Improving Heavy-Duty Diesel Truck 

Ergonomics to Reduce Fatigue and Improve 

Driver Health and Performance

December 2010
FOREWORD

In this study sponsored by the Federal Motor Carrier Safety Administration, noise levels, wholebody vibration from the driver and passenger seats, and the in-cab air quality of heavy-duty 

diesel trucks were measured while the vehicles were parked with the engine idling at a truck stop 

rest area and while they were driven over a prescribed route. The air quality was determined by 

measuring in-cab concentrations of carbon monoxide, oxides of nitrogen, and particulate matter 

less than 2.5 μm in aerodynamic diameter. These factors were selected because they are 

suspected to have some influence on the health and performance of drivers. Also the intention 

was that the data sets will serve as baseline data from which future similar studies may determine 

if (new) truck designs have changed the existing state of these conditions for the drivers. 

Twenty-seven trucks from four manufacturers were tested. Model years of the trucks were 

between 2006 and 2008. 

This final report would be of interest to health and wellness professionals: occupational safety 

and health management, researchers, and academicians; commercial motor vehicle industry: 

drivers, carriers, manufacturers, and truck travel centers. 

NOTICE

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

in the interest of information exchange. The United States 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 United States Government does not endorse products or manufacturers named herein. Trade 

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

of this report.
Technical Report Documentation Page

1. Report No.

FMCSA-RRR-10-010

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

4. Title and Subtitle

IMPROVING HEAVY DUTY DIESEL TRUCK ERGONOMICS TO 

REDUCE FATIGUE AND IMPROVE DRIVER HEALTH AND 

PERFORMANCE

5. Report Date

December 2010

6. Performing Organization Code

7. Author(s)

Joshua S. Fu, James A. Calcagno III, Wayne T. Davis, J.A.M Boulet, and 

Jack F. Wasserman

8. Performing Organization Report No.

9. Performing Organization Name and Address

The University of Tennessee

Dept. of Civil & Environmental Engineering

1506 Middle Drive; 223 Perkins Hall

Knoxville, TN 37996

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

Department of Transportation

Federal Motor Carrier Safety Administration

1200 New Jersey Ave SE

Washington, DC 20590

13. Type of Report

Final Report 

14. Sponsoring Agency Code

15. Supplementary Notes

This research was sponsored by the Federal Motor Carrier Safety Administration.

Contracting Officer’s Technical Representative was Albert Alvarez.

16. Abstract

Factors are suspected to influence health and performance of drivers—noise level, seat vibration, and cabin air 

quality of heavy-duty diesel trucks—were measured while vehicles were parked with engine idling and driven. 

Resulting data will serve as baseline data from which future similar studies may determine if new truck designs 

have changed the existing state of these conditions for long-haul freight truck drivers. Twenty-seven trucks (model 

years 2006–2008) from four manufacturers were tested. Overall in-cab noise levels were found to be below 8-hour

standard limit values. Results indicated slightly higher noise levels occurred while driving on interstates compared

to driving on the State highways. Average vibrations from the seats were generally found to be below standard 

exposures for an 8-hour driving day. Air quality was determined by measuring in-cab concentrations of carbon 

monoxide (CO), nitrogen oxides (NOX), and particulate matter less than 2.5 microns aerodynamic diameter (PM2.5). 

Results indicated trucks have a tendency to self-pollute the cabs during periods of extended parked engine idling; 

the on-road concentrations were several magnitudes lower. CO and NOX concentrations were well below standard 

permissible exposure levels. However during several parked-idling scenarios, PM2.5 concentrations were slightly 

higher than ambient air quality standards. 

17. Key Words

Air quality, diesel, diesel truck, ergonomics, heavy duty, 

in-, noise, noise level, seats, vibration, whole18. Distribution Statement

No restrictions

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

129

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 1000 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 (2000 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 (2000 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

LIST OF ACRONYMS ..............................................................................................................IX

EXECUTIVE SUMMARY .....................................................................................................XIII

1. INTRODUCTION.................................................................................................................1

1.1 NOISE LEVEL..............................................................................................................1

1.2 WHOLE-BODY VIBRATION .....................................................................................3

1.3 AIR QUALITY..............................................................................................................7

2. OBJECTIVE .......................................................................................................................11

3. EXPERIMENTAL METHOD...........................................................................................13

3.1 SAMPLING EQUIPMENT.........................................................................................17

3.1.1 Noise Level ..................................................................................................... 17

3.1.2 Whole-Body Vibration.................................................................................... 17

3.1.3 Air Quality ...................................................................................................... 18

3.2 DATA ANALYSIS......................................................................................................20

4. RESULTS AND DISCUSSION .........................................................................................23

4.1 NOISE LEVEL............................................................................................................23

4.2 WHOLE-BODY VIBRATION ...................................................................................29

4.3 DRIVER’S SEAT CUSHION MONITORING...........................................................30

4.4 DUAL-SEAT MONITORING ....................................................................................35

4.4.1 Root Mean Square........................................................................................... 35

4.4.2 Crest Factor..................................................................................................... 39

4.4.3 Vibration Dose Values.................................................................................... 41

4.4.4 Jerk.................................................................................................................. 41

4.5 AIR QUALITY............................................................................................................41

4.5.1 Calibration of Measured Concentrations........................................................ 42

4.5.2 Truck Air Exchange Rates.............................................................................. 44

4.5.3 Parked-Idling Test........................................................................................... 45

4.5.4 On-Road Test.................................................................................................. 52

4.5.5 In-Cab Air Filters............................................................................................ 58

4.5.6 Chemical Analysis of Particulate Matter........................................................ 60

5. CONCLUSIONS .................................................................................................................65
iv

5.1 NOISE LEVEL............................................................................................................65

5.2 WHOLE-BODY VIBRATION ...................................................................................65

5.3 AIR QUALITY............................................................................................................66

5.3.1 Parked-Idling Test........................................................................................... 66

5.3.2 On-Road Test.................................................................................................. 66

6. RECOMMENDATIONS....................................................................................................69

REFERENCES.............................................................................................................................83
v

LIST OF APPENDICES

APPENDIX A—EXPOSURE STANDARDS OR RECOMMENDED VALUES .................71

APPENDIX B—ON-ROAD IN-CAB AVERAGE NOISE LEVELS PER TRUCK .............72

APPENDIX C—DRIVER SEAT CUSHION RMS VALUES PER ROADWAY .................73

APPENDIX D—DRIVER SEAT CUSHION RMS VALUES PER ROADWAY .................74

APPENDIX E—DRIVER BACK REST RMS VALUES PER ROADWAY.........................75

APPENDIX F—PASSENGER SEAT CUSHION RMS VALUES PER ROADWAY..........76

APPENDIX G—DRIVER SEAT CUSHION VDV PER ROADWAY...................................77

APPENDIX H—DRIVER BACK REST VDV PER ROADWAY..........................................79

APPENDIX I—PASSENGER SEAT CUSHION VDV PER ROADWAY............................81
vi

LIST OF FIGURES (AND FORMULAS)

Figure 1. Equation. Instantaneous sound pressure level equation ...................................................1

Figure 2. Equation. Average sound level equation for discrete sound-level measurements ...........2

Figure 3. Diagram. Vibration measurement coordinate system for the seated person ....................4

Figure 4. Equation. Weighted root mean square acceleration equation ..........................................5

Figure 5. Equation. Crest factor equation ........................................................................................6

Figure 6. Equation. Fourth-power vibration dose method equation ................................................7

Figure 7. Photo. Trucks parked at a study-selected travel center rest area....................................13

Figure 8. Map. Map showing the driving route along I-40, US-27 & TN-68, and I-75................14

Figure 9. Map. Relief map showing terrain contrast along the driving route................................15

Figure 10. Equation. Exponential dilution law..............................................................................16

Figure 11. Diagram. Transducer placement for each HDDV ........................................................18

Figure 12. Photo. Assorted equipment located in sleeper berth area of truck ...............................20

Figure 13. Graph. LS means peak noise level vs. truck manufacturer ..........................................24

Figure 14. Graph. LS means peak noise level vs. roadway ...........................................................25

Figure 15. Graph. LS means peak noise level vs. roadway and manufacturer..............................25

Figure 16. Graph. LS means maximum equivalent noise level vs. truck manufacturer................26

Figure 17. Graph. LS means maximum equivalent noise level vs. roadway.................................26

Figure 18. Graph. LS means max equivalent noise level vs. roadway and manufacturer.............26

Figure 19. Graph. LS means Leq from Integrator-1 vs. truck manufacturer ..................................27

Figure 20. Graph. LS means Leq from Integrator-1 vs. roadway...................................................27

Figure 21. Graph. LS means Leq from Integrator-1 vs. roadway and manufacturer......................28

Figure 22. Graph. LS means Leq from Integrator-3 vs. truck manufacturer.................................28

Figure 23. Graph. LS means Leq from Integrator-3 vs. roadway..................................................29

Figure 24. Graph. LS means Leq from Integrator-3 vs. roadway and manufacturer.....................29

Figure 25. Graph. LS means x-axis vibration vs. truck manufacturer...........................................30

Figure 26. Graph. LS means x-axis vibration vs. roadway............................................................31

Figure 27. Graph. LS means x-axis vibration vs. roadway and manufacturer...............................31

Figure 28. Graph. LS means y-axis vibration vs. truck manufacturer...........................................31

Figure 29. Graph. LS means y-axis vibration vs. roadway............................................................32

Figure 30. Graph. LS means y-axis vibration vs. roadway and manufacturer...............................32

Figure 31. Graph. LS means z-axis vibration vs. truck manufacturer...........................................33

Figure 32. Graph. LS means z-axis vibration vs. roadway............................................................33

Figure 33. Graph. LS means z-axis vibration vs. roadway and manufacturer...............................33

Figure 34. Graph. LS means Σ (comfort) value vs. truck manufacturer........................................34

Figure 35. Graph. LS means Σ (comfort) value vs. roadway.........................................................34

Figure 36. Graph. LS means Σ (comfort) value vs. roadway and manufacturer ...........................34

Figure 37. Graph. LS means comfort value (driver cushion) vs. truck manufacturer...................36

Figure 38. Graph. LS means comfort value (driver cushion) vs. roadway....................................36

Figure 39. Graph. LS means comfort value (driver cushion) vs. roadway and manufacturer.......36
vii

Figure 40. Graph. LS means comfort value (driver back) vs. truck manufacturer........................37

Figure 41. Graph. LS means comfort value (driver back) vs. roadway.........................................37

Figure 42. Graph. LS means comfort value (driver back) vs. roadway and manufacturer............37

Figure 43. Graph. LS means comfort value (passenger cushion) vs. truck manufacturer.............38

Figure 44. Graph. LS means comfort value (passenger cushion) vs. roadway..............................38

Figure 45. Graph. LS means comfort value (passenger cushion) vs. roadway and manufacturer.38

Figure 46. Graph. OPC to TEOM calibrations curve for PM2.5.....................................................43

Figure 47. Graph. DRam to TEOM calibration curve for PM2.5 ...................................................43

Figure 48. Graph. TEOM corrected DRam vs. OPC calibration data for PM2.5............................43

Figure 49. Graph. Decay curve for CO2 recirculaton air shifting to fresh-air mode .....................45

Figure 50. Graph. Overall average 1-h CO and NOX concentrations from parked-idling test ......46

Figure 51. Graph. Overall average 1-h PM2.5 concentrations from parked-idling test..................46

Figure 52. Graph. LS means CO concentration vs. truck manufacturer........................................47

Figure 53. Graph. LS means CO concentration vs. engine/HVAC condition ...............................47

Figure 54. Graph. LS means CO concentration vs. engine/HVAC and manufacturer..................48

Figure 55. Graph. LS means NOX concentration vs. truck manufacturer.....................................48

Figure 56. Graph. LS means NOX concentration vs. engine/HVAC condition.............................49

Figure 57. Graph. LS means NOX concentration vs. engine/HVAC and manufacturer...............49

Figure 58. Graph. LS means PM2.5 (OPC) concentration vs. truck manufacturer.......................50

Figure 59. Graph. LS means PM2.5 (OPC) concentration vs. engine/HVAC condition ................50

Figure 60. Graph. LS means PM2.5 (OPC) concentration vs. engine/HVAC and manufacturer .50

Figure 61. Graph. LS means PM2.5 (DRam) concentration vs. truck manufacturer ....................51

Figure 62. Graph. LS means PM2.5 (DRam) concentration vs. engine/HVAC condition .............51

Figure 63. Graph. LS means PM2.5 (DRam) concentration vs. engine/HVAC and manufacturer51

Figure 64. Graph. Overall average 15-min CO and NOX concentrations from on-road test.........53

Figure 65. Graph. Overall average 15-min PM2.5 concentrations from on-road test.....................53

Figure 66. Graph. LS means CO concentration vs. truck manufacturer........................................54

Figure 67. Graph. LS means CO concentration vs. roadway.........................................................54

Figure 68. Graph. LS means CO concentration vs. roadway and truck manufacturer ..................54

Figure 69. Graph. LS means NOX concentration vs. truck manufacturer......................................55

Figure 70. Graph. LS means NOX concentration vs. roadway ......................................................55

Figure 71. Graph. LS means NOX concentration vs. roadway and truck manufacturer................55

Figure 72. Graph. LS means PM2.5 (OPC) concentration vs. truck manufacturer.........................56

Figure 73. Graph. LS means PM2.5 (OPC) concentration vs. roadway..........................................56

Figure 74. Graph. LS means PM2.5 (OPC) concentration vs. roadway and truck manufacturer ...56

Figure 75. Graph. LS means PM2.5 (DRam) concentration vs. truck manufacturer......................57

Figure 76. Graph. LS means PM2.5 (DRam) concentration vs. roadway.......................................57

Figure 77. Graph. LS means PM2.5 (DRam) concentration vs. roadway and truck manufacturer.57

Figure 78. Photo. Outside HVAC pre-filter accessible from the engine compartment .................58

Figure 79. Photo. Auxiliary air filtration system located under passenger seat ............................59

Figure 80. Photo. Auxiliary HVAC system located under sleeper berth not filtered ....................59
viii

Figure 81. Photo. Internal air-filter removed from auxiliary HVAC unit. ....................................59

Figure 82. Photo. TEM micrograph of PM during parked-idling test (0.2-μm scale)...................60

Figure 83. Photo. TEM micrograph of PM during parked-idling test (0.1-μm scale)...................61

Figure 84. Photo. TEM micrograph of PM during on-road test (0.2-μm scale)............................61

Figure 85. Photo. TEM micrograph of PM during on-road test (0.1-μm scale)............................62

LIST OF TABLES

Table 1. Comfort Reactions to a Vibration Environment (Seating Position) ..................................5

Table 2. Multivariate Correlations between Driver and Passenger Seating ..................................39

Table 3. Range of Values for Crest Factor from Driver and Passenger Seats...............................40

Table 4. Total Number of Trucks with CF Values Greater than 9 ................................................40

Table 5. Range of Values for Jerk from Driver and Passenger Seats............................................41

Table 6. Air Exchange Rates for a Subset of Trucks.....................................................................44

Table 7. Overall Average 1-h Concentrations from Parked-Idling Test........................................45

Table 8. Overall Average 15-min Concentrations from On-Road Test.........................................52

Table 9: Exposure Standards or Recommended Values................................................................71

Table 10: On-Road In-Cab Average Noise Levels Per Truck Manufacturer, and OSHA and ISO 

Integrator Measurements................................................................................................72

Table 11. Driver Seat Cushion RMS Values Axis of Translation or m/s2 Comfort vs. Roadway 73

Table 12. Driver Seat Cushion RMS Values Axis of Translation m/s2 or Comfort vs. Roadway 74

Table 13. Driver Back Rest RMS Values Axis of Translation m/s2 or Comfort vs. Roadway .....75

Table 14. Passenger Seat Cushion RMS Values Axis of Translation m/s2 or Comfort vs. 

Roadway.........................................................................................................................76

Table 15. Driver Seat Cushion VDV Axis of Translation m/s2 or Comfort vs. Roadway ............77

Table 16. Driver Back Rest VDV Axis of Translation m/s1.75 and Roadway................................79

Table 17. Passenger Seat Cushion VDV Axis of Translation m/s1.75 and Roadway .....................81
ix

LIST OF ACRONYMS

AC alternating current

A/C air conditioning

ACGIH American Conference of Governmental Industrial Hygienists

AER air exchange rate

AL action level

ANSI American National Standards Institute

av acceleration total value

aw acceleration weighted value

aWRMS acceleration weighted root mean square

C Concentration of gas at measurement interval

C0 concentration of gas at time zero

CF correction factor or crest factor

CL criterion level

CMV commercial motor vehicle

CO carbon monoxide

CO2 carbon dioxide

Conc Concentration

dB decibel scale

dBA decibel scale using the A-filter weighting

dBC decibel using the C-filter weighting

DC direct current

Deg Degree

DEWE Dewetron

DOF degrees of freedom

Dram DataRAM

EAV exposure action value

EC elemental carbon 
x

ELV exposure limit value

EPA Environmental Protection Agency

EU European Union

FEA finite element analysis

Exp exponential function

FMCSA Federal Motor Carrier Safety Administration

G Gram

HDDV heavy-duty diesel vehicle

HEPA High-Efficiency Particulate Air filter

HOS hours of service

Hp Horsepower

HVAC heating, ventilation, and air-conditioning

HVM human vibration meter

H Hour

HSD honest significant difference

I measurement interval

Id Identification

ID inside diameter

ISO International Organization for Standardization

K correction factor constant

Km/h kilometer per hour

LAeq equivalent continuous sound level, A-weighted

LAMax maximum recorded sound level, A-weighted

LAMin minimum recorded sound level, A-weighted

LAve average measured sound level

LBP lower back pain

Leq equivalent continuous sound level

Lp sound pressure level
xi

LS least-square

M Meter

Max Maximum

MBS multi-body simulation

Mfr Manufacturer

Min Minute

mi/h miles per hour

N sample count

N number of intervals

NA not available

NAAQS National Ambient Air Quality Standards

NIHL noise-induced hearing loss

NIOSH National Institute for Occupational Safety and Health

NO nitrogen monoxide or nitric oxide

NO2 nitrogen dioxide

NOX oxides of nitrogen or nitrogen oxides

OC organic carbon

OPC optical particle counter

OSHA Occupational Safety and Health Administration

P sound pressure

PA instantaneous sound pressure level, A-weighted

PB-PAH particulate bound polycyclic aromatic hydrocarbons

PEL permissible exposure limit

PM2.5 and PM10 particulate matter less than 2.5 and 10 μm in aerodynamic diameter

Ppb parts per billion by volume

Ppm parts per million by volume

Pref reference sound pressure level

Q specific or actual exchange rate
xii

Q exchange rate

REL recommended exposure limit

REML residual (or restricted) maximum likelihood estimation

RMS root mean square

Rpm revolutions per minute

S Second

SEM/EDS scanning electron microscopy with energy dispersive x-ray spectrometry

SPL sound pressure level

Stdev standard deviation

STEL short-term exposure limit

T total measurement time period

TEM transmission electron microscopy

TEOM tapered element oscillating microbalance

TC total carbon

ti time period at measurement interval

TLV threshold limit value

TruckId truck identification

TruckMfr truck manufacturer

TWA time-weighted average

VDV vibration dose value

VIN vehicle identification number

WBV whole-body vibration

WHO World Health Organization

μ Greek letter mu for micro

μg Microgram

μm Micrometer

∑ Greek letter sigma for summation symbol or comfort index

P probability or significance level
xiii

EXECUTIVE SUMMARY

PURPOSE

This study focused on measuring several factors that may influence the health and performance 

of long-haul freight truck drivers. The data sets will serve as baseline data for future similar 

studies that may determine whether new truck designs may have changed these factors. 

PROCESS

The evaluated factors were noise level, whole-body vibration (WBV) from driver and passenger 

seats, and the air quality inside the cabin. Noise data were collected continuously during the onroad driving test using an integrating, averaging sound-level meter. Vibration data were collected 

using transducer pads installed on the driver and passenger seats. For computer modeling 

purposes, vibration transducers also were installed on the cab and truck frame. However, 

computer modeling results will not be discussed in this report. The in-cab air quality was 

evaluated using emission analyzers for carbon monoxide (CO), oxides of nitrogen (NOX), and 

particulate matter less than 2.5-μm in aerodynamic diameter (PM2.5). The sample of heavy-duty 

diesel trucks included the latest-model-year vehicles available at the time of the study from four 

different truck manufacturers. Measurements were conducted while the trucks were parked with 

the engines idling at a truck-stop rest area and during an actual on-road driving episode that 

included interstates and State highways, over moderately steep and relatively flat terrains. The 

parked engine-idling test involved measuring in-cab air quality under several engine and heating, 

ventilation, and air-conditioning (HVAC) modes of operation. 

STUDY FINDINGS

Noise Level: Overall results indicated that the noise levels measured in the trucks during the onroad tests were well below the Occupational Safety and Health Administration (OSHA) 

permissible exposure level (PEL)—90 decibels (dBA)—and/or the National Institute for 

Occupational Safety and Health (NIOSH) recommended value—85 dBA for an 8-hour (h) work 

day.*

 

*

According to Federal Motor Carrier Safety Regulations (49 CFR part 393.94) the interior sound level at the driver’s seating position must not 

exceed 90 dBA, as measured when the truck is parked with all doors, windows, and vents closed; all power-operated accessories turned off; and, 

with the transmission in neutral, the engine is accelerated to—and stabilized at—either its maximum governed engine speed if it is equipped with 

an engine governor, or its maximum rated horsepower. The regulation does not specify a maximum time-weighted-average dBA level for an 8-h 

work day, which was the standard used in this study.

The noise levels in the test trucks also did not exceed the Action Level (AL), which is 50 

percent of the maximum PEL. When the current 11-h driving time limit is considered for the 

worst case truck, the estimated dose percent was still not exceeded for the AL. This study 

showed overall noise levels to be somewhat lower than those reported in the literature from other 

studies, which showed noise levels greater than the AL. Slightly higher noise levels were 

measured during interstate travel relative to State highway travel. It is believed that noise from 
xiv

tires, engine revolutions per minute (rpm), and wind impacting the cab at higher road speeds 

contributed to the elevated noise levels during interstate driving because higher road speeds are 

permitted on the interstate system. Slightly higher noise levels were also noticed while driving 

on steeper terrains relative to driving on flat terrain. Basically, the noise levels were similar 

across the truck manufacturers, although some slight differences were observed. 

Whole-body Vibration: Evaluation for seat vibration utilized the International Organization for 

Standardization (ISO) guidelines. Analysis of WBV from the driver and passenger seats involved 

two instrument measurement systems and two assessment methodologies. Overall results in all 

cases indicated that vibration from the seats was generally below the European Union (EU) 

exposure action level (EAV)—0.5 m/s2 for the root-mean square (RMS) and 9.1 m/s1.75 for the 

vibration dose value (VDV) methods for an 8-h day. Exposure limits were exceeded in a few 

trucks, but for the most part these were isolated and were probably due to the poor condition of 

the roadway pavement. Significant differences in WBV existed between truck manufacturers, 

and between interstate and State highway driving, with the higher WBV occurring on the rural 

highway. If the EAV is projected to the current 11-h limit just three or four vehicles came close 

or were actually over this limit but this occurred mostly in the y-axis, which is less serious than 

vibration in the z-axis because the z-axis is the linear direction of the spinal column for a seated 

person. The comfort index of the seats, in the majority of the trucks, fell within the “a little 

uncomfortable” region. This was one comfort indicator removed from the best possible rating, 

which is the “not uncomfortable” region. It should be noted that very few studies have been 

conducted in the United States on WBV from heavy-duty diesel truck seats. 

Air Quality

Nonetheless, the measured concentrations of CO for all engine/HVAC modes of operation were 

well below the OSHA 8-h time weighted average (TWA)—50 parts per million (ppm) by volume 

and should not pose health problems for the drivers sleeping in the cab during rest periods. The 

NOX concentrations were also below occupational or industrial exposure limits. However during 

several parked-idling scenarios, the PM2.5 concentrations were around the limits set by the U.S. 

Environmental Protection Agency (EPA) through the National Ambient Air Quality Standards 

(NAAQS) for the 24-h and annual means. It should be noted that these EPA standards are 

ambient air monitoring standards and that were set to protect general public health, including the 

health of sensitive populations such as asthmatics, children, and the elderly. In this study they 

were used for comparison purposes because industrial or workplace PM2.5 limits have not been 

established by OSHA. Primary and secondary NAAQS exist for CO, lead, nitrogen dioxide

: For the parked engine-idling tests, overall CO, NOX and PM2.5 concentrations were 

relatively low inside the cab when the truck engine and the HVAC system were in off modes.

Highest CO and NOX concentrations occurred during engine-on and HVAC in recirculation 

modes; high PM2.5 concentrations occurred during engine-on and HVAC in fresh-air mode and 

during engine-on and fan-off modes. The results demonstrate that long-haul trucks have a 

tendency to self-pollute the cab during extended periods of parked-idling conditions. Selfpollution occurs when a percentage of the vehicle’s own exhaust enters the cab. It is believed this 

problem and the close proximity of many trucks idling at the same time in the truck-stop rest 

areas create conditions for diesel exhaust to enter the cab via the HVAC system or naturally from 

air infiltration around window and door seals and other areas. These results were also in line with 

a similar study that measured in-cab concentrations during parked-engine idling conditions at 

another truck-stop rest area. 
xv

(NO2), particulate matter, ozone, and sulfur dioxide. The averaging times for the NAAQS are 

different from typical workplace averaging times. Areas not meeting these NAAQS are required 

to create an implementation plan to meet the standards within a certain time period. For PM2.5

the EPA regulatory language (40 CFR part 81) is expressed in terms of attainment levels 

establishing that the 3-year averages of a population-oriented monitor in the area must not 

exceed 35 μg/m3 and 15 μg/m3 for the 24-h and annual means, respectively. 

For the on-road tests, the in-cab concentrations of the three air pollutants were much lower than 

were the concentrations measured during the parked-idling tests. However, while driving on the 

interstate, the inside concentrations were slightly higher relative to the concentrations measured 

while driving on the State highway. This condition is thought to be caused by the higher vehicle 

densities normally present on the interstate—a larger number of vehicles producing a greater 

quantity of pollutants that enter trucks through their HVAC systems. Average CO, NOX, and 

PM2.5 concentrations during parked-idling were approximately 1.5, 7.1, and 3.0 times greater, 

respectively, than the average on-road concentrations. These results suggest that less of a chance 

exists for the exhaust of the truck to self-pollute the cab while the truck is driven than while it is 

parked and idling, and that the highway environment, rather than the truck itself, is the primary 

cause of the truck driver’s in-cab exposure to air pollutants. 

RECOMMENDATIONS

Results of this study suggest that the two main areas of concern are the overall perceived riding 

comfort index of the seats and the elevated PM2.5 concentrations measured in the cabin during 

several of the parked, engines idling conditions at the truck-stop rest area. Although the noise 

levels inside the cab were reasonably low, this fact was most likely the result of sound 

attenuation from cabin wall padding, privacy curtains, and floor carpeting installed by the truck 

manufacturer. In the future, if manufacturers decide to reduce material costs in the construction 

of truck cabs, the noise levels could rise and possibly become cause for alarm. 

Seating

While the seats for these test trucks were adequate in reducing WBV, opportunity still exists for 

improvements to be made on the comfort index since the levels reported in this study were not 

the best rating possible. In support of this view, several questionnaire-type studies in the past 

have also indicated driver seating discomfort. The potential for spinal damage from seating 

vibration is not well understood and should be investigated. Two additional areas that could have 

an impact on seat vibration should also be examined: the location of the fifth-wheel and the use 

of single-wide tires. The fifth-wheel is the coupling device used on trucks or tractors to connect 

trailers. The location of the fifth-wheel is not fixed and can be adjusted to distribute trailer load 

over the drive axles, thus influencing truck ride quality. Single-wide tires are slightly wider than 

: The sample of test trucks was relatively small in this study. At least 90 percent of the 

seats were manufactured by a single company. Also the vehicles were lease or rental-trucks, so it 

was likely that the standard (not the optional) seats were installed in the trucks for reasons of 

cost. Since a wider range of seats was not adequately represented in this study, it is unknown if 

all seats perform identically in the ability to attenuate vibration exposures for the driver. 

Therefore, it is recommended that a broader range of trucks are tested in future studies which 

will include more models from several different seat manufacturers. 
xvi

traditional dual tires and can replace the double tires on each end of a drive or trailer axle. By

reducing rolling friction, single-wide tires are a fuel savings innovation. 

Heavy-duty truck seats are basically air or pneumatically operated with multiple adjustments to 

control the cushion, lumbar (or back) support, isolator engagement, fore and aft adjustment, 

height adjustment, cushion angle, and armrest angle. For the most part, none of these features 

were controlled or standardized to any degree in this study. It is noteworthy that the same driver 

also drove all the test trucks, and he was very knowledgeable in the operation of the seats. 

Currently, human exposure guidelines do not reflect the relationships between poor posture and 

driving posture, various seat configurations (e.g., seat back/cushion reclining angle) and/or 

sitting postures (e.g., torso/knee angle) and possible adjustments of the seat relative to the 

steering wheel. Additional research is suggested to determine optimal active seat settings which 

can minimize WBV. Also, it may be necessary to develop an effective strategy to train drivers in 

the proper use of the seating adjustments, so that they use the seat controls to full effect. 

Air Quality

The idling engine self-pollutes the cab for the resting driver. Numerous trucks parked and idling 

together in close proximity at a truck-stop rest area also create the potential for air-quality 

problems in the cabs for the drivers, as well as for persons working at the truck-stop. Since a 

possible PM2.5 problem exists, it is also likely that other gaseous hydrocarbon emissions, such as 

1-3 butadiene, formaldehyde, or acetaldehyde, may be present in the cab during extended periods 

of parked idling. A diesel particulate matter exposure limit has been established by the U.S. Mine 

Safety and Health Administration (MSHA) for personal working in underground mines. This 

PEL is based on the airborne concentration of total carbon (TC). However, it should also be 

pointed out that the MSHA standard, while applicable in the mining workplace environment, 

does not apply to drivers who are resting in a travel center, as this is not defined at this time as a 

workplace environment. Additional research is needed to better define and identify whether other 

diesel engine combustion hydrocarbons, including TC, are present above acceptable workplace 

exposure limits inside the cabin during periods of idling. 

: Offering a recommendation in this area is somewhat complicated because the most 

straightforward solution for improving the air quality in the cabin during periods of parked idling 

would be simply to prohibit engine idling while a driver is resting in the sleeper berth. However, 

to do this would severely limit the driver’s use of the vehicle’s heat and air conditioning or 

comfort appliances such as microwave or television that depend on the idling engine to operate. 

The in-cab air quality during periods of parked-engine idling at truck-stop rest areas continues to 

be an issue which warrants further study. Design and testing of cabin air-filtration/purification 

systems are several possible areas for research. However, these systems, with typical low air 

flow rates may prove to be inadequate in reducing concentrations within the cabin environment 

because of the high cabin air exchange rates which exist in current cabs between inside and 

outside air, as measured and described elsewhere in this report. 

External HVAC systems have been reported to be successful in reducing in-cab pollutant

concentrations. Such systems use a high air exchange rate, which provides a mechanism for 

external air filtration while the truck engine is off, thus substantially reducing in-cab 

concentrations. Other technologies also are aimed at idle reduction, such as auxiliary power units 
xvii

(APU). The APU provides an alternative to the truck’s main engine when power is needed for 

electricity or heating and cooling the cab during rest periods.
xviii

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1

1. INTRODUCTION

The Federal Motor Carrier Safety Administration (FMCSA) promulgates Hours of Service 

(HOS) regulations limiting the total of daily and weekly hours during which long-haul truck 

drivers are permitted to operate their vehicles on the public roadways.1 A heavy-duty diesel 

vehicle (HDDV) used for long-distance freight hauling usually has a sleeper berth behind the 

driver seat so the driver can rest during these Federally mandated restorative rest periods. Driver

safety and public motor safety are the primary concerns influencing HOS regulation.

Understanding the factors contributing to commercial vehicle operator health and performance is 

important in developing future regulations. 

1.1 NOISE LEVEL

The vibratory disturbance of air pressure on the ear drum is perceived as sound. Undesirable 

sound is defined as noise. Sound pressure is measured on a logarithmic scale, called the decibel

scale (dB). Sound pressure level (SPL) or Lp is defined by the equation shown in Figure 1, where 

P is the measured sound pressure level, and Pref is a reference sound pressure level. For studies 

involving human subjects, Pref equals 20 μPa, which is normally considered to be the threshold 

of human hearing.2

Figure 1. Equation. Instantaneous sound pressure level equation

The human ear also does not sense sound pressure uniformly because the ear is not equally 

sensitive to all frequencies. Thus, different filters or weightings are used for measuring noise 

levels. The A-weighting filter emphasizes frequencies at which the human ear is most sensitive; 

in other words, the A-filter attenuates the very high and very low frequencies to which the ear is 

insensitive. The C-weighting filter is used for subjective measurements at very high or peak 

sound pressure levels. The A-weighted sound level measurements are typically used in 

regulations for the protection of workers against occupational noise-induced hearing loss 

(NIHL), as well as for the purpose of evaluating noise annoyances in the community. 

Since noise fluctuates over time, average measurements are normally used to describe noise. 

Additionally, both noise amplitude and duration establish the energy in the exposure, so simple 

computational procedures or exchange rates are used to combine amplitude and time. A general 

form of the equation used to determine SPL, or LAvg for discrete sound measurements is shown 

in Figure 2, where Li is the dB level in the measurement interval i; Q is the exchange rate in dB, 

N is the number of intervals, T is the total measurement time period, and ti is the time period of 

interval i. The variable q, the specific or actual exchange rate, is defined by the relationship q = 

Q/log10 2. The Occupational Safety and Health Administration (OSHA) currently uses a 5-dB 

exchange rate; the National Institute for Occupation Safety and Health (NIOSH) and most 

European countries use a 3-dB exchange rate. 

dB

P

P L 10 log

2

ref

P 10 













 =
2

Figure 2. Equation. Average sound level equation for discrete sound-level measurements

Most occupational noise regulations stipulate that personnel exposure may not exceed a 

maximum daily accumulation of noise energy, where the combination of duration of exposure 

and intensity of noise defines the total noise exposure. The OSHA permissible exposure limit 

(PEL) for noise is 90 dBA time-weighted average (TWA) for an 8-h workday.3 and NIOSH 

recommends 85 dBA for the 8-h TWA.

4 The PEL is also referred to as a 100-percent noise 

exposure. The action level (AL) is computed to be 50-percent of the maximum PEL. The 

exchange rate refers to how the sound energy is averaged over time. A 5-dB exchange rate

means that an increase (or decrease) in decibel exposure by 5 dB is equivalent to a doubling (or 

halving) of exposure time. For instance, if noise is at 95 dBA, the allowable exposure per 

workday is half of 8 h, or 4 h; correspondingly, if noise is at 85 dBA, the allowable exposure 

time is twice 8 h, or 16 h. At the present, noise levels in commercial motor vehicles are not 

governed by OSHA regulations or NIOSH guidelines. †

Background: Robinson et al.5 measured the in-cab noise level for nine trucks under different 

highway speed conditions of actual driving and compared these noise measurements to previous 

historical values to determine whether truck-cab noise has increased or decreased with modelyear changes. All trucks in their study were conventional engine-ahead-of-cab design, as 

opposed to cab-over engine. Trucks had standard sleeper berths. Model years were between 1992 

and 1997. The overall broadband SPL across the several different driving conditions for the nine 

trucks was 89.1 dBA, which is just below the OSHA PEL of 90 dBA for an 8-h period. Average 

sleeper-berth SPL was 81.6 dBA, and during engine idling, the in-cab SPL level was 68.7 dBA. 

Hessel et al.6 used a sound level meter to measure noise levels in eight truck-tractors that were 

pulling loaded 40-foot trailers under a standardized condition. This condition included cruising—

neither accelerating nor decelerating—in the highest gear, on dry, level, concrete pavement, 

usually of the interstate system with the driver’s window and wing window fully open, the 

passenger’s wing window partially open, and the radio off. A noise dosimeter was also used and 

was in operation during the entire driving shift. The average reported noise level in the cabs from 

the sound level meter was 83.4 dBA. None of the tractors tested under the standardized 

conditions exceeded the OSHA standard of 90 dBA for an 8-h exposure. However, the calculated 

dBA levels obtained from the dosimeter readings were significantly higher than the sound level 

meter readings. The researchers concluded that since the dosimeter was used throughout the 

driving shift, those readings probably represented the actual exposure of the drivers better than 

 

†

According to Federal Motor Carrier Safety Regulations (49 CFR part 393.94) the interior sound level at the driver’s seating position must not 

exceed 90 dBA, as measured when the truck is parked with all doors, windows, and vents closed; all power-operated accessories turned off; and, 

with the transmission in neutral, the engine is accelerated to—and stabilized at—either its maximum governed engine speed if it is equipped with 

an engine governor, or its maximum rated horsepower. The regulation does not specify a maximum time-weighted-average dBA level for an 8-h 

work day, which was the standard used in this study.































 = ∑=

N

i 1

i

q

L

Avg 10 10 t

T

1 L (Q) q log

i
3

the sound level meter reading taken under the standardized conditions. Sound level meters are 

more inclusive that dosimeters; they measure real-time sound and can have functions such as 

signal analysis, noise dose measurement, and the different time and frequency weightings. Noise 

dosimeters are used for specific measurement capability for defined industrial safety criteria. 

Usually a dosimeter is worn by the employee in order to determine the personal noise during the 

work shift or sampling period. 

Van den Heever et al.7 compared noise levels in the cabs of two different makes of trucks in 

South Africa. Triplicate measurements were made daily on each truck, with a different driver for 

each truck during a full work shift of 8 h or more. A total of 16 tests were made. The A-weighed 

sound pressure level, maximum sound pressure level, percentage dose, and exposure time were 

measured. Noise assessments were computed on a 3 dB exchange rate using the safety standard 

that prescribes 85 dBA for an 8-h work shift. The results of the arithmetic average showed the 

Leq were 84.7 dBA and 85.5 dBA, LMax were 108.9 dBA and 110.5 dBA, and dose percent were 

8.29 and 109.2, respectively for the two trucks. It was concluded that the high sound pressure 

levels were caused, partly because of driving with the open windows and proposed that drivers of 

such trucks wear hearing protection devices while driving. 

To evaluate the noise exposure of truck drivers under normal operating conditions, Seshagiri8

conducted tests under several scenarios of highway driving in Canada, including different 

terrains and conditions—windows open or closed, radio on or off. Eight trucking companies 

voluntarily took part in the study. Measurements were restricted to long-haul and pick-up-anddelivery types of operations. Most of the tractors were double-axle, and most of the tractortrailers were 18 wheelers. Virtually all had vertical exhaust, either single or twin, located behind 

the cab. Two sound level meters were used for most tests, one to measure the personal noise 

exposure of the driver, and the other as an area sample in the cab. In a few instances, a third 

meter was also used to measure the noise level in the sleeper compartment. The exposure of the 

driver was evaluated using both 3-dB and 5-dB exchange rates. The Leq ranged from 78 to 89 

dBA, with a mean of 82.7 dBA; operating the radio increased the mean by 2.8 dB; driving with 

the driver’s side window open increased the mean exposure by 1.3 dB; and driving with the 

window open and operating the ratio resulted in an increase of 3.9 dB. Trucks with the cab 

mounted over the engine appeared to be quieter than standard trucks by about 2.6 dB. Operations 

on four-lane highways were 1.6 dB noisier than on two-lane highways; operations on hilly 

terrain appeared to be quieter than on flat terrain by about 2.2 dB. The researcher concluded that 

the differences between noise levels between both the number of lanes and the terrain conditions 

were most likely caused by higher speeds. Previous studies, where the noise evaluations were 

higher, included only real driving time measurements, and for the most part did not contain any 

non-driving time in the dose calculations. However, studies of noise levels in truck cabs as 

reported over the past 25 years have dramatically shown an overall decrease in noise.5,9

1.2 WHOLE-BODY VIBRATION

Vibration is a mechanical movement that oscillates about a fixed point. By definition, this 

movement is not constant but alternates between being greater than and being less than some 

equilibrium position. Whole-body vibration (WBV) results when a person’s whole body mass is 

subjected to the mechanical vibration—for example, from a supporting surface, such as the seat 
4

of a vehicle. Hand-arm vibration (HAV) is vibration in which the body parts—hand and arm—

are subjected to the mechanical vibration. For example, in the operation of an electric drill, the 

hand is in direct contact with the vibrating medium and the bulk of the body rests on a stationary 

surface. This classification of vibration, however, does not necessarily imply that parts of the 

body other than those in direct contact with the vibrating surface are immune to the effects of the 

vibration. In any case, occupational vibration issues are of concern because of possible harm or 

injury to the lumbar region of the spine or of personal discomfort and annoyance.10

In the United States, occupational vibration is an emerging topic. Standards or guidelines 

currently in use are available from the International Organization for Standardization (ISO), the 

British Standards Institution, and the American National Standards Institute (ANSI). The oldest 

standard for WBV is the ISO-2631-1.11 Occupational vibration standards are voluntary 

guidelines in the U.S., since OSHA has not established WBV standards for industry. On the 

other hand, ISO guidelines will be followed in the present study because this standard appears to 

be the most commonly referenced for WBV, and most of the other standards are practically 

identical to ISO-2631-1. The narrative that follows below was taken almost exclusively from the 

ISO2631-1 standard. 

The three-dimensional coordinate system for the human body in a seated position is shown in 

Figure 3. The direction of the x-axis is the orientation of back-to-front; rotation about the x-axis 

is called roll. The direction of the y-axis is the orientation of right-to-left side; rotation about the 

y-axis is called pitch. The direction of the z-axis is the orientation of head-to-buttocks; rotation 

about the z-axis is called yaw. 

Figure 3. Diagram. Vibration measurement coordinate system for the seated person

According to ISO 2631-1, vibrations are determined using the frequency-weighted root mean 

square (RMS) acceleration for each axis of translational (or rotational) vibration on the surface 

which supports the person. The weighted RMS acceleration (aWRMS) is calculated with the 

equation shown in Figure 4, where aw(t) is the weighted acceleration as a function of time, and T 
5

is the time duration of the measurement. Translational acceleration is expressed in units of meter 

per second squared (m/s2) and assessments are made independently along each axis with respect 

to the highest frequency-weighted RMS acceleration determined in any axis. Vibrations in the 

horizontal plane are also scaled by a correction factor (k) for the seated persons (k = 1.4), as the 

critical frequencies with respect to the possible harmful effects on the human body are different 

for the vertical (z) axis and the two horizontal (x and y) axes. 

Figure 4. Equation. Weighted root mean square acceleration equation

The three translational axes of acceleration, (x, y and z) can also be combined into a single value, 

which will be called sigma (Σ) for brevity, where Σ = av = (kx

2

awx2 + ky

2

awy

2 + kz2

awz2)

0.5. On its 

own, Σ is used as relative value for the perception of comfort. In ISO 2631-1, the recommended 

correction factors for a seated person are kx = ky = ky = 1. Since acceptable values for comfort 

depend on many factors, which can vary with each application, overall limits are not absolutely 

defined. However, the following ranges of values, listed in table 1, are recommended in ISO 

2631-1 to illustrate the likely reactions. It should be noted that this quantitative evaluation of the 

“degree of comfort” is a subjective scaling to various degrees of WBV experienced in 

transportation vehicles. The presence of areas of overlap between the reaction groups by the 

range of scales is also problematic in determining the appropriate presumed reaction concerning 

the degree of comfort based on the physically recorded vibration level. This problem makes the 

evaluation of the nature of the establishment of a target characteristic value of design more 

difficult. 

Table 1. Comfort Reactions to a Vibration Environment (Seating Position)

Vibration Magnitude (Σ) Likely Reaction

Less than 0.315 m/s2 Not uncomfortable

0.315 m/s2 to 0.63 m/s2 A little uncomfortable

0.5 m/s2 to 1 m/s2 Fairly uncomfortable

0.8 m/s2 to 1.6 m/s2 Uncomfortable

1.25 m/s2 to 2.5 m/s2 Very uncomfortable

Greater than 2 m/s2 Extremely uncomfortable

In the areas of occupational health and safety, standards are always evolving. As with most 

regulations, the emphasis is on minimizing worker exposure levels, so that a predetermined daily 

accumulation level will not be exceeded during the work period. Debates continue over the 

appropriate minimum level of exposure to use as a standard. The over-exposure levels that cause 

fatigue, decrease in proficiency, reduced comfort, or actual damage to muscles, organs, and 

nervous system are not currently known with certainty. It is not the purpose of this study to enter 

into this discussion; nonetheless, a growing body of research is showing some health and safety 

consequences from occupational vibration exposures.2,10,12

a (t)dt T

1

a

T

0

2

WRMS = ∫ w
6

For comparison purposes, the European Parliament Directive for Vibration13 will be used for 

health guidance; the European Union (EU) recommends 0.5 m/s2 as the exposure action value 

(EAV) for an 8-h day and 1.15 m/s2 as the exposure limit value (ELV). The EAV is that level of 

daily exposure at which, or beyond which, specific action must be taken to reduce the risk. The 

ELV is the level of a daily exposure that must not be exceeded. It is possible to project the daily 

exposure of a person to vibration from an 8-h level to 11 h by multiplying the health guidance 

recommendations above by the correction factor (8/11).

1/2 Thus, the EAV and ELV for an 11-h 

work day are 0.43 m/s2 and 0.98 m/s2

, respectively.14

For certain types of vibration, especially those involving occasional shocks or transient vibration 

(i.e., impulsive vibrations which have short-duration high peaks), the basic evaluation method 

(i.e., the frequency-weighted RMS method) may underestimate the severity with respect to 

human discomfort. Therefore, a dimensionless quantity called the crest factor (CF) is used to 

determine the suitability of the RMS method for describing the severity of the vibration.11 The 

CF is defined as the ratio of the peak acceleration to the RMS acceleration; as shown in Figure 5, 

where the peak acceleration is the maximum (max) instantaneous acceleration at any time during 

the measurement period, and the RMS acceleration is the weighted acceleration mentioned in the 

above paragraphs. 

Figure 5. Equation. Crest factor equation

Normally, the basic evaluation method is sufficient for evaluating vibration with CF below or 

equal to nine. However, in cases where the CF is greater than nine, two alternative measures are 

recommended in ISO-2631-1: 

• The running RMS method.

• The fourth-power vibration dose method. 

The former method takes into account occasional shocks and transient vibration by use of a short 

integration time constant. Since this method is used infrequently, it will not be discussed further 

in this study. The latter method is more sensitive to peaks than the basic evaluation method 

because it uses the fourth power instead of the second power of the acceleration time history as 

the basis for averaging. The fourth-power vibration dose value (VDV) is defined in Figure 6, 

where aw is the instantaneous frequency weighted acceleration and T is the duration of 

measurement. The units for VDV are meters per second raised to the 1.75 power (m/s1.75). As an 

alternative measure of WBV, the EU-recommended VDVs are 9.1 m/s1.75 for the EAV and 21 

m/s1.75 for the ELV. Finally, it is useful to mention that one additional human response indicator, 

called motion jerk, is sometimes used to characterize vibration. At low frequencies, motion jerk 

is related to riding comfort and can be important for determining load tie-down in freight 

hauling. Jerk is defined as the change of acceleration over time. The units for motion jerk are 

meters per second raised to the cubed power (m/s3). No standards exist at present for limiting 

human exposure to motion jerk. 

RMS(a (t))

max(a (t)) CF

w

w =
7

Figure 6. Equation. Fourth-power vibration dose method equation

Background: Exposure to WBV in heavy equipment operators and commercial vehicle drivers 

has been associated with an excess risk of back symptoms and disorders of the lumbar region of 

the spine.15–17 Miyamoto et al.18 investigated lower-back pain (LBP) in professional truck drivers 

indirectly, using the self-reporting method. The survey found that 52.9 percent of the drivers 

participating in the questionnaire reported that LBP was related to work. Additionally, most of 

these drivers claimed that vibration and road shock accounted for their LBP. 

Bovenzi et al.19 investigated LBP in Italian drivers exposed to WBV. The sample of professional 

drivers included drivers of earth-moving machines, forklifts, commercial trucks, and buses. 

Questionnaires also were employed. However, more important, vibration measurements were 

made at the driver-seat interface under actual operating conditions on a representative sample of 

the industrial machines and vehicles used by the drivers. The z-axis (vertical) weighted 

acceleration was the dominant directional component of vibration measured in most of the 

machines and vehicles, and the horizontal vibrations were scaled by the correction factor for 

seated persons (i.e., k = 1.4). In earth-moving machines the total weighted RMS accelerations 

averaged 0.57–0.69 m/s2

; in transport vehicles, it was 0.5–1.1 m/s2. The lowest values were 

measured on garbage trucks (0.29–0.31 m/s2). Vibrations on buses varied from 0.51 m/s2

(minibus) to 0.61 m/s2 (city bus). 

Cann et al.20 investigated the predictors of WBV on four truck manufacturers and compared the 

levels of WBV to the standards in ISO 2631. Each truck was tested using 5-min random samples 

at speeds greater than 80 km/h on four separate highways whose surfaces ranged from smooth 

and resurfaced to rough and potholed. Truck type, seat type, road condition, driver experience, 

and truck mileage were the areas of interest used to predict WBV. The trucks used in the 

research study were cab-over trucks, designed with a freight container attached directly to 

tractor, and cab-behind trucks, day cabs, or sleeper trucks. The research discovered that the test 

trucks did not exceed the ISO 8-h driving day standard on average, but the standard was 

exceeded in certain instances while the trucks were driven on rough or potholed highways. The 

study also demonstrated that road condition and truck type showed a statistically significant 

relationship with the frequency-weighted RMS acceleration in regression analysis. Road 

condition showed a significant relationship for the three translational axes of direction, while 

truck type showed a significant relationship with the vertical axis. 

1.3 AIR QUALITY

Long-haul truck drivers may be exposed to air pollutants within the cab and sleeper berth during 

conditions of driving and while the vehicle is parked with the engine idling at truck-travel/rest 

centers. Relationships between diesel vehicle emissions and detrimental human health effects 

have been demonstrated in numerous studies.21 The U.S. Environmental Protection Agency 

(EPA) has also concluded that diesel exhaust causes acute and chronic health effects.22

4

T

0

4

w VDV a (t)dt ∫ =
8

Background: Doraiswamy et al.23 measured air-pollutant concentrations of carbon monoxide 

(CO), oxides of nitrogen (NOX) and particulate matter less than 2.5-μm in aerodynamic diameter 

(PM2.5) inside and outside of six HDDVs, while the vehicles were idling at a commercial truckstop rest area. All trucks were conventional engine-ahead-of-cab design, all had standard sleeper 

berths; truck model years were between 1996 and 2003. The air samples were taken during 

several different modes of heating, ventilation, and air-conditioning (HVAC) settings and truck 

engine operating conditions. The study showed that average 1-h in-cab concentrations were: (1) 

424 ppb CO, 312 ppb NOX, and 19 μg/m3 PM2.5 for both engine and HVAC in off-mode; (2) 820 

ppb CO, 1,013 ppb NOX, and 71μg/m3 PM2.5 for both engine and HVAC in on-mode with air 

recirculation; (3) 493 ppb CO, 694 ppb NOX, and 144 μg/m3 PM2.5 for both engine and HVAC in 

on-mode with fresh air; and (4) 780 ppb CO, 531 ppb NOX, and 209 μg/m3 PM2.5 for engine in 

on-mode and HVAC in off-mode, where ppb is parts per billion by volume. This suggested that 

different modes of engine idling and HVAC operation influenced the in-cab air quality. For 

instance, emissions were lowest when both the truck engine and HVAC were off, and emissions 

were highest when both the truck engine and HVAC were on in the fresh-air mode. 

Sabina et al.24 were concerned with health effects in children from diesel emissions in school 

buses. In-cab concentrations of soot or black carbon, particulate-bound polycyclic aromatic 

hydrocarbons (PB-PAH), and nitrogen dioxide (NO2) were measured in school buses. The study 

found that for bus commutes with windows open, mean black carbon concentration inside the 

test buses were highest when the bus was following another diesel school bus. Also, the levels of 

black carbon and PB-PAH were 8 to 11 times higher when the test bus was following a dieselfueled bus rather than following a gasoline-fueled bus or no vehicle. 

Diesel exhaust exposure was measured by Davis et al.25 at 36 trucking terminals across the 

United States. Both organic and elemental carbon (OC and EC, respectively) and PM2.5 were 

measured inside the cabs. (Analytical chemical methods are required to distinguish between OC 

and EC.) Diesel particulate matter is mostly unburned carbon. However, EC or soot is a selective 

marker of exposure in workplaces where diesel equipment is operated, so it is a good surrogate 

measure of exposure to this pollutant. OC includes hydrocarbons which can come from unburned 

fuel—but other sources of hydrocarbons exist besides gasoline and diesel fuel. Both short- and 

long-distance trips were observed, as well as information on the smoking status of the driver and 

characteristics of the truck. For the long-haul drivers, average EC, OC, and PM2.5 concentrations 

were 1.4, 21.6, and 52.6 μg/m3

, respectively. These results also suggested that in-cab particle 

exposures were positively related to driver smoking, background or ambient particle 

concentrations, truck age and open windows. Laden et al.26 also provided insight into mortality 

patterns that were associated with job-specific exposures in the trucking industry. In this detailed 

assessment of specific job categories, an excess of mortality due to lung cancer and ischemic 

heart disease were noted particularly among commercial truck drivers. 

The PEL established by OSHA for CO, average over an 8-h time period, is 50 parts per million 

by volume (ppm).27 The summation of nitrogen oxide (NO) and nitrogen dioxide (NO2) is NOX

concentration. By far, the most dominant nitrogen compound formed during combustion in spark 

or compression ignition engines is NO for gases burned at flame temperatures, and chemical 

equilibrium considerations indicate that NO2/NO ratios are negligible. While experimental data 

show this is true for spark-ignition engines, in diesel or compression-ignition engines, the NO2

concentration can be 10 to 30 percent of the total NOX exhaust emissions.28 Also in ambient air, 
9

NO can oxidize to NO2. Though no specific occupational standard exists for NOX, OSHA has set 

the PEL for NO at 25 ppm and has established a short term exposure limit (STEL) for NO2 at 1 

ppm. For PM2.5, no enforceable workplace exposure limit has been established by OSHA, so in 

this case, the EPA National Ambient Air Quality Standards (NAAQS) for PM2.5 will be used for 

comparison purposes. It should be noted here that the NAAQS are outside air monitoring, 

standards set to protect general public health, including the health of sensitive populations such 

as asthmatics, children, and the elderly. Also, averaging times for the NAAQS are usually 

different from typical occupation or workplace averaging times. The EPA has set NAAQS for

CO, lead, NO2, particulate matter, ozone, and sulfur dioxide.29 Areas not meeting any of the 

NAAQS are required by EPA to create a State Implementation Plan to meet the standards within 

a certain time period. 

The NAAQS for PM2.5 are 35 μg/m3 (24-h average) and 15 μg/m3 (annual mean). In EPA 

parlance, for the former, the 3-year average of the 98th percentile of 24-h concentrations at each 

population-oriented monitor within an area must not exceed the standard, and for the latter, the 

3-year average of the weighted annual mean concentrations from single or multiple communityoriented monitors must not exceed the standard. The NAAQS for PM10 is 150 μg/m3 (24-h

average). Particulate matter less than 10 μm in aerodynamic diameter is PM10, and the standard 

is not to be exceeded more than once per year on average over 3-years. For comparison purposes, 

the World Health Organization (WHO) ambient air quality guidelines for PM2.5 are 25 μg/m3

(24-h mean) and 10 μg/m3 (annual mean). For PM10, the WHO ambient air quality guidelines are 

50 μg/m3 (24-h mean) and 20 μg/m3 (annual mean).30 In closure, the NAAQS for CO for a 1-h

exposure is 35 ppm and 9 ppm for an 8-h exposure, both not to be exceeded more than once per 

year. The NAAQS for NO2 is 0.053 ppm (annual arithmetic mean). 
10

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11

2. OBJECTIVE

The purpose of the present study was to measure several factors inside the cab of heavy-duty 

diesel vehicles that may affect the health and performance of drivers. The evaluated factors were 

the noise level, whole body vibration from driver and passenger seats, and the in-cab air quality. 

The concentrations of CO, NOX, and PM2.5 were measured inside the cab to determine the air 

quality. Vibration data from sensors located on the cab and truck body were also collected for 

computer modeling purposes; however, these results will not be discussed in this report. All 

measurements were conducted while the vehicles were parked with the engine idling at a truckstop rest area and/or during an actual on-road driving episode that included interstate and State 

highway driving over moderately steep and relatively flat terrains. A further aim of this study 

was to test the latest model year trucks available at the time and to have trucks represented from 

at least four different manufacturing companies since this data set will ultimately serve as 

baseline data for future studies. 
12

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13

3. EXPERIMENTAL METHOD

The parked-idling and on-road tests for each truck were conducted over the course of a 2-day 

time period. On the first day of testing, the sampling equipment was installed; the truck was 

attached to a utility trailer, driven to a commercial travel center, and parked in the rest area 

reserved for extended or overnight truck parking. Each truck was tested at the same travel center, 

which was located approximately 8 km (5 mi) west of the city limits of Knoxville, TN and about 

1.6 km (1 mi) north of Interstate 40. Figure 7 is a photograph of a number of trucks parked at the 

travel center where the engine-idling testing occurred. The white truck located in the center of 

the photograph was one of the vehicles tested in this study. 

Figure 7. Photo. Trucks parked at a study-selected travel center rest area

On the second day of testing, the truck (with utility trailer) was driven over a prescribed route. 

The driving course included a mixture of interstate and rural highway travel. The round trip was 

approximately 260 km (160 mi), of which 120 km (75 mi) were interstate travel (I-40) over 

rolling hills and moderately steep terrain, 80 km (50 mi) were rural highway travel (US-27 and 

TN-68) over rolling hills, and 60 km (35 mi) were interstate travel (I-75) over relatively flat 

terrain. Figure 8 is a map showing the entire route from start to finish. Figure 9 is a map showing 

the variation in elevation of the hills and valleys along the route. For simplicity, the combination 

route US-27 and TN-68 will be identified as US-27 in this report. The average speed on the 

interstates was between 105 and 115 km/h (65 and 70 mi/h), and on the U.S. and State roads, it was 

90 km/h (55 mi/h). The US-27 highway went through two small (rural) towns where the speed 

dropped to 55 km/h (35 mi/h). However, it took only about 5-min of driving time to pass through 

each town. For the most part, all measurements were conducted at the average speeds for the 

interstates and State highways. 

The vehicles are classified by the EPA, as HDDV, Class (8b); they are truck and trailer 

configurations with a gross vehicle weight rating that is greater than 27,216 kg (60,000 lb).31 On 

occasion, the truck is called a tractor, and the tractor-trailer configuration is commonly referred 

to as an 18-wheeler. Each truck hauled a 16.2-m (53-ft) long, fully enclosed utility trailer that 

was pre-loaded with approximately 13,610 kg (30,000 lb) of palletized top-soil. The model year 

of the trailer was 2007. Fewer than 12,875 road-kilometers (8,000 road-miles) had been logged 
14

on the trailer before it was rented, and the same trailer was used for all road testing. In total, 27 

trucks were rented and tested: 2 trucks were from model year 2006, 22 trucks were from 2007, 

and 3 were from 2008. Vehicles from four truck manufacturing companies were represented in 

the study. All trucks were conventional engine-ahead-of-cab design and had in-cab sleeper

berths, such as are used for long-haul highway driving. 

Since the sample of test vehicles consisted of trucks from four separate manufacturers, it was 

appropriate—if differences became apparent between manufacturers after the test data were 

examined, that these differences would be reported. The purpose of this study however, was not 

to demonstrate that unwarranted differences exist between truck manufacturers, so in the interest 

of being impartial, the specific manufacturers will not be named directly for reporting purposes; 

instead, different truck manufacturers will be referred to as A, B, C, and D. 

Figure 8. Map. Map showing the driving route along I-40, US-27 & TN-68, and I-75
15

Figure 9. Map. Relief map showing terrain contrast along the driving route

No truck had a closed crankcase ventilation system—i.e., combustion gases that leak past the 

piston rings (blow-by) were vented to the atmosphere and were not routed back into the intake 

manifold of the engine, as is common for automobile gasoline-driven engines. Only one truck 

was equipped with a catalyzed regenerative particulate trap. All trucks were tested as received or 

as rented, and no trucks were subjected to any special maintenance procedures. All trucks used 

locally available standard diesel fuel.

Instantaneous or real-time measurements for noise, vibration, and PM2.5 concentrations were 

collected during the on-road test only. Measurements for CO and NOX concentrations were not 

collected instantaneously during the on-road test. Instead, air samples from inside the cab were 

collected and later analyzed for CO and NOx concentrations. This procedure was adopted 

because it was impossible to maintain the CO and NOX instruments on the DC-voltage battery 

system of the truck during the on-road test. However, during the parked-idling test, real-time 

measurements for all the parameters were collected—here, an external source of AC-voltage was 

available on-site that could be used simultaneously to power all analyzers and auxiliary 

equipment (e.g., data loggers, sampling pump, etc.). 

During the parked-idling test, air sampling occurred according to several predetermined modes 

of truck engine and HVAC system operation: 

• Engine Off/Inside

•

—the truck engine was off, and all the windows were closed. This 

condition allowed for the determination of the in-cab air quality while the engine and 

HVAC system were both in off mode. 

Engine On/Recirculation—the truck engine was on with the idling speed adjusted via the 

cruise-control in the range of 900–1,000 revolutions per minute (rpm), and the windows 
16

were closed. The HVAC system was on recirculation mode. In some truck models, this 

would be the “Max A/C” setting. However, most new model vehicles have a recirculation 

button on the climate control panel that dedicates the HVAC system to recirculation of 

the inside air. The HVAC dash fan switch and the sleeper berth fan switch were both set 

at the medium speed. 

• Engine On/Fresh Air

•

—the truck engine was on and was set to idle between 900 and 

1,000 rpm, and the windows were closed. The HVAC system was on. This setting 

typically allows the (fresh) outside air to be brought into the cab of the truck. The dash 

fan switch and the sleeper berth fan switch were both set at the medium speed. 

Engine On/Ventilation Off

•

—the truck engine was on and set to idle at between 900 and 

1,000 rpm, and the windows were closed. However, the HVAC system and both fans 

(dash and sleeper) were off. This condition allowed for the determination of the in-cab air 

quality while only the engine was idling. 

Engine Off/Outside

During the on-road test, the ventilation system was always in fresh-air mode, and both dash and 

sleeper berth fan switches were set to the medium speeds. Outside air was not sampled during 

the on-road test. The temperature or climate control setting during all HVAC system operations 

was adjusted by the occupant(s) at their discretion to maintain the cabin temperature in the 

comfort region, which was usually between 70 and 80 degrees F. In essence, the recirculation 

mode limits the amount of outside air entering the cab to decrease the time required to cool or 

heat the cab interior during extreme outside temperature conditions. It should be noted that 

depending on the truck HVAC configuration, the fresh air or recirculation mode might not be 

100 percent outside air or 100 percent internal air recirculation, but may involve a mix of both to 

prevent the buildup of fumes or odors and to prevent in-cab oxygen depletion. 

—the truck engine was off, and the windows were open. This 

permitted outside air to enter the truck, and background ambient air concentrations could 

be established to determine whether a relationship existed between outside and inside air. 

An attempt was also made to estimate the approximate cabin air exchange rate (AER) in several 

of the test trucks because this information would assist in characterizing the effects of the HVAC 

system and air leakage rates. The method was derived from the EPA Method IP-4B33 which is 

used to determine the AER between the outside and inside of buildings. Essentially, the 

procedure involves introducing a small amount of tracer gas into the cab with the windows 

closed, thoroughly mixing the air in the cab, and then measuring the rate of change or decay in 

the tracer gas concentration. The loss rate of a tracer gas concentration conforms to the 

exponential dilution law, which states that the dilution or loss rate of an escaping gas is 

proportional to its concentration. The AER is determined from the decay in tracer concentration, 

expressed mathematically by the equation shown in Figure 10: 

Figure 10. Equation. Exponential dilution law

-(AER) t C = C0Exp
17

where C is the tracer gas concentration at time t; C0 is the tracer concentration at time zero, AER 

is the air exchange rate. In this experiment, 99.9 percent pure carbon dioxide (CO2) was used as 

the tracer gas, and several conditions of HVAC and fan settings were tested. 

3.1 SAMPLING EQUIPMENT

3.1.1 Noise Level

Noise data were collected using an integrating, averaging sound-level meter. The instrument had 

been factory-calibrated at the beginning of this study. The sound meter was attached to the righthand arm-rest of the driver seat during noise-level measurements. Data were collected 

continuously for the duration of the on-road driving test. The sound meter takes three sets of 

measurements known as Integrators-1,-2, and -3. Integrator-1 provides measurements required 

by OSHA regulations. Integrator-2 is configured for the OSHA hearing conservation program.

Integrator-3 provides ISO Leq measurements. For the current project, only Integrator-1 and 

Integrator-3 were selected. The criterion level (CL) is the normalized 8-h average weighted 

sound level that corresponds to the maximum permitted daily exposure. The CL for Integrator-1 

and Integrator-3 were 90 dB and 85 dB, respectively. The criterion time for both integrators was 

8 h. A threshold value of 80 dB is used by Integrator-1, to calculate the average weighted sound 

level. This means that sound levels below the threshold are excluded from all averaging for 

Integrator-1. A threshold value is not used by Integrator-3. The exchange rates for Integrator-1 

and Integrator-3 are 5 dB and 3 dB, respectively. The highest value reached by the sound 

pressure at any instant during a measurement period is called the peak value; it is used with the 

C-frequency weighting. The LAMin and LAMax are the minimum and maximum recorded sound 

levels, respectively; both use the A-frequency weighting. The TWA is the average of the 

measured LAve over an 8-h period; TWA will be lower than the LAve when the measurement 

duration is less than 8 h; TWA will be equal to the LAve for a measurement of 8 h; TWA will be 

higher than the LAve for measurements more than 8 h. The sound meter logged or stored the data 

internally, and after the road test, all data were downloaded to a personal computer for later 

analysis.

3.1.2 Whole-Body Vibration

Several transducer accelerometer pads were used to measure WBV from the driver and 

passenger seats. On the driver seat, one pad each was installed on the back support (S1) and on 

the rump or cushion area (S2) of the seat. On the passenger seat, only a single pad was installed 

on the cushion area (S3) of the seat. Several accelerometers, also were used to measure vibration 

from the cab and truck body frame. Figure 11 is a top and side schematic of a truck showing the 

locations of all the vibration sensors. 
18

Figure 11. Diagram. Transducer placement for each HDDV

Three sensors were located inside the cab: one each on the floor beneath the driver (T1) and 

passenger seat (T2); one attached to the driver seat frame (T4); one attached to the center of the 

steering wheel (T5). Four sensors were located outside the cab: one was attached directly to the 

truck cab behind the driver seat (T3), and three sensors were attached to the structural frame of 

the truck directly beneath the cab (T6, T7, and T8). A linear position transducer also was used to 

measure the vertical displacement of the driver seat (SP). Vibration data (x-, y- and z-axes) 

collected from the seating pads were used for WBV analysis and data collected from other triaxial accelerometers were used for computer simulation experiments. Data from the driver seat 

pads (only) were collected using a human vibration meter. Vibration data from the driver and 

passenger seat pads and other transducers located throughout the truck cab and body were also 

collected with a data acquisition system (DAS).All data related to the measurement of vibration 

were then transferred to personal computers for storage and later analysis. As mentioned 

previously, the results from any data that were collected for computer modeling purposes will 

not be discussed in this report. 

3.1.3 Air Quality

The in-cab air quality was determined by measuring mass concentrations of CO, NOX, and 

PM2.5. An analyzer which employs infrared adsorption as the detection principle was used to 

measure CO concentration. An analyzer, which employs chemiluminescence as the detection 

principle, was used to measure NO and NO2 concentrations. This instrument also reports NOX
19

concentration, the summation of NO and NO2 concentrations. During the parked-idling test, 

these instruments were located in the bedding or trough area of the sleeper berth after the bottom 

mattress had been removed. Probes were connected to the input sampling port of the analyzers to 

bring continuous air into the analyzers during the parked-idling test. The sampling probes 

consisted of 6.35 mm (0.25-in) tubing about 0.92 m (3 ft) long. The intake sides of both probes 

were mounted in the center area of the sleeper berth. During the on-road test, a low-flow portable 

personal sampling pump was used to collect and bag air samples. The flow rate for the sampling 

pump was 1.0 L/min. The bagged samples were subsequently analyzed in the laboratory for CO 

and NOX concentrations.

Two instruments were used for measuring PM2.5 concentrations. A Thermo Electron, DataRAM 

4, Model DR-4000 (DRam) employs light-scattering as the detection principle, and the second, a 

Met One, Model EBam, employs beta-attenuation as the detection principle. Both units 

employed cyclonic type 2.5-μm cutoff separators. Flow-rates were 2 L/min and 16.7 L/min, 

respectively. It should be noted that there was initial concern regarding the sampling of PM2.5

because unusually high PM concentrations were measured inside several trucks during several 

initial on-road tests. After further examination, it was found that the EBam monitor was not able 

to sample concentrations in the vibrating environment of the truck—apparently, the PM2.5

separator vibrates to such an extent that most of the particles passed through the separator, and 

thus the separator was unable to cut off sizes above 2.5 μm. This meant that it loaded all particles

onto the filter, not just the PM2.5, and this resulted in an overestimation of the PM2.5.

Consequently, the EBam was removed from the project, and none of its data will be reported. 

This information about the problem associated with the monitor was provided in the report as a 

note of caution to other researchers when using cyclonic type cutoff separators to estimate PM2.5

concentration in vehicles that are driven over uneven road pavement conditions. For those 

uninitiated in cyclonic separation devices, fundamentally, a vortex of air containing particles is 

swirled down a conical tube. Larger or denser particles in the rotating air stream because of 

inertia cannot follow the tight curves of the air stream, strike the outside wall of the container, 

and fall to the bottom of the cone because of gravity and are not analyzed. The smaller particles 

remain in the air stream and eventually are directed to the analyzer. It is believed that vibration 

or shaking causes larger particles to re-enter the air stream and thus passed on to the analyzer. 

As a follow-up, an optical particle counter (OPC) which is a more sophisticated instrument not 

requiring a PM2.5 separator, was substituted for the EBam. The detection principle for the OPC is 

also based on the principle of light-scattering from particles. The unit samples continuously in 

six channels ranging from 0.3 μm up to >10 μm. Size ranges were 0.3–0.5 μm, 0.5–0.7 μm, 0.7–

1.0 μm, 1.0–5.0 μm, 5.0–10.0 μm, and >10 μm. The sampling flow rate for the OPC was 28.3 

L/min. Using counts of the number of particles in each size range or channel from the OPC, the 

PM2.5 concentration was calculated using a numerical algorithm that converted particle size 

number to total mass and then to the fraction of the total mass concentration that was less than or 

equal to the 2.5-μm in aerodynamic diameter associated with the PM2.5. For simplicity, it was 

assumed that all particles were spherical in shape (where volume = 4πr3/3) with a constant 

density of 2.5 g/cm3

. (Particulate mass is equal to volume multiplied by density.) A sampling 

probe that consisted of 6.35 mm (0.25-in) tubing, about 0.31 m (1 ft) long, was used with the 

OPC. The inlet to the first monitor was provided by a (factory-supplied) nonflexible 

omnidirectional inlet device. Both analyzers were situated in the trough area of the sleeper berth 
20

during the entire parked-idling and/or the on-road tests. Also, to prevent the possible extraneous 

release of any particulate material into the cab environment from the sampling equipment located 

in the truck, high-efficiency particulate air (HEPA) filters were placed on the discharge side of 

all analyzers and/or sampling pumps. A photograph of several instruments situated in the sleeper

berth area of a test truck is shown in Figure 12. 

Figure 12. Photo. Assorted equipment located in sleeper berth area of truck

A mass flow calibrator was used with EPA protocol calibration gas to calibrate the CO and NOX

analyzers. No certifiable standards exist to calibrate the PM instruments. However, vivificated

calibration was performed on the analyzers as specified by manufacturer operating instructions. 

As an additional check to the accuracy of the analyzers, several collocation experiments were 

conducted using a tapered element oscillating microbalance (TEOM) particulate analyzer located 

at the Knox Air Pollution Board’s ambient monitoring site in Knoxville, TN.

A portable gas analyzer was used to measure the decay rate of the CO2 that was released into the 

cab to determine the cabin AER. The gas analyzer is a single-beam spectrometer, scanning in the 

infrared spectral range. A portable GPS unit was also used to track the movement of trucks 

during the on-road test. This allowed verification between measured factors with spatial location 

along the route. It should be noted that most of the instruments used in air quality measurements 

also had internal data logging capability. However, to ensure data collection redundancy, an 

external unit also was used for data logging. All collected data were eventually saved to laptop 

and desktop personal computers. 

3.2 DATA ANALYSIS

To analyze the data, a restricted (or residual) maximum likelihood (REML) method was selected 

to determine the significance or probability level of the condition or model effects. The REML 

method fits (or regresses) empirical data to a linear mixed factorial model using standard least 

squares algorithms. 
21

Mixed models contain both fixed and random effects. Fixed effects are factors chosen by the 

experimenter; for example, the truck manufacturer (TruckMfr), road types (Roadway), and 

engine/ventilation modes of operation (engine/HVAC) are fixed-effect factors. Random effect 

factors are beyond the control of the experimenter; for example, any truck (TruckId) that was 

selected for testing is a random effect factor because this truck was available at the leasing 

agency at the time it was rented for testing purposes, and information about a particular truck is 

relatively useless. Nonetheless, each particular truck adds variance when the data set is 

statistically analyzed. By using the REML method, any superfluous variance produced from a 

nuisance parameter or the random effects are ignored in determining the overall significance of 

any of the fixed effects. In general, REML is conservative in its restriction of nuisance 

parameters and can produce unbiased estimates of variance and covariance parameters. The 

objective is to construct the F-statistic (or F-test) and the associated DOF to obtain a p-value for 

the significance test. A probability level is simply a number that expresses the likelihood of the 

outcome of an event. Observed significant probabilities (p) of 0.05 or less (meaning 95 out of 

100) are often considered evidence that the model fits the data.

When a main effect from the REML method was found to be significant, pair-wise comparisons

of the least-squares means differences between truck manufacturers and the various test 

conditions, such as roadway type or engine-idling/HVAC modes of operation, were achieved 

using the Tukey-HSD (honest significant difference) test. This test was selected because it is an 

excellent data-probing method when differences between pairs of means are the interest of focus 

and the sample sizes are unequal. Also the method minimizes the Type 1 error rate because when 

multiple comparisons are made the probability of making Type I error increases. (A Type 1 error 

is committed when the null hypothesis is rejected when in fact the null hypothesis is true.) Thus, 

when multiple comparisons are made, the Tukey-HSD test gives a more conservative estimation 

of pair-wise differences between conditions (i.e., means) than the standard t-test.34
22

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23

4. RESULTS AND DISCUSSION

All regulatory standards or guidelines are summarized in appendix A for reference purposes.

4.1 NOISE LEVEL

In-cab noise-level data were collected and analyzed from only 22 trucks of the 27 trucks that 

were road-tested in this study. Seven trucks were from company A, four trucks were from 

company B, five trucks were from company C, and six trucks were from company D. As with the 

air-quality testing, in the interest of being impartial, the specific trucking companies will not be 

named. Data are missing from five trucks because of problems that were encountered with the 

sound level meter. A summary of the average noise-level data for each truck is given in appendix 

B for the peak value (C-filter), the minimum and maximum (A-filter) values, and the dose 

percent, estimated dose percent, Leq and TWA used with Integrators-1 and -3. The minimum and 

maximum values in the table are represented in bold blue and bold red, respectively or by 

asterisks. On average, the sampling rate was about 10 minutes in duration encompassing a total 

period of between 2.5 and 3 h per truck test. It should be noted that this sampling period was 

selected to coincide with the vibration sampling period in time duration because the file size of 

the vibration data was in the gigabyte range, and for convince, sound data were saved in 10 min 

intervals. 

Since sound measurements were not collected over a full 8-h shift, the estimated dose percent 

and the Leq or LAvg are more suitable for comparison to the PEL values, than are dose percent and 

TWA because both of these parameters depended on an 8-h CL. Note also in appendix B that the 

dose, estimated dose, Leq, and TWA values for Integrator-1 are considerably lower than the 

corresponding values for Integrator-3. This is because the CL for Integrator-1 was higher than 

the CL for Integrator-3, Integrator-1 used a threshold value of 80 dB for calculating the average 

weighted sound level, which means that sound levels below this threshold were excluded from 

averaging for Integrator-1, and the exchange rate for ntegrator-3 is more stringent. 

Dose is the total noise exposure expressed as a percentage of the PEL. It is the summation of the 

individual exposure times at the noise level divided by the reference duration time, which is 

based on the PEL and exchange rate. For example, the OSHA PEL for an 8-h daily noise 

exposure is 90 dBA. Thus, if the noise level were a constant 90 dBA for 8 h, this would generate 

a dose of 100 percent—that is, (8/8) × 100. However, if during a total 8-h measurement, the 

noise was 90 dBA for 4-h, 95 dBA for 1.5-h, 75 dBA for 1.5-h, and 85 dBA for 1-h, then the 

dose percent would be approximately 93.8 percent—that is, (4/8 + 1.5/4 + 1/16) × 100. Note that 

a threshold value of 80 dBA is used when calculating the OSHA dose percent, so the 75 dBA 

noise level is ignored. The estimated dose percent for an 8-h working day is {8 × (dose percent ÷ 

total time period)}. To determine the estimated dose percent for an 11-h working day, the 

number 8 in the equation is replaced with an 11. 

Overall, as shown in appendix B, truck A4 recorded the highest on-road in-cab noise levels, so it 

will be used in the following discussion. For Integrator-1 the average dose was 3.8 percent, 

which means that the driver experienced about 4 percent of an 8-h noise dose of 90 dBA. 

Average estimated dose is the percentage received by a person if the average level measured had 
24

existed for the period defined by the criterion time. This is a computation estimation of what the 

projected dose would have been for an actual 8-h work shift. For instance, if during a 4-h 

measurement the dose was 50 percent, then the estimated dose would be 100 percent for the 8-h 

time—that is, (8/4) × 50 percent. Again referring to truck A4, for Integrator-1, the average 

estimated dose was 10.7 percent, which is much less than 100 percent, which implies that the 8-h 

TWA would not have been exceeded. 

An estimated dose of 50 percent is usually referred to as the action level (AL). For the 

occupational exposure to noise according to OSHA, this means that within 6 months of an 

employee’s first exposure at or above the AL, the employer must establish a valid baseline 

audiogram for the employee against which subsequent audiograms can be compared. In the 

previous example, the dose was 93.8 percent, thus the AL was exceeded, although the PEL was 

not exceeded. As shown in the appendix B, no average estimated dose from Integrator-1 or 

Integrator-3 exceeded the AL. When an 11-h shift is evaluated for truck A4 (the worst case), the 

estimated doses are 14.7 percent for Integrator-1 and 40.5 percent for Integrator-3. So the AL 

still was not exceeded even when an 11-h shift was considered. 

Graphs of the peak LS means for truck manufacturer, roadway, and the interaction effect of truck 

manufacturer and roadway are shown in the three figures below: REML statistical analysis 

showed that the truck-manufacturer effect (Figure 13) was not significant. REML analysis 

showed that the roadway effect (Figure 14) was significant (p = 0.01). Accordingly, post-hoc 

Tukey’s HSD tests showed that the I-40 condition had significantly higher peak values than the 

I-75 condition at the 0.05 level of significance; all other comparisons were not significant.

REML analysis showed that the interaction effect between truck manufacturer and roadway 

(Figure 15) was not significant.

Figure 13. Graph. LS means peak noise level vs. truck manufacturer

105

115

125

135

Peak (dBC)

A B C D

Truck Mfr
25

Figure 14. Graph. LS means peak noise level vs. roadway

Figure 15. Graph. LS means peak noise level vs. roadway and manufacturer

Graphs of the LMax LS means for truck manufacturer, roadway, and the interaction effect of truck 

manufacturer and roadway are shown in the three figures below: REML analysis showed that the 

truck manufacturer effect (Figure 16) was not significant. REML analysis showed that the 

roadway effect (Figure 17) was significant (p < 0.0001). Accordingly, post-hoc Tukey’s HSD 

tests showed that the I-40 condition had significantly higher LMax values than the I-75 and US-27 

conditions at the 0.05 level of significance; all other comparisons were not significant. REML 

analysis showed that the interaction effect between manufacturer and roadway (Figure 18) was 

not significant. 

105

115

125

135

Peak (dBC)

I-40 I-75 US-27

Roadway

105

115

125

135

Peak (dBC)

I-40 I-75 US-27

Roadway

A

B

C

D
26

Figure 16. Graph. LS means maximum equivalent noise level vs. truck manufacturer

Figure 17. Graph. LS means maximum equivalent noise level vs. roadway

Figure 18. Graph. LS means max equivalent noise level vs. roadway and manufacturer

Graphs of the Leq LS means for truck manufacturer, roadway, and the interaction effect of truck 

manufacturer and roadway from Integrator-1 are shown in the three figures below: REML 

analysis showed that the truck manufacturer effect (Figure 19) was significant (p = 0.003). 

Accordingly, post-hoc Tukey’s HSD tests showed that the trucks from manufacturer A had 

significantly higher Leq values than the trucks from manufacturers B, C and D at the 0.05 level of 

80

85

90

95

100

LMax (dBA)

A B C D

Truck Mfr

80

85

90

95

100

LMax (dBA)

I-40 I-75 US-27

Roadway

80

85

90

95

100

LMax (dBA)

I-40 I-75 US-27

Roadway

A

B

C

D
27

significance; all other comparisons were not significant. REML analysis showed that the 

roadway effect (Figure 20) was significant (p = 0.0002). Accordingly, post-hoc Tukey’s HSD 

tests showed that the I-40 condition had significantly higher Leq values than the I-75 and US-27 

conditions at the 0.05 level of significance; all other comparisons were not significant. REML 

analysis showed that the interaction effect between manufacturer and roadway (Figure 21) was 

not significant. 

Figure 19. Graph. LS means Leq from Integrator-1 vs. truck manufacturer

Figure 20. Graph. LS means Leq from Integrator-1 vs. roadway

20

40

60

80

Leq (dBA)

A B C D

Truck Mfr

20

40

60

80

Leq (dBA)

I-40 I-75 US-27

Roadway
28

Figure 21. Graph. LS means Leq from Integrator-1 vs. roadway and manufacturer

Graphs of the Leq LS means for truck manufacturer, roadway, and the interaction effect of truck 

manufacturer and roadway from Integrator-3 are shown in the three figures below: REML 

analysis showed that the truck manufacturer effect (Figure 22) was significant (p = 0.01). 

Accordingly, post-hoc Tukey’s HSD tests showed that the trucks from manufacturer A had 

significantly higher Leq values than the trucks from manufacturers B, C and D at the 0.05 level of 

significance; all other comparisons were not significant. REML analysis showed that the 

roadway effect (Figure 23) was significant (p < 0.001). Accordingly, post-hoc Tukey’s HSD tests 

showed that the I-40 and I-75 conditions had significantly higher Leq values than the US-27 

condition and the I-40 condition had significantly higher Leq values than the I-75 condition both 

at the 0.05 level of significance; all other comparisons were not significant. REML analysis 

showed that the interaction effect between manufacturer and roadway (Figure 24) was not 

significant. 

Figure 22. Graph. LS means Leq from Integrator-3 vs. truck manufacturer

20

40

60

80

Leq (dBA)

I-40 I-75 US-27

Roadway

A

B

C

D

70

75

80

85

90

Leq (dBA)

A B C D

Truck Mfr
29

Figure 23. Graph. LS means Leq from Integrator-3 vs. roadway

Figure 24. Graph. LS means Leq from Integrator-3 vs. roadway and manufacturer

In summary, slightly higher noise averages were observed from the trucks manufactured by 

company A, but for the most part, the noise conditions were quite similar for all the trucks. 

Higher noise averages were also generally observed while the trucks were driven on the 

interstate, as compared to the State highway. However, peak and maximum noise levels were 

generally higher on I-40 and US-27 and lower on I-75. The primary conclusions were (1) the Leq

or LAve values were well below the OSHA (90 dBA) standard and the NIOSH (85 dBA) 

recommended value and (2) the in-cab AL noise level, as measured by the estimated dose 

percent was not exceeded by any truck; even when an 11-h shift is considered for the worst case 

truck, the estimated dose for the AL was still not exceeded. 

4.2 WHOLE-BODY VIBRATION

Two methods were used to acquire and analyze the vibration data. The first system collected data 

from the driver seat (cushion) only. The second system collected data from the driver seat 

(cushion) and the driver seat (back) rest and from the passenger seat (cushion). 

70

75

80

85

90

Leq (dBA)

I-40 I-75 US-27

Roadway

70

75

80

85

90

Leq (dBA)

I-40 I-75 US-27

Roadway

A

B

C

D
30

4.3 DRIVER’S SEAT CUSHION MONITORING

Data from the driver’s seat cushion were collected and analyzed from 23 trucks of the 27 trucks 

that were road-tested in this study. Five trucks were from company A and six trucks each were 

from companies B, C, and D. Data are missing from four trucks because of problems that were 

encountered with the monitoring equipment. In general, the ranges of instantaneous frequencyweighted RMS accelerations measured in the three axes were between 0.1 and 0.6 m/s2 in the xaxis, 0.15 and 0.7 m/s2 in the y-axis, and 0.15 and 0.8 m/s2 in the z-axis. Three events occurred in 

which the instantaneous acceleration exceeded 1 m/s2 while driving over rough road conditions. 

The TWA equivalent RMS accelerations for the three translational axes for vibration and the Σ 

(comfort) values from the driver seat cushion are listed in the table located in appendix C for 

each truck per type of roadway. Overall, driver seat cushion vibrations were highest from 

company B. However, as shown in the appendix, the EAV for a standard 8-h shift (0.5 m/s2

) was 

not exceeded by any of the trucks in the x-, y-, and z-axes. If the EAV is projected to an 11-h 

shift (0.43 m/s2

), two trucks from company B and one truck from company C approached this 

limit in the y- and z-axes mainly while driving on I-75 and US-27. Finally, reviewing the 

indicator for comfort, it is shown that all sigma values for interstate and highway driving fell 

within the “little uncomfortable region” (i.e., between 0.315 and 0.63 m/s2) for all trucks. 

Graphs of the RMS vibration LS means for truck manufacturer, roadway, and the interaction 

effect of truck manufacturer and roadway for the x-axis are shown in the three figures below: 

REML statistical analysis showed that the truck manufacturer effect (Figure 25) was not 

significant. REML analysis showed that the roadway effect (Figure 26) was significant (p < 

0.001). Accordingly, post-hoc Tukey’s HSD tests showed that the I-75 and US-27 conditions had 

significantly higher RMS vibration values in the x-axis than the I-40 condition at the 0.05 level 

of significance; all other comparisons were not significant. REML analysis also showed a 

significant (p = 0.002) interaction effect between manufacturer and roadway (Figure 27) which 

suggests that the vibration effect of one parameter (e.g., roadway) depends on the effect from the 

other parameter (e.g., truck manufacturer). 

Figure 25. Graph. LS means x-axis vibration vs. truck manufacturer

0.2

0.25

0.3

0.35

RMS (m/s2)

A B C D

Truck Mfr
31

Figure 26. Graph. LS means x-axis vibration vs. roadway

Figure 27. Graph. LS means x-axis vibration vs. roadway and manufacturer

Graphs of the RMS vibration LS means for truck manufacturer, roadway, and the interaction 

effect of truck manufacturer and roadway for the y-axis are shown in the three figures below: 

REML statistical analysis showed that the truck manufacturer effect (Figure 28) was significant 

(p = 0.02). Accordingly, post-hoc Tukey’s HSD tests showed that the trucks from manufacturer 

B had significantly higher RMS vibration values in the y-axis than the trucks from manufacturer 

A at the 0.05 level of significance; all other comparisons were not significant. REML statistical 

analysis showed that the roadway effect (Figure 29) and the roadway-manufacturer interaction 

effect (Figure 30) were both not significant. 

Figure 28. Graph. LS means y-axis vibration vs. truck manufacturer

0.2

0.25

0.3

0.35

RMS (m/s2)

I-40 I-75 US-27

Roadway

0.2

0.25

0.3

0.35

RMS (m/s2)

I-40 I-75 US-27

Roadway

A

B

C

D

0.2

0.3

0.4

RMS (m/s2)

A B C D

Truck Mfr
32

Figure 29. Graph. LS means y-axis vibration vs. roadway

Figure 30. Graph. LS means y-axis vibration vs. roadway and manufacturer

Graphs of the RMS vibration LS means for truck manufacturer, roadway, and the interaction 

effect of truck manufacturer and roadway for the z-axis are shown in the three figures below: 

REML statistical analysis showed that the truck manufacturer effect (Figure 31) was significant 

(p < 0.0001). Accordingly, post-hoc Tukey’s HSD tests showed that the trucks from 

manufacturer B had significantly higher RMS vibration values in the z-axis than the trucks from 

manufacturers A, C and D and trucks from manufacturers C and D had significantly higher RMS 

vibration values than the trucks from manufacturer A, both at the 0.05 level of significance; all 

other comparisons were not significant. REML analysis showed that the roadway effect (Figure 

32) was significant (p < 0.0001). Accordingly, post-hoc Tukey’s HSD tests showed that the I-75 

and US-27 conditions had significantly higher RMS vibration values in the z-axis than the I-40 

condition at the 0.05 level of significance; all other comparisons were not significant. REML 

analysis also showed a significant (p = 0.005) interaction effect between roadway and 

manufacturer (Figure 33) which suggests that the vibration effect of one parameter (e.g., 

roadway) depends on the effect from the other parameter (e.g., truck manufacturer). 

0.2

0.3

0.4

RMS (m/s2)

I-40 I-75 US-27

Roadway

0.2

0.3

0.4

RMS (m/s2)

I-40 I-75 US-27

Roadway

A

B

C

D
33

Figure 31. Graph. LS means z-axis vibration vs. truck manufacturer

Figure 32. Graph. LS means z-axis vibration vs. roadway

Figure 33. Graph. LS means z-axis vibration vs. roadway and manufacturer

Graphs of the RMS vibration LS means for truck manufacturer, roadway, and the interaction 

effect of truck manufacturer and roadway for comfort (Σ values) are shown in the three figures 

below: REML statistical analysis showed that the truck manufacturer effect (Figure 34) was 

significant (p = 0.0001). Accordingly, post-hoc Tukey’s HSD tests showed that the trucks from 

manufacturer B had significantly higher RMS vibration values for comfort than the trucks from 

manufacturers A, C and D and trucks from manufacturers C and D had significantly higher RMS 

vibration values than the trucks from manufacturer A, both at the 0.05 level of significance; all 

other comparisons were not significant. REML analysis showed that the roadway effect (Figure 

35) was significant (p < 0.0001). Accordingly, post-hoc Tukey’s HSD tests showed that the I-75 

and US-27 conditions had significantly higher RMS vibration values for comfort than the I-40 

condition at the 0.05 level of significance; all other comparisons were not significant. REML 

analysis also showed a significant (p = 0.03) interaction effect between roadway and truck 

0.25

0.3

0.35

0.4

RMS (m/s2)

A B C D

Truck Mfr

0.25

0.3

0.35

0.4

RMS (m/s2)

I-40 I-75 US-27

Roadway

0.25

0.3

0.35

0.4

RMS (m/s2)

I-40 I-75 US-27

Roadway

A

B

C

D
34

manufacturer (Figure 36) which suggests that the vibration effect of one parameter (e.g., 

roadway) depends on the effect from the other parameter (e.g., truck manufacturer). 

Figure 34. Graph. LS means Σ (comfort) value vs. truck manufacturer

Figure 35. Graph. LS means Σ (comfort) value vs. roadway

Figure 36. Graph. LS means Σ (comfort) value vs. roadway and manufacturer

In summary, as is typical for most trucks, vibrations in the x-axis and y-axis were generally 

found to be well below the EAV (0.5 m/s2) for an 8-h driving day. In the z-axis, vibrations were 

also found to be below the EAV for an 8-h driving day. Trucks from company A had the lowest 

vibrations overall in the z-axis, relative to trucks from companies B, C, and D. Additionally, as 

seen from the comfort index, trucks from company A had the best comfort performance overall; 

trucks from companies C and D performed similarly in comfort, and trucks from company B fell 

well within the region of a little uncomfortable, which is the Σ range 0.315 to 0.63 m/s2. In 

almost all cases, vibrations from the driver seat cushion were lowest while driving on I-40, as 

compared to driving on I-75 or US-27.

0.35

0.4

0.45

0.5

0.55

RMS (m/s2)

A B C D

Truck Mfr

0.35

0.4

0.45

0.5

0.55

RMS (m/s2)

I-40 I-75 US-27

Roadway

0.35

0.4

0.45

0.5

0.55

RMS (m/s2)

I-40 I-75 US-27

Roadway

A

B

C

D
35

4.4 DUAL-SEAT MONITORING

Analysis of vibrations using accelerometers in both seats will proceed in several stages because 

of the vast amount of data collected and analyzed. The data sets that will be discussed are 

frequency-weighted RMS accelerations, crest factors (CFs), vibration dose values (VDVs), and 

jerk. Of the total of 27 trucks that were road-tested in the study, dual-seat data were collected and 

analyzed from only 24. Seven trucks were from company A, five trucks were from company B, 

and six trucks each were from companies C and D. Missing data from three trucks were caused 

mainly by problems encountered with the instrumentation. 

4.4.1 Root Mean Square

For reference purposes, the TWA equivalent RMS accelerations for the three translational axes 

for vibration and the Σ (comfort) values from the driver seat cushion, the driver back rest, and the 

passenger seat cushion are shown in Appendices F, G, and H, respectively. As shown in these 

tables, vibrations in the x-axis were relatively low across all truck manufacturers. For the driver 

seat cushion of vibration in the y-axis, four trucks exceeded the 8-h EAV (0.5 m/s2

). The 

maximum level in the y-axis was 0.56 m/s2. For the passenger seat cushion of vibration in the yaxis, one truck exceeded the 8-h EAV. In almost every case, the highest vibrations occurred 

while the vehicles were driven on either I-75 or US-27. In the z-axis for the driver and passenger 

seat cushions, the vibrations were lowest for the A trucks and slightly higher for the B, C, and D 

trucks. No trucks however, exceeded the 8-h EAV in the z-axis. If the EAV is projected to an 11-

h shift (0.43 m/s2), seven trucks exceeded the 11-h EAV. These were the same trucks that 

exceeded the 8-h value with the addition of three more vehicles for the driver seat cushion. 

Again these high EAVs were always in the y-axis. Finally, in reviewing the indicators for 

comfort, it is apparent that all sigma values for the driver seat cushion and back rest and the 

passenger seat cushion fell within the “little uncomfortable region“ (i.e., between 0.315 and 0.63 

m/s2) for interstate and highway driving in all trucks.

Graphs of the RMS vibration LS means from the driver seat cushion for truck manufacturer, 

roadway, and the interaction effect of truck manufacturer and roadway just for the comfort (Σ) 

values are shown in the three figures below: REML statistical analysis showed that the truck 

manufacturer effect (Figure 37) was significant (p < 0.0001). Accordingly, post-hoc Tukey’s 

HSD tests showed that the trucks from manufacturers B, C and D had significantly higher RMS 

vibration values for comfort than the trucks from manufacturer A at the 0.05 level of 

significance; all other comparisons were not significant. REML analysis showed that the 

roadway effect (Figure 38) was significant (p < 0.0001). Accordingly, post-hoc Tukey’s HSD 

tests showed that the I-75 and US-27 conditions had significantly higher RMS vibration values 

for comfort than the I-40 condition at the 0.05 level of significance; all other comparisons were 

not significant. REML analysis for the interaction effect between roadway and manufacturer was 

not significant (figure 39). 
36

Figure 37. Graph. LS means comfort value (driver cushion) vs. truck manufacturer

Figure 38. Graph. LS means comfort value (driver cushion) vs. roadway

Figure 39. Graph. LS means comfort value (driver cushion) vs. roadway and manufacturer

Graphs of the RMS vibration (LS means) from the driver back pad for truck manufacturer, 

roadway, and the interaction effect of truck manufacturer and roadway just for the comfort (Σ) 

values are shown in the three figures below: REML statistical analysis showed that the truck 

manufacturer effect (Figure 40) was significant (p = 0.004). Accordingly, post-hoc Tukey’s HSD 

tests showed that the trucks from manufacturers B and D had significantly higher RMS vibration 

values for comfort than the trucks from manufacturer A at the 0.05 level of significance; all other 

comparisons were not significant. REML analysis showed that the roadway effect (Figure 41) 

was significant (p < 0.0001). Accordingly, post-hoc Tukey’s HSD tests showed that the I-75 and 

US-27 conditions had significantly higher RMS vibration values for comfort than the I-40 

condition and the I-75 condition had significantly higher RMS vibration values than the US-27 

condition, both at the 0.05 level of significance; all other comparisons were not significant.

REML analysis for the interaction effect between roadway and manufacturer (Figure 42) was 

0.25

0.35

0.45

0.55

RMS (m/s2)

A B C D

Truck Mfr

0.25

0.35

0.45

0.55

RMS (m/s2)

I-40 I-75 US-27

Roadway

0.25

0.35

0.45

0.55

RMS (m/s2)

I-40 I-75 US-27

Roadway

A

B

C

D
37

also significant (p = 0.006) which suggests that the vibration effect of one parameter (e.g., 

roadway) depends on the effect from the other parameter (e.g., truck manufacturer). 

Figure 40. Graph. LS means comfort value (driver back) vs. truck manufacturer

Figure 41. Graph. LS means comfort value (driver back) vs. roadway

Figure 42. Graph. LS means comfort value (driver back) vs. roadway and manufacturer

Graphs of the RMS vibration (LS means) from the passenger seat cushion for truck 

manufacturer, roadway, and the interaction effect of truck manufacturer and roadway just for the 

comfort (Σ) values are shown in the three figures below: REML statistical analysis showed that 

the truck manufacturer effect was significant (p = 0.009). Accordingly, post-hoc Tukey’s HSD 

tests showed that the trucks from manufacturers B and C had significantly higher RMS vibration 

values for comfort than the trucks from manufacturer A at the 0.05 level of significance; all other 

comparisons were not significant. REML analysis showed that the roadway effect was 

significant (p < 0.0001). Accordingly, post-hoc Tukey’s HSD tests showed that the I-75 and US27 conditions had significantly higher RMS vibration values for comfort than the I-40 condition 

0.3

0.35

0.4

0.45

0.5

RMS (m/s2)

A B C D

Truck Mfr

0.3

0.35

0.4

0.45

0.5

RMS (m/s2)

I-40 I-75 US-27

Roadway

0.3

0.35

0.4

0.45

0.5

RMS (m/s2)

I-40 I-75 US-27

Roadway

A

B

C

D
38

and the I-75 condition had significantly higher RMS vibration values than the US-27 condition, 

both at the 0.05 level of significance; all other comparisons were not significant. REML analysis 

for the interaction effect between roadway and manufacturer was also significant (p = 0.04) 

which suggests that the vibration effect of one parameter (e.g., roadway) depends on the effect 

from the other parameter (e.g., truck manufacturer). 

Figure 43. Graph. LS means comfort value (passenger cushion) vs. truck manufacturer

Figure 44. Graph. LS means comfort value (passenger cushion) vs. roadway

Figure 45. Graph. LS means comfort value (passenger cushion) vs. roadway and manufacturer

In summary, the RMS results from the dual-seat system were very similar to the results from the 

driver’s seat cushion system. Vibrations in the x- and z-axes were generally found to be well 

below the EAV. However, the EAV was exceeded in several trucks for the driver seat cushion in 

the y-axis. Trucks from company A had the lowest vibrations overall in the z-axis relative to 

trucks from companies B, C, and D. Trucks from company A performed best in terms of the 

comfort index, and trucks from company B tended to perform more poorly on comfort. Again in 

0.3

0.4

0.5

0.6

RMS (m/s2)

A B C D

Truck Mfr

0.3

0.4

0.5

0.6

RMS (m/s2)

I-40 I-75 US-27

Roadway

0.3

0.4

0.5

0.6

RMS (m/s2)

I-40 I-75 US-27

Roadway

A

B

C

D
39

almost all cases, the seat vibrations were lowest while driving on I-40 relative to driving on I-75 

or US-27.

Pair-wise correlations between driver and passenger RMS accelerations for the different 

components or sections of the seats are shown in Table 2 for the three translational axes of 

vibration and the Σ values. As shown in the table, the R-values or the correlation coefficients 

between the driver seat cushion and back rest and between the driver and passenger seat cushions 

showed that higher (positive) linear relationships existed for vibrations measured in the z-axis 

and for the comfort index for both sections of the seating comparisons relative to the correlations 

between the x- and y-axes. Moreover, all of the pair-wise correlations, except one in the y-axis 

between the driver cushion and back rest, were statistically significant at greater than the 0.05 

probability level. However, these correlations indicated that there were some moderate 

differences in responses to vibration between the driver and passenger seats and between the 

cushion and back of the driver seat. It should be noted that the driver and passenger seats were 

predominantly identical in construction, except that more seating adjustment controls were 

usually available on the driver seat. In addition, the driver of the trucks was more knowledgeable 

in using the seating adjustments than the person who rode in the passenger seat. 

Table 2. Multivariate Correlations between Driver and Passenger Seating

Pair-wise Correlation Axis or Comfort R-value Probability

Driver Cushion vs. Driver Back Pad X 0.42 0.0003*

Driver Cushion vs. Driver Back Pad Y 0.29 0.0121*

Driver Cushion vs. Driver Back Pad Z 0.74 < 0.0001*

Driver Cushion vs. Driver Back Pad Σ 0.56 < 0.0001*

Driver Cushion vs. Passenger Cushion X 0.49 < 0.0001*

Driver Cushion vs. Passenger Cushion Y 0.13 0.2705

Driver Cushion vs. Passenger Cushion Z 0.78 < 0.0001*

Driver Cushion vs. Passenger Cushion Σ 0.70 < 0.0001*

Note: Data for correlations were from the dual-seat system RMS acceleration values.

* Correlation statistic less than 0.05 probability.

4.4.2 Crest Factor

The ranges of CF values are shown in Table 3 for the three translational axes from the driver seat 

cushion, the driver back rest, and the passenger seat cushion. As previously mentioned, if the CF 

value is greater than 9.0, the basic evaluation method (i.e., the frequency weighted RMS method) 

may be insufficient for evaluating WBV. 
40

Table 3. Range of Values for Crest Factor from Driver and Passenger Seats

Seat CF X-axis CF Y-axis CF Z-axis

Driver Back 8.8–12.5 6.2–8.6 8.2–12.0

Driver Cushion 8.4–19.7 7.4–9.6 7.9–11.1

Passenger Cushion 9.6–14.9 6.7–13.1 7.1–14.8

Table 4 lists the number of trucks in the study that had CF values over 9.0 during vibration 

testing. Inspection of the table shows that high CF values over 9.0 typically occurred in the xand z-axes. According to ISO guidelines, where an additional method of evaluation is used, both 

the basic (RMS) and the (VDV) evaluation data should be reported, and this recommendation 

was followed in the present report. 

Table 4. Total Number of Trucks with CF Values Greater than 9

Seat CF X-axis CF Y-axis CF Z-axis

Driver Back 21 0 18

Driver Cushion 23 6 11

Passenger Cushion 24 1 20
41

4.4.3 Vibration Dose Values

The VDVs for the three axes of translation from the driver seat cushion, the driver back rest, and 

the passenger seat cushion are shown in Appendices I, J, and K, respectively. As shown in these 

tables, the ELV of 21 m/s1.75 was exceeded only once, by the driver seat cushion of truck A6 in 

the x-axis while the truck was driven on US-27. The EAV of 9.1 m/s1.75 was exceeded several 

times. In particular, the EAV was exceeded by the driver seat cushion of truck A6 in the y-axis 

while it was driven again on US-27 and of truck B2 in the x-axis while driving on I-75 and US27. For the driver back rest, the EAV was exceeded only once by the truck C4 in the z-axis while 

driving on I-75. For the passenger seat cushion, the EAV was exceeded again by truck B2, but 

this time in the z-axis while driving on I-75 and US-27 and by truck C4 in the z-axis while 

driving on I-75. In summary, the VDV results from the dual-seat system showed that overall the 

driver and passenger seats were fairly satisfactory in curtailing vibration. Once more, as 

demonstrated in the RMS method, the seat vibrations were lowest while the trucks were driven 

on I-40, as compared to driving on I-75 or US-27.

4.4.4 Jerk

The ranges of jerk values are shown for the three translational axes from the driver seat cushion, 

the driver back rest, and the passenger seat cushion in Table 5. From these comparisons of 

ranges, it is apparent that the driver and passenger seat cushions responded similarly to 

measurements of jerk, with the passenger seat cushion slightly higher overall in jerk values than 

the driver seat cushion. In addition, for the driver and passenger seat cushion, jerk values were 

higher in the x- and y-axes than were the jerk values in the z-axis. This effect was reversed for 

the driver back rest, that is, the jerk values were higher in the z-axis for the driver back rest than 

in the x- and y-axes. These results tend to indicate that the seat cushions and the back rest 

responded differently to conditions of jerk. 

Table 5. Range of Values for Jerk from Driver and Passenger Seats

Seat Jerk X-axis (m/s3) Jerk Y-axis (m/s3) Jerk Z-axis (m/s3)

Driver Back 13–70 22–121 36–305

Driver Cushion 30–339 20–231 12–85

Passenger Cushion 60–463 44–248 25–98

4.5 AIR QUALITY

Air quality data were collected from 27 trucks. Nine trucks were from company A, and six trucks 

each were from companies B, C, and D. There were several instances in which data were not 

collected from an instrument during a particular truck test because of various sampling problems, 

but for the most part, data were collected from all trucks that were rented or leased in this study. 
42

4.5.1 Calibration of Measured Concentrations

4.5.1.1 CO and NOX Analyzers

Calibration for the CO and NOX instruments was confirmed before each truck test, and both 

instruments were recalibrated as the need arose. Zero calibrations were achieved using ultra-pure 

zero air. The CO analyzer was calibrated using 1 ppm CO. The NOX analyzer was calibrated 

using 2 ppm NO and was checked using 0.1 ppm NO2. Spot checks using other concentration 

also were conducted using the dilution mass flow controller. During the early phase of the 

project neither instrument maintained the span calibration over time. These problems were 

remedied by replacing the infrared energy source and the correlation-chopper wheel on the CO 

instrument in-house and having the NOX instrument completely refurbished by the manufacturer. 

After the repairs the zero and span calibrations remained fairly consistent for both instruments 

during the latter stages of the project. 

4.5.1.2 PM Analyzers

The PM2.5 instruments were collocated with a TEOM on 4 separate days, 2 days each for 5-h and 

6-h time periods. Graphs of the 1-h average PM2.5 concentrations for the OPC and DRam versus 

the TEOM are shown in Figure 46 and Figure 47, respectively. The best-fit regression equations 

used to correct the actual DRam and OPC data also are shown in the graphs. A linear equation 

(R2 ~ 0.91) was the best-fit for the OPC and TEOM data. A two-level polynomial or quadratic 

equation (R2 ~ 0.94) was the best-fit equation for the DRam and TEOM data. The probability (p) 

or significance levels associated with the analysis of variance or F-statistic for the two regression 

equations were both less than 0.0001. Significance levels for the parameter estimates were 

determined by Student t-tests. The parameter estimate probability levels for the linear correction 

equation were intercept (3.0), p = 0.004 and slope (0.68), p < 0.0001. For the polynomial 

equation the parameter estimate probability levels were intercept (5.7), p = 0.0019, x-coefficient 

(-0.24), p = 0.03 and x2 coefficient (0.01), p < 0.0001. For the purpose of comparison, a plot of 

the TEOM-corrected DRam and OPC data is shown in Figure 48. The R2 value (~ 0.86) for this 

comparison was reasonable (p < 0.0001) and the slope (~ 0.91) of the best-fit line for the 

corrected data was close to 1.0 (p < 0.0001). It should be noted that all PM2.5 data presented in 

this report were corrected to TEOM values unless otherwise specified, and concentrations are 

reported separately for DRam and OPC. 
43

Figure 46. Graph. OPC to TEOM calibrations curve for PM2.5

Figure 47. Graph. DRam to TEOM calibration curve for PM2.5

Figure 48. Graph. TEOM corrected DRam vs. OPC calibration data for PM2.5

0

5

10

15

20

25

30

35

TEOM (μg/m3)

0 5 10 15 20 25 30 35 40 45 50

OPC (μg/m3)

Y = 0.6818X + 3.0002

R2 = 0.9096

0

5

10

15

20

25

30

35

40

TEOM (μg/m3)

0 10 20 30 40 50 60 70

DRam (μg/m3)

Y = 0.0097X2 - 0.2382X + 5.719

R2 = 0.9368

0

5

10

15

20

25

30

35

OPC (μg/m3)

0 5 10 15 20 25 30 35 40

DRam (μg/m3)

Y = 0.9096X + 1.117

R2 = 0.8555
44

4.5.2 Truck Air Exchange Rates 

The air exchange rates were estimated by releasing the CO2 tracer gas into the cab and measuring 

the decay of the CO2 concentration over a period of time. The average results from this test are 

shown in Table 6 for several different truck engine/HVAC modes of operation and ventilation 

fan speeds. The exchange rate conveys the time in minutes for one cabin volume to replenish or 

exchange itself. The higher the exchange rate, the longer it takes to replenish the outside air in 

the cab. The standard deviation is the plus/minus value reported after the average values listed in 

Table 6. The highest or longest exchange rate occurred when the truck engine and the HVAC 

were both off, which was expected, since this is the extreme case for no mixing of inside and 

outside air. The most rapid exchange rate occurred during engine idling and HVAC on fresh-air 

mode, with dash and sleeper ventilation fans on four and two fan speeds, respectively. 

Table 6. Air Exchange Rates for a Subset of Trucks

Truck 

Count 

(n)

Engine

Mode

HVAC

Mode

Dash Fan 

Speed

Mode

Sleeper 

Fan Speed

Mode

Cabin Air Change Rate 

(min/exchange) Average

± Standard Deviation

3 Off Off 0 0 130 ± 40

1 On Off 0 0 76 ± 0

2 On Recirculated Air 4 0 45.9 ± 16.1

9 On Recirculated Air 4 2 44.1 ± 47.1

3 On Fresh Air 2 2 11.6 ± 5.7

3 On Fresh Air 4 0 5.3 ± 1.8

9 On Fresh Air 4 2 2.7 ± 0.8

As previously mentioned, recirculation may not always be 100 percent recirculated air, to 

prevent the depletion of oxygen in the cab. In fact, the HVAC system from one of the truck 

manufacturers was designed to switch from full recirculation to partial recirculation mode after 

approximately 20 min. This effect is demonstrated in Figure 49, which is a plot of the CO2 decay 

rate during engine idling while the HVAC was in recirculation air mode. Notice that between 

1200 and 1400 seconds(s) on the graph, the slope of the decay curve changed shape. Slopes of 

the best-fit lines for each segment were 0.000387 exchange/s and 0.003582 exchange/s. 

Converting seconds into minutes and inverting the values produce the air exchange rates, which 

are approximately 43 min/exchange and 4.7 min/exchange, respectively, for the earlier and later 

time segments of the CO2 decay curve shown in the figure. Note again that these values are well 

within the range of the values shown in table 6 for the average recirculation and fresh air modes 

of operation for the trucks that were tested. 
45

Figure 49. Graph. Decay curve for CO2 recirculaton air shifting to fresh-air mode

4.5.3 Parked-Idling Test 

Average 1-h concentrations for CO, NOX, and PM2.5 and the ratio of NO to NOX are shown in 

table 7 for the five truck engine/HVAC modes of operation. Bar graphs of this data, excluding 

the NO/NOX ratio, are also shown in Figure 50 and Figure 51. Cursory inspection of the overall 

average data suggests immediately that the different modes of truck engine and HVAC operation 

have a definite influence on the air quality inside the cab. Highest average CO and NOX

concentrations occurred during engine on (or idling) and with the HVAC system in recirculation 

air mode; highest average PM2.5 concentrations occurred during engine on and with the HVAC 

system in fresh air mode. Concentrations of all pollutants were lowest when both the truck 

engine and HVAC were off. Even when the HVAC system was off and the truck engine was on, 

the in-cab concentrations were still generally higher than both the inside or outside background 

concentrations that were measured during the engine off conditions. The relative magnitudes of 

the NO/NOX ratios for the engine/HVAC modes also demonstrated that when the truck engine 

was off, lower ratios were observed especially during the outside air sampling period. 

Table 7. Overall Average 1-h Concentrations from Parked-Idling Test

Truck

Engine

HVAC

System

Sample

Location

CO 

(ppb)

NOX (ppb) NO/NOX PM2.5 DRam 

(μg/m3)

PM2.5 OPC 

(μg/m3)

Off Fan Off In-cab 396 120 0.73 7 14

Off Fan Off Outside 295 119 0.61 13 27

On Fan Off In-cab 508 624 0.85 19 48

On Fresh Air In-cab 472 466 0.81 22 51

On Recirculation In-cab 585 643 0.85 9 28

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Concentration (amp units)

0 200 400 600 800 1000 1200 1400 1600 1800

Time (seconds)

~ 1200 seconds

Y = 0.52 Exp-0.000387X

R2 = 0.99

Y = 29 Exp-0.003582X

R2 = 0.99
46

Figure 50. Graph. Overall average 1-h CO and NOX concentrations from parked-idling test

Figure 51. Graph. Overall average 1-h PM2.5 concentrations from parked-idling test

0

100

200

300

400

500

600

700

Concentration (ppb)

Eng-Off/Inside

Eng-Off/Outside

Eng-On/Fan-Off

Eng-On/FreshA

Eng-On/RecirA

Engine/HVAC Condition

Y

Mean(CO)

Mean(NOx) 0

100

200

300

400

500

600

700

Concentration (ppb)

Eng-Off/Inside

Eng-Off/Outside

Eng-On/Fan-Off

Eng-On/FreshA

Eng-On/RecirA

Engine/HVAC Condition

Y

Mean(CO)

Mean(NOx)

0

10

20

30

40

50

60

Concentration (

μg/m3)

Eng-Off/Inside

Eng-Off/OutsideEng-On/Fan-Off

Eng-On/FreshA

Eng-On/RecirA

Engine/HVAC Condition

Y

Mean(PM2.5 OPC)

Mean(PM2.5 DRam) 0

10

20

30

40

50

60

Concentration (

μg/m3)

Eng-Off/Inside

Eng-Off/OutsideEng-On/Fan-Off

Eng-On/FreshA

Eng-On/RecirA

Engine/HVAC Condition

Y

Mean(PM2.5 OPC)

Mean(PM2.5 DRam) 0

10

20

30

40

50

60

Concentration (

μg/m3)

Eng-Off/Inside

Eng-Off/OutsideEng-On/Fan-Off

Eng-On/FreshA

Eng-On/RecirA

Engine/HVAC Condition

Y

Mean(PM2.5 OPC)

Mean(PM2.5 DRam)
47

Graphs of the CO concentration LS means for truck manufacturer, engine/HVAC condition, and 

the interaction effect of truck manufacturer and engine/HVAC condition are shown in the three 

figures below: REML statistical analysis showed that the truck manufacturer effect (Figure 52) 

was significant (p = 0.01). Accordingly, post-hoc Tukey’s HSD tests showed that the trucks 

from manufacturer A had significantly higher CO concentrations than the trucks from 

manufacturers B and C at the 0.05 level of significance; all other comparisons were not 

significant. REML analysis showed that the engine/HVAC effect (Figure 53) was significant (p 

= 0.005). Accordingly, post-hoc Tukey’s HSD tests showed that the Eng-On/Fan-Off and EngOn/Recirculation Air conditions had significantly higher CO concentrations than the EngOff/Outside condition at the 0.05 level of significance; all other comparisons were not 

significant. REML analysis for the interaction effect between truck manufacturer and 

engine/HVAC condition (Figure 54) was not significant. 

Figure 52. Graph. LS means CO concentration vs. truck manufacturer

Figure 53. Graph. LS means CO concentration vs. engine/HVAC condition

0

500

1000

1500

2000

Conc (ppb)

A B C D

Truck Mfr

0

500

1000

1500

2000

Conc (ppb)

Eng-Off/InsideEng-Off/Outside

Eng-On/Fan-OffEng-On/FreshAEng-On/RecirA

Engine/HVAC Condition
48

Figure 54. Graph. LS means CO concentration vs. engine/HVAC and manufacturer

Graphs of the NOX concentration LS means for truck manufacturer, engine/HVAC condition, 

and the interaction effect of truck manufacturer and engine/HVAC condition are shown in the 

three figures below: REML statistical analysis showed that the truck manufacturer effect (Figure 

55) was not significant. REML analysis showed that the engine/HVAC effect (Figure 56) was 

significant (p = 0.003). Accordingly, post-hoc Tukey’s HSD tests showed that the Eng-On/FanOff and Eng-On/Recirculation Air conditions had significantly higher NOX concentrations than 

the Eng-Off/Inside and Eng-Off Outside conditions at the 0.05 level of significance; all other 

comparisons were not significant. REML analysis for the interaction effect between truck 

manufacturer and engine/HVAC condition (Figure 57) was not significant. 

Figure 55. Graph. LS means NOX concentration vs. truck manufacturer

0

500

1000

1500

2000

Conc (ppb)

Eng-Off/InsideEng-Off/Outside

Eng-On/Fan-OffEng-On/FreshAEng-On/RecirA

Engine/HVAC Condition

A

B

C

D

0

1000

2000

3000

Conc (ppb)

A B C D

Truck Mfr
49

Figure 56. Graph. LS means NOX concentration vs. engine/HVAC condition

Figure 57. Graph. LS means NOX concentration vs. engine/HVAC and manufacturer

Graphs of the PM2.5 (OPC) concentration LS means for truck manufacturer, engine/HVAC 

condition, and the interaction effect of truck manufacturer and engine/HVAC condition are 

shown in the three figures below: REML statistical analysis showed that the truck manufacturer 

effect (Figure 58) was not significant. REML analysis showed that the engine/HVAC effect 

(Figure 59) was significant (p = 0.0001). Accordingly, post-hoc Tukey’s HSD tests showed that 

the Eng-On/Fan-Off and Eng-On/Fresh Air conditions had significantly higher PM2.5 (OPC) 

concentrations than the Eng-Off/Inside condition at the 0.05 level of significance; all other 

comparisons were not significant. REML analysis for the interaction effect between truck 

manufacturer and engine/HVAC condition (Figure 60) was statistically significant (p = 0.05) 

which suggests that the effect of one parameter (e.g., engine/HVAC) depends on the effect from 

the other parameter (e.g., truck manufacturer). 

0

1000

2000

3000

Conc (ppb)

Eng-Off/InsideEng-Off/Outside

Eng-On/Fan-OffEng-On/FreshAEng-On/RecirA

Engine/HVAC Condition

0

1000

2000

3000

Conc (ppb)

Eng-Off/InsideEng-Off/Outside

Eng-On/Fan-OffEng-On/FreshAEng-On/RecirA

Engine/HVAC Condition

A

B

C

D
50

. 

Figure 58. Graph. LS means PM2.5 (OPC) concentration vs. truck manufacturer

Figure 59. Graph. LS means PM2.5 (OPC) concentration vs. engine/HVAC condition

Figure 60. Graph. LS means PM2.5 (OPC) concentration vs. engine/HVAC and manufacturer

Graphs of the PM2.5 (DRam) concentration LS means for truck manufacturer, engine/HVAC 

condition, and the interaction effect of truck manufacturer and engine/HVAC condition are 

shown in the three figures below: REML statistical analysis showed that the truck manufacturer 

effect (Figure 61) was not significant. REML analysis showed that the engine/HVAC effect 

(Figure 62) was significant (p = 0.007). Accordingly, post-hoc Tukey’s HSD tests showed that 

the Eng-On/Fresh Air condition had significantly higher PM2.5 (DRam) concentrations than the 

Eng-Off/Inside condition at the 0.05 level of significance; all other comparisons were not 

0

30

60

90

120

Conc (μg/m3)

A B C D

Truck Mfr

0

30

60

90

120

Conc (μg/m3)

Eng-Off/Inside

Eng-Off/Outside

Eng-On/Fan-Off

Eng-On/FreshAEng-On/RecirA

Engine/HVAC Condition

0

30

60

90

120

Conc (μg/m3)

Eng-Off/Inside

Eng-Off/Outside

Eng-On/Fan-OffEng-On/FreshAEng-On/RecirA

Engine/HVAC Condition

A

B

C

D
51

significant. REML analysis for the interaction effect between truck manufacturer and 

engine/HVAC condition (Figure 63) was not significant. 

Figure 61. Graph. LS means PM2.5 (DRam) concentration vs. truck manufacturer

Figure 62. Graph. LS means PM2.5 (DRam) concentration vs. engine/HVAC condition

Figure 63. Graph. LS means PM2.5 (DRam) concentration vs. engine/HVAC and manufacturer

In summary, trucks manufactured by company A had slightly higher average CO concentration, 

however, no differences between truck manufacturers were observed for the NOX and PM2.5

concentrations. Overall, the average concentrations for all three pollutants were highest for the 

engine-on conditions, as compared to the engine-off conditions. Maximum average CO 

concentration was only approximately 3.5 ppm, and it occurred during Engine-On/Recirculation 

0

20

40

60

Conc (μg/m3)

A B C D

Truck Mfr

0

20

40

60

Conc (μg/m3)

Eng-Off/InsideEng-Off/Outside

Eng-On/Fan-Off

Eng-On/FreshAEng-On/RecirA

Engine/HVAC Condition

0

20

40

60

Conc (μg/m3)

Eng-Off/InsideEng-Off/Outside

Eng-On/Fan-OffEng-On/FreshAEng-On/RecirA

Engine/HVAC Condition

A

B

C

D
52

mode. Nonetheless, the CO concentrations were very low in comparison to the OSHA TWA (50 

ppm). The maximum NOX concentration was approximately 7.3 ppm, and this condition also 

occurred during Engine-On/Recirculation. An OSHA TWA does not exist for NOX. However, 

the TWA for NO is 25 ppm, and the ceiling for NO2 is 5 ppm. Usually between 70 and 80 

percent of the NOX is NO concentration. Since the 90 percent quartile for NOX was about 0.8 

ppm, it is unlikely that the NO or NO2 OSHA standards were exceeded during parked idling. 

The PM2.5 concentrations measured by the OPC and the DRam were relatively high for most of 

the trucks tested, especially during the three engine-on conditions. Several instances occurred in 

which the PM2.5 concentrations were also high in the outside air. It must be noted that most of 

these high concentrations were in reference to the EPA NAAQS for the 24-h (35 μg/m3) and 

annual (15μg/m3) averages. Again, the NAAQS were used for comparison purposes since a 

PM2.5 occupational standard does not exist. Overall, the PM2.5 concentrations as measured by the 

OCP were about 2.5 times larger than the PM2.5 values reported by the DRam for the same group 

of trucks. Approximately 70 percent of the trucks had concentrations around or higher than the 

NAAQS, with these higher concentrations occurring during the several engine-on conditions. 

The correlation coefficient or the R-value between the OPC and the DRam using the 1-h average 

PM2.5 data was approximately 0.81 (p <0.0001) which indicates a fairly good agreement between 

the OPC and the DRam measurements. 

4.5.4 On-Road Test

The average 15-min concentrations from the 27 trucks for CO, NOX, and PM2.5 and the ratio of 

NO to NOX are shown in Table 8 for the three roadways or routes driven during the on-road test. 

Bar graphs of this data, excluding the NO/NOX results, are also shown in Figure 64 and Figure 

65. Cursory inspection of the overall average data shows that the on-road in-cab concentrations 

were relatively low for all the measured pollutants. In particular for the gaseous pollutants, the 

in-cab concentrations were somewhat higher while driving on the interstates than while driving 

on the rural highway and the concentrations on I-40 were somewhat higher than concentrations 

measured on I-75. The overall average CO and NOX concentrations were around 350 ppb and 80 

ppb, respectively. The ratios of NO to NOX were closer to what would normally be expected 

from background air than from NO/NOX ratios, which also indicated that the vehicles were not 

self-polluting themselves while being driven on these roadways. Finally, the overall average 

PM2.5 concentrations were approximately 8 and 12 μg/m3

, as measured by the OPC and DRam 

monitors, respectively. 

Table 8. Overall Average 15-min Concentrations from On-Road Test

Road Type CO (ppb) NOX (ppb) NO/NOX PM2.5 OPC 

(μg/m3)

PM2.5 DRam 

(μg/m3)

Interstate (I-40) 414 109 0.74 9 12

Rural Highway (US-27) 285 39 0.52 7 12

Interstate (I-75) 362 96 0.65 7 13
53

Figure 64. Graph. Overall average 15-min CO and NOX concentrations from on-road test

Figure 65. Graph. Overall average 15-min PM2.5 concentrations from on-road test

Graphs of the CO concentration (LS means) for truck manufacturer, roadway, and the interaction 

effect of truck manufacturer and roadway are shown in Figure 66, Figure 67, and Figure 68, 

respectively. REML statistical analysis showed that the truck manufacturer effect was significant 

(p = 0.006). Tukey-HSD analysis of LS means differences showed that CO concentration for 

truck manufacturer A was significantly different (p = 0.05) from manufacturer C when pair-wise 

comparisons were made among truck companies. REML analysis showed that the roadway effect 

was significant (p < 0.0001). Tukey-HSD analysis of LS means differences showed that CO 

concentrations for roadway I-40 and I-75 were significantly different (p = 0.05) when pair-wise 

comparisons were made with US-27. REML analysis for the interaction effect between truck 

manufacturer and roadway were not significant. 

0

100

200

300

400

500

Concentration (ppb)

I-40 I-75 US-27

Roadway

Y

Mean(CO)

Mean(NOx) 0

100

200

300

400

500

Concentration (ppb)

I-40 I-75 US-27

Roadway

Y

Mean(CO)

Mean(NOx)

0

5

10

15

Concentration (

μg/m3)

I-40 I-75 US-27

Roadway

Y

Mean(PM2.5 OPC)

Mean(PM2.5 DRam) 0

5

10

15

Concentration (

μg/m3)

I-40 I-75 US-27

Roadway

Y

Mean(PM2.5 OPC)

Mean(PM2.5 DRam)
54

Figure 66. Graph. LS means CO concentration vs. truck manufacturer

Figure 67. Graph. LS means CO concentration vs. roadway

Figure 68. Graph. LS means CO concentration vs. roadway and truck manufacturer

Graphs of the NOX concentration (LS means) for truck manufacturer, roadway, and the 

interaction effect of truck manufacturer and roadway are shown in Figure 69, Figure 70, and 

Figure 71, respectively. REML statistical analysis showed that the truck manufacturer effect was 

not significant. REML analysis showed that the roadway effect was significant (p < 0.0001). 

Tukey-HSD analysis of LS means differences showed that NOX concentrations for roadways I40 and I-75 were significantly different (p = 0.05) when pair-wise comparisons were made with 

US-27. REML analysis for the interaction effect between truck manufacturer and roadway were 

not statistically significant. 

0

200

400

600

800

Conc (ppb)

A B C D

Truck Mfr

0

200

400

600

800

Conc (ppb)

I-40 I-75 US-27

Roadway

0

200

400

600

800

Conc (ppb)

I-40 I-75 US-27

Roadway

A

B

C

D
55

Figure 69. Graph. LS means NOX concentration vs. truck manufacturer

Figure 70. Graph. LS means NOX concentration vs. roadway

Figure 71. Graph. LS means NOX concentration vs. roadway and truck manufacturer

Graphs of the PM2.5 (OPC) concentration (LS means) for truck manufacturer, roadway, and the 

interaction effect of truck manufacturer and roadway are shown in Figure 72, Figure 73, and 

Figure 74, respectively. REML statistical analysis showed that the truck manufacturer effect, the 

roadway effect, and the interaction effect between truck manufacturer and roadway were all not 

statistically significant. 

0

100

200

Conc (ppb)

A B C D

Truck Mfr

0

100

200

Conc (ppb)

I-40 I-75 US-27

Roadway

0

100

200

Conc (ppb)

I-40 I-75 US-27

Roadway

A

B

C

D
56

Figure 72. Graph. LS means PM2.5 (OPC) concentration vs. truck manufacturer

Figure 73. Graph. LS means PM2.5 (OPC) concentration vs. roadway

Figure 74. Graph. LS means PM2.5 (OPC) concentration vs. roadway and truck manufacturer

Graphs of the PM2.5 (DRam) concentration (LS means) for truck manufacturer, roadway, and the 

interaction effect of truck manufacturer and roadway are shown in Figure 75, Figure 76, and 

Figure 77, respectively. REML statistical analysis, like the OPC results, showed that the truck 

manufacturer effect, the roadway effect, and the interaction effect between truck manufacturer 

and roadway were all not statistically significant. 

0

4

8

12

16

Conc (μg/m3)

A B C D

Truck Mfr

0

4

8

12

16

Conc (μg/m3)

I-40 I-75 US-27

Roadway

0

4

8

12

16

Conc (μg/m3)

I-40 I-75 US-27

Roadway

A

B

C

D
57

Figure 75. Graph. LS means PM2.5 (DRam) concentration vs. truck manufacturer

Figure 76. Graph. LS means PM2.5 (DRam) concentration vs. roadway

Figure 77. Graph. LS means PM2.5 (DRam) concentration vs. roadway and truck manufacturer

In summary, the in-cab CO and NOX concentrations were higher while driving on the interstate 

than while driving on the State highway. It should be noted that highway traffic was usually 

heavier or more dense on I-40 or I-75, and it is probably this condition that attributed to the 

slightly higher concentrations measured inside the cab. At any rate, the in-cab on-road CO 

concentrations do not appear to be a health-safety problem because even the highest CO 

concentration was less than 1 ppm, which is well below the OSHA 8-h TWA of 50 ppm. Turning 

next to NOX concentration, the maximum overall average was much less than 0.5 ppm. Thus, the 

separate concentrations of NO and NO2 would also be expected to be much less than the OSHA 

PELs of 25 ppm and 5 ppm, respectively. 

The PM2.5 concentrations, in general, were relatively flat across all the trucks except for several 

trucks from company C, where usually high concentrations were measured by the DRam, and 

0

50

100

Conc (μg/m3)

A B C D

Truck Mfr

0

50

100

Conc (μg/m3)

I-40 I-75 US-27

Roadway

0

50

100

Conc (μg/m3)

I-40 I-75 US-27

Roadway

A

B

C

D
58

with higher variability between the trucks from company A. At this juncture, it is strongly felt 

that these values are outliers caused by the vibrating environment of the truck because the DRam 

uses a cyclonic separation device to divert the less than 2.5 μm sized particles to the analyzer 

away from the total size range of particles that initially enters the sampling head. Average PM2.5

measured by the DRam and OPC were 12.2 and 7.4 μg/m3, respectively. The correlation 

coefficient (or the R-value) between the DRam and the OPC using the average 15-min PM2.5

data was approximately 0.65 (p <0.0001).

4.5.5 In-Cab Air Filters

Outside air enters the HVAC system of the cab by way of a vent between the engine hood and 

the glass windshield along the passenger side of the vehicle. The outside air passes a pre-filter 

located in the engine compartment on the right front side of the cab. Almost all sleeper cabs 

today are also equipped with an auxiliary air handling system for recirculating air in the cab. 

This auxiliary system is either located behind the passenger seat under the bunk in the luggage 

storage compartment or in the front of the cab directly beneath the passenger seat. Again, there is 

an air filter for the auxiliary system. Truck manufacturers recommend that these filters be 

inspected, cleaned, and/or replaced after 70,000 mi under normal conditions, and as often as 

every 20,000 mi in dusty conditions. In general, regular replacement of dirty air filters may 

reduce in-cab dust and allergens, and it extends the efficiency and life of the air handling system.

Several photographs showing the general condition of the in-cab air filters and air handling 

systems of the test trucks are shown in Figure 78–Figure 81. As revealed in the photographs, 

good housekeeping maintenance practices were not generally followed. 

Figure 78. Photo. Outside HVAC pre-filter accessible from the engine compartment
59

Figure 79. Photo. Auxiliary air filtration system located under passenger seat

Figure 80. Photo. Auxiliary HVAC system located under sleeper berth not filtered

Figure 81. Photo. Internal air-filter removed from auxiliary HVAC unit.
60

4.5.6 Chemical Analysis of Particulate Matter 

Two fiber filter samples from the EBam analyzers containing PM were sent to a laboratory for 

general chemical evaluation. The filters from the EBam were used because they were the only 

ones available from the study and were considered to most closely characterize a representative 

sample of total particulate matter (TPM) from the cabin environment. One sample respectively 

was collected during the park-idling and on-road tests. The idling filter had heavy deposits of 

very fine, dark particulate in the filtered area. The on-road filter showed similar deposits, as well 

as a number of silvery metallic flakes. Small sections of each filter were sonicated in filtered 

ethanol to remove particulate and the samples of sonicate were spotted onto TEM (transmission 

electron microscopy) grids and allowed to dry. Several of the silvery metallic flakes observed the 

on-road filter were also mounted for elemental analysis by scanning electron microscopy with 

energy dispersive X-ray spectrometry (SEM/EDS). 

4.5.6.1 Parked-Idling Filter

The TEM examination of the particulate from this filter showed abundant aciniform clusters, 

with the characteristic morphology of soot. Individual soot particles ranged from approximately 

10 to 50 nanometers (nm) in size, with an average size of approximately 10–15 nm. The soot 

appeared to be amorphous, and contained traces of sodium and oxygen, along with bulk carbon. 

A representative TEM micrograph is included in Figure 82. Higher magnification of this area is 

shown in Figure 83. Note that some short sections of glass fibers from the filter are visible in the 

images. In addition to the soot, small particles rich in barium, sulfur, and oxygen, and calcium or 

sodium, were also seen, presumably representing various sulfate salts. Zinc was also detected in 

various areas, but its association with the other elements was not clear. 

Figure 82. Photo. TEM micrograph of PM during parked-idling test (0.2-μm scale)
61

Figure 83. Photo. TEM micrograph of PM during parked-idling test (0.1-μm scale)

4.5.6.2 On-Road Filter

This filter also showed predominantly aciniform clusters of sub-micron soot, although they were 

not as well formed as those on the idling filter. Individual spherical particles were not as easily 

discernible as in the other sample; those that could be measured were about 25–30 nm in 

diameter. In addition to carbon, traces of other elements including oxygen, sodium, sulfur, 

chlorine, and silicon were detected in the soot agglomerates. Representative TEM micrographs 

are shown in Figure 84 and Figure 85. Small particles with primarily aluminum silicate 

chemistries were also seen, as well as aluminum oxide particles. The SEM/EDS analysis of the 

larger metal flakes showed that they were an aluminum alloy, with small amounts of magnesium, 

silicon, iron, and copper. The smaller aluminum oxide particles are most likely related to these 

elements. 

Figure 84. Photo. TEM micrograph of PM during on-road test (0.2-μm scale)
62

Figure 85. Photo. TEM micrograph of PM during on-road test (0.1-μm scale)
63

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65

5. CONCLUSIONS

A clear limit to the scope of this study was the small sample size of the test vehicles given that 

the heavy-duty diesel truck population in the U.S. varies greatly by manufacturer and model 

configuration. In this study, only six trucks, each from four different manufacturers were 

represented. A certain evenness of model configuration was achieved however because the truck 

leasing companies that provided the vehicles usually had only the standard model from a single 

manufacturer. On the other hand, none of the test vehicles actually came directly from a 

commercial freight hauling company. So the population of trucks in this sample only represented 

trucks from the rental fleet of trucks. Likewise the sample size of the air cushion seats that were 

represented in the study was small. A single seating supply company represented more than 90 

percent of the seats that were in the vehicles. 

5.1 NOISE LEVEL

Slight differences in noise level were observed between truck manufacturers, but for the most 

part, noise-level conditions were quite similar for all the trucks tested in this study. Higher noise 

averages were generally observed while the trucks were driven on interstates relative to State 

highways. It is thought that noise from tires, engine rpm, and wind impacting the cab at higher 

road speeds contributed to the elevated noise levels measured during interstate travel because 

higher vehicle speeds are permitted on the interstates. Yet, peak and maximum noise levels were 

generally higher on I-40 and US-27 and lower on I-75 which may be due to the fact that the I-75 

terrain was relatively flat compared to I-40 or US-27. Nonetheless, the PEL values from OSHA 

and/or NIOSH were not exceeded by any test truck for the 8-h work standard. Also the action 

limit (AL) was not reached in any tested vehicle. A projection made to the current 11-h driving 

time limit using the worst case truck showed that the estimated dose percent was still below the 

AL. This study tended to show overall noise levels to be somewhat lower than those reported in 

historical studies, which generally revealed noise levels closer but below the PEL and greater 

than the AL. However, it should be noted that in several of the historical studies, the truck 

windows were open and noise levels were measured during the entire driving shift, which could 

include certain warehouse activities like the loading and unloading of freight. In the present 

study the windows were always closed on the test trucks and noise levels were measured only 

while the trucks were driven at a regular cruising speed on the interstate or State highway. 

5.2 WHOLE-BODY VIBRATION

Differences between truck manufacturers with respect to vibration were somewhat more 

pronounced than the noise-level differences observed between truck manufacturers. Overall 

however, the vibrations from the driver and passenger seats were generally well below the 

European Union (EU) exposure action value (EAV) for an 8-h driving day. Several isolated 

incidents occurred in which the exposure limit value (ELV) was exceeded, but for the most part, 

these occurred while the trucks were being driven over poorer road pavement conditions. 

Generally, the interstate roads are better maintained than most State highways; but variability in 

roadway maintenance exists from region to region, even on the interstate system. 
66

When projections were made to the current 11-h driving time limit, seven trucks were actually 

over the EAV, but these occurrences were always in the y-axis, which is side-to-side vibration, 

rather than in the z-axis, which is up-and-down vibration. It must be mentioned again that a

much higher health risk to the lumbar spine region from WBV in the z-axis exists for the seated 

person than from vibration in the y-axis. Finally, the comfort index of the seats, by and large 

these indicators fell within the “a little uncomfortable” region—one step removed from the best 

possible index, which is the “not uncomfortable” region. One needs to be aware that this is a 

relative category scale resulting from extensive research conducted mainly in Europe over the 

past several decades, but since the comfort index of these seats did not fall below the optimal 

level, some possibility however still exists for future improvement in the comfort level of the 

seats. 

5.3 AIR QUALITY

5.3.1 Parked-Idling Test

Overall CO, NOX, and PM2.5 concentrations were relatively low inside the cab when both the 

engine and HVAC were in off modes. Highest CO and NOX concentrations occurred during 

engine-on and HVAC-recirculation modes; high PM2.5 concentrations occurred during engine-on 

and HVAC-fresh-air modes and during engine-on and fan-off modes. These results suggest that 

long-haul trucks have a tendency to self-pollute the cab during extended periods of parked idling.

Self-pollution occurs when a percentage of the vehicle’s own exhaust enters the cab. It is 

believed that this problem and the close proximity of many trucks idling at the same time in the 

truck-stop rest areas create the conditions for diesel exhaust to enter the cab via the HVAC 

system or naturally from air infiltration around window and door seals and from other areas. 

These results were in line with a similar study that measured in-cab concentrations during several 

parked-engine-idling conditions at another truck-stop rest area. 

The measured concentrations of CO and NOX for all of the engine/HVAC modes of operation 

were well below the OSHA 8-h TWA and should not pose health problems for drivers sleeping 

in the cabs during rest periods. However, measured concentrations of PM2.5, which is known to 

cause certain respiratory and other health problems, were around the limits set by the EPA for 

the NAAQS for the 24-h and annual averages. It should be noted that these EPA standards are 

ambient air monitoring standards that were set to protect general public health, including the 

health of sensitive populations such as asthmatics, children, and the elderly and were used only 

for comparison purposes in this study because industrial or workplace PM2.5 limits have not been 

established by OSHA. Primary and secondary NAAQS exist for CO, lead, nitrogen dioxide, 

particulate matter, ozone, and sulfur dioxide. Areas not meeting these NAAQS are required to 

create an implementation plan to meet the standards within a certain time period. The regulatory 

language is framed in terms of attainment levels, and the averaging times for the NAAQS are 

different from typical workplace averaging times. Also, some doubt exists as to whether the 

sleeper berth area of HDDVs and the workplace setting are in fact identical environments. 

5.3.2 On-Road Test

The CO, NOX, and PM2.5 concentrations were relatively low inside the cab while driving on the 

roadways, which suggests that under those conditions, there was much less likelihood of trucks 
67

self-polluting the cabin areas. In comparison, the overall average concentrations during parked 

idling were approximately 1.5, 7.1, and 3.0 times greater, respectively, than the overall average 

on-road concentrations. The in-cab concentrations were usually higher, however, while driving 

on interstates than while driving on the State highways, even though the overall concentrations 

were low. This is believed to be caused by the higher vehicle densities prevalent on the interstate 

system, as a result of which more pollutants enter the vehicle via the HVAC system. These 

results suggest that the highway environment, rather than the truck itself, is the cause of the air 

pollution exposure for the truck driver. 
68

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69

6. RECOMMENDATIONS

Results of this study suggests that two main areas of concern are the comfort level of the seats 

and the high PM2.5 concentrations measured in the cab during periods of extended engine idling. 

Although the noise levels inside the cabs were reasonably low, this condition was likely the 

result of furnishings by the manufacturer, such as wall padding, privacy curtains, floor carpeting, 

and engine firewall insulation which have the combined effect of attenuating sound. 

Seating

It is noteworthy to mention that the same driver drove all the test trucks and was knowledgeable 

in the operation of the seats. Heavy-duty trucks have pneumatically operated seats with multiple 

adjustments to control the cushion, lumbar (or back) support, isolator engagement, fore and aft 

adjustment, height adjustment, cushion angle, and armrest angle. For the most part, none of these 

factors were controlled or standardized to any degree in this study. Current human exposure 

guidelines do not reflect the relationships between poor posture and driving posture, various seat 

configurations (e.g., seat back/cushion reclining angle) and/or sitting postures (e.g., torso/knee 

angle) and possible adjustments of the seat relative to the steering wheel. Additional research is 

required to determine the optimal active seating adjustments which can minimize WBV. Also, it 

may be necessary to develop an effective strategy to train drivers in the proper use of the seating 

adjustments, so that they may use the seat controls to the full effect. 

: Nearly all of the seats in the test vehicles came from a single seating manufacturer. In 

addition, the vehicles were lease- or rental- trucks, so it was likely that the standard (not the 

optional) seats had been furnished in the trucks because of cost. Even though, the seats in these 

test vehicles were adequate in reducing WBV, opportunity still exists for improvement in the 

comfort index, since the levels reported in this study were not optimal ones. Past questionnairetype studies have also indicated driver seating discomfort. Additional areas that should be 

investigated are potential spinal damage from vibration, and how seating vibration might be 

affected by fore and aft location of the fifth-wheel and/or from the usage of single-wide tires. 

The fifth-wheel is the coupling device used on truck-tractors to connect trailers. The location of 

the fifth-wheel is not fixed and can be adjusted to distribute trailer load over the drive axels, thus 

possibly influencing truck ride quality. Single-wide tires are slightly wider than traditional dual 

tires and can replace the double tires on each end of a drive or trailer axle. By reducing rolling 

friction, single-wide tires are a fuel savings innovation and can also possibly influence truck ride 

quality. 

Air Quality

The idling engine self-pollutes the cab for the resting driver. In addition, numerous trucks parked 

and idling together in close proximity at a rest area exacerbates the air-quality problem in the 

cabs for the drivers, as well as for persons working at the truck-stop. Since a possible PM2.5

problem exists, it is likely that other gaseous hydrocarbon emissions, such as 1-3 butadiene, 

formaldehyde or acetaldehyde, may also be present in the cab during extended periods of parked 

: Offering a recommendation in this area is somewhat complicated because the most 

straightforward solution for improving the air quality in the cabin during periods of parked idling 

would be simply to prohibit engine idling while a driver is resting in the sleeper berth. However, 

to do this would severely limit the driver’s use of the vehicle’s heat and air conditioning, and 

comfort appliances such as a microwave or television, that depend on the idling engine to 

operate. 
70

engine idling. Several of these substances are toxic hazardous air contaminants which are 

regulated in the workplace by OSHA, unlike PM2.5 concentration. 

A diesel particulate matter exposure limit has been established by the U.S Mine Safety and 

Health Administration (MSHA) for personal working in underground mines. This PEL (160 

μg/m3) is based on the airborne concentration of total carbon (TC)35. (TC = EC + OC) However, 

it should also be pointed out that the MSHA standard, while applicable in the mining workplace 

environment, does not apply to drivers who are resting in a travel center, as this is not defined at 

the present time as a workplace environment. Additional research is needed to better define and 

identify whether other diesel engine combustion hydrocarbons, including TC, are present above 

acceptable workplace exposure limits in the cabin during periods of extended idling. 

The in-cab air quality during periods of parked-engine idling at truck-stop rest areas continues to 

be an issue which warrants further study. Design and testing of cabin air-filtration/purification 

systems are several possible areas for research. However, these systems, with typical low air 

flow rates may prove to be inadequate in reducing concentrations within the cabin environment 

because of the high cabin air exchange rates which exist in current cabs between inside and 

outside air, as measured and described elsewhere in this report. 

External HVAC systems have also been reported to be successful in reducing in-cab pollutant 

concentrations These systems use a high air exchange rate, provide a mechanism for the truck 

engine to be off, and provide external air filtration, thus substantially reducing in-cab 

concentrations. Other technologies aimed at idle reduction include auxiliary power units (APU). 

The APU provides an alternative to the truck’s main engine when power is needed for electricity 

or heating and cooling the cab during rest periods. They can be small diesel-fired generators or 

heaters, battery air conditioning units and other thermal storage systems. 
71

APPENDIX A—EXPOSURE STANDARDS OR RECOMMENDED VALUES

Table 9: Exposure Standards or Recommended Values

Item ACGIH (TLV) NIOSH (REL) OSHA (PEL) EPA (NAAQS) ISO/EU (RMS) EU (VDM) Jerk

Noise - 85 dBA

8-h TWA

90 dBA

8-h TWA - - -

WBV - - - -

EAV 0.5 m/s2

ELV 1.15 m/s2

Driving 8-h day

EAV 9.1 m/s1.75

ELV 21 m/s1.75

Driving 8-h day

None

CO 50 ppm

TWA

35 ppm

TWA

50 ppm

TWA

9 ppm

8-h average1 - - -

CO 400 ppm

STEL

200 ppm

Ceiling

50 ppm

TWA

35 ppm

1-h average1 - - -

NO 25 ppm

TWA

25 ppm

TWA

25 ppm

TWA - - - -

NO2

3 ppm

TWA

1 ppm

STEL

1 ppm

STEL

0.053 ppm NO2

Annual average2 - - -

NO2

5 ppm

STEL

1 ppm

STEL

5 ppm

Ceiling

0.053 ppm NO2

Annual average2 - - -

PM2.5 None None None 15 ug/m3

Annual average2 - - -

PM2.5 None None None 35 ug/m3

24-h average3 - - -

Symbols: AGCIH = American Conference of Governmental Industrial Hygienists; CO = Carbon monoxide; dBA = Decibel (A-filter); EAV = Exposure action value; ELV = 

Exposure limit value; EPA = Environmental Protection Agency; EU = European Union; ISO = International Organization for Standardization; NAAQS = National ambient 

air quality standards; NIOSH = National Industrial of Occupational Safety and Health; NO = Nitrogen oxide; NO2 = Nitrogen dioxide; NOX = Oxides of nitrogen; OSHA = 

Occupational Safety and Health Administration; PEL = Permissible exposure limit; PM2.5 = Particulate matter; REL = Recommended exposure limit; RMS = Root mean 

square; STEL = Short-term exposure limit; TLV = Threshold limit value; TWA = Time weighted average; VDV = Vibration dose method; WBV = Whole-body vibration. 

Footnotes: 1 not to be exceeded more than once per year; 2 3-yr average must not exceed this value; 3 3-yr average of the 98th percentile must not exceed this value.
72

APPENDIX B—ON-ROAD IN-CAB AVERAGE NOISE LEVELS PER TRUCK

Table 10: On-Road In-Cab Average Noise Levels Per Truck Manufacturer, and OSHA and ISO Integrator Measurements

Truck 

Mfr

Truck 

Test 

No.

Peak 

(dBC)

Min 

LMin

(dBA)

Max 

LMax

(dBA)

OSHA 

Dose

(%)

OSHA 

Estimated 

Dose (%)

OSHA 

Leq

(dBA)

OSHA 8-h 

TWA 

(dBA)

ISO

Dose

(%)

ISO

Estimated 

Dose (%)

ISO

Leq

(dBA)

ISO 8-h 

TWA 

(dBA)

A 2 127.2 64.7 93.8 2.9 8.1 71.8 64.5 8.8 24.1 78.8 74.4

A 3 120.8 64.7 93.9 2.2 6.4 70.1 62.2 7.2 21.2 78.2 73.5

A 4 138.8† 65.4 95.4 3.8† 10.7† 73.8† 66.3† 10.5† 29.5† 79.6† 75.1†

A 6 118.0 64.0 97.5† 2.0 5.1 68.2 61.4 7.4 18.7 77.6 73.5

A 7 111.6 65.7 88.6 1.8 4.8 68.0 60.9 6.7 18.0 77.5 73.2

A 8 114.4 65.2 90.2 3.0 9.5 72.9 64.6 8.7 27.3 79.3 74.3

A 9 113.6 65.2 88.6 1.1 3.2 65.1 57.3 5.3 15.7 76.9 72.2

B 1 117.6 64.8 94.8 1.3 3.7 66.1 58.8 6.3 17.3 77.3 72.9

B 2 116.8 66.5 89.1 0.1* 0.2* 44.5* 36.6* 3.8 11.4 75.5 70.8

B 3 118.8 65.7 95.3 0.2 0.5 52.4 44.3 3.4 10.5 75.2 70.3

B 5 118.8 65.8 91.9 0.2 0.5 52.1 44.2 3.8 11.4 75.5 70.8

C 1 111.2* 63.5 87.8* 0.4 1.2 58.3 50.7 3.0* 8.6* 74.3* 69.7*

C 2 112.8 66.0 92.1 0.3 0.9 56.4 48.7 4.4 12.8 76.0 71.4

C 3 116.0 67.7 95.5 0.3 0.7 54.5 47.6 4.9 13.0 76.1 71.9

C 4 118.4 69.3† 90.8 0.5 1.5 59.9 51.8 6.1 18.8 77.7 72.8

C 5 112.8 66.5 90.8 0.4 1.2 57.9 50.1 4.6 13.5 76.3 71.5

D 1 120.8 65.6 93.4 1.0 2.7 64.3 56.8 5.3 14.9 76.9 72.4

D 2 116.4 64.9 93.8 0.1* 0.4 50.4 42.5 3.0* 9.0 74.5 69.8

D 3 114.8 65.5 91.5 0.1* 0.4 50.0 42.1 3.3 10.0 74.9 70.2

D 4 115.2 64.6 93.6 0.9 2.6 63.6 55.7 5.4 16.1 77.0 72.2

D 5 115.2 61.3* 93.5 0.3 1.1 57.4 48.9 3.8 12.4 75.9 70.8

D 6 128.0 63.5 93.8 1.6 4.7 67.9 60.2 6.7 19.5 77.9 73.2

* Minimum values; †Maximum values; Dose (%) and TWA values are not referenced over an actual or total 8-h work shift. 
73

APPENDIX C—DRIVER SEAT CUSHION RMS VALUES PER ROADWAY

Table 11. Driver Seat Cushion RMS Values Axis of Translation or m/s2 Comfort vs. Roadway

Truck 

Mfr.

Truck 

Test 

No.

X-axis 

I-40

X-axis 

US-27

X-axis 

I-75

Y-axis 

I-40

Y-axis 

US-27

Y-axis 

I-75

Z-axis 

I-40

Z-axis 

US-27

Z-axis 

I-75

Σ I-40 Σ US27Σ I-75

A 5 0.24 0.24 0.28 0.25 0.20 0.28 0.23 0.26 0.27 0.34 0.34 0.39

A 6 0.25 0.26 0.31 0.23 0.24 0.28 0.25 0.32 0.31 0.35 0.41 0.43

A 7 0.29 0.31 0.32 0.24 0.25 0.29 0.23 0.29 0.29 0.36 0.41 0.43

A 8 0.24 0.24 0.24 0.21 0.23 0.23 0.24 0.25 0.26 0.33 0.35 0.35

A 9 0.20 0.19 0.21 0.33 0.38 0.35 0.29 0.32 0.32 0.40 0.45 0.43

B 1 0.30 0.34 0.32 0.31 0.31 0.31 0.35 0.40 0.38 0.47 0.52 0.50

B 2 0.29 0.36 0.30 0.36 0.35 0.32 0.36 0.38 0.38 0.49 0.53 0.50

B 3 0.24 0.28 0.27 0.31 0.36 0.33 0.36 0.40 0.40 0.45 0.52 0.50

B 4 0.25 0.25 0.25 0.35 0.31 0.29 0.41† 0.40 0.41 0.51† 0.49 0.50

B 5 0.24 0.29 0.30 0.36 0.40 0.39 0.33 0.42† 0.40 0.45 0.54 0.53

B 6 0.28 0.31 0.30 0.37 0.45† 0.44† 0.33 0.40 0.39 0.47 0.55† 0.55†

C 1 0.20 0.25 0.24 0.22 0.26 0.27 0.31 0.37 0.37 0.37 0.45 0.45

C 2 0.21 0.24 0.25 0.36 0.32 0.30 0.34 0.42 0.41† 0.46 0.51 0.48

C 3 0.21 0.25 0.24 0.25 0.27 0.26 0.31 0.38 0.37 0.39 0.46 0.45

C 4 0.28 0.36† 0.34† 0.27 0.34 0.33 0.30 0.38 0.39 0.41 0.52 0.51

C 5 0.26 0.31 0.29 0.34 0.39 0.37 0.30 0.38 0.38 0.43 0.52 0.51

C 6 0.23 0.26 0.29 0.27 0.29 0.32 0.28 0.33 0.38 0.38 0.43 0.49

D 1 0.27 0.28 0.30 0.36 0.35 0.31 0.30 0.32 0.32 0.44 0.44 0.44

D 2 0.20 0.23 0.24 0.34 0.34 0.34 0.31 0.34 0.35 0.42 0.45 0.46

D 3 0.29 0.28 0.31 0.28 0.29 0.29 0.32 0.31 0.34 0.42 0.42 0.46

D 4 0.28 0.28 0.30 0.30 0.41 0.36 0.31 0.34 0.34 0.43 0.50 0.48

D 5 0.35† 0.33 0.33 0.37† 0.37 0.34 0.31 0.34 0.32 0.48 0.49 0.46

D 6 0.24 0.26 0.29 0.33 0.34 0.32 0.31 0.32 0.35 0.43 0.43 0.47

†Maximum values; if the 8-h EAV has been exceeded, the values are underlined.
74

APPENDIX D—DRIVER SEAT CUSHION RMS VALUES PER ROADWAY

Table 12. Driver Seat Cushion RMS Values Axis of Translation m/s2 or Comfort vs. Roadway

Truck 

Mfr.

Truck 

Test 

No.

X-axis 

I-40

X-axis 

US-27

X-axis 

I-75

Y-axis 

I-40

Y-axis 

US-27

Y-axis 

I-75

Z-axis 

I-40

Z-axis 

US-27

Z-axis 

I-75

Σ I-40 Σ US27Σ I-75

A 3 0.17 0.21 0.20 0.21 0.23 0.23 0.18 0.24 0.21 0.27 0.33 0.30

A 4 0.22 0.23 0.23 0.22 0.21 0.23 0.20 0.22 0.21 0.30 0.31 0.32

A 5 0.20 0.22 0.20 0.21 0.21 0.23 0.21 0.22 0.23 0.30 0.31 0.31

A 6 0.20 0.24 0.23 0.20 0.22 0.23 0.20 0.21 0.22 0.29 0.31 0.31

A 7 0.20 0.22 0.24 0.22 0.24 0.24 0.25 0.27 0.29 0.33 0.35 0.38

A 8 0.16 0.18 0.17 0.21 0.22 0.21 0.23 0.23 0.23 0.30 0.31 0.30

A 9 0.16 0.18 0.17 0.39 0.53 0.43 0.23 0.24 0.25 0.38 0.46 0.42

B 2 0.23† 0.42† 0.35† 0.37 0.40 0.35 0.31 0.34 0.34 0.44 0.54 0.49

B 3 0.20 0.23 0.22 0.36 0.41 0.38 0.31 0.32 0.35 0.43 0.47 0.47

B 4 0.19 0.22 0.20 0.39 0.38 0.33 0.35† 0.36 0.39 0.47 0.48 0.48

B 5 0.20 0.24 0.24 0.41 0.44 0.42 0.30 0.35 0.38 0.44 0.50 0.51

B 6 0.21 0.26 0.23 0.38 0.50 0.45 0.31 0.36 0.36 0.44 0.54 0.52

C 1 0.20 0.26 0.24 0.29 0.35 0.34 0.23 0.27 0.27 0.35 0.41 0.40

C 2 0.17 0.20 0.22 0.49† 0.41 0.38 0.30 0.35 0.37 0.48 0.48 0.48

C 3 0.17 0.21 0.21 0.31 0.31 0.29 0.26 0.32 0.32 0.36 0.41 0.41

C 4 0.18 0.23 0.21 0.30 0.39 0.35 0.32 0.37† 0.39† 0.40 0.49 0.49

C 5 0.23 0.27 0.26 0.45 0.55† 0.56† 0.34 0.35 0.34 0.50† 0.56† 0.56†

C 6 0.21 0.24 0.23 0.30 0.31 0.31 0.26 0.30 0.33 0.37 0.41 0.43

D 1 0.21 0.25 0.23 0.40 0.40 0.34 0.27 0.31 0.31 0.42 0.46 0.42

D 2 0.16 0.20 0.20 0.42 0.37 0.34 0.27 0.30 0.31 0.42 0.43 0.42

D 3 0.19 0.20 0.21 0.30 0.29 0.29 0.29 0.29 0.32 0.38 0.38 0.41

D 4 0.19 0.22 0.21 0.35 0.52 0.41 0.26 0.29 0.29 0.39 0.50 0.43

D 5 0.21 0.24 0.22 0.30 0.30 0.29 0.24 0.27 0.27 0.36 0.39 0.37

D 6 0.18 0.20 0.21 0.43 0.43 0.37 0.28 0.30 0.32 0.44 0.45 0.44

†Maximum values and/or if the 8-h EAV has been exceeded, the values are underlined. 
75

APPENDIX E—DRIVER BACK REST RMS VALUES PER ROADWAY

Table 13. Driver Back Rest RMS Values Axis of Translation m/s2 or Comfort vs. Roadway

Truck 

Mfr.

Truck 

Test 

No.

X-axis 

I-40

X-axis 

US-27

X-axis 

I-75

Y-axis 

I-40

Y-axis 

US-27

Y-axis 

I-75

Z-axis 

I-40

Z-axis 

US-27

Z-axis 

I-75

Σ I-40 Σ US27Σ I-75

A 3 0.23 0.30 0.29 0.22 0.23 0.25 0.22 0.27 0.25 0.32 0.38 0.37

A 4 0.26 0.29 0.28 0.23 0.23 0.25 0.23 0.25 0.24 0.34 0.37 0.36

A 5 0.23 0.27 0.26 0.22 0.23 0.27 0.26 0.26 0.27 0.35 0.37 0.38

A 6 0.27 0.28 0.30 0.21 0.22 0.25 0.23 0.24 0.26 0.34 0.35 0.38

A 7 0.23 0.25 0.27 0.23 0.23 0.24 0.33 0.32 0.33 0.40 0.41 0.42

A 8 0.21 0.23 0.22 0.23 0.21 0.21 0.32 0.31 0.30 0.39 0.38 0.37

A 9 0.21 0.23 0.24 0.22 0.21 0.24 0.23 0.22 0.24 0.31 0.31 0.34

B 2 0.24 0.27 0.26 0.24 0.23 0.23 0.33 0.33 0.35 0.41 0.42 0.43

B 3 0.25 0.29 0.29 0.23 0.23 0.24 0.30 0.29 0.32 0.39 0.39 0.42

B 4 0.25 0.28 0.26 0.22 0.23 0.25 0.32 0.31 0.35 0.40 0.40 0.44

B 5 0.25 0.29 0.30 0.23 0.24 0.27 0.34 0.36 0.42 0.42 0.45 0.51

B 6 0.22 0.27 0.26 0.23 0.24 0.23 0.37† 0.35 0.39 0.44† 0.43 0.46

C 1 0.25 0.31† 0.29 0.21 0.23 0.23 0.20 0.24 0.23 0.31 0.36 0.35

C 2 0.24 0.27 0.30 0.26 0.25 0.30 0.27 0.29 0.33 0.37 0.39 0.45

C 3 0.23 0.27 0.28 0.23 0.24 0.27 0.22 0.28 0.29 0.32 0.39 0.40

C 4 0.22 0.29 0.26 0.19 0.22 0.24 0.35 0.39† 0.45† 0.41 0.47** 0.52**

C 5 0.24 0.29 0.29 0.27 0.25 0.31† 0.30 0.36 0.37 0.40 0.45 0.48

C 6 0.22 0.25 0.25 0.25 0.24 0.27 0.28 0.30 0.33 0.37 0.39 0.42

D 1 0.25 0.28 0.30 0.31† 0.25 0.25 0.29 0.33 0.32 0.41 0.42 0.42

D 2 0.20 0.24 0.23 0.27 0.23 0.26 0.31 0.33 0.34 0.40 0.41 0.43

D 3 0.24 0.27 0.28 0.23 0.21 0.24 0.33 0.32 0.37 0.41 0.40 0.46

D 4 0.24 0.30 0.29 0.23 0.24 0.25 0.32 0.35 0.36 0.40 0.45 0.45

D 5 0.22 0.28 0.27 0.26 0.26† 0.28 0.32 0.34 0.36 0.41 0.44 0.45

D 6 0.28† 0.29 0.33† 0.27 0.23 0.25 0.31 0.32 0.35 0.42 0.41 0.46

†Maximum values and/or if the 8-h EAV has been exceeded, the values are underlined. 
76

APPENDIX F—PASSENGER SEAT CUSHION RMS VALUES PER ROADWAY

Table 14. Passenger Seat Cushion RMS Values Axis of Translation m/s2 or Comfort vs. Roadway

Truck 

Mfr.

Truck 

Test 

No.

X-axis 

I-40

X-axis 

US-27

X-axis 

I-75

Y-axis 

I-40

Y-axis 

US-27

Y-axis 

I-75

Z-axis 

I-40

Z-axis 

US-27

Z-axis 

I-75

Σ I-40 Σ US27Σ I-75

A 3 0.17 0.23 0.22 0.21 0.23 0.23 0.18 0.23 0.21 0.32 0.40 0.38

4 0.17 0.17 0.19 0.23 0.24 0.26 0.26 0.28 0.25 0.39 0.41 0.41

5 0.16 0.20 0.18 0.22 0.25 0.24 0.24 0.24 0.25 0.37 0.40 0.39

6 0.15 0.21 0.18 0.22 0.25 0.23 0.26 0.25 0.27 0.37 0.41 0.40

7 0.15 0.17 0.18 0.20 0.20 0.20 0.30 0.30 0.33 0.39 0.40 0.43

8 0.15 0.17 0.17 0.20 0.19 0.18 0.26 0.27 0.26 0.36 0.37 0.36

9 0.18 0.19 0.19 0.21 0.21 0.22 0.28 0.27 0.30 0.40 0.39 0.42

B 2 0.24 0.32 0.27 0.25 0.30† 0.26 0.31 0.35 0.35 0.46 0.56 0.51

3 0.21 0.22 0.23 0.21 0.21 0.21 0.28 0.29 0.32 0.41 0.43 0.45

4 0.22 0.21 0.20 0.19 0.20 0.20 0.28 0.31 0.35 0.40 0.43 0.45

5 0.29† 0.32† 0.37† 0.20 0.21 0.23 0.30 0.34 0.37 0.47 0.51 0.57

6 0.18 0.20 0.20 0.21 0.21 0.21 0.32 0.33 0.36 0.42 0.44 0.46

C 1 0.16 0.21 0.19 0.20 0.23 0.21 0.19 0.22 0.20 0.32 0.38 0.35

2 0.23 0.27 0.33 0.24 0.23 0.27 0.31 0.31 0.39 0.46 0.48 0.57

3 0.18 0.21 0.21 0.21 0.23 0.24 0.25 0.31 0.34 0.37 0.44 0.46

4 0.19 0.23 0.24 0.19 0.21 0.21 0.39† 0.43† 0.51† 0.47 0.53 0.61

5 0.21 0.24 0.25 0.25 0.23 0.27† 0.36 0.37 0.38 0.48 0.50 0.53

6 0.18 0.20 0.23 0.24 0.22 0.24 0.31 0.32 0.38 0.43 0.44 0.50

D 1 0.16 0.19 0.19 0.26† 0.22 0.21 0.29 0.33 0.32 0.42 0.44 0.43

2 0.17 0.21 0.19 0.25 0.23 0.25 0.26 0.29 0.29 0.40 0.43 0.43

3 0.16 0.19 0.19 0.20 0.22 0.22 0.29 0.32 0.34 0.39 0.43 0.45

4 0.16 0.20 0.19 0.21 0.22 0.22 0.29 0.32 0.34 0.39 0.44 0.45

5 0.16 0.19 0.18 0.25 0.25 0.26 0.30 0.32 0.33 0.42 0.45 0.46

6 0.17 0.19 0.20 0.24 0.21 0.22 0.28 0.30 0.34 0.41 0.41 0.46

†Maximum values; if the 8-h EAV has been exceeded, the values are underlined. 
77

APPENDIX G—DRIVER SEAT CUSHION VDV PER ROADWAY

Table 15. Driver Seat Cushion VDV Axis of Translation m/s2 or Comfort vs. Roadway

Truck Mfr. Truck 

Test No.

X-axis

I-40

X-axis US27X-axis 

I-75

Y-axis 

I-40

Y-axis 

US-27

Y-axis 

I-75

Z-axis 

I-40

Z-axis 

US-27

Z-axis 

I-75

A 3 2.9 3.3 3.1 3.2 3.4 3.4 3.7 4.9 4.0

A 4 3.7 3.7 3.6 3.2 3.1 3.5 4.1 4.3 4.5

A 5 3.3 3.3 3.0 3.2 3.2 3.2 3.9 4.5 4.1

A 6 3.3 23.7† 3.6 3.2 11.6† 3.4 3.8 4.2 4.3

A 7 3.2 3.3 3.5 3.0 3.3 3.4 4.7 5.3 6.0

A 8 2.9 3.1 2.6 2.9 3.1 3.0 4.3 4.6 4.5

A 9 2.6 2.8 2.5 6.9 8.8 7.2 4.7 4.9 4.8

B 2 3.9 14.8† 12.7† 5.4 6.9 6.0 6.1 7.7† 7.5

B 3 3.7 3.5 3.4 5.6 6.4 5.7 6.4 6.6 7.0

B 4 3.7 3.4 3.1 5.9 5.8 4.7 6.9† 7.4 7.6

B 5 3.4 3.5 3.5 6.8 6.9 6.4 6.3 7.0 7.4

B 6 3.4 3.8 3.4 6.0 7.8 6.7 6.5 7.2 7.2

C 1 4.0 4.2 4.1 4.3 5.0 4.7 4.5 5.3 4.9

C 2 3.0 3.3 3.7 8.1† 6.7 5.6 6.2 7.0 7.4

C 3 3.5 3.6 3.8 4.5 4.5 4.1 5.2 6.5 6.3

C 4 2.8 3.5 3.1 4.9 6.6 5.6 6.4 7.2 8.0†

C 5 4.1† 4.4 5.0 7.3 8.8 8.5† 6.4 6.3 6.4

C 6 3.8 4.1 3.8 4.6 4.7 4.4 5.3 6.1 6.4

D 1 3.7 4.1 3.6 5.8 6.3 4.9 5.5 6.7 6.1

D 2 2.9 3.4 3.2 7.0 6.0 4.8 5.5 6.1 6.0

D 3 3.0 3.0 3.2 4.7 4.5 4.3 6.0 5.5 6.1

D 4 3.0 3.4 3.1 5.7 8.5 6.7 5.4 5.8 5.8

D 5 3.9 4.2 3.5 4.5 4.2 3.9 4.8 5.6 5.1

D 6 3.1 3.3 3.1 7.4 7.1 6.2 5.8 6.3 6.1

†Maximum values; if the 8-h EAV has been exceeded, the values are underlined. 

79

APPENDIX H—DRIVER BACK REST VDV PER ROADWAY

Table 16. Driver Back Rest VDV Axis of Translation m/s1.75 and Roadway

Truck 

Mfr.

Truck 

Test No.

X-axis

I-40

X-axis 

US-27

X-axis 

I-75

Y-axis 

I-40

Y-axis 

US-27

Y-axis 

I-75

Z-axis 

I-40

Z-axis 

US-27

Z-axis 

I-75

A 3 4.0 4.8 4.5 3.1 3.3 3.5 4.2 5.1 4.7

A 4 4.8 4.8 4.6 3.2 3.4 3.8 4.7 5.1 4.9

A 5 3.8 4.2 4.1 3.0 3.2 3.7 4.8 5.2 4.9

A 6 4.4 4.2 4.7 2.9 3.2 3.5 4.6 4.8 5.0

A 7 4.0 3.8 4.3 3.1 3.3 3.4 6.0 6.0 6.4

A 8 3.7 3.8 3.4 3.2 3.1 3.0 5.8 5.7 5.5

A 9 3.6 3.6 3.7 3.0 3.1 3.2 4.4 4.6 4.4

B 2 4.1 4.1 4.0 3.6 3.3 3.6 6.3 6.8 7.0

B 3 4.2 4.1 4.3 3.1 3.5 3.4 5.8 6.0 6.5

B 4 4.7 4.4 4.1 3.2 3.5 3.6 6.4 6.6 7.2

B 5 4.2 4.3 4.5 3.2 3.4 4.0 6.7 7.2 8.2

B 6 3.7 4.0 3.8 3.1 3.4 3.0 7.0 7.1 7.4

C 1 4.7 4.9 4.7 2.9 3.3 3.4 4.0 4.7 4.4

C 2 4.2 4.4 5.0 3.5 3.5 4.2 5.7 6.0 7.0

C 3 4.3 4.7 5.1 3.3 3.5 3.9 4.5 5.8 6.0

C 4 3.5 4.2 4.0 3.1 3.2 3.7 7.3† 8.1† 10.5

C

†

5 4.4 4.6 5.7† 3.5 3.5 4.4† 6.2 6.9 7.6

C 6 3.9 4.0 4.1 3.5 3.6 3.9 5.4 6.0 6.9

D 1 4.3 4.9† 4.7 4.0† 3.7† 3.5 6.0 6.6 6.5

D 2 3.6 4.0 3.5 3.6 3.2 3.4 6.4 6.6 7.2

D 3 3.8 4.0 4.1 3.0 3.1 3.2 7.1 6.2 7.3

D 4 4.1 4.7 4.4 3.2 3.4 3.4 6.4 7.2 7.6

D 5 4.0 4.8 4.2 3.6 3.5 3.6 6.1 6.7 6.6

D 6 4.8† 4.8 5.0 3.7 3.3 3.4 6.7 6.4 6.7

†Maximum values; if the 8-h EAV has been exceeded, the values are underlined. 

81

APPENDIX I—PASSENGER SEAT CUSHION VDV PER ROADWAY

Table 17. Passenger Seat Cushion VDV Axis of Translation m/s1.75 and Roadway

Truck Mfr. Truck 

Test No.

X-axis

I-40

X-axis 

US-27

X-axis 

I-75

Y-axis 

I-40

Y-axis 

US-27

Y-axis 

I-75

Z-axis 

I-40

Z-axis 

US-27

Z-axis 

I-75

A 3 3.4 4.0 3.8 3.0 3.4 3.1 3.7 4.7 4.1

A 4 2.9 2.6 3.1 3.3 3.5 3.7 5.1 5.5 6.0

A 5 2.9 3.2 3.1 3.1 3.6 3.3 4.7 4.8 4.7

A 6 2.3 3.4 2.8 3.0 4.1 3.0 5.2 5.3 5.7

A 7 2.4 2.7 2.8 2.7 2.8 2.8 6.2 6.7 8.5

A 8 2.6 2.8 2.6 3.0 2.6 2.6 6.2 5.9 6.1

A 9 2.7 3.0 2.8 2.8 3.0 3.0 5.0 5.1 5.5

B 2 4.3 7.3† 6.6† 3.9† 6.5† 5.8† 6.1 9.2† 9.5

B

†

3 3.6 3.3 3.7 2.8 3.2 3.0 5.7 6.0 6.7

B 4 3.6 3.5 3.2 2.8 3.0 2.8 5.5 6.3 7.0

B 5 5.7† 5.2 6.3 2.8 3.0 3.5 5.9 6.4 7.2

B 6 3.2 3.1 3.1 2.7 3.0 2.7 6.0 6.4 6.5

C 1 2.7 3.4 2.9 2.8 3.4 3.1 4.0 4.4 3.8

C 2 5.1 5.1 6.0 3.3 3.3 3.8 7.1 7.0 8.4

C 3 3.7 3.7 3.7 2.9 3.3 3.4 6.1 6.8 7.7

C 4 3.1 4.0 3.8 2.9 2.9 3.2 7.7† 8.7 10.8

C

†

5 4.1 4.3 4.3 3.3 3.2 4.0 7.3 7.4 8.0

C 6 3.3 3.6 3.9 3.4 3.4 3.4 6.4 6.8 7.8

D 1 2.7 3.4 3.0 3.4 3.2 3.0 5.8 6.7 6.4

D 2 3.3 3.9 3.2 3.4 3.1 3.3 5.3 5.8 6.0

D 3 2.5 3.3 3.1 2.7 3.0 3.0 6.1 6.4 7.0

D 4 2.6 3.3 3.0 2.8 3.1 3.0 6.0 6.6 7.0

D 5 2.7 3.3 2.9 3.3 3.5 3.4 6.1 6.5 6.5

D 6 2.9 3.5 3.1 3.3 3.0 3.1 6.2 6.6 7.1

†Maximum values if the 8-h EAV has been exceeded, the values are underlined. 
82

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83

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