NIOSH HEALTH HAZARD EVALUATION REPORT:

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

TM

HETA #2002-0239-2922

United States Postal Service

Norman, Oklahoma

January 2004

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports
ii

PREFACE

The Hazard Evaluations and Technical Assistance Branch (HETAB) of the National Institute for

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational

Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health and

Human Services, following a written request from any employer or authorized representative of employees,

to determine whether any substance normally found in the place of employment has potentially toxic effects

in such concentrations as used or found.

HETAB also provides, upon request, technical and consultative assistance to federal, state, and local agencies;

labor; industry; and other groups or individuals to control occupational health hazards and to prevent related

trauma and disease. Mention of company names or products does not constitute endorsement by NIOSH.

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Daniel J. Habes and Randy L. Tubbs, HETAB, Division of Surveillance, Hazard

Evaluations and Field Studies (DSHEFS) and E. Lee Husting, Analysis and Field Evaluations Branch

(AFEB), Division of Safety Research. Desktop publishing was performed by Robin Smith. Review and

preparation for printing were performed by Penny Arthur.

Copies of this report have been sent to employee and management representatives at USPS and the OSHA

Regional Office. This report is not copyrighted and may be freely reproduced. Single copies of this report

will be available for a period of three years from the date of this report. To expedite your request, include

a self-addressed mailing label along with your written request to:

NIOSH Publications Office

4676 Columbia Parkway

Cincinnati, Ohio 45226

800-356-4674

After this time, copies may be purchased from the National Technical Information Service (NTIS) at

5825 Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be

obtained from the NIOSH Publications Office at the Cincinnati address.

For the purpose of informing affected employees, copies of this report shall be

posted by the employer in a prominent place accessible to the employees for a period

of 30 calendar days.
iii

Highlights of the NIOSH Health Hazard Evaluation

Evaluation of a Human Transporter to Deliver Mail

NIOSH was asked by the National Association of Letter Carriers to determine if using a human

transporter to deliver mail would present health risks to workers who deliver mail.

What NIOSH Did

# We measured how much the human transporter

jolts as it is driven on sidewalks, roads, driveways, and

lawns.

# We measured the handlebars, the grips, and the

mail bins to see if the human transporter could be used

by most mail carriers.

# We videotaped workers delivering mail to see if

using the human transporter changed the amount of

reaching needed to deliver mail.

# We talked to mail carriers to see how they liked

the human transporter.

# We looked at the procedures the post office uses

to record injuries to see if new ones were needed to

report accidents that occur using the human

transporter.

What NIOSH Found

# Driving the human transporter over bumps on

lawns, streets, driveways, and sidewalks causes a lot of

jolts, but there is no easy way to determine if this is

bad for mail carriers.

# The human transporter can be adjusted to fit the

size of most mail carriers.

# Delivering mail with the human transporter

causes less reaching in some situations and more

reaching in other situations. Because the mail carriers

have to get off the human transporter so often to

deliver mail to a box, the motions needed are about

the same no matter how it is done.

# Workers liked not having to walk or carry a mail

bag, but weren’t sure if using the human transporter

was safer or faster than walking. Some wondered

what it would be like to use the human transporter all

year round.

# The post office probably doesn’t need any new

procedures or forms to record injuries to mail carriers

using the human transporter.

What Managers Can Do

# The Post Office should make more jolt and

vibration measurements and closely watch the health

of mail carriers using human transporters.

# Continue to make improvements to the human

transporter by redesigning the mail carrier bins, and

making it easier to change the batteries.

# Make it easier to carry the human transporter on

the long life vehicle.

What the Employees Can Do

# Follow the procedures for using the human

transporter that they were taught during training

sessions.

# Try to avoid bumps and debris while driving the

human transporter to deliver mail.

# Report to management any safety and health

concerns you have using the human transporter.

What To Do For More Information:

We encourage you to read the full report. If

you would like a copy, either ask your health

and safety representative to make you a copy

or call 1-513/841-4252 and ask for

 HETA Report #2002-0239-2922
iv

Health Hazard Evaluation Report 2002-0239-2922

United States Postal Service

Norman, Oklahoma

January 2004

Daniel J. Habes, MSE, CPE

Randy L. Tubbs, Ph.D.

E. Lee Husting, Ph.D.

SUMMARY

On April 29, 2002, the National Institute for Occupational Safety and Health (NIOSH) received a request for a

Health Hazard Evaluation (HHE) from the Director of Safety and Health of the National Association of Letter

Carriers (NALC) in Washington, D.C. The HHE requesters wanted NIOSH investigators to evaluate whether use

of a personal human transporter (HT) to deliver mail presented health hazards or risk of injury to its member.

On June 24, 2002, an opening conference took place in Washington, D.C. The meeting was attended by NIOSH

investigators and representatives of the United States Postal Service (USPS), the NALC, and the Segway

corporation, manufacturer of the HT. During July 15-18, 2002, NIOSH investigators evaluated the HT in Norman,

Oklahoma. The NIOSH team included an ergonomics specialist, a noise and vibration specialist, and an

epidemiologist with expertise in injury surveillance.

The ergonomics evaluation indicated that the HT is designed for and can be adjusted to fit the size range of most

mail carriers who would use it. Mail carriers at the far end of the spectrum of height and weight may not be able

to comfortably use the HT. The analysis of videotapes taken during the evaluation indicated that improvements

to the HT could and should be made, but these would affect the usability and efficiency more than reduce the risk

of injury to the worker.

The whole-body vibration evaluation indicated that postal employees are exposed to measurable levels of wholebody vibration while using the SegwayTM HT. The greatest weighted and peak acceleration levels were from headto-toe, which occurred while traveling over bumps in streets, sidewalks, or driveways and travel over lawns.

However, since little of the published epidemiological research on vibration effects is specific to people who are

exposed to whole-body vibration while standing on a movable vehicle, it could not be determined if the health of

the employees would be compromised from the use of the Segway HT.

The epidemiology/injury surveillance evaluation indicated that existing accident report forms, if completed and

available, contain useful data regarding safety aspects of the HT. If these forms are filled out in detail after

accidents occur, no new procedures would be needed to implement a surveillance system for tracking HT accidents

during mail delivery.

NIOSH investigators conclude that using a HT to deliver mail may result in harmful vibration and jolts

to mail carriers but that there is lack of sufficient comparison data or standards to determine the extent of

the hazard. The HT can be adjusted to fit most mail carriers, so there should be little additional risk of

injury from design aspects. If the HT is used to deliver mail, the USPS should make more vibration

measurements and establish a surveillance system for tracking the health status of workers using it.

Additional recommendations pertaining to the use of the HT to deliver mail are contained in this report.

Keywords: SIC 4311 (The U.S. Postal Service), ergonomics, injury surveillance, vibration exposure, mail delivery,

Segway Human Transporter, musculoskeletal disorders
TABLE OF CONTENTS

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Acknowledgments and Availability of Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Introduction ......................................................................... 1

Background ......................................................................... 1

Methods ........................................................................... 2

Whole-Body Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Ergonomics ...................................................................... 2

Interviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Human Transporter Injury Surveillance ................................................. 3

Evaluation Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Whole-Body Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Ergonomics ...................................................................... 4

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Whole-Body Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Ergonomics ...................................................................... 5

Handlebar Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Side Carriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Front Mail Carrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Hand Grips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Other Design Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Changing the Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Transport Ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Effect of the HT on Work Load and Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Interviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Human Transporter Injury Surveillance ................................................. 9

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Whole-Body Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Ergonomics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Human Transporter Injury Surveillance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Health Hazard Evaluation Report No. 2002-0239-2922 Page 1

INTRODUCTION

On April 29, 2002, the National Institute for

Occupational Safety and Health (NIOSH) received a

request for a Health Hazard Evaluation (HHE) from

the Director of Safety and Health of the National

Association of Letter Carriers (NALC) in

Washington, D.C. The HHE request pertained to the

alpha tests being conducted by the United States

Postal Service (USPS) to determine if mail could be

delivered safely and efficiently using a SegwayTM

Human Transporter (HT) on delivery routes

throughout the country. The HHE requesters wanted

NIOSH investigators to evaluate whether or not use

of the HT presented health hazards or risk of injury

to its member mail carriers. Potential health hazards

contained in the HHE request included fatigue and

tension from having to concentrate while operating

the HT and wear and tear on the body from riding the

vehicle over the many surfaces and terrain

encountered while delivering mail.

On June 24, 2002, an opening conference took place

in Washington, D.C. The meeting was attended by

two NIOSH investigators and representatives of the

USPS, the NALC, and the Segway corporation. The

purpose of the meeting was to discuss the evaluation

that was to be conducted by NIOSH.

During July 15-18, 2002, NIOSH investigators

evaluated the HT at the Norman, Oklahoma, test site.

The postal facility in Norman was one of five

locations where use of the HT to deliver mail was

being evaluated by the USPS. The others were

Memphis, Tennessee; City Island (Bronx), NY;

Phoenix, Arizona; and San Francisco, California.

Prior to the HHE request, the USPS had conducted

feasibility tests in Tampa, Florida, and Concord,

New Hampshire.

The NIOSH team included an ergonomics specialist,

a noise and vibration specialist, and an

epidemiologist with expertise in injury surveillance.

The investigation consisted of an evaluation of the

ergonomics aspects of the HT unit, measurement of

the vibration at the base of the HT during mail

delivery, and a review of medical records and injury

reporting procedures used at the facility. Informal

interviews of the postal workers using the HT were

also conducted by the NIOSH team.

BACKGROUND

The Segway HT was first introduced in December

2001 on ABC’s Good Morning America. Prior to its

introduction, the developers of the HT had been

planning feasibility trials with the USPS and the

Atlanta, Georgia, police department. The USPS was

interested in delivering mail with the HT as part of its

continued efforts to improve efficiency and cut costs.

The feasibility tests in Tampa and Concord were

successful enough to justify further testing at the five

selected sites.

The base of the Segway is comprised of two wheels

situated on each side of a platform. The rider stands

on the platform and grasps a T-shaped handlebar.

The personal Segway (p-series) model resembles a

push lawn mower. The Segway, a self-balancing

unit, uses motors, computer processors, and

gyroscopes to mimic human equilibrium. Riders can

propel the scooter by grasping the handlebars and

gently leaning forward or backward, and stop it by

standing straight. The top speed of a Segway HT is

12 miles per hour (mph) and can be adjusted

depending on which key is placed in the ignition

module. During the testing in Norman, Oklahoma,

the key which limits the top speed to 9 mph was

used.

The business (e-series) Segway , which was used by

the USPS in its tests, weighs 95 pounds and has a

range of about 17 miles per battery charge, a payload

of 325 pounds, and a zero turning radius. The 40

units purchased by the USPS were equipped with

two side carriers and one front carrier. The units also

had an adjustable-height handlebar, and some had

kick stands. Figure 1 shows a comparison of the

basic e-series HT to the version of the HT used

during the test in Norman, Oklahoma.

The sites selected for testing were all “park and loop”

residential delivery routes, each with about 500
Page 2 Health Hazard Evaluation Report No. 2002-0239-2922

delivery addresses. The anticipated benefits of the

HT in mail delivery were that letter carriers would

not have to carry approximately 35 pounds of mail

on their shoulders, more mail could be loaded onto

the Segway to reduce the number of trips back to the

truck to get more mail, and travel time between

successive delivery residences would be reduced.

Because the “park and loop” style of mail delivery

requires that letter carriers load a mail truck (usually

the “long life vehicle” or LLV) and drive to their

route, a method of transporting the Segway to the

mail routes was needed. Originally, the HT was

loaded into the cargo area of the LLV, but by the

time of the NIOSH site visit, which was the fifth

week of a six-week evaluation in Norman,

Oklahoma, a ramp system attached to the back of the

LLV had been developed (Figure 2). During the

tests, USPS data collectors followed the mail carriers

on their routes and logged delivery times and other

mail delivery statistics.

METHODS

Whole-Body Vibration

Vibration acceleration measurements were collected

on four different HT units that had been assigned to

postal workers delivering mail on their routes. Each

HT had a different mail delivery route serviced by

four different letter carriers. Space limitations on the

unit determined how much sampling instrumentation

could be placed by NIOSH investigators on it and

still allow the employee to complete their mail

delivery tasks. Acceleration data were collected with

a Larson Davis Human Vibration Meter (Model

HVM100; North Provo, Utah). Triaxial

accelerometers mounted in a rubber disk (PCB

Piezotronics Model 339M19; Depew, New York)

were fastened to the platform of the Segway HT with

four pieces of double-sided carpet tape. The cable

connecting the disk to the HVM100 was secured

with wire wraps around the vertical post and the

HVM100 was placed in one of the side

compartments of the mail container near the letter

carrier’s hands. The triaxial accelerometers were

calibrated by a factory authorized laboratory just

prior to the evaluation and the determined voltage

sensitivities were used to calibrate the HVM100.

The HVM100 was set to two different criteria for

vibration measurements on each of the four HT units.

The first criterion used the weighting functions

specified by the International Organization for

Standardization (ISO) International Standard for

evaluation of the comfort of a standing person.1

 This

criterion uses a weighting function (Wd) for the xaxis (belly-to-back) and y-axis (side-to-side) and a

weighting function (Wk) for the z-axis (head-to-feet)

over the frequency range of 0.4 Hertz (Hz) to 100

Hz. Both root-mean-square (rms) and peak

acceleration values were calculated over a 30-second

averaging period and stored in the vibration meter.

The meter was set to the autostore mode so that each

30-second averaging period was stored over a 1-hour

measurement period. The second criterion used a flat

weighting function on each of the three directional

axes. Both peak and rms acceleration values were

calculated and stored over 30-second averaging

periods for an entire hour of measurements. In cases

where the mail delivery route was not long enough to

complete one hour of data collection, the HVM100

was stopped when the letter carrier completed that

portion of the route. 

Ergonomics

The ergonomics evaluation consisted of a

comparison of the physical dimensions and

adjustability features of the HT to what is described

in the ergonomics literature as acceptable to the

various percentiles of the adult population. Analysis

of video tapes taken during the evaluation served as

a means of determining if use of the HT to deliver

mail was associated with any postural demands

(excessive reaching, awkward body positions or

wrist postures) that would not occur during

traditional mail delivery (see Figure 3).

Interviews
Health Hazard Evaluation Report No. 2002-0239-2922 Page 3

Each of the four mail carrier participants was

interviewed informally after their day of evaluation.

A list of questions that served as a guide to the

interviewers can be found in the Appendix.

Human Transporter Injury

Surveillance

To determine if it was feasible or necessary to design

and implement a separate surveillance system for

tracking future injuries and accidents involving use

of the HT, blank forms routinely used by the USPS

to record data on carrier activities were reviewed. 

These forms were obtained from the USPS

Inspector/Manager in Norman, Oklahoma.

EVALUATION CRITERIA

Whole-Body Vibration

In the United States, it has been estimated that 8

million people are exposed to occupational vibration,

with 7 million exposed to whole-body vibration and

the remaining 1 million exposed to hand-arm

vibration.2

 Workers who are exposed to whole-body

vibration include truck and bus drivers, heavy

equipment operators, farmers, civilian pilots and

flight crews, and train locomotive operators. The

National Occupational Exposure Survey estimates

that 1.08 million workers from 42 different 2-digit

Standard Industrial Classification (SIC) codes are

exposed to whole-body vibration.3

 These latter

estimates include only the 3- and 4-digit SIC codes

surveyed within the 2-digit SIC. Not all SIC codes

were included in the NIOSH survey. The largest

categories of workers exposed to whole-body

vibration were in heavy construction contractors

(SIC 16), special trade contractors (SIC 17), and

trucking and warehousing (SIC 42).

Whole-body vibration initially received attention

from the military, which was concerned with the

effects of vibration on the completion of their

missions.4,5 The concern for most occupational

exposures involves acute effects which can affect

worker safety, and chronic effects impacting

workers’ health.6,7 An example of an acute effect is

whole-body vibration that results in a driver losing

the grip on a steering wheel, potentially leading to an

accident. Most of the chronic effects of whole-body

vibration which have been looked at are concerned

with changes in the spines and backs of affected

workers. Strong evidence of an association between

whole-body vibration and low-back disorder was

found in 15 of 19 studies reviewed by NIOSH. Both

experimental and epidemiological evidence suggest

that whole-body vibration may act in combination

with other work factors, such as prolonged sitting,

lifting, and awkward positions, to cause increased

risk of back disorders.8

 

Neither NIOSH nor the Occupational Safety and

Health Administration (OSHA) have published

exposure limits for whole-body vibration. The

American Conference of Governmental Industrial

Hygienists (ACGIH®) has a Threshold Limit Value

(TLV®) for whole-body vibration that measures rms

acceleration in meters per second per second (m/s2

)

for the one-third octave bands from 1 Hertz (Hz) to

80 Hz.9

 The one-third octave bands are weighted the

same for the x- and y-axes but differently for the zaxis. The x- and y-axes are maximally sensitive at

the frequencies of 1 to 2 Hz, while the z-axis is most

sensitive between 4 Hz and 8 Hz. These most

sensitive bands correspond to the natural resonances

of the human body when it is vibrated in these

directions. Resonance is the condition where

vibration is optimally transmitted from the vibrating

source to the person, with the individual actually

amplifying the acceleration, possibly exacerbating

the effects of the whole-body vibration.10

Acceleration measurements are simultaneously

collected in each of the three orthogonal axes and

compared to the TLV’s two weighting functions.

The criterion has exposure time limits from 1 minute

to 24 hours that correspond to the rms acceleration

measured at each one-third octave band. The TLV

also presents formulas to calculate the single-vector

sum of the weighted accelerations from all three

orthogonal axes. According to the ACGIH TLV, this

single value of the sum of the weighted accelerations

can then be compared to the Commission of the

European Communities (CEC) directive.11

Specifically, the directive requires a daily exposure

limit value standardized to an 8-hour reference

period of 1.15 m/s2

 and a daily exposure action value
Page 4 Health Hazard Evaluation Report No. 2002-0239-2922

of 0.5 m/s2 for the same standardized period. Once

the exposure action value has been exceeded, the

employer is to establish a program of technical and

organizational measures to reduce exposure to

mechanical vibration. The program can include

changes in work practices, new equipment that

produces lower levels of vibration, and training

programs to instruct workers in the use of their

equipment to safely reduce vibration.

The ISO has defined methods for the measurement of

periodic, random, and transient whole-body

vibration to indicate the degree to which vibration

exposure will be acceptable.1

 The standard presents

different weighting factors of one-third octave bands

for the frequency range of 0.5 to 80 Hz in each of the

three orthogonal directional axes. The principal

weighting curves vary depending on whether the

standard is being applied to health, comfort, or

perception guidelines and whether the worker is

seated, standing, or recumbent. As is the case with

the ACGIH TLV, the weighting curves are

maximally sensitive at the natural resonance of the

human body, 1 to 2 Hz in the x and y directions, and

4 to 8 Hz in the z direction. The standard contains

informative guides to the effects of vibration on

health, comfort, and perception in a series of

appendices attached to the standard. The guidance

on health effects is primarily intended to reduce the

risk of injury to the lumbar spine and the nervous

system. A health guidance caution zone is presented

in the standard to which the rms value of the

frequency-weighted accelerations can be compared

for varying exposure durations from 10 minutes to 24

hours. The lower boundary of the health guidance

caution zone runs from approximately 3 m/s2

 for 10

minutes or less to 0.25 m/s2

 for 24 hour exposures.

Ergonomics

Overexertion injuries and musculoskeletal disorders

such as low back pain, tendinitis, and carpal tunnel

syndrome, are often associated with certain job tasks:

(1) repetitive, stereotyped movement about the

joints; (2) forceful manual exertions; (3) lifting; (4)

awkward and/or static work postures; (5) direct

pressure on nerves and soft tissues; (6) work in cold

environments; or (7) exposure to whole–body or

segmental vibration.8,12,13,14 

The risk of injury appears to increase as the intensity

and duration of exposures to these factors increases

and recovery time is reduced.15 Although personal

factors (e.g., age, gender, weight, fitness) may affect

an individual’s susceptibility to overexertion

injuries/disorders, studies conducted in high–risk

industries show that the risk associated with personal

factors is small compared to that associated with

occupational exposures.16

In all cases, the preferred method for

preventing/controlling work–related musculoskeletal

disorders (WMSDs) is to design jobs, work stations,

tools, and other equipment to match the

physiological, anatomical, and psychological

characteristics and capabilities of the worker. Under

these conditions, exposures to task factors considered

potentially hazardous will be reduced or eliminated.

The primary ergonomic risk factor of concern in this

study was awkward and/or static work postures. It

was presumed beforehand that if the HT could not be

adjusted to fit the physical size of various percentiles

of the general population or if mail carriers

approached a mail box while standing on a HT

instead of walking as is customary, awkward body

postures would result. 

RESULTS

Whole-Body Vibration

Four letter carriers were observed for two hours each.

The HVM100 was placed on the HT and one hour of

weighted and one hour of unweighted (flat) data were
Health Hazard Evaluation Report No. 2002-0239-2922 Page 5

collected and stored for analysis. During the

observations, videotape records of the carriers’

activities were made to correlate with the

acceleration data. The overall results are shown in

Table 1. All of the measurements were highest in the

z-axis, ranging from 0.47 m/s2

 to 1.99 m/s2 for the

unweighted accelerations and from 0.97 m/s2

 to 1.67

m/s2

 for the weighted accelerations. The peak values

were also greatest in the z-axis, ranging from 17.2

m/s2

 to 39.6 m/s2 for the flat measurements and from

13.0 m/s2

 to 19.4 m/s2 for the weighted acceleration

measurements. The associated crest factors (ratio of

peak to rms) for the four Segway units were 11.0 and

11.4 in the weighted and unweighted z-axis for #34,

7.8 and 16.3 for #08, 17.7 and 36.6 for #20, and 11.9

and 19.9 for #S2.

The videotapes of the letter carriers on their Segway

units were viewed and the activities performed by the

employees were noted for each 30-second

acceleration measurement period. Major activities

included travel on streets, lawns, sidewalks, and

driveways, mounting and dismounting the HT, and

idle time when the unit was not in motion. Other

notable activities included driving the HT over

bumps, battery changes, and moving the Segway up

or down the LLV’s ramp. Each instance of an

activity was checked on the data sheet when

observed during the 30 seconds and the results were

tabulated (Table 2). In this analysis, it is possible for

each of the activities to occur during the 30-second

period, with multiple occurrences of a single activity

also possible. Three of the eight observation periods

were less than one hour because of the logistics of

the mail carrier’s route. The route also determined

the amount of time spent on each activity, with three

of the four routes characterized as suburban with

long driveways and few sidewalks. The mail carriers

on these routes would generally travel the streets

until reaching the home’s driveway. The fourth

route (Segway unit #08) was more urban with

sidewalks in front of the houses parallel to the

streets. The letter carrier on this route seldom used

the street to deliver the mail.

If a single activity dominated a 30-second period, it

was scored positive for that activity. If more than

one activity occurred during the observation, then no

category was scored positive with the exception of

driveway and street activity both occurring in the

same period. The mean acceleration values and

standard deviations for each activity were calculated

for both the weighted and flat measurement

conditions in the z-axis and are presented in Figures

4-7, which represent the four Segway units. Each

activity was not observed for each measurement

period and for instances where only one observation

of an activity was seen, there is no standard deviation

given on the figure. The greatest mean acceleration

values were measured at approximately 2 m/sec2

(which is equivalent to the m/sec/sec metric on the

figures). Travel on lawns and over observable

bumps generally were found to have the greatest

amount of vibration in the z-axis.

Ergonomics

Figure 1 shows a comparison between the HT with

cargo carrying accessories and the modified HT the

USPS used in Norman, Oklahoma. The dimensions

of the modified HT are shown in Table 3.

The main dimensions of the HT used in Norman that

could influence the comfort and usability for letter

carriers of various sizes are the height adjustment of

the handle bar, the height and size of the mail carrier

bins, and the length and diameter of the handle grips.

Handlebar Height

In general, for standing tasks, work should be

situated 2 inches to 3 inches below elbow height for

light work, lower than that for heavier work, and

slightly above elbow height for precision work.17

One source of worker anthropometric data reports

elbow heights for the 5th percentile female and the

95th percentile male to be 38.6 inches and 47.3

inches, respectively.18 Another source reports

standing elbow height in a 5th to 95th range of a 50-50

mix of males and females to be 37.9 and 45.8 inches,

respectively.19 Subtracting 3 inches from the

extremes of these values would result in a desired

adjustability range for the HT of 34.9 inches to 44.3

inches. From Table 3, it can be seen that the actual

adjustability range of the handle bar for the HT

varies from 32.5 to 42 inches. Another way to

evaluate handle height adjustability is to use
Page 6 Health Hazard Evaluation Report No. 2002-0239-2922

anthropometric correlation statistics. It is estimated

that standing elbow height is 0.63 times stature.20

Using this method, a female would have to be fewer

than 56.3 inches tall (< 1st percentile) and a male

would have to be taller than 71.5 inches (85th

percentile) to be out of the calculated range.21 Table

4 shows the height of the four participants in the

study, their percentile heights, their predicted ideal

handle height based on the above correlation

between height and standing elbow height, and the

height of the handle bar that they chose while using

the HT to deliver mail.

Analysis of the video tapes indicated that all four

letter carrier participants selected handle bar heights

that were below their elbows, were well within the

adjustability range of the HT, and from Table 4, were

below what anthropometry would have predicted,

with the discrepancy being greatest for the tallest

mail carriers. It appears the workers felt control of

the handle bar was important so they chose lower

handle bar positions to achieve that end.

Side Carriers

Unlike the handle bar, the side mail carriers were not

height adjustable. They were fixed at 35 inches

(about 28 inches from the HT platform) and 13

inches deep. The dactylion height (measure from the

floor to the tip of the fingers while standing) range

for the 5th percentile female and the 95th percentile

male is 21.7 inches and 29 inches, respectively. The

reach to the bottom of the side mail carrier, 15 inches

above the HT platform, is about 6 inches lower than

the 1st percentile female dactylion height of 21

inches.

These measures indicate that the side carriers could

not be used by individuals of any height without

bending in some way, either at the knee to lower the

hands or the trunk to reach into the carriers, neither of

which could likely be accomplished while moving on

the HT. Analysis of the video tapes indicated that the

mail carriers did not use the side carriers for mail

delivery except for large bulk items such as catalogs

or small parcels. Most often, they loaded the side

carriers with mail, and then transferred mail to the

front carrier at various mail stops. That is, mail was

delivered from the front carriers, and the side carriers

were used for “carrying cargo.” Another reason the

side carriers were seldom used was because the spare

batteries were carried in them. The added weight of

the batteries served to stabilize the HT by offsetting

the weight of the front carrier, which was 1 inch

longer than wide, and also raised the bottom of the

side carriers by virtue of being in them. Still, the

workers could not effectively use the side carriers for

other than cargo due to the small opening and the

long reach. Even with the top of the carrier

expanded fully, it was difficult for the workers to

retrieve mail from the bottom. 

Front Mail Carrier

The front mail carrier was a three-pocket bin

mounted in front of the handlebar. The dimensions

were 14 inches long and 13 inches wide. The

compartment closest to the mail carrier was the

deepest at 7 inches, the second was 6 inches deep,

and the one furthest from the worker was 5 1⁄2 inches

deep. The angle of the front carrier increased with its

length to allow for easier access by the workers (see

Figure 1). The furthest compartment was about 3

inches higher than the handle bar. The front mail

carrier was the one the workers delivered mail from,

adding mail to it from the side carriers as deliveries

were made. The compartments seemed easy for the

mail carriers to reach, but their location blocked the

view of the ground directly in front of the HT as it

was driven, making it more difficult to see hazards.

Hand Grips

For a cylindrical handle, a diameter of about 1.5

inches is considered to be the most efficient and least

fatiguing to the hand.22 Handle length should be

such that it spans the fatty tissue of the hand and not

dig into the soft tissue in the middle of the hand.

Hand breadth for the 5th percentile female and the 95th

percentile male is about 2.8 inches and 3.8 inches,

respectively.23 A comfortable handle length for most

adults is somewhere between 4 and 5 inches.24

Comparison of these values to the grip
Health Hazard Evaluation Report No. 2002-0239-2922 Page 7

measurements listed in Table 3 indicates that the

design of the HT would be suitable for most workers.

Other Design Aspects

Changing the Batteries

Replacing the batteries involved stopping the HT,

placing it in a disabled mode, removing the mail

from the side carriers, retrieving the batteries and the

cordless screwdriver, setting the HT on the ground,

removing the screws (4 per battery, 2 battery halves),

positioning the charged batteries, replacing the

screws, restoring the HT to its upright position,

restarting the motor, and placing the spent batteries

and mail back into the side carriers. Each battery

half weighed about 11 pounds. The batteries can be

replaced in about 2 1⁄2 to 3 minutes, and total down

time can range from 4 to 6 minutes. During the

course of the NIOSH study, the batteries were

replaced once for each mail carrier observed.

Transport Ramp

The HT is carried by the LLV by means of a

platform attached to the rear frame, 17 inches above

ground level. The HT is placed on the platform by

means of a retractable dual ramp. The HT can be

dragged up the ramp or “walked” up with the HT in

“follow mode,” one of the many selections provided

by the unit’s control switch. The HT can go up and

down the loading ramps with the left side carrier on,

but the right side bin must be removed for clearance.

It is easier to lock the ramps in the vertical position if

the left carrier is also not on the HT. 

It seemed fairly easy for the mail carriers to guide the

HT up to the platform in “follow mode,” but since

the unit is on, it may rock back and forth when it

reaches the platform, requiring the attention of the

mail carrier. The HT must also be controlled by the

worker as it is guided down the ramps. It is easiest to

place the ramps on a curb, but the HT can be guided

down the ramps onto any flat surface.

At the time of the NIOSH evaluation, the transport

platform had been in use for only a few days.

Having to remove the side carriers before going up

the ramp seemed like a nuisance and added to the

work load of the mail carrier. Likewise, when the

right side bin remained on the HT to stabilize the unit

as it was being guided up the ramp, the result was an

above shoulder lift to remove the bin once the HT

was secured on the platform. 

Depending on the height of the handlebar

adjustment, the front mail bin could block the view

of one or more of the four vertically-situated rear

lights on the LLV. Also, the placement of the

transport platform on the right side of the truck

blocked one half of the access to the rear of the truck

where the mail is stored during transport with the

LLV.

Effect of the HT on Work Load and Posture

The physical advantages of the HT for the mail

carrier are the relief from walking and carrying a

sack of mail that typically weighs about 35 pounds.

This could have an effect on the long term incidence

of foot, leg, back, and shoulder musculoskeletal

disorders. In the near term, use of the HT to deliver

mail could have a positive or negative effect on the

postures assumed by the mail carriers as the mail is

delivered to specific locations (Figure 3). Analysis

of the video tapes taken during the NIOSH

evaluation indicated that in some cases the mail

carriers reached a little farther to deliver mail to a box

while standing on the HT. In other cases, delivering

mail while on the HT made the task easier and faster,

most notably in instances where the mail slot was

located on a garage door, enabling the mail carrier to

drive up, drop the mail into the slot, and drive to the

next house. Even in these cases, though, the mail

carrier could not always get as close to the mail box

or slot as would be possible on foot, and because

being on the HT elevates one’s stature, the worker

often had to reach and/or bend over to put mail into

the slots. Reaching and bending were greatest on

those occasions when mail was taken from the side

carriers instead of the front carrier. However, most

often the mail carrier had to drive as close to the

house as possible, get off the HT and deliver the

mail. In these cases, there would be no difference in

work load and posture between delivering mail with

the HT or as done conventionally, except that the

mail bag is not being carried.
Page 8 Health Hazard Evaluation Report No. 2002-0239-2922

Analysis of the videotapes also indicated that being

on the HT seemed stressful to the lower leg. The

lower leg muscles appeared to be most stressed when

the HT was driven on grass or over bumps, and when

the mail carriers dropped their hips down to slow the

momentum of the HT when making turns or when

negotiating the transition between a driveway and the

street.

Interviews

Two of the mail carriers studied were men and two

were women. They ranged in height from 60.5 to 71

inches. The four subjects’ weight range was from 95

to 180 pounds, and their experience as mail carriers

ranged in years from 3 to 25. They were selected to

be in the USPS time and motion studies because of

the mail routes they were delivering, not for any

reason related to gender, age, prior injury record, or

efficiency as a mail carrier. The NIOSH interviews

lasted between 15 and 30 minutes. Main topics

discussed during the interviews are contained in the

Appendix.

Each mail carrier reported they had received two

days of training on the HT, three had been in the

study since it began and the other had missed two of

five weeks. Three of the four mail carriers reported

they had fallen off or lost control of the HT during

the initial days of the evaluation.

In general, all four mail carriers liked the HT, two

wanted to use it exclusively, but none thought it

would be fully deployed in the Norman, Oklahoma,

delivery area. None reported any new aches or pains

from using the HT, and one reported relief from foot

problems experienced prior to using the HT. No one

felt mentally fatigued from using the HT or reported

any motion sickness, but all admitted that the HT

required their constant attention to avoid the pitfalls

of the surfaces which they traversed.

Other comments made are listed below. If more than

one worker made the same comment, that number

appears in parentheses.

# Not sure the HT will save time (2) 

# HT not safer, but healthier

# Like not carrying mail (2) 

# Don’t like wearing a helmet (2)

# HT needs shocks

# Would like a lift on the LLV instead of ramp (2)

# Can not keep mail dry in the rain

# Cool in summer, but concern about winter chill

# Lower legs get tired (2) 

# Don’t like side carriers

# Feels natural to be on the HT (2) 

# Feel good after a day of work, more energy

# I could make it to retirement using the HT (2)

# Segway is a good first effort, very elegant

machine

# Flaps should go inside out on bags, not outside

in, don’t need to be expandable

# Front carrier throws off balance of HT, bigger

than it has to be, should have cargo nets on side

# Going to my truck every 15 minutes warms me

up in the winter

# Riding HT requires development of new driving

skills

# There may be a loss of physical fitness from

riding instead of walking

# Higher side bags would interfere with body

space, why not have conventional mail tubs on side

Human Transporter Injury

Surveillance

The following forms were reviewed by the NIOSH

epidemiologist during a meeting with the

Inspector/Manager in Norman, Oklahoma. The

purpose of the meeting and the form review was to

become familiar with methods and procedures in use

to record injuries and accidents at the USPS for

purposes of determining if alternative procedures

would be feasible or necessary if the HT were to be

deployed for regular mail delivery.

Form 1769 “Accident Report” is used by the USPS

to record information on accidents and injuries

including location and conditions, persons involved,

a description of the event, and suggested preventive

actions. It has space for a map of the incident. It is
Health Hazard Evaluation Report No. 2002-0239-2922 Page 9

used by the USPS instead of forms OSHA 101 and

OSHA 301. Items 44, 45, and 46 on Form 1769

relate to the nature and severity of an injury and the

body part affected, which would be useful

information in the event of an incident involving the

HT.

Form CA-1 “Federal Employee’s Notice of

Traumatic Injury and Claim for Continuation of

Pay/Compensation” is used when an employee

reports an injury, and as a result requests

continuation of compensation. Form CA-1 is usually

accompanied by Form 1769 for the incident

associated with the injury.

Another form, CA-2 “Notice of Occupational

Disease Claim for Compensation” is used to record

work-related disease or illness. This form would

probably not be needed in a system to record HT

safety-related incidents, but could still be used to

record chronic MSD thought to be from HT.

Form CA-16 “Authorization for Examination

And/Or Treatment” authorizes a medical facility or

physician to provide medical service with regard to

a specific disease or injury. Part A is completed by

the authorizing official, and Item 5 should contain a

description of the injury or disease. Part B is

completed by the attending physician and Item 15

should contain a history provided by the employee.

These and some additional items on the form would

be useful in an accident surveillance system.

Form CA- 17 "Duty Status Report" was completed

for carriers using the HT. This form specified the

usual work requirements of the employee. For the

HT trial, the postal inspector specified a Maximum

Lifting and Carrying Weight of 35 pounds (both

continuous and intermittent) for six hours a day. It

also pre-specified sitting (two hours intermittent),

standing (six hours continuous), walking (six hours

continuous), as well as other requirements including

twisting (five hours intermittent), pulling, pushing,

grasping, and outdoor work involving temperature

extremes and high humidity. The total number of

hours exceeds the daily duty hours since some

activities occur simultaneously.

While workers were being trained to use the HT,

some minor incidents occurred. Some of these

occurred during initial training while maneuvering

between traffic cones, and others occurred on mail

routes, usually upon encountering hidden sticks or

crevices on lawns. All such incidents were reported

on Form 1769 and CA-1.

Other forms of possible value for an HT accident

surveillance system might include PS Form 4584

"Observation of Driving Practices," PS form 1700

"Accident Investigation Worksheet," and Form 1767

"Report of Hazard, Unsafe Condition or Practice."

Three forms, 1769, CA-1, and CA-16, are most

likely to have useful information regarding

occupational injury or safety problems related to use

of the HT during the USPS trials. 

DISCUSSION

Whole-Body Vibration

The logistics of this evaluation partly dictated what

could be accomplished in the measurement of wholebody vibration to the postal employees who were

chosen to participate in the USPS trial of the Segway

HT. NIOSH investigators could not interfere with

the delivery of the mail or the time-motion study that

was being simultaneously conducted by the USPS.

Space was very limited on the unit for vibration

analysis equipment. Because of this, it was decided

to use the HVM100 to collect data. It was also

predetermined to set the unit for the comfort

parameters stipulated in ISO 2631 for half of the

trials and on a flat, unweighted function for the other

half of the trials. This procedure did not allow for

any spectral analysis of the acceleration levels for the

individual axes as dictated in the ACGIH TLV for

whole-body vibration.9

Also, because of the uniqueness of using the Segway

HT unit to deliver the mail, it is difficult to compare

the results obtained in this evaluation to any

guideline or standard and conclude that there is

increased risk of injury to the rider or that the unit

does not increase the risk of an adverse effect on the
Page 10 Health Hazard Evaluation Report No. 2002-0239-2922

postal employees’ health. The ISO standard states

that most of the guidance in Annex B describing the

effects of vibration on health... “is based on data

available from research on human response to z-axis

vibration of seated persons. There is only limited

experience in applying this part of ISO 2631 for xand y-axes seating and for all standing, reclining, and

recumbent positions.” The ISO standard further

limits the applicability of its evaluation method when

crest factors are greater than 9. The measured crest

factors in this evaluation for the weighted

measurements ranged from 7.8 to 17.7 in the z-axis.

The standard states that for these situations with high

crest factors, the method may underestimate the

severity with respect to discomfort. Finally, the

multiplying factors (k) used when combining

vibrations from the three orthogonal directions were

set at k=1 as stipulated for evaluation of comfort for

standing persons.1

 This differs from the CEC

directive which uses multiplying factors of k=1.4 in

the x- and y-axes as stipulated for seated subjects.11

In spite of these limitations, the data collected over

the two days on the four Segway units does indicate

that the postal employees are exposed to vertical (zaxis) vibration as they maneuver the unit. All four

units had measurement periods while they were on

streets, driveways, sidewalks, and lawns. There were

also many periods where the units were not moving

while the postal employee left the vehicle to walk to

mailboxes or stood on the HT while the mail was put

into mail boxes or slots. Whole-body vibration in the

z-axis always exhibited the greatest acceleration

values for both peak and rms measurements. For the

rms accelerations in the z-axis, the values ranged

from 1.0 to 1.7 m/s2

 which corresponds to the health

guidance caution zones of ISO 2631 of about 1 to 6

hours of exposure per day. For the comfort reactions

of seated passengers, these acceleration values fall

into the uncomfortable category presented in Annex

C of the ISO standard.1

 However, because of the

limitations noted earlier, it cannot be determined with

these data if the HT units will lead to an increased

risk of adverse health effects from using them on

postal delivery routes. 

Ergonomics

The purpose of the NIOSH evaluation of the HT in

Norman, Oklahoma, was to determine if its use

would have an effect on the health status of mail

carriers who had previously delivered mail on foot

carrying sacks of mail on their shoulders. As noted

in the Results Section, the unit seemed to have the

adjustability features to accommodate the majority of

mail carriers who would use it. The exception to this

is the height of the side carriers, but the analyses

indicated that mail was mostly delivered from the

front carrier and the side carriers were used to hold

the batteries and store mail until it was transferred to

the front carriers. Delivering mail to slots and boxes

while on the HT seemed to place the mail carriers in

more awkward and extreme postures, but whether or

not these instances would add to the risk of a mail

carrier developing a musculoskeletal disorder is

difficult to estimate because the observed norm for

delivery to the mail endpoint was to get off the HT,

walk to the mailbox and deliver the mail as usual.

The main difference is that the mail carrier was not

carrying a mail sack, which likely is a factor reducing

the risk of injury. A meaningful comparison of the

relative risk of injury due to postural differences

could only be made on a route where most of the

mail deliveries were made while the carrier was

situated on the HT.

As noted in the Results Section, driving the HT

seemed to considerably involve the calf muscles of

the lower leg. These muscles appeared to be the

main absorber of the energy transmitted to the body

through the feet. The mail carriers also used their

legs to control the HT and slow it down when

transitioning to and from unlike surfaces. Except for

two comments by the mail carriers about lower leg

fatigue and one expressing a need for shock

absorbers on the HT, the effect of using the HT on

the lower leg muscles was not assessed by this

evaluation. A non-invasive measuring technique

called electromyography (EMG)25 could be used in

further studies to quantify the effect of HT use on the

lower leg muscles. Using EMG, surface electrodes

could be placed on the lower leg to record the

amount of electrical activity of muscles during HT

use. The magnitude of electrical output increases
Health Hazard Evaluation Report No. 2002-0239-2922 Page 11

linearly as muscle activity increases and provides an

objective indication of muscle fatigue. A

comparison of the lower leg muscle EMG while on

the HT to that while walking to deliver mail would

further clarify any physiological differences that may

exist between the two methods of mail delivery.

Many of the comments made in the Results Section

about the design of the ramp, the method used to

change the batteries, or the design of the front

carriers pertained to efficiency and ease of use, not

necessarily to safety and health. It would be better to

have batteries that could be secured into place with a

clip instead of by removing eight screws, but it is not

certain that doing so would make the workers any

safer. The ergonomics aspects of changing the

batteries was addressed by providing the data

collectors with a cordless electric screwdriver to

remove and replace the screws. Likewise, it would

be more convenient if the mail carrier did not have to

walk the HT up and down the transport ramp and

remove the side carriers to transport the HT, and it

would be more convenient if the transport ramp did

not block one half of the access to the rear of the

LLV, but it could not be said for certain that use of

an alternative design, such as a lift gate, would

reduce the risk of injury to the worker. 

Undoubtedly, some of the features of the HT could

be improved as noted above, but it is likely that

modifications and improvements will be made as the

feasibility testing of the unit progresses. Ultimately

the extent to which the HT is deployed (if at all) will

be based on many factors such as efficiency, cost

savings, and safety.

Human Transporter Injury

Surveillance

Injury might occur to a HT rider from being thrown

forward, to the side, or off the machine. This could

occur if the HT encounters an unseen obstacle, hole,

or depression. It could also occur if one wheel sticks,

for example on a curb. Most injuries would probably

be minor, for example sprains, strains, or contusions,

and might involve the ankle, lower leg, knee, hand,

or wrist. If these did not result in a lost workday they

would be classified as non-injuries or first aid

injuries. However there might be a possibility of

more serious injury to the face or eyes. A collision

between a larger vehicle such as a car and a HT

could be extremely dangerous for the HT rider.

Although this report focuses on the evaluation of the

HT for occupational purposes, its use has also

aroused some public interest and controversy. The

HT has been used by members of the current

administration and by the President at his retreat

home. The City of San Francisco banned the HT

temporarily because of concern for public safety.26

On the other hand, the HT has been tested and used

in a variety of situations including Walt Disney

World and the Atlanta Police Department. Use of

the HT by the USPS would represent a large-scale

interaction of the unit with the public. An accurate

and thorough surveillance system to track injuries

and other incidents related to HT use should be a

high priority for the USPS from the standpoint of

occupational and public health.

CONCLUSIONS

1. Postal employees are exposed to measurable

levels of whole-body vibration while using the

Segway HT. The greatest weighted rms and peak

acceleration levels were measured in the z-axis, or

from head-to-toe. Also, traveling over bumps in

streets, sidewalks, or driveways and traveling over

lawns was found to have the highest levels of

vibration. The unweighted, flat functions collected

on each Segway HT unit did not add any additional

information to this evaluation as the values were

found to be similar to the weighted functions. 

2. Because of very limited epidemiological data for

people who are exposed to whole-body vibration

while standing on a movable vehicle, it cannot be

determined if the health of the employees would be

compromised from the use of the Segway HT. None

of the published standards or guidelines are

appropriate for this kind of whole-body vibration

exposure. 

3. If the USPS decides that continued use of this

vehicle should proceed, then additional vibration data

should be collected. A better comparison to existing
Page 12 Health Hazard Evaluation Report No. 2002-0239-2922

standards and guidelines can be accomplished with

one-third octave data collected on the units while

they travel over existing mail routes. Because

additional measurement equipment would be

necessary, these data could possibly be collected on

Segway HT units that are not actually delivering

customers’ mail. Even with this more thorough

analysis, there is still little or no epidemiological data

on the health effects of whole-body vibration on

standing subjects. The USPS would have to collect

these health data over time, paying attention to

changes in feet and leg muscles and joints, as well as

complaints of back and neck pain. 

4. The HT is designed and can be adjusted to fit the

size range of most mail carriers that would use it.

Mail carriers at the far end of the spectrum of height

and weight may not be able to find accommodation

using the HT.

5. Improvements to the HT could and should be

made, but these would affect the usability and

efficiency more than reduce the risk of injury to the

worker.

6. Several forms used by the USPS contain useful

data regarding safety aspects of the HT if completed

and available. The three forms, 1769, CA-1, and

CA-16 are most likely to have useful information

regarding occupational injury or safety problems

related to use of the HT during mail delivery. If

these forms are filled out in detail after accidents

occur, the data obtained could be used to implement

a surveillance system for tracking HT accidents

during mail delivery.

RECOMMENDATIONS

# Continue to collect vibration data from the

Segway HT unit as it is used in the field. Similar

methods to the ones used in this evaluation that

collect only weighted acceleration levels along with

more elaborate procedures that collect spectral

information are both warranted. The unweighted,

flat functions that were collected in this evaluation

are probably not needed since there are no published

standards for comparison.

# If use of the Segway HT unit is continued, then

a system of tracking injuries, accidents, and

associated musculoskeletal disorders should be

implemented. Attention should be given to muscle

and joint complaints and problems in the feet, legs,

back, and neck. Also, symptoms consistent with low

frequency, whole-body vibration that leads to motion

sickness should be recorded.

# Evaluate the muscle activity and fatigue levels of

the lower leg muscles using an objective technique

like surface EMG. EMG could also be used to

evaluate back, shoulder, and arm muscles while

delivering mail on the HT.

# Redesign the side carriers so that their size and

placement allows mail to be delivered directly from

them. Design criteria would include height

adjustment, convenient access without interfering

with the space and vision of the mail carrier, and

protection of the mail during bad weather. A design

utilizing a platform onto which a mail bin filled at the

Post Office can be attached, would avoid multiple

handling and transfer of mail from bin to bin.

# Redesign the front carrier to be as small as

needed by the mail carrier to improve vision while

driving the HT, while at the same time satisfying

weight distribution and balance requirements of the

HT.

# Redesign the coupling mechanism used to

transport the HT from the mail facility to the routes

and between routes during delivery. Design criteria

would include convenient attachment to the transport

vehicle without need to remove mail bins from the

HT, and easy access to the rear of the truck when the

HT is attached.

# Redesign the method used to attach the batteries

to the HT. A quick release clamp requiring no tools

would be most effective.

REFERENCES
Health Hazard Evaluation Report No. 2002-0239-2922 Page 13

1. ISO [1997]. Mechanical vibration and shock

– Evaluation of human exposure to whole-body

vibration. Part 1: General requirements. Geneva,

Switzerland: International Organization for

Standardization, Reference number ISO 2631-1:

1997(E).

2. Wasserman DE, Badger DW, Doyle TE,

Margolies L [1974]. Industrial vibration – An

overview. Journal of the American Society of

Safety Engineers, 19:38-43.

3. NIOSH [1990]. Estimated numbers of

employees potentially exposed to specific agents

by 2-digit standard industrial classification (SIC).

National Occupational Exposure Survey (1981 -

1983), Cincinnati, Ohio: U.S. Department of

Health and Human Services,Public Health Service,

Centers For Disease Control and Prevention,

National Institute for Occupational Safety and

Health, unpublished provisional data as of

7/1/1990.

4. Schoenberger RW, Harris CS [1971].

Psychophysical assessment of whole-body

vibration. Human Factors, 13:41-50. 

5. Schoenberger RW [1976]. Comparison of the

subjective intensity of sinusoidal, multifrequency

and random whole-body vibration. Aviation,

Space, and Environmental Medicine, 47:856-862.

6. Wasserman DE, Badger DW [1973].

Vibration and its relationship to occupational

health and safety. Bulletin of the N.Y. Academy

of Medicine, 49:887-984.

7. Cohen HH, Wasserman DE, Hornung R

[1977]. Human performance and transmissibility

under sinusoidal and mixed vertical vibration.

Ergonomics, 20:207-216.

8. NIOSH [1997]. Musculoskeletal disorders

and workplace factors. A critical review of

epidemiological evidence for work-related

musculoskeletal disorders of the neck, upper

extremity, and low back. Cincinnati, Ohio: U.S.

Department of Health and Human Services, Public

Health Service, Centers For Disease Control and

Prevention, National Institute for Occupational

Safety and Health, DHHS (NIOSH) Publication

No. 97-141.

9. ACGIH [2003]. 2003 TLVs® and BEIs®:

based on the documentation of the threshold limit

values for chemical substances and physical

agents and biological exposure indices.

Cincinnati, OH: American Conference of

Governmental Industrial Hygienists.

10. Coermann R [1962]. The mechanical

impedance of the human body in sitting and

standing positions at low frequencies. Human

Factors, 4:225-227.

11. CEC [2002]. Council directive on the

minimum health and safety requirements

regarding the exposure of workers to the risks

arising from physical agents (vibration).

Luxembourg: Commission of the European

Communities, European Union, Official Journal of

the European Communities, Directive

2002/44/EC. 

12. Armstrong TA, Radwin RG, Hansen DJ

[1986]. Repetitive trauma disorders: job

evaluation and design. Human Factors 28(3):

325–336.

13. Gerr F, Letz R, Landrigan P [1991].

Upper–extremity musculoskeletal disorders of

occupational origin. Annu Rev Publ Health

12:543–66.

14. Rempel D, Harrison R, Barnhart S [1992].

Work–related cumulative trauma disorders of the

upper extremity. JAMA 267(6):838–842.

15. Moore JS and Garg A [1995]. The strain

index: a proposed method to analyze jobs for risk

of distal upper extremity disorders. Am Ind Hyg

Assoc J 56:443–458.

16. Armstrong TJ, Buckle P, Fine LJ, et al.

[1993]. A conceptual model for work–related

neck and upper–limb musculoskeletal disorders.

Scand J Work Environ Health 19:73–84.
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17. Grandjean, E. [1971]. Fitting the Task to

the Man, an Ergonomic Approach, Taylor &

Francis, Ltd., London.

18. Panero, J and Zelnik, M. [1979]. Human

Dimension and Interior Space: A source Book of

Design Reference Standards, Whitney Library of

Design, NY, NY.

19. Eastman Kodak Co, Rodgers SH, editor

[1986]. Ergonomic Design for People at Work.

Volume 2, Van Nostrand Reinhold, New York,

NY.

20. Roebuck, J.A., Kroemer, K.H.E., and

Thompson, W.G. [1975]. Engineering

Anthropometric Methods, Wiley, New York, NY.

21. U.S. Army Natick Research, Development

and Engineering Center [1989]. 1988

Anthropometric Survey of U.S. Army Personnel:

Summary Statistics Interim Report, TR-89/027.

22. Ayoub M.M. and LoPresti P. [1971]. The

Determination of an Optimum Size Cylindrical

Handle by Use of Electromyography.

Ergonomics, Vol.14, No. 4, 509-518.

23. Garrett J.W. [1971]. The adult human

hand: some anthropometric and

biomechanical considerations. Human

Factors 13(20):117-131.

24. Konz, Stephan, [1979]. Work Design, Grid

Inc., Columbus, Ohio, page 313.

25. Http://www.techtv.com/news/culture/

story/0.24195,3392405,00.html

26. USDHHS [1992]. Selected topics in surface

electromyography for use in the occupational

setting: expert perspectives, Cincinnati, Ohio:

U.S. Department of Health and Human Services,

Public Health Service, Centers For Disease

Control and Prevention, National Institute for

Occupational Safety and Health, DHHS (NIOSH)

Publication No. 91-100.
Health Hazard Evaluation Report No. 2002-0239-2922 Page 15

Figure 1: A view of the basic e-series cargo carrying human transporter (left) and the modified human 

transporter (right) used in Norman, Oklahoma.
Page 16 Health Hazard Evaluation Report No. 2002-0239-2922

Figure 2: Mail carrier guiding the HT down the transport ramp.
Health Hazard Evaluation Report No. 2002-0239-2922 Page 17

 (a) (b)

 

 (c) 

 (d)

Figure 3: Neutral body postures while delivering mail on the HT (a, b); Reaching and bending to deliver 

 mail while standing on the HT (c, d).
Page 18 Health Hazard Evaluation Report No. 2002-0239-2922

Segway Unit #34

Weighted Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other

 









A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Weighted st. dev 

Figure 4

U. S. Postal Service

Norman, OK

HETA 2002-0239

July 16-17. 2002

Flat Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other

 

A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Flat st. dev 
Health Hazard Evaluation Report No. 2002-0239-2922 Page 19

Flat Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other













A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Flat st. dev 

Segway Unit #08

Weighted Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other





 







A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Weighted st. dev 

Figure 5

U. S. Postal Service

Norman, OK

HETA 2002-0239

July 16-17. 2002
Page 20 Health Hazard Evaluation Report No. 2002-0239-2922

Flat Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other



 





A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Flat st. dev 

Segway Unit #20

Weighted Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other













A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Weighted st. dev 

Figure 6

U. S. Postal Service

Norman, OK

HETA 2002-0239

July 16-17. 2002
Health Hazard Evaluation Report No. 2002-0239-2922 Page 21

Flat Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other

  

 



A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Flat st. dev 

Segway Unit #S2

Weighted Mean RMS Acceleration Values - Z axis

A - drive & street; B - street; C - lawn; D - sidewalk; E - idle; F - bump; G - other

 





A B C D E F G

Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

Acce el rat oi n m[ /sec/sec]

Weighted st. dev 

Figure 7

U. S. Postal Service

Norman, OK

HETA 2002-0239

July 16-17. 2002
Page 22 Health Hazard Evaluation Report No. 2002-0239-2922

Table 1

Triaxial Acceleration data - Segway HT units

U. S. Postal Service

Norman, OK

HETA 2002-0239

July 16-17, 2002

Unit #34 Unit #08 Unit #20 Unit #S2

rms

[m/s2

]

peak

[m/s2]

rms

[m/s2]

peak

[m/s2]

rms

[m/s2]

peak

[m/s2]

rms

[m/s2]

peak

[m/s2]

X - axis

weighted 0.65 4.15 0.41 1.85 0.62 5.92 0.50 2.13

Y - axis

weighted 0.55 4.32 0.59 3.06 0.41 2.88 0.40 1.95

Z - axis

weighted 1.26 13.90 1.67 13.00 0.97 17.20 1.63 19.40

X - axis

flat 0.95 7.71 0.54 4.84 0.37 2.58 0.66 4.84

Y - axis

flat 1.18 11.60 0.94 6.28 0.32 2.46 0.91 10.00

Z - axis

flat 1.59 18.20 1.60 26.10 0.47 17.20 1.99 39.60

Sum

weighted 1.51 13.90 1.81 13.00 1.21 17.20 1.75 19.40

Sum

flat 2.20 18.20 1.93 26.10 0.68 17.20 2.28 39.60

rms = root mean square

m/s2

 = meters per second squared

X-, Y-, Z- axis flat = raw acceleration data

X-, Y-, Z- axis weighted = acceleration data with ISO weighting function applied
Health Hazard Evaluation Report No. 2002-0239-2922 Page 23

Table 2

Major Segway Activity Results - Total Instances per Observation

U. S. Postal Service

Norman, OK

HETA 2002-0239

July 16-17, 2002

Unit # /Weighting Street Lawn Driveway Sidewalk Mount Dismount Idle

34 - weighted

 (120) *

76 34 81 9 71 70 88

34 - flat

 (120)

83 24 96 4 72 70 88

08 - weighted

 (120)

21 20 39 64 49 50 88

08 - flat

 (120)

10 34 46 75 53 52 106

20 - weighted

 (118)

64 23 78 37 44 43 98

20 - flat

 (109)

82 9 90 56 49 47 90

S2 - weighted

 (85)

68 2 67 20 47 47 80

S2 - flat

 (120)

95 1 91 27 57 55 99

*

 Number in parentheses is total 30-second observation periods. 
Page 24 Health Hazard Evaluation Report No. 2002-0239-2922

Table 3: Human Transporter Dimensions

Component USPS Cargo HT

Wheel Diameter, Width 18 in., 3.5 in.

Wheel Base Length 21.5 in.

Foot Pad (L x W) 15.5 in. x 14.5 in.

Side Mail Carriers (L x W x D) 17.5 in x 7 in. x 13 in. Opening can be expanded an

additional 6 in. to 23.5 in., no height adjustability,

fixed at 35 in. (from ground, 28 inches from HT

platform)

Front Mail Carrier (L x W x D) 14 in. x 13 in. depth varies from 7 in. to 5.5 in. front to

back

Center Post Height (Handlebar) Adjustable from 32.5 in. to 42 in.

Handle grips (diameter, length) 1.5 in., 4 in.

Hand grip separation ( left to right hand) 18.5 in., at end of grip, 17 in. center to center

Tire pressure (pounds) 26.5

Table 4: Study Participant Height and Chosen Handle Positions

Mail Carrier Height (in.) Population % Predicted Handle height (in) Actual Height (in)

1 (female) 64 50 37.3 35.5

2 (female) 60.5 5 35.3 32.5

3 (male) 67 25 39.2 35.25

4 (male) 71 75 41.7 35.5
Health Hazard Evaluation Report No. 2002-0239-2922 Page 25

APPENDIX

General Topics of Discussion with Letter Carriers Studied at Norman, Oklahoma

1. Whether or not they were the regular carrier on their route?

2. Number of weeks having used the HT?

3. Extent of training using the HT?

4. Likes and dislikes regarding the HT?

5. Suggested improvements for the HT?

6. Any accidents using the HT?

7. How do you feel after using HT - any new aches and pains? Any aches and pains that don’t occur anymore?

8. Ever feel dizzy or otherwise mentally fatigued using the HT?

9. Would you like to use the HT exclusively to deliver mail?
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