 

Figure 28. Grouped photo. Second-generation wheel module (fill valve) failure.

Unknown Failures (Potential Wheel Module Failures)

Drivers and technicians submitted 14 reports that did not include detailed descriptions of the 

failures. In the majority of the cases, the technicians replaced the wheel module during the next 

periodic inspection. Each of the unknown failure reports likely was due to a wheel module 

failure. When the wheel module was replaced, the IVTM equipment began to correctly monitor 
41 

the tire pressure at the affected location again. The replacement of these wheel modules was 

accounted for in the total replacement discussed above. 

Air Leak

As described earlier, the wheel modules monitor the tire pressure through a hose connection to 

the valve stem (as shown in Figure 29). With the hose connected to the valve stem, the tire valve 

is held in the open position to permit monitoring of the internal tire pressure. As a result, the tires 

will lose air if the hose-to-valve stem connection is not securely fastened.

Figure 29. Photo. IVTM wheel module installation. 

At the beginning of the field test, loose hose connections contributed to 14 reported incidents that 

resulted in the IVTM system issuing low-pressure warnings. Upon investigation, the driver or 

technician identified an air leak at the hose connection. In two instances, the tire pressure 

dropped below 80 psi. As the field test progressed, reports of air loss at the hose connections 

decreased. 

4.1.4.2 Inflation System

The drivers did not report any failures of the MTIS equipment, and the technicians reported only 

nine failures of the MTIS equipment. As shown in Table 18, rotary-tee failures were the largest 

single cause of failures of the inflation system. In addition, technicians reported single failures 

caused by air leaks, hardware failures, and oil leaks. 

Table 18. PSI failure reports (CLI). 

System Failures Driver Report Technician Report

Rotary Tee 0 5

Air Leak 0 1

Hardware Failure 0 1

Oil Leak 0 1

Unknown 0 1

Total 0 9
42

Rotary Tee Failures

In July 2008, CLI requested additional rotary tees to replace tees that were slinging oil from the 

wheel end. CLI suspected the rotary tees had faulty seals that were allowing oil to escape from 

the wheel end. CLI removed the rotary tees and returned the components to PSI for analysis.

PSI tested the returned components on a test bench in an effort to replicate the failure. No failure 

was found. PSI stated that the failure was likely due to overfilled or leaking wheel ends. When 

filling the wheel ends with oil, a sight window on the hubcap provides an indication of the least 

and the most oil allowed in the wheel end. With a non-MTIS-outfitted hubcap, the level of oil is 

not a large concern. Overfilling the wheel end will not cause leaks. The PSI-outfitted hubcap 

includes vents at the center of the hubcap to allow the release of air in the event of a system 

failure. If oil is added above the “maximum fill” line, the oil will encroach on the hubcap vents 

and escape from the wheel end. In addition, oil has been known to leak from the windows on 

specific hubcaps manufactured to accept the MTIS equipment. PSI recommended that CLI

ensure oil was not added beyond the maximum fill line and recommended the replacement of the

faulty hubcaps with a proven alternative. After these actions were taken, there were no more 

reports of incidents of slinging oil.

Other Failures

The remaining failure reports were single occurrences, including an air leak, a hardware failure,

and an oil leak.

Air Leak: In July 2008, a technician identified an air leak at the line nut between the pressure 

regulator valve and the flow-sensing switch. The technician tightened the line nut, resolving the 

air leak. The test fleet did not have any additional air leaks at this location. The failure was a 

one-time occurrence.

In addition, the CLI field representative reported several air leaks during the first month of the 

field test that were not recorded in the failure reports. CLI stated that the system had air leaks at 

the connection between the hose and the tire’s valve stem (as shown in Figure 30). The MTIS

equipment inflates the tires in a manner similar to the way the IVTM system monitors the tires. 

A hose connects between the T-fitting at the hubcap and the tire stem. The technicians 

disconnected the hose from the valve stem to measure the tire pressures during the periodic 

inspections. Similar to the IVTM air leaks, the MTIS air leaks occurred at the connection 

between the hose and the tire’s valve stem. Similar to the IVTM equipment, the technicians

properly tightened the hose connections, stopping the air leaks at this location. PSI stated that the 

inflation system does not require regular measurements of the tire pressure. The regular tire 

pressure measurements occurred during the field test to collect data on the accuracy of the tire 

inflation system. PSI recommends verifying the system pressure during the annual inspection of 

the inflation system.
43

Figure 30. Photo. PSI equipment on tire: oil leaks at the output port and air leaks at the valve stem.

Hardware Failure: In April 2008, a technician identified an air leak at the T-connection near 

the rear axle. The connection splits the air line to supply air for the front and rear axles. The 

hardware failure occurred within 1 month of the initial installation of the MTIS equipment. No 

other hardware failures to the T-connection were reported during the field test. The failure was 

attributed to either a manufacturing or an installation flaw that resulted in a leak at the Tconnection. After identification and repair of the leak, there were no further reports of air leaks.

Oil Leak: In June 2008, a technician identified oil leaking at the face of the hubcap at wheel 

location #8. The MTIS equipment did not contribute to the failure. The PSI representatives 

reviewed the failure report and the installed equipment. The representatives stated that the 

hubcap used by CLI had a history of oil leaking from the oil fill window. PSI recommended that 

CLI replace the hubcaps with others from a different manufacturer. After replacing the 

equipment, CLI did not experience any more oil leaks at the hubcaps.

4.1.5 Driver Feedback

The study team conducted a driver’s survey at the completion of the field test. The survey 

addressed three areas of interest—driver knowledge, driver display experience, and field test 

experience. CLI distributed the surveys to the entire driver pool, with 100 percent of the drivers 

returning completed surveys (59 responses). Drivers of the TPMS-equipped tractors and ATISequipped tankers represented 64 percent of the survey responses. The remaining survey 

responses represented the control vehicle drivers.

4.1.5.1 Driver Knowledge

The drivers answered a series of questions on their exposure to and opinion of TPMS and ATIS 

technologies. Figure 31 breaks down the “Driver Knowledge” survey responses. The drivers had 

limited experience with TPMS and ATIS technologies. The survey responses showed that the 

majority of the drivers did not have previous knowledge of (83 percent) or driving experience 

with (92 percent) TPMS or ATIS technologies. Therefore, prior to starting the field test, the 

majority of the drivers stated that their perception of the technology was either neutral (20 

percent) or they had no previous knowledge (64 percent). After completion of the field test, the 

drivers’ perception of TPMS and ATIS technologies improved significantly. The 
44

positive/slightly positive perception of TPMS and ATIS improved to 72 percent of the drivers 

surveyed. No drivers had a negative perception of the equipment.

During the surveys, one driver stated that he had worked with ATIS equipment while enlisted in 

the Army Reserves. He stated that the technology was a high-maintenance item with minimal 

benefits. In his opinion, the technology did not work very well on the Army’s vehicles. After 

driving an equipped vehicle for the field test, the driver stated that the technology was very 

useful (positive perception). The driver did not have any tire-related issues after installation of 

the technology.

Although some drivers did not have previous exposure to the technology, they believed the 

technology would cause more maintenance without any benefit for the driver. At the completion 

of the test, these drivers also stated that they believed the technology was very useful. One driver 

stated that the technology warned him of a slow leak on his vehicle before he left the terminal at 

the start of his shift.

Figure 31. Pie charts. Driver survey results: driver knowledge (CLI).

Overall, the drivers’ opinions of the TPMS and ATIS technologies improved after completion of 

the field test. Several drivers stated that the equipment warned them of a tire failure before a road 

call was required. In addition, the drivers of the control vehicles requested expanding the 

installation of the TPMS and ATIS equipment to the entire fleet. The drivers believed the TPMS

and ATIS technologies were very useful for tracking the status of the tires. 
45

4.1.5.2 TPMS and ATIS Display Experience

The team surveyed the drivers to document their opinions on the TPMS and ATIS displays. As 

stated previously, the tractor display and the tanker display offered different interfaces. The 

tractor display was mounted on the dashboard to the right of the driver. The display allowed the 

driver to scroll through each tire position to monitor the tire pressures. In addition, the display 

alerted the driver with an audible and visual warning when a tire dropped below a preset tire 

pressure. The tanker display was an indicator light that the driver could view through his side 

mirror mounted on the fender of the tanker. The light illuminated when air was being added to 

the tanker tires.

The charts in Figure 32 highlight the drivers’ responses to the accuracy, location, and 

functionality of the tractor display. The majority of the drivers (74 percent) stated that the tractor 

display was accurate “most of the time.” From comments received during the survey, the authors

linked the lower rating to the wheel sensor failures. As stated earlier, if a wheel sensor failed, the 

tire pressures at the in-cab display would be invalid. The majority of the drivers (72 percent) 

stated that the tractor display never interfered with the operation of the vehicle. The survey did 

identify a single driver who stated that the displays always interfered with vehicle operation. A 

review of this driver’s responses found that he was very receptive to the TPMS and ATIS 

technology and offered only positive feedback on both systems. Therefore, it was assumed that 

the driver responded inaccurately to this question. Finally, most drivers (62 percent) found the 

interactive display very easy to use. As shown in the exhibit, the drivers had only positive 

feedback on the display’s ease of use. 

Figure 32. Pie charts. Driver survey results: TPMS tractor display experience (CLI).
46

The charts in Figure 33 highlight the drivers’ responses to the accuracy and location of the tanker 

indicator light. The drivers’ opinions of the accuracy of the MTIS fault indicator did not reflect 

the written and verbal reports delivered to the team. The survey results showed that only 47 

percent of the drivers found the tanker display to be accurate. An additional 29 percent of the 

drivers stated that the tanker display was accurate “most of the time” (more than 75 percent 

accurate). Although the combined responses result in a satisfactory rating for more than 76 

percent of the drivers, the results do not reflect the verbal comments received. In addition, 

approximately 24 percent of the drivers ranked the fault display unit as less than satisfactory (i.e. 

inaccurate more than 25 percent of the time or never accurate). 

A review of the survey comments did not clarify the reason for the lower rankings. The team 

identified several possibilities for the discrepancy, including misunderstanding of the survey 

question, misunderstanding of rank severity (high versus low), or misunderstanding of the 

capability of the MTIS indicator light (i.e., it does not provide an actual pressure reading). When 

asked to rank the location of the tanker display, 77 percent of the drivers stated that the display 

never interfered with vehicle operation. Although 77 percent of the drivers responded positively 

to the location of the tanker display, an additional 17 percent of the drivers stated that the tanker

display was intrusive either all the time or most of the time. These drivers offered no reasoning 

for rating the display location so low. Again, the study team believes these drivers may have 

misunderstood the ranking for the survey question. Because the fault indicator for the tanker

inflation system was installed on the tanker’s fender, it would be unlikely for the indicator to 

interfere with vehicle operation.

Figure 33. Pie charts. Driver survey results: ATIS tanker display experience (CLI).

4.1.5.3 Field Test Experience

The team surveyed the drivers to document events that occurred during the field test, including 

tire failures and system failures. The drivers answered questions on the frequency of tire failures 

on the tractors and the tankers.

The majority of the drivers experienced fewer than five tire failures during the field test. The 

drivers identified more failures on the tractor (55 percent) than on the tanker (41 percent), as 

shown in Figure 34. In all but one case, the displays accurately alerted the drivers of the tire 

failure. In this single case, the driver stated that the display did not accurately show the fault

location. The screen indicated a tire warning for the right front drive tire. Upon inspection, the 
47

tire failure was found on the right rear drive. The test team did not witness this failure but 

suspects the failure was the result of one of two maintenance events: the sensors were not 

returned to their original locations after a tire rotation, or the sensor locations were not properly 

assigned during installation. Therefore, the failure was likely the result of improper maintenance 

rather than equipment failure.

Figure 34. Pie charts. Driver survey results: tire failure experiences (CLI).

The chart labeled “Actions Required to Return to Service” in Figure 34 breaks down the steps 

that had to be taken after identifying a tire failure. Most of the drivers (66 percent) identified at 

least a single tire failure during the field test. In most cases, the drivers were able to either 

continue driving their route or return to the maintenance facility without requiring a road call. 

Six drivers required a road call because of the tire failure. In these cases, the catastrophic tire 

failure would not allow the driver to continue operation (e.g., sidewall blowout, failed valve 

stem, nail in the tread). In two cases, the drivers identified a leak in the tanker tires and were able 

to maintain proper tire pressure to return to the facility. In seven cases, the system warned of a 

leak, and the driver identified the source and determined he could safely return to the facility 

before taking any maintenance actions. The drivers stated that the use of the TPMS and ATIS

equipment in these cases saved the tire casing and prevented a road call.

The drivers answered questions on the reliability of the tractor TPMS and tanker ATIS 

equipment. The survey divided the failures into three categories—never, infrequent (less than 

five failures), moderately frequent (less than one per month), and frequent (more than one per 

month). As stated earlier, the tractor TPMS equipment experienced a high number of sensor 

failures. As a result, the majority of the drivers experienced infrequent tractor TPMS failures (as 
48

shown in Figure 35). Although the number of failures may appear insignificant, 18 drivers made 

at least one comment on the sensors failing during the field test. Only nine drivers, of whom five 

regularly drove the test vehicles, reported no system failures during the field test.

Figure 35. Pie charts. Driver survey results: system failures experience (CLI).

The drivers experienced far fewer failures on the tanker ATIS equipment. The majority of the 

drivers (52 percent) did not experience a single system failure during the field test. The drivers 

offered little insight into the system failures for the MTIS equipment. Drivers commented on 

loosening hoses, a “flickering” indicator light, and a faulty valve. The faulty valve was a true 

system failure, but the other instances were due to either improper maintenance techniques or a

misunderstanding of the capabilities of the system. The hoses leading from the wheel hub to the 

tire valve would become loose at the tire valve. The mechanics identified the failure to be the 

result of improperly tightening the hose after removing it to record the tire pressure for the field 

test. Although the tire pressure measurements are not required for normal installations, the field 

test required the collection of tire pressures on a monthly basis. The problem was resolved when 

the mechanics modified their maintenance procedures to ensure proper tightening of the hoses. 

The second issue, the flickering of the fault indicator light, demonstrates the proper operation of 

the equipment. The light will illuminate whenever air is being added to the tires. Therefore, the 

light will “flicker” at the start of a shift if the vehicle has been sitting for an extended period. The 

system is adding “make-up” air to the tires to bring them back to the proper pressure. No actions 

by the driver or the technician are required. The final issue relates to a faulty valve. The 

technicians noted on the data sheets that a valve had to be replaced due to leaking. This was the 

only component that was replaced due to a true failure.
49 

The survey responses indicate that the drivers were receptive to the TPMS and ATIS 

technologies, although they expressed frustration at the frequent sensor failures on the in-cab 

system. The drivers stated that when the equipment was working, the pressure readings in the 

cab allowed them to monitor the tire pressure during daily operations. Similarly, the drivers 

stated that the tanker inflation system permitted them to maintain tire pressures when a foreign 

object was in the tires. The drivers stated that an in-cab monitor for the inflation system would be 

beneficial to provide actual air pressures. In this instance, further information on the inflation 

system would have allowed the drivers to understand that the tanker tire pressures remained 

constant. 

4.2 GFS

The GFS field test began in June 2009 and continued through November 2010. The GFS tractors

operate a single delivery shift per day and average 350 miles per day per tractor. The tractor fleet 

operated a total of 3,406,570 miles during the field test (as shown in Table 19). The GFS trailers 

operate independently from the tractors and are not assigned a daily route. The tractors operated 

a total of 5,461,159 miles during the field test, averaging 140 miles per day. The trailers 

experienced higher mileage because the reefer pups were operating as dual units. 

Table 19. Total field test mileage (GFS). 

GFS Tractor Trailer

Test Fleet 1,463,193 2,861,016

Control Fleet 1,943,377 2,600,143

Total Mileage 3,406,570 5,461,159

4.2.1 Fuel

The GFS field test only tracked the fuel economy of tractors pulling 50-foot trailers equipped 

with the tire monitoring system. Due to GFS’s operational model for reefer pups, the team could 

not guarantee that tractors equipped with TPMS equipment would always pull trailers equipped 

with inflation systems. Therefore, the reefer pups were monitored for wheel wear, tire 

replacements, tire failures, and system reliability. The fuel economy improvement findings do 

not apply to the trailers equipped with inflation systems.

The study team downloaded GFS’s daily fuel logs from its maintenance database. The fuel logs 

recorded fueling date, vehicle identification, vehicle odometer, and fuel quantity. The fleet 

consumed a total of 520,546.6 gallons of fuel during the 18-month field test (as shown in Table 

20). 

Table 20. Fleet fuel consumption (GFS). 

GFS Mileage Under Test Fuel Consumed Average mi/gal

Test Tractors 1,463,193 220,036.8 6.59

Control Tractors 1,943,377 300,509.8 6.50

Total 3,406,570 520,546.6 6.54 (Average)
50

The team tracked the average monthly fuel economy of the test tractors and control tractors. As 

shown in Figure 36, the fleet fuel economy followed the cyclic expectations of seasonal 

operation. The fuel economy of each fleet reached the lowest in December and the highest in 

July. The test fleet consistently exceeded the control fleet’s average monthly fuel economy. The 

test fleet averaged a 1.38-percent improvement over the control fleet during the field test.

Figure 36. Graph. Monthly average fuel economy (GFS) for control and test fleets.

4.2.2 Tires

An independent tire company performs all tire maintenance for GFS. GFS removes a failed or 

worn tire from the axle and installs a tire from stock. The tire company representative services 

the GFS maintenance facility on a daily basis. During the service trip, the representative 

addresses all tires accumulated since the last visit. The tire company repairs punctures, replaces

worn tires, and in general, replenishes the GFS tire supply with functional tires. For the field test, 

the tire company installed, replaced, and tracked tire sensors on the wheel rims. The tire 

company stocks the GFS maintenance facility with new and retreaded tires. Retreaded tires are 

used only on drive and trailer axles. New tires may be used at all axle locations.

4.2.2.1 Tire Maintenance Actions

GFS technicians inspected tires for current pressure, wear condition, and foreign object presence 

during periodic inspections. Technicians documented the findings according to their current 

maintenance procedures. All tire replacements, repairs, failures, and rotations were recorded in 

the maintenance database. The authors tracked the remaining tire incidents using GFS’s internal 

maintenance database. The database tracked tire replacements, repairs, failures, and rotations.

GFS conducted 355 tire maintenance actions during the 18-month field test, as shown in Table 

21. The authors downloaded all tire maintenance actions from the maintenance database. Tire 

wear, at 78 percent, represented the largest contributor to tire maintenance. GFS replaced 278 

tires due to wear, 44 due to failure, and 19 due to road calls. GFS performed 14 tire repairs 

during the field test.
51 

Table 21. Tire maintenance actions (GFS). 

GFS Tire 

Wear

Tire 

Failure

Repair 

Only

Road 

Call

Total 

Tire 

Actions

Test Tractor 28 6 0 1 35

Test Trailer—Pup 42 11 1 2 56

Test Trailer—50-Foot 40 12 6 5 63

Control Tractor 100 8 0 2 110

Control Trailer—Pup 24 1 2 6 33

Control Trailer—50-Foot 44 6 5 3 58

Total Tire Actions 278 44 14 19 355

Percent 78.3% 12.4% 4.0% 5.3% N/A

Tire wear contributed to 78 percent of the tire maintenance actions. Significantly fewer tires 

were replaced for wear on the test tractors compared to the control tractors, which will be 

discussed in the following section. The rate of tire maintenance actions, as shown in Table 22, 

shows that the steer and drive axles of the test fleet outperformed those of the control fleet. The 

test tractors experienced fewer tire failures, repairs, and road calls. In comparison, the test trailers 

performed marginally better than the control trailers. The control trailers experienced fewer tire 

failures, but more tire repairs and road calls.

Table 22. Maintenance actions per million miles, by axle (GFS). 

GFS Tire 

Wear

Tire 

Failure

Repair 

Only

Road 

Call

Total 

Tire 

Actions

Test Fleet Steer Axle 6.2 0.0 0.0 0.0 6.2

Test Fleet Drive Axle 13.0 4.1 0.0 0.7 17.8

Test Fleet Trailer Axle—Pup 25.8 6.8 0.6 1.2 45.4

Test Fleet Trailer Axle—50-foot 32.4 9.7 4.9 4.1 51.1

Test Fleet Total 25.4 6.7 1.6 1.9 35.6

Control Fleet Steer Axle 11.3 1.0 0.0 0.0 16.4

Control Fleet Drive Axle 40.1 3.1 0.0 1.0 58.8

Control Fleet Trailer Axle—Pup 15.3 0.6 1.3 3.8 34.2

Control Fleet Trailer Axle—50-foot 45.5 6.2 5.2 3.1 60.0

Control Fleet Total 37.0 3.3 1.5 2.4 44.2

Average Maintenance Actions 

between Fleets

31.3 5.0 1.6 2.1 40.0

Table 23 and Table 24 break down the tire failures for the test and control fleets. The study team

downloaded all tire failure reports from the maintenance database and identified the failure type, 

the failure cause, and any road calls through the database’s comments section. The database did 

not provide feedback on the ability of the equipped fleet to warn the driver or the mechanic of 

the failure. 
52 

The analysis identified 44 tire failures for the test fleet and 33 tire failures for the control fleet. 

Similar to CLI, the GFS test fleet had more tire failures during the test period. Although the test 

fleet had a higher overall number of tire failures, it had fewer road calls. Foreign objects in the 

tractor tires contributed to the largest difference between the two fleets. The test trailers had 20 

tire failures due to foreign objects—compared to the control fleet that had 5 tire failures due to 

foreign objects. The team could not establish a link between the test fleet and the higher number 

of tire failures due to foreign objects. 

Table 23 breaks down the test fleet tire failures. As the information was downloaded from the 

maintenance database, minimal information was available to document the ability of the test 

equipment to reduce or prevent tire failures. The database identified a single occurrence of the 

inflation system warning the driver of a potential tire failure. Upon inspection, the maintenance 

technicians identified a foreign object. The technicians repaired the tire, preventing a road call. 

Prior to the start of the test period, a reefer pup equipped with the MTIS experienced a 

catastrophic failure. A wheel end overheated due to a dragging brake. The MTIS attempted to 

maintain the tire pressure, but when the trailer’s air system dropped below the required pressure 

for minimum brake operation, the safety valve isolated the system from the trailer’s air supply. 

Table 23. Test fleet tire failures (GFS). 

Incident No. of 

Events 

Road 

Call 

Comment

Tractor Event Flat 1 No –

Tractor Event Foreign Object Detected 4 No All tires replaced. None repaired.

Tractor Event Air Leak 1 No –

Tractor Event Tire Failure 1 Yes Night service call in yard. 

Total Tractor Events 7 No

(Average)

–

Trailer Events—Pup Flat 3 No Drivers identified screws, nails, and bolts. 

Illuminated light reported for one event.

Trailer Events—Pup Foreign Object 

Detected

7 No Tires repaired—1.

Tires replaced—6.

Trailer Events—Pup Tire Damage 1 No Cut in sidewall identified. 

Trailer Events—Pup Air Leak 1 No –

Trailer Events—Pup Tire Failure 2 Yes –

Trailer Events—50-Foot Flat 5 No Drivers identified screws, nails, and bolts. 

Trailer Events—50-Foot Foreign Object 

Detected

13 No Tires repaired—6.

Tires replaced—7.

Trailer Events—50-Foot Tire Failure 5 Yes –

Total Trailer Events 37 No

(Average)

–

Grand Total 44 No

(Average)

–

Table 24 breaks down the control fleet tire failures. Due to GFS’s reporting methods, an analysis 

of the tire failures on the control fleet was difficult. The team conducted an analysis of all 
53 

failures for the control fleet and the test fleet using the descriptions written in the maintenance 

database. 

As stated earlier, the test fleet had fewer road calls due to tire failures. In addition, if TPMS or 

ATIS equipment had been installed on the control fleet, the total number of road calls for the 

fleet might have been reduced. For example, the team identified a road call due to a flat tire from 

a foreign object. The road call was reported for a 50-foot trailer due to a flat inner tire. The tire 

servicing company conducted an inspection and determined that the tire could be repaired on

site. If the trailer had been equipped with a monitoring system, the driver would have received a 

warning before the tire became flat (while in service). If the trailer had been equipped with an 

inflation system, the system would have likely maintained the proper tire pressure until the driver 

returned to the maintenance facility. In either event, the TPMS or ATIS equipment likely would 

have prevented a road call. 

Table 24. Control fleet tire failures (GFS). 

Incident No. of 

Events 

Road 

Call 

Comment

Tractor Events Flat 1 No –

Tractor Events Foreign Object Detected 5 No All tires replaced. None repaired.

Tractor Events Air Leak 2 No –

Tractor Events Tire Failure 2 Yes One steer tire failure caused progressive 

damage to surrounding equipment.

Total Tractor Events 10 No

(Average)

–

Trailer Events—Pup Flat 1 No –

Trailer Events—Pup Foreign Object 

Detected

2 No All tires repaired.

Trailer Events—Pup Tire Failure 6 Yes One tire failure involved the catastrophic 

failure of two inner tires.

Trailer Events—50-Foot Flat 8 No –

Trailer Events—50-Foot Foreign Object 

Detected

3 No All tires repaired.

Trailer Events—50-Foot Tire Failure 3 Yes –

Total Trailer Events 23 No

(Average)

–

Grand Total 33 No

(Average)

–

In summary, the test tractors outperformed the control tractors in the number of tire failures 

accumulated (7 tire failures on the test fleet versus 11 failures on the control fleet). The single 

road call for the test tractors occurred in a maintenance yard, but occurred after hours. As a 

result, the driver required the tire servicing company to perform a road call to return the unit to 

service. The control trailers outperformed the test trailers in the number of tire failures 

accumulated (23 tire failures on the control fleet versus 37 tire failures on the test fleet). Most 

importantly, the test fleet experienced fewer road calls during the field test, which reflects

significant cost savings to the owner. 
54 

4.2.2.2 Tire Wear Data

The authors originally intended to complete a thorough analysis of tire wear on the GFS fleet, 

similar to the analysis for the CLI fleet. The CLI analysis calculated the tire wear rate at each of 

the axle positions for the fleet. However, due to the technicians’ limited interaction with the tires, 

tire wear depth data were insufficient for a thorough analysis. As an alternative, the team 

attempted to use the data to identify the average mileage between tire wear replacements. This 

type of analysis proved difficult for two reasons: 

• GFS does not necessarily replace worn tires with new tires. GFS’s replacement policy 

permits the installation of used tires. If a used tire was installed, the accumulated mileage 

for the tire would be significantly less. The analysis could not track total mileage 

accumulated when a used tire was installed.

• GFS replaced a significant number of tires for failure, not wear. When a tire was replaced 

for failure, the tire had not reached its end of life. To perform a sound assessment of 

average mileage between tire wear replacements, the team must calculate the mileage 

accumulated over the entire life of the tire. A failed tire is removed prior to reaching the 

minimum tread depth allowed for the wheel position. 

For these reasons, the team only conducted an analysis on the number of tires replaced on each 

fleet. The team identified 278 tire wear replacements (as shown in Table 25) during the test 

period. Comparing the tire wear during the test period, the control fleet replaced more tires than

the test fleet. 

Table 25. Tire maintenance actions (GFS). 

GFS Tire Wear

(Test Period)

Tire Wear

(2008–10)

Test Tractor 28 87

Test Trailer—Pup 42 61

Test Trailer—50-Foot 40 61

Control Tractor 100 116

Control Trailer—Pup 24 48

Control Trailer—50-Foot 44 51

Total Tire Actions 278 424

The analysis identified a significant difference between the test tractors and the control tractors. 

According to the maintenance database, the test tractors experienced a significant improvement 

in tire wear, replacing less than one-third of the number of tires that the control fleet replaced. 

The team expanded the analysis of the tire replacement to identify any cyclic patterns in the tire 

replacement schedules for both fleets.

Figure 37 tracks the tire replacements for the test and control fleets between January 2008 and 

November 2010. The replacement of the test tractor tires spiked in early 2009. The team 

attributed the spike in the test fleet to the installation of the TPMS equipment. The installation of 

the TPMS sensors required the tire technician to remove the tire carcass from the rim. The tire 

technician may have installed the first three sets of sensors on new tires. Then, as the 
55

maintenance technicians removed tires from the tractors to install the equipment, there was no 

downtime to mount the sensors to the rims. Sensors were mounted on the removed tires during 

the tire technician’s next service call. This method of installation provided minimal downtime for 

both the maintenance and the tire technicians.

Figure 37. Graph. Analysis of tractor tire wear for control and test tractors (GFS).

Upon reviewing all the available data, the authors determined that an analysis of the tire wear 

patterns between the test fleet and the control fleet could not be completed. The team identified 

too many variables (e.g., tire replacement policies, premature tire replacement on test fleet)

during the study that did not allow a clear distinction on tire wear between the fleets.

4.2.3 System Reliability

The authors tracked system reliability through staff interviews, database queries, and component 

returns. The team identified two recurring complaints for the equipment: 

• Inflation systems inflated tires beyond preset pressure.

• Monitoring systems lost communication with wheel sensors. 

In addition, two catastrophic failures occurred during the field test:

• An overheated wheel end.

• A failed wire harness.
56

4.2.3.1 Overinflated Tires

Early in the field test, the GFS technicians identified increased tire pressures on several of the 

ATIS-equipped reefer pups. Tire pressures measured up to 15 psi higher than the fleet’s 

recommended tire inflation pressure. The team identified two conditions that could contribute to 

the increased pressures: an improperly set regulator valve, or an extended layover period during 

cold temperatures. The authors contacted PSI to conduct an analysis of the failure. PSI inspected 

various systems at the facility but could not identify any discrepancies. PSI also tested the 

pressure setting of the regulators and confirmed the pressure setting of 95 psi. 

Figure 38. Photo. GFS reefer pups in yard.

In addition, the authors reviewed the operation of the GFS fleet and determined that the reefer 

pups experienced extended layovers between trips. During these layovers, the trailers likely 

experienced a cold-soak event. A cold-soak event exposes the tires to an extended period of 

below-average temperatures. As a result, the tire pressure decreases due to the temperature drop.

Therefore, during the cold winters and cool evenings in Grand Rapids, the tire pressure dropped 

during the reefer pup’s layover. When the GFS driver hooked up the reefer pup, power was 

restored to the inflation system, and it re-inflated the tires to the proper pressure. The operation 

of the trailer throughout its route raised the temperature in the tire, and thus the tire pressure. 

Depending on the ambient temperature during the technician’s maintenance, the tire pressure 

readings would exceed the pressure set by the inflation system during the startup procedure. If 

this is the cause for the raised pressures, the tire industry advises not to remove air pressure from 

tires during a cold pressure reading (after the tire was properly inflated). 

4.2.3.2 Communication Loss with Sensors

During the field test, technicians expressed concern over the intermittent communication 

between the wheel sensors and the cab display. Reported concerns included communication loss 

between trailer and display, communication loss at specific tire locations, and lack of sensor 

tracking ability.

Drivers reported the absence of all trailer tire information on the in-cab display when dispatched 

from the distribution facility (as shown in Figure 39). The cab display recognized the trailer tire 

information after driving a short distance down the road (less than 2 miles). As stated earlier, 
57

Tire-SafeGuard provided a system capable of monitoring unmarried tractor-trailer pairs. To 

accommodate unmarried pairs, the system conducts a handshake sequence at startup to validate 

and link the correct tractor-trailer pair. Two scenarios generate the handshake startup: a keyup/key-down sequence, or a verification of a single trailer in the area. For the GFS test, the 

drivers were not informed of the key-up/key-down procedure. Therefore, the system delayed 

linking to the trailer until the system verified the sensors on the trailer. The verification process 

could take up to 5 minutes due to other sensors communicating in the surroundings. After a 

trailer linked to a tractor, the DDU stored the trailer’s identification in the control unit. Future 

communication links would occur within seconds. In summary, the latency in the display of the 

trailer tire pressures results from the design of the system programming. A discussion with the 

manufacturer identified potential areas for improvement, including an automatic startup

sequence to eliminate the key-up/key-down requirement for tractor-trailer linkage.

Figure 39. Photo. Tire-SafeGuard reliability, displaying tractor tire data only (GFS).

Technicians commented on the difficulty of monitoring trailer tire pressures in the maintenance 

yard. Due to the size of GFS’s trailer fleet, trailers frequently remained in the maintenance yard 

for several days without use. The technicians could not monitor the trailer tires without a linked 

tractor. In addition, due to the standby mode of the sensors, the trailer sensors had to sense 

movement prior to decreasing the time between system messages. As a result, the connection of 

a tractor to the trailer would not resolve the issue unless the tractor moved the trailer and a link 

was established between the two units. The fleet managers recommended a standalone unit that 

could query a tire’s pressure by passing a handheld reader over the tire. The manufacturer stated 

that a new standalone trailer system includes an external display for the trailer. The unit monitors 

the trailer’s tires, allowing technicians to view tire pressures without the tractor display unit. The 

trailer-only system will transmit the trailer’s tire pressures to the in-cab display unit when a link 

is established.

Drivers and technicians reported missing tire pressure measurements at varying tire locations on 

the in-cab display unit. The display would provide tire measurements for some tire locations, but

would not display a tire measurement at other tire locations on the same tractor (as shown in 

Figure 40, the left inside tire on the front axle is not displaying tire information). While 

conducting interviews with the technicians and the tire representative, the authors identified 
58

inconsistent maintenance practices that may have contributed to this phenomenon. When 

conducting tire rotations or replacements, the technicians must ensure that a wheel sensor is 

installed at each location and the cab display is updated to reflect the changes. Interviews with 

the technicians and tire representative uncovered a lack of diligence in conducting these 

maintenance tasks. As a result, many “blank” tire pressures on the display may have been due to 

not updating the sensor locations or not installing sensors on new tires. These issues would be 

less apparent if an entire fleet were outfitted with the wheel modules. The tire technicians would 

only have tires with wheel sensors installed. When replacing a wheel, the technician would 

install the tire and immediately reprogram the cab display to recognize new tires and new tire 

locations. After establishing a maintenance procedure, the number of “missing” wheel modules 

should decrease. As a result, no additional downtime would be required to install wheel sensors 

on new rims.

Figure 40. Photo. Tire-SafeGuard reliability; display missing left inside tire data (GFS).

4.2.3.3 Equipment Failures

GFS management reported a single equipment failure for the inflation system and one for the 

monitoring system. The inflation system failed when a wheel end overheated due to a dragging 

brake. The monitoring system failed due to an overheated wiring harness for the trailer

monitoring system. The fleet technicians identified this.

Prior to the start of the test period, a reefer pup equipped with the inflation system experienced a 

catastrophic failure. The driver reported a smoking wheel end while conducting the daily service

route. The valve stem on the inner tire failed, causing a blown tire. The failure required a 

roadside service call to replace the tire and failed equipment. An investigation into the failure 

identified a dragging brake as the cause of the overheated wheel end. An analysis of the event 

attributed the failure to a faulty brake valve. One of the MTIS safety features related to the 

inflation system was effective during this event. While attempting to maintain the trailer’s tire 

pressure, the trailer’s air system dropped below the required pressure for minimum brake 

operation. As a result, the inflation system’s safety valve cut off the air supply to the tires. 
59

GFS identified a failed TPMS wiring harness on a tractor in November 2010. The wire harness 

routed the tractor’s power to the in-cab display unit. The harness consisted of three wrapped 

wires connected to the in-cab display, as follows: 

• A red wire connected to the tractor’s primary power.

• A yellow wire connected to the tractor’s auxiliary power.

• A black wire connected to the tractor’s ground source.

Two fuses were installed on the cables carrying power to the cab display. A preliminary 

inspection of the wire harness concluded that it experienced an extreme heat event. The casing 

on the yellow wire, leading from the tractor’s ignition, completely melted off the wire. 

Surrounding wires in the harness were charred. The state of the harness did not lend itself to a 

complete failure analysis. The technicians did not supply the system’s in-cab tractor display as 

part of the failed equipment. The harness was returned to the manufacturer for a failure analysis, 

but no conclusive results were received.

Figure 41. Photo Tire-SafeGuard reliability; failed wire harness.

4.2.4 Technician Feedback

At the completion of the field test, the authors administered a survey to the GFS maintenance 

technicians. The survey questioned the technicians in three areas—mechanical knowledge, 

display interaction, and overall equipment interaction. Due to the limited responses from the 

written surveys, the authors also conducted interviews with technicians in the facility to gather 

feedback on their overall experiences during the field test.

The survey documented the mechanics’ knowledge of TPMS and ATIS prior to and following 

the field test. The survey requested pretest opinions on the systems to document the technicians’ 

preconceptions of them. A followup question at the end of the test documented whether there 

were any changes in the technicians’ views of the products. The survey found that the GFS

technicians had no previous experience with TPMS or ATIS. Despite the lack of experience with 

the systems, the technicians expressed varying opinions on the perceived usefulness of the 
60

equipment. Technician responses ranged from the equipment providing a moderate aid to their 

daily tasks to the equipment increasing maintenance requirements with little return in terms of 

safety, maintenance, and troubleshooting. 

At the conclusion of the field test, the majority of the technicians stated that the equipment 

increased the maintenance requirements with minimal advantages. The technicians identified 

reliability issues that increased the maintenance requirements for not only the installed system 

but also GFS equipment. For example, a technician stated that the ATIS routinely overinflated 

the trailer tires, requiring the technicians to bleed air from the tires during periodic inspections. 

As discussed previously, GFS’s practice of adding or removing air to meet the fleet tire-pressure 

requirement increased the additional maintenance requirements. Industry procedures strongly 

discourage the removal of air from the fleet’s tires in all circumstances. A change in the 

maintenance practice to discourage bleeding air pressure from the tires could reduce the 

increased maintenance interaction. In addition to overinflated reefer pup tires, a technician 

commented on the inability of the TPMS to provide tire pressures at all locations on the tractor 

or trailer. He stated that the cab display frequently lost communication with various tire 

positions. To resolve the issue, GFS mounted new tires to the faulty location and reprogrammed 

the in-cab display. After removing the non-functioning tires, the technicians did not always

inspect the wheel rims to confirm installation of a wheel sensor. As a result, the team could not 

conduct a failure analysis. From prior experience with the equipment, the team identified three 

scenarios that could have contributed to the failure: loss of communication between the sensor 

and the in-cab display, missing wheel sensor, and replacement of the tire without resetting the incab display. In the future, the technicians must monitor and record the location of wheel sensors. 

If a sensor fails, it must be returned to the manufacturer for analysis. In addition, the technicians 

must ensure that all tires installed on equipped tractors or trailers contain wheel sensors. After 

installing a new tire or rotating tires, technicians must reprogram the in-cab display to recognize 

the new sensors or the new sensor locations.

For display interaction, the survey documented the display’s ability to accurately reflect the 

current pressures of the unit’s tires. For the TPMS, the display had to accurately display the tire 

pressures at each location and represent all locations outfitted with wheel sensors. For the ATIS, 

the indicator light had to illuminate when the system was providing supplemental air to the 

wheel ends. The truck technicians stated that the TPMS in-cab display provided intermittent 

feedback on tire pressures. For example, a technician stated that the display would not provide 

tire pressures for all tire locations. At the beginning of the test, he stated that the system worked 

accurately, providing tire pressures for all locations. As the test progressed, the display began to 

omit tire pressures at various locations. As stated above, the cause for this failure could not be

documented, because failed sensors were not returned for analysis. In addition, due to the lack of 

failure reports, the team cannot validate that wheel sensors were installed at these locations when 

the failure occurred. Again, the fleet must make sure to document tires with wheel sensors 

installed. In addition, all equipped units must have wheel sensors at all tire locations, and the incab display must be reprogrammed during tire installations or rotations. The trailer technicians 

stated that the trailer systems rarely provided accurate fault status. In one example, the technician 

stated that he did not experience the tractor and trailer units married to validate the ability of the 

systems to communicate. In addition, the technicians expressed concern throughout the test about 

the in-cab display’s delay in communicating the trailer tire pressures. For the ATIS, the 

technicians rarely experienced the illumination of the indicator light. Therefore, the trailer 
61

system was not adding pressure to the tires. In these cases, the system accurately provided fault 

status.

In general, the installation of TPMS and ATIS increased the daily maintenance tasks for the 

technicians, from adjusting tire pressures on the reefer pups to replacing wheels due to failed 

wheel sensors. Although the technicians understood the benefits of a functioning TPMS or ATIS, 

they felt that the systems under test hindered their daily tasks. The technicians stated that the 

systems provided little assistance in the maintenance of tires. Comments gathered during 

personal interviews identified system improvements that would allow for easy incorporation of 

the systems into GFS maintenance procedures. Technicians requested a method to read the tire 

pressures of trailer monitoring systems without requiring the tractor to be connected. GFS’s 

operation model is not conducive to requiring the tractor to read tire pressures in the yard. The 

technicians would prefer to be able to monitor the trailer tires prior to releasing a trailer to 

service. In addition, technicians requested an ATIS capable of inflating and deflating tires. 

Throughout the test, technicians released air from trailer tires equipped with the ATIS. As stated 

earlier, deflating tires after properly setting the pressure is not recommended. Instead, the authors 

recommend that the manufacturer advise the technicians to allow the ATIS to maintain the tire 

pressures. The technicians would not release air from the tires, accepting that the pressure was 

set to the recommended cold pressure setting.
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63 

5. CONCLUSIONS 

This section reviews the findings from the entire field test. The team conducted a hypothesis 

analysis to determine the success of the field test, based on the hypotheses established as part of 

the field test plan. In addition, the team conducted a cost-benefit analysis to identify the ROI for 

the purchase of the TPMS and ATIS for a single unit (tractor and trailer/tanker).

5.1 HYPOTHESIS ANALYSIS

The authors analyzed the hypotheses established as part of the test plan for the field test. The 

analysis determined that each of the hypotheses met one of three criteria: valid, inconclusive, or 

invalid. Due to the variations between the test fleets, the team independently evaluated the 

findings from each fleet against the hypotheses. Table 26 summarizes these evaluations, 

including the analysis technique used to evaluate each hypothesis. The evaluation concluded that 

60 percent of the hypotheses were valid using the field test data. The following subsections detail 

the basis for these findings. The authors conducted a statistical evaluation of the appropriate 

hypothesis to determine the significance of the conclusion. The detailed analysis of each 

hypothesis provides the results. Note: The statistical evaluations assumed that the control fleet

and test fleet were homoscedastic (i.e., having equal variance). The statistical evaluation 

assumed a two-tailed test, with α = 0.05 to test for 95-percent confidence.

Table 26. Analysis of field test hypotheses. 

No. Hypothesis Analysis CLI GFS

1 The use of TPMS and ATIS will 

increase the life of TPMS/ATISequipped tires. 

Analyze tread wear per 

mile. Analyze based on 

tire location (steer, 

drive, trailer). 

Valid Inconclusive

2 The use of TPMS and ATIS will 

reduce the fuel consumption of 

equipped tractors.

Analyze average 

mi/gal. 

Valid Valid

3 The use of TPMS and ATIS will 

reduce road calls for damaged/flat 

tires for equipped tractor-trailers.

Analyze overall road 

calls. Analyze tire 

failures.

Inconclusive Valid

4 TPMS and ATIS will accurately 

display the tire pressure of 

equipped tractor-trailers at the 

driver interface.

Analyze accuracy of 

equipment. 

Inconclusive Valid

5 TPMS and ATIS will not introduce 

unscheduled maintenance that will 

affect the day-to-day fleet 

operations. 

Analyze unscheduled 

maintenance actions. 

Valid Valid

Hypothesis #1—The use of TPMS and ATIS equipment will increase the life of TPMS and 

ATIS-equipped tires. 

The team analyzed tread-depth measurements and tire replacement reports to calculate the tire 

wear incurred and the miles traveled for each tire replaced during the field test. The team plotted 
64

the data on a scatter plot to generate trend lines showing the rate of tire wear at each axle 

location. 

Conclusion: At CLI, the use of TPMS equipment increased the life of the drive tires of TPMSequipped units. The steer and tanker tires experienced nearly identical wear rates. The trend lines 

for the tire wear rate (as shown in Figure 42) validated that the test fleet’s drive tires experienced 

a slower rate of wear than the control fleet’s drive tires. In addition, the wear rate calculations 

provided in Figure 42 further clarify the rate of wear at each axle location. The statistical 

evaluation confirmed the wear rate of the drive tires to be significant at the 95-percent 

confidence level (t = 38.4 [Mileage] and 5.8 [Variable A]). The wear rates of the steer and trailer 

tires were nearly identical.

Figure 42. Graph. Hypothesis #1—comparison of tire wear per mile (CLI).

At GFS, the ability of TPMS or ATIS to increase the life of TPMS and ATIS-equipped tires was 

inconclusive. The tread-depth measurements provided during the field test did not provide a 

large enough sample size to determine statistical significance. The installation of the monitoring 

systems unintentionally skewed the tire replacement schedule. Complete sets of tractor and 

trailer tires were replaced earlier than they normally would have been on the test fleet in order to 

install the wheel modules during the initial phase of the field test. As a result, the control tires 

experienced a significantly higher tire replacement rate during the field test. By extending the 

analysis period (Figure 43), the team determined that a significant number of the test fleet’s tires 

were replaced just prior to the official start of the field test. The advantages of TPMS and ATIS 

with respect to increased tire life could not be proven on the GFS fleet.
65

Figure 43. Graph. Hypothesis #1—comparison of tire wear (GFS).

Hypothesis #2—The use of TPMS and ATIS will reduce the fuel consumption of equipped 

tractor-trailers.

The team analyzed fleet fuel reports to calculate the average monthly fuel economy of the 

control fleet and the test fleet. At CLI, the fleet supervisor provided a fuel report at the end of 

each month of the field test. The fuel report summarized the total fuel used and mileage 

accumulated during the month for each tractor in the fleet. At GFS, the team downloaded the fuel 

logs for each tractor. The fuel logs recorded the current odometer reading and the gallons of fuel 

added for each fueling operation. 

Conclusion: The use of TPMS and ATIS equipment reduced the fuel consumption of equipped 

tractors for both fleets. CLI collected fuel data between May 2008 and May 2009 (as shown in 

Figure 44). The test fleet improved its average fuel economy by 0.085 mi/gal as compared to the 

control fleet, an average improvement of 1.4 percent. The statistical evaluation confirmed the 

value to be significant at the 95-percent confidence level. Specifically, the fuel economy 

improvement was achieved with 97.7-percent confidence (t = 2.29, 95-percent confidence =

1.97).
66

Figure 44. Hypothesis #2—fuel economy analysis (CLI).

GFS collected fuel data between June 2009 and November 2010 (as shown in Figure 45). The 

test fleet improved its average fuel economy by 0.09 mi/gal as compared to the control fleet, an 

average improvement of 1.4 percent. The statistical evaluation confirmed the value to be 

significant at the 95-percent confidence level. Specifically, the fuel economy improvement was 

achieved with 99.996-percent confidence (t = 4.13, 95-percent confidence = 1.96).

Figure 45. Graph. Hypothesis #2—fuel economy analysis (GFS).

Hypothesis #3—The use of TPMS and ATIS will reduce road calls for damaged/flat tires for 

equipped tractor-trailers.

The team reviewed failure reports and maintenance records to identify instances of road calls

during the field test. The team analyzed the findings based on the number of road calls per 

million miles per axle.
67 

Conclusion: The use of TPMS and ATIS reduced the overall number of road calls on GFS’s test 

fleet. GFS reported fewer road calls on the test fleet’s drive axles and reefer pup axles (as shown 

in Table 27). The steer axles of both the test and control fleets did not require a road call during 

the field test. The 50-foot trailer axles experienced more failures on the test fleet. Although 

findings were not statistically significant at the 95-percent confidence level, this value was 

achieved with 80-percent significance (t = 1.27, 95-percent confidence = 1.99), which is too low 

to draw a solid, statistically significant conclusion, but indicates a trend that the test vehicles had 

fewer road calls than the control fleet.

Table 27. Hypothesis #3—road calls per million miles, by axle. 

Axle Type GFS CLI

Test Fleet Steer Axle 0.0 0.0

Test Fleet Drive Axle 0.7 1.5

Test Fleet Trailer Axle—Pup 1.2 N/A

Test Fleet Trailer Axle—50-foot 4.1 –

Test Fleet Trailer Axle—Tanker – 0.5

Test Fleet Total 6.0 2.0

Control Fleet Steer Axle 0.0 1.1

Control Fleet Drive Axle 1.0 0.0

Control Fleet Trailer Axle—Pup 3.8 –

Control Fleet Trailer Axle—50-foot 3.1 –

Control Fleet Trailer Axle—Tanker – 0.0

Control Fleet Total 7.9 1.1

The use of TPMS and ATIS did not reduce the overall number of road calls on CLI’s test fleet.

Only the steer tires of the test fleet experienced a lower number of road calls. The drive and 

tanker axles experienced more road calls on the test fleet. 

Hypothesis #4—TPMS and ATIS will accurately display the tire pressure of equipped tractortrailers at the driver interface.

The team evaluated the periodic inspection reports submitted by the fleet supervisors. The 

technicians recorded tire pressures at each tire location using a calibrated tire pressure gauge. For 

the monitoring systems, the technicians also recorded the pressures displayed on the in-cab 

display. The inflation systems were supposed to maintain a preset tire pressure.

Conclusion: Overall, the field test did not conclusively prove that the TPMS and ATIS 

accurately displayed the tire pressure of equipped tractors, trailers, and tankers. Each fleet 

experienced minor issues with the equipment, which are explained below. 

At CLI, the ATIS accurately inflated the tanker tires to the system’s preset pressure. Of the 788 

tire pressure measurements, the inflation system properly inflated the tires for 98 percent of the 

measurements. The technicians recorded 18 manual tire pressure measurements that did not meet 

the factory-set threshold for the ATIS. The inaccurate tire pressure measurements were found 

during five periodic inspections. In three of the inspections, the manual tire measurements were 

within 2 psi of the expected tire pressure. For the remaining two periodic inspections, the 
68

technicians measured 105 psi at all tire locations on one tanker and 100 psi at all tire locations on 

a second tanker. These measurements were assumed to be one-off occurrences, not affecting the 

overall accuracy of the inflation system.

At CLI, the team could not conclusively prove that the TPMS accurately displayed the tire 

pressures on the in-cab display. The technicians’ feedback during interviews provided subjective 

evidence on the accuracy of the in-cab display. The technicians stated that the system accurately 

represented the tire pressures after faulty wheel sensors were identified and replaced.

Unfortunately, the objective measurements obtained from the periodic inspection reports did not 

reflect the technicians’ opinions. The reports frequently recorded system tire pressures that were 

higher than the measured tire pressures. The suspected cause of the discrepancy is the 

methodology for collecting tire pressure data. The team suspects that the technicians recorded the 

pressures represented at the in-cab display after adjusting the tire pressures due to low readings 

identified during the manual tire pressure measurements. In these cases, the TPMS would be 

correctly representing the current tire pressure of 110 psi, but analysis of tire pressure data 

cannot prove this. In addition, faulty wheel sensors also influenced the accuracy of the recorded 

tire pressure data. As the sensors failed, the in-cab display reported excessively high (i.e., 120 

psi) or excessively low (i.e., 40 psi) tire pressures. The technicians verified these inaccurate tire 

pressure readings by conducting manual pressure measurements. The manual measurements 

validated that the tire pressures were inflated to the recommended tire pressure. In summary, the 

findings could not prove the accuracy of the monitoring system.

At GFS, the team could not conclusively prove that the ATIS accurately inflated the trailer tires 

to the system’s preset pressure. Throughout the field test, the technicians reported that the 

equipped trailers had tire pressures exceeding the fleet’s recommended inflation pressure. An 

investigation could not determine why the ATIS overinflated the tires. The manufacturer 

inspected the regulator valves and verified that they were properly set to 95 psi, the 

recommended inflation pressure. The increased tire pressures may be attributed to the extended 

layovers during Michigan’s cold evenings. Tire pressures drop during colder temperatures. When 

the trailer power is restored, the ATIS registers a low tire pressure condition and inflates the tire 

pressures to the preset pressure. As the temperature in the tire rises, the tires become 

overinflated. The tire industry does not recommend adjusting tire pressures due to overinflation, 

as the tires return to the proper pressure as they cool. In summary, the equipped trailers 

experienced overinflated tires, which could not be attributed to a fault in the system.

At GFS, the team qualitatively determined that the TPMS accurately displayed the tire pressures 

on the in-cab display. During interviews, the technicians raised no concerns with the in-cab 

display. They stated that the system operated correctly after the tractors and the trailers were 

linked. Unfortunately, a review of the field test data did not reflect these findings. A pressure 

differential was frequently recorded between the system tire pressure measurement and the 

manual tire pressure measurement. The team conducted a thorough review of the discrepancies 

and identified a repeatable pattern. If a significant difference was recorded between the two 

measurements, the manual measurement would be recorded as 95 psi, the recommended fleet tire 

pressure. The team suspects that the technicians would record the in-cab display prior to 

adjusting the tire pressures. If an adjustment was required, the technicians adjusted the tire 

pressures and then recorded the new tire pressure setting. As a result, the manual tire pressure did 

not equate to the original system tire pressure. The team conducted an analysis of the remaining 
69 

data and determined that the system tire pressures were routinely within 2 psi of the manual tire 

pressure. The team did not conduct an extensive analysis of these data, as the final number of 

data points yielded a sample size that was not statistically significant. 

Hypothesis #5—TPMS and ATIS technologies will not introduce unscheduled maintenance 

that will affect day-to-day fleet operations. 

The team conducted several informal interviews and asked the maintenance technicians to 

complete a written assessment after the test was completed. The technicians provided feedback 

on the maintainability of the equipment and the effect on daily maintenance tasks. In addition, 

the team monitored unscheduled maintenance tasks related to system failures and equipment 

maintenance.

Conclusion: The TPMS and ATIS equipment did not introduce unscheduled maintenance that 

affected day-to-day fleet operations. The team sought to ensure that equipment failures and 

periodic maintenance requirements did not hinder the fleet’s operations. Although the field test 

identified various system reliability issues, these issues did not require the test fleet to be 

removed from the operating fleet. For example, the failure of the wheel sensors rendered portions 

of the IVTM system inoperable, but did not require the tractor to be removed from service.

5.2 COST-BENEFIT ANALYSIS

The findings from this report may encourage the use of TPMS or ATIS technologies due to their 

potential to reduce CMV operating costs. The authors conducted a cost-benefit analysis of TPMS 

and ATIS use to determine the length of time required to recover the costs of purchasing TPMS 

and/or ATIS for a tractor-trailer unit. The authors conducted the ROI analysis for both GFS (a 

low-mileage, standard-tire fleet) and CLI (a high-mileage, wide-base tire fleet). Table 28

presents the assumptions for conducting the ROI analysis. The fuel costs represent the fuel prices 

identified in mid-2011, and potential high and low fuel prices in the future. The authors 

researched tire prices for Michelin standard and wide-base tires. The prices for Michelin tires 

were used, as both fleets currently use these tires. Finally, the allowable tire wear is based on the 

tire wear permitted for CLI’s drive axles. Because these axles were the only axles to show 

significant improvement in tire wear, they were the focus of this analysis.

Table 28. Assumptions for ROI calculations. 

Characteristic GFS CLI

Average Mileage (Daily) 225 450

Average Mileage (Monthly) 6,840 13,680

Average Mileage (Yearly) 81,450 162,900

Estimated Diesel Fuel Cost (Current) $3.976 $3.976

Estimated Diesel Fuel Cost (High) $5.000 $5.000

Estimated Diesel Fuel Cost (Low) $3.000 $3.000

Allowable 32nds of Tire Wear 11 11

Standard Tire Cost $329.00 $329.00

Wide-base Tire Cost – $795.00
70 

Table 29 identifies the commercial cost of each TPMS and ATIS used in the field test. The prices 

incorporate any discounts offered due to bulk purchases. For the ROI analysis, the team 

estimated the cost of a complete system to include a TPMS on the tractor and an ATIS on the 

trailer, for a total system cost of $1,535. 

Table 29. Cost of TPMS equipment. 

System Cost

PSI—Tanker/Trailer $750

IVTM—Tractor $785

Tire-SafeGuard—Tractor $709

Tire-SafeGuard—Trailer $503

Estimated Cost for Tractor-trailer $1,535

The analysis showed that the test fleets experienced a 1.4-percent improvement in fuel economy. 

Using the average mi/gal calculated previously, the authors identified a 1.4-percent savings in 

monthly and annual fuel costs (as shown in Table 30, Table 31, and Table 32). 

For CLI, a single equipped tractor would save $130 per month or $1,544 per year with the diesel 

fuel price set at $3.976 per gallon. The savings would drop to $98 per month and $1,165 per year 

with diesel fuel priced at $3.00 per gallon. With a lower annual mileage accumulation, the 

equipped GFS tractors experienced lower annual fuel savings. They would save $680 per year 

with diesel fuel priced at $3.976 per gallon and $513 per year with diesel fuel priced at $3.00 per 

gallon. 
71 

Table 30. ROI calculation for fuel savings (fuel at $3.976 per gallon). 

Characteristic GFS Test GFS Control CLI Test CLI Control

Average Annual mi/gal 6.59 6.50 6.19 6.10

Monthly Fuel Usage 1,037.94 1,052.31 2,210.02 2,242.62

Monthly Fuel Costs $4,126.83 $4,183.98 $8,787.02 $8,916.67

Percent Improvement 1.4% – 1.5% –

Calculated Savings Over Control $57.14 – $129.64 –

Annual Fuel Usage 12,359.64 12,530.77 26,316.64 26,704.92

Annual Fuel Costs $49,141.91 $49,822.34 $104,634.96 $106,178.75

Percent Improvement 1.4% – 1.5% –

Calculated Savings Over Control $680.43 – $1,543.79 –

Table 31. ROI calculation for fuel savings (fuel at $3.000 per gallon). 

Characteristic GFS Test GFS 

Control

CLI Test CLI Control

Average Annual mi/gal 6.59 6.50 6.19 6.10

Monthly Fuel Usage 1,037.94 1,052.31 2,210.02 2,242.62

Monthly Fuel Costs $3,113.81 $3,156.92 $6,630.05 $6,727.87

Percent Improvement 1.4% – 1.5% –

Calculated Savings Over Control $43.11 – $97.82 –

Annual Fuel Usage 12,359.64 12,530.77 26,316.64 26,704.92

Annual Fuel Costs $37,078.91 $37.592.31 $78,949.92 $80,114.75

Percent Improvement 1.4% – 1.5% –

Calculated Savings Over Control $513.40 – $1,164.83 –
72 

Table 32. ROI calculation for fuel savings (fuel at $5.000 per gallon). 

Characteristic GFS Test GFS 

Control

CLI Test CLI Control

Average Annual mi/gal 6.59 6.50 6.19 6.10

Monthly Fuel Usage 1,037.94 1,052.31 2,210.02 2,242.62

Monthly Fuel Costs $5,189.68 $5,261.54 $11,050.08 $11,213.11

Percent Improvement 1.4% – 1.5% –

Calculated Savings Over Control $71.86 – $163.03 –

Annual Fuel Usage 12,359.64 12,530.77 26,316.64 26,704.92

Annual Fuel Costs $61,798.18 $62,653.85 $131,583.20 $133,524.59

Percent Improvement 1.4% – 1.5% –

Calculated Savings Over Control $855.67 – $1,941.39 –

Although wheel-wear savings are based on the findings from the drive tires of the CLI tractors, 

the analysis calculates the savings based on the number of drive tires in each fleet (i.e., four 

drives at CLI and eight drives at GFS). Table 33 shows the annual savings in tire purchases. The 

authors conducted the ROI analysis based on a replacement of tires after 11/32nds of an inch of 

wear, which was the replacement parameter for the drive tires at CLI. In addition, the ROI 

analysis estimates the overall savings based on the pricing of standard tires for GFS and widebase single tires for CLI. During the field test, the TPMS-equipped vehicles experienced a 20-

percent reduction in tire wear as compared to the control fleet. The equipped CLI tractor-tankers 

saved $117 per month in tire purchases and $1,389 annually. The equipped GFS tractor-trailers 

saved $48 per month in tire purchases and $575 annually.

Table 33. ROI calculations for tire replacements due to wear. 

Characteristic GFS Test GFS

Control

CLI Test CLI

Control

Average Drive Axle Tire Wear

(32nds of Wear Per Million Miles)

125 154.5 125 154.5

Monthly 32nds of Wear/Tire 0.86 1.06 1.71 2.11

Monthly 32nds of Wear/Tractor 6.84 8.45 6.84 8.45

Monthly Tires Replaced/Tractor 0.62 0.77 0.62 0.77

Monthly Tire Cost/Tractor $204.58 $252.86 $494.35 $611.01

Percent Improvement 19% – 19% –

Calculated Savings Over Control $48.28 – $116.67 – 

Annual 32nds of Wear/Tire 10.18 12.58 20.36 25.17

Annual 32nds of Wear/Tractor 81.45 100.67 81.45 100.67

Annual Tires Replaced/Tractor 7.40 9.15 7.40 9.15

Annual Tire Cost/Tractor $2,436.10 $3,011.01 $5,886.61 $7,275.85

Percent Improvement 19% – 19% –

Calculated Savings Over Control $574.92 – $1,389.24 –
73 

The analysis showed that the equipped tractor-trailers eliminated an average of 1.1 road calls per 

million miles traveled. The authors estimated the cost of a single road call and analyzed the 

overall savings per equipped tractor-trailer, as shown in Table 34. The complete cost incurred by 

a fleet for a single road call includes the labor billed by the roadside service provider, the labor 

lost to the driver, and the cost of a replacement tire. As stated earlier, the authors estimated the 

cost of a standard tire for GFS and a wide-base single tire for CLI. The study estimated the cost 

of a single road call at $797 for GFS and $1,265 for CLI. Using these estimates, GFS-equipped 

tractor-trailers saved $72 annually. CLI-equipped tractor-tankers saved $227 annually. 

Table 34. ROI calculations for road calls eliminated. 

Characteristic GFS Test GFS

Control

CLI Test CLI

Control

Average Road Call Differential (Per Million Miles) Baseline 1.1 Baseline 1.1

Road Call Costs: On-call Labor $265.00 $266.00 $267.00 $268.00

Road Call Costs: Driver Pay Lost $203.13 $203.13 $203.13 $203.13

Cost of Driver Pay Lost: Driver Pay/Mile $1.25 $1.25 $1.25 $1.25

Cost of Driver Pay Lost: Average Time Delayed 2.5 2.5 2.5 2.5

Cost of Driver Pay Lost: Average Speed (mi/h) 65 65 65 65

Cost of Driver Pay Lost: Average Miles Lost 162.5 162.5 162.5 162.5

Total Cost of Road Call (Including Tire) $797.13 $797.13 $1,265.13 $1,266.13

Monthly Savings: Monthly Road Calls 0 0.01 0 0.02

Monthly Savings: Monthly Cost of Road Calls/Tractor $0 $6.01 $0 $19.05

Calculated Savings Over Control $6.01 – $19.05 –

Annual Savings: Annual Road Calls Savings 0 0.09 0 0.18

Annual Savings: Annual Cost of Road Calls/Tractor

Savings

$0 $71.51 $0 $226.88

Calculated Annual Savings Over Control $71.51 – $226.88 –

In summary, the reduction in fuel costs and tire purchases offered the largest savings for 

equipped tractor-trailers. The ROI analysis calculated the overall annual savings to be between 

$3,557.51 (CLI with $5.00 diesel fuel prices) and $1,159.82 (GFS with $3.00 diesel fuel prices). 

Figure 46 shows the complete results. 
74

Figure 46. Chart. Annual savings per TPMS/ATIS-equipped tractor-trailer.

CLI could recover the initial cost of the installed equipment in less than 6 months of operation at 

current fuel costs, as shown in Figure 47. CLI would experience a quick ROI due to the high cost 

of the wide-base single tires and high daily mileage. In comparison, GFS has a lower daily 

mileage and uses standard-width tires, which would require less than 14 months to recover the 

cost of the installed equipment. These findings are based on a single tractor-trailer. The fleet 

savings would increase with the installation of the TPMS and/or ATIS equipment on additional 

vehicles.
75

Figure 47. Graph. Accumulated monthly savings per TPMS/ATIS-equipped tractor-trailer.
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REFERENCES

1. Fisher, P., Kreeb, R., & Nicosia, B. (December 2003). Commercial Vehicle Tire 

Condition Sensors. Task Order 5 of the Commercial Vehicle Technology Diagnostics and 

Performance Enhancement Program.

2. Brady, S., Fisher, P., Kreeb R., & Nicosia, B. (October 2006). Tire Pressure Monitoring 

and Maintenance Systems Performance Report. Task Order 8 of the Commercial Vehicle 

Technology Diagnostics and Performance Enhancement Program.

3. Van Order, D., Skorupski, D., Stinebiser, R., & Kreeb, R. (February 2009). Fleet Study of 

Brake Performance and Tire Pressure Sensors. Task Order 9 of the Commercial Vehicle 

Technology Diagnostics and Performance Enhancement Program.
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