Workplace

Safety and Health

Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Evaluation of Systems to Monitor Blind Areas

Behind Trucks Used in Road Construction

and Maintenance: Phase 1

RI 9660

REPORT OF INVESTIGATIONS/2003
Report of Investigations 9660

Evaluation of Systems to Monitor Blind Areas

Behind Trucks Used in Road Construction 

and Maintenance: Phase 1

Todd M. Ruff

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Pittsburgh Research Laboratory

Pittsburgh, PA

February 2003
This document is the public domain and may be freely copied or reprinted.

Disclaimer: Mention of any company or product does not constitute endorsement by NIOSH.

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about occupational safety and health are available from

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 Web site: www.cdc.gov/niosh

DHHS (NIOSH) Publication No. 2003-113
CONTENTS

Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction ................................................................................... 2

Short-term test procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Long-term test procedure ....................................................................... 3

Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

System 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Short-term test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Long-term test ............................................................................. 5

System 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Short-term test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Long-term test–sanding truck ................................................................. 5

Long-term test–dump truck ................................................................... 7

System 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Short-term test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Long-term test–sanding truck ................................................................. 9

Long-term test–dump truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

System 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Short-term test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Long-term test–dump truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

System 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Short-term test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Long-term test–dump truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Appendix A.–Data collection form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

ILLUSTRATIONS

1. WSDOT sanding truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. WSDOT dump truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3. Test area and test subject . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4. Guardian Alert radar system on sanding truck for short-term use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5. Detection zones for person and Guardian Alert radar system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

6. Preview radar system temporarily mounted above hitch on sanding truck ............................. 5

7. Preview radar system mounted on sand hopper .................................................. 5

8. Detection zone for person and Preview radar system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

9. Final mounting of Preview radar system on sanding truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

10. Clarion video monitor with Preview alarm display mounted on top .................................. 6

11. Detection zone for Preview radar system and field of view for Clarion camera on sanding truck . . . . . . . . . . . 6

12. Mud build-up on radar enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

13. Thin layer of snow on Preview radar that caused alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

14. A, Mounting bridge; B, radar and camera mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

15. Detection zone for Preview radar system and field of view for Clarion camera on dump truck . . . . . . . . . . . . . 8

16. Summer test site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

17. Clarion camera mounted on back of sand hopper ................................................ 9

18. Mud build-up on Clarion camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

cm centimeter km/hr kilometer per hour

ft foot lb pound

ft3 cubic foot m meter

hr hour m3 cubic meter

in inch N degree

kg kilogram

CONTENTS—Continued

Page

19. Intec camera mounted for short-term test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

20. Field of view for person and Intec camera system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

21. Final installation of Intec camera on dump truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

22. Intec camera installed in truck cab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

23. Hindsight sensors mounted on dump box for short-term use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

24. Detection zone for person and Hindsight sensors mounted on dump box corners . . . . . . . . . . . . . . . . . . . . . . . . 12

25. Final mounting position of Hindsight sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

26. Detection zone for person and Hindsight sensors mounted on hitch plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
EVALUATION OF SYSTEMS TO MONITOR BLIND AREAS 

BEHIND TRUCKS USED IN ROAD CONSTRUCTION 

AND MAINTENANCE: PHASE 1

By Todd M. Ruff

ABSTRACT

The majority of fatalities that occur in road construction work zones in the United States involve a worker

being struck by a piece of construction equipment or other vehicle. The Spokane Research Laboratory of the

National Institute for Occupational Safety and Health, in cooperation with the Washington State Department

of Transportation, is evaluating methods to decrease these accidents. One such method uses devices that assist

equipment operators in monitoring blind areas around the equipment to prevent collisions with workers on foot

or other objects. Several cameras and sensor systems are available for this application, and a study was

conducted to evaluate these systems on various trucks used in road construction and maintenance. Tests were

conducted using sanding trucks during the winter months, which allowed researchers to investigate the

effectiveness and limitations of various technologies under the most extreme conditions. Tests were also

conducted using dump trucks during the warmer months to study the effectiveness of the systems in highway

work zones. Results show that many difficulties arise when using camera and sensor systems in cold, snowy

climates. And, while the operation of these systems is more reliable during the warmer months, challenges still

exist in using them on equipment in crowded work areas.

1

Electrical engineer, Spokane Research Laboratory, National Institute for Occupational Safety and Health, Spokane, WA.
2

Figure 1.—WSDOT sanding truck.

INTRODUCTION

The Spokane Research Laboratory of the National Institute

for Occupational Safety and Health (NIOSH) is cooperating

with the Washington State Department of Transportation

(WSDOT) in an evaluation of methods to decrease injuries

and fatalities caused when road construction equipment strikes

a worker or another vehicle. NIOSH has previously tested

various technologies that monitor the blind areas around mining

equipment (Ruff, 2001). These technologies consist of cameras

that provide a view of the blind area, and sensor-based collision

warning systems that warn the driver if an object or person is

nearby. Significant differences in size and function between

mining and construction equipment required another study to

determine the most effective technologies for road construction

equipment.

Road construction workers must work very close to moving

equipment. According to Pratt et al. (2001), the majority of

fatalities occurring in highway construction work zones nationwide involve a worker being struck by construction equipment

or another type of vehicle, and a worker in this industry is just

as likely to be struck by a piece of construction equipment

inside the work zone as by passing traffic. Also, half the

fatalities involving construction equipment occur while the

equipment is backing. These conditions and the blind areas

associated with construction equipment contribute to making

road construction a dangerous occupation. 

In the state of Washington, accidents involving WSDOT

equipment most often involve some type of truck hitting a

worker or another vehicle. For this reason, a study was initiated

to evaluate methods of monitoring blind areas around trucks

used in road construction and maintenance. Several cameras

and sensor systems are available for this application, and understanding the difficulties in implementing these systems on trucks

used in all types of weather was important. Tests were conducted using WSDOT sanding trucks during the winter months,

which allowed researchers to investigate the effectiveness and

limitations of various technologies under the most extreme

conditions. Other tests were conducted on dump trucks during

the warmer months to study the effectiveness of the systems

in highway work zones. Results of these tests could then be

used to determine an effective technology for other types of

equipment. 

NIOSH researchers’ experience with camera systems and

collision warning systems on mining equipment helped narrow

the list of technologies to be evaluated. Systems were selected

on the basis of their ability to see through snow and rain, to

handle the tough environment of roadway construction, and to

meet minimum standards regarding mounting position and

detection range. All systems went through an initial short-term

test to determine if the system could be mounted on a particular

piece of equipment and function according to minimum

specifications. If the system operated satisfactorily in this initial

test, then long-term tests were conducted over several months

while the equipment was used in actual road construction and

maintenance activities. 

SHORT-TERM TEST PROCEDURE

Several systems were selected by NIOSH engineers for shortterm tests on a WSDOT sanding truck (figure 1) or dump truck

(figure 2), depending on the time of year and the type of test

to be conducted. These tests consisted of temporarily mounting

each system on the truck to determine if a suitable mounting

location could be found and to determine the system’s effectiveness in detecting a person standing or crouching behind the

truck. 

The temporary test area consisted of a large empty area in

the WSDOT office parking lot (figure 3). The area was approximately 30 m (100 ft) wide and 150 m (500 ft) long. A grid

was marked on the asphalt pavement in order to record the

detection zone for each system. The grid was 9 m (30 ft) wide

by 14 m (45 ft) long with test points marked every 0.76 m (2.5

ft).

The reliable detection zone for sensor-based collision

warning systems, or the field of view (FOV) for a camera, was

evaluated using a person as the test subject. At actual road

construction sites, the most serious accidents involve a worker

on foot being struck by moving equipment, so each system’s

ability to detect a person was thoroughly evaluated. The test

subject was a NIOSH engineer, 1.9 m (75 in) tall, weighing

84 kg (185 lb), and wearing a cotton jacket and jeans. Other
3

Figure 2.—WSDOT dump truck.

Figure 3.—Test area and test subject.

personnel from NIOSH and WSDOT were occasionally used

to verify the size of the detection zone, but results from those

test subjects were not recorded.

 Each system was temporarily and separately mounted on the

back of the truck. The alarm display normally mounted in the

cab was also mounted on the back of the truck so the state of the

alarm could be seen by the test subject. The sensing or camera

portion of the system was mounted in various locations and with

various tilt angles so the optimum detection zone could be

determined and false alarms minimized.

After the system was installed, the truck was moved slowly

in reverse (3-5 km/hr [2-3 mile/hr]) with no obstacles or people

behind the truck to determine if false alarms would be generated. If false alarms occurred, the system was moved or tilted

differently to minimize them. Tests continued if an acceptable

mounting location was found.

The next step was to determine the reliable detection zone for

a person. For these tests, the test subject walked toward the

stationary truck (motor running) along the grid lines that ran

parallel to the long axis of the truck. A marker was placed on

the ground along each line where detection began and where it

ended so the zone could be recorded on a graph. After this zone

was marked, reliable detection was verified by moving the

truck in reverse toward the stationary test subject. For safety, a

spotter was used during this test to tell the driver to stop the

truck at a safe distance from the test subject. Another test

was performed in which the test subject crouched near the tires

of the stationary truck. The ability of the system to detect a

crouching person near the truck was also recorded on the

detection zone graph.

LONG-TERM TEST PROCEDURE

After a system went through the short-term test, a determination was made whether to continue testing the system under

actual field conditions. This determination was based on several

criteria.

C Low probability of a false alarm.

C Reliable detection of a person in a zone starting immediately

behind the truck, extending at least 4.6 m (15 ft) behind the

truck and at least the width of the truck.

C Apparent ability of the system to handle harsh conditions.

C Minimal maintenance requirements.

C Favorable impression of the system by the driver.

C Feasible mounting configuration.

Systems selected for long-term tests were permanently

mounted on a WSDOT truck according to the manufacturer’s

suggestions. Long-term tests in the winter were conducted on

a tandem-axle sanding truck (figure 1), and long-term tests

during the warmer months were conducted on a 7.6-m3

 (10-yd3)

dump truck (figure 2). Test duration was 2 months or more.

To evaluate the systems, a form was available in the cab of

the truck so the driver could make daily comments and record

the effectiveness of the system (appendix A). Informal discussions with drivers also helped researchers understand a

system’s problems and capabilities. Finally, a NIOSH engineer

rode in the truck during actual construction or maintenance to

observe how the driver used and reacted to the system. When

the long-term test was completed, the system was removed from

the truck and inspected for damage or abnormal wear.
4

 Figure 4.—Guardian Alert radar system on sanding truck for

short-term test. Figure 5.—Detection zones for person and Guardian Alert radar

system.

TEST RESULTS

SYSTEM 1: GUARDIAN ALERT RADAR SYSTEM1

Distributor: S&S Distributing, Elkhorn, NE 

System Description

This radar system (model 1700) uses Doppler radar techniques to detect an object or person and consists of a radar

antenna and processing electronics, an alarm display, and

cables. The radar generates an alarm only when the distance to

an object decreases. This can be achieved by an object moving

toward the radar or by moving the vehicle in reverse. There are

no sensitivity or range adjustments available on this system, and

the radar is only active in reverse gear. The alarm display is

mounted in the cab and consists of warning lights (LED’s) and

an audible tone that changes frequency depending on the distance to the detected object.

Short-Term Test

For the first set of tests, this radar system was mounted level

on a sanding truck on the right side of the hitch plate at a height

of 79 cm (31 in) (figure 4). The alarm display was mounted on

the back of the truck so the state of the alarm could be easily

recorded during tests. No false alarms occurred when the truck

was moved in reverse in a clear area.

To determine the detection zone of a person, the test subject

walked toward the rear of the truck and recorded where reliable

detection occurred. The detection zone for a person with a

stationary truck is shown by the solid line in figure 5. The total

 1

Mention of specific products or manufacturers does not imply endorsement

by the National Institute for Occupational Safety and Health.

range of this radar was 6 m (20 ft) for detecting a person, and

the width was adequate to detect a person near the tires.

Significant differences in the detection zone were seen when

tests were conducted with the truck moving in reverse. The

dashed line of figure 5 shows the detection zone for a person

standing still and facing the radar while the truck moved slowly

 (3-5 km/hr [2-3 mile/hr]) in reverse. The range of the system

decreased to approximately 3 m (10 ft), and the width no longer

covered the width of the truck. An exact reason for this

decrease in the detection zone was not found, but the manufacturer suggested the cause could be vibration or moving at a

speed too slow for reliable detection (Guardian Alert, 2000).

However, tests conducted by moving at the same reverse speed

toward other objects, such as a building or vehicle, did not show

the same decrease in detection. It is suspected that a combination of slow reverse speeds and the smaller radar cross

section of a person contributed to the decrease in the detection

zone. 

Several different mounting locations were tried to determine

if the detection zone could be improved for a moving truck. The

radar unit was relocated to the center of the bumper area, just

above the hitch, and no improvement was seen. The radar unit

was then moved to a higher location in the center of the sand

hopper at a height of 1.8 m (6 ft). Still no improvement in

detecting a person was seen when the truck moved. The system

was also tested on a dump truck with several different mounting

configurations, and the same problems were seen.
5

 Figure 6.—Preview radar system temporarily mounted above

hitch on sanding truck.

Figure 7.—Preview radar system mounted on sand hopper.

Long-Term Test

Long-term tests were not conducted with this radar on a

sanding truck or dump truck because of poor detection of a

person when the truck was moved in reverse. However, it did

adequately detect other objects, such as cars, buildings, and

guard rails. WSDOT independently conducted long-term tests

of this system on a truck used for bridge inspection. Results of

these tests are not published here, but may be obtained from the

WSDOT Eastern Region Office.

SYSTEM 2: PREVIEW RADAR SYSTEM

Manufacturer: Preco Electronics, Boise, ID

System Description

This radar system uses a pulsed signal technique to detect

the presence of an object. It consists of a radar antenna and

processing electronics, an alarm display, and cables. No motion

of the object or vehicle is needed for detection. The alarm

display shows distance in 1-m increments using a series of

LED’s, and an audible alarm is generated that changes in

frequency as the distance to an object changes. The radar

system is activated when the vehicle’s ignition is on, but the

audible portion of the alarm is activated only when in reverse.

There are no user-adjustable settings on this model.

Short-Term Test

Initially, the radar unit was mounted on the sanding truck’s

hitch plate area on the right side of the hitch at a height of

86 cm (34 in). The alarm display was mounted on the back of

the truck so the state of the display could be easily recorded

during tests. Because the radar system’s presence-sensing

abilities do not require motion, false alarms occurred in a clear

area because the system sensed the nearby hitch. False alarms

also occurred when the unit was moved to a position just above

the hitch (figure 6). Because of the size of the radar antenna and

its sensitivity to any nearby metal, the antenna could not be

mounted on the hitch plate or frame and was reinstalled at

the center of the sand hopper at a height of 188 cm (74 in)

(figure 7). The radar was tilted downward 20° to improve

detection of a person close to the truck. At this mounting

position, no false alarms occurred when the truck was moved in

reverse in a clear area.

To determine the detection zone for a person, the test subject

walked toward the rear of the sanding truck and recorded

where reliable detection occurred (figure 8). The test subject

then remained stationary while the truck was moved slowly

(3-5 km/hr [2-3 mile/hr]) in reverse. No significant changes

were seen in the detection zone. The range for both scenarios

was 7.6 m (25 ft), and the width of the detection zone was

adequate to detect a person standing 30 to 60 cm (1 to 2 ft) away

from the outer edge of the rear tires. However, at this mounting

height, a crouching person might not be detected immediately

next to the tires, and the tilt of the radar would need to be

increased if possible.

Long-Term Test–Sanding Truck

The Preview radar system’s reliable detection of a person,

low false alarm rate, and apparent ability to handle tough environments made it a candidate for continued testing. The radar

system was selected for tests on both a sanding truck during the

winter and a dump truck the following spring. This system was

tested in combination with a Clarion camera system on the same

truck. Results for the camera system are discussed later.

A 2-month test (December through January) was planned

to evaluate the effectiveness of the radar system on the sanding

truck in winter conditions. The radar system was mounted at

a height of 1.7 m (68 in) and downward tilt of 20° (figure 9).
6

 Figure 8.—Detection zone for person and Preview radar system.

 Figure 9.—Final mounting of Preview radar

system on sanding truck.

 Figure 10.—Clarion video monitor with

Preview alarm display mounted on top.

 Figure 11.—Detection zone for Preview radar system and field

of view for Clarion camera on a sanding truck.

The downward tilt was required in order to detect a crouching

person as close as possible to the rear tires. The radar unit

was mounted inside a polyethylene enclosure to protect the

radar’s aluminum case from corrosion (the salt and magnesium

chloride used for de-icing are notorious for quickly corroding

aluminum parts on the truck). The radar alarm display was

mounted on the top of the camera system’s video monitor in

the cab and can be seen as a gray-colored box with LED’s in

figure 10. 

After mounting the systems, the final radar detection

zone and the FOV for the camera were recorded as shown

in figure 11. The radar’s detection zone for a person standing

behind the truck (inner solid line) adequately covered the

width of the truck and extended 7.6 m (25 ft) from the back.

However, the system did not detect a person crouching or
7

Figure 12.—Mud build-up on radar enclosure.

 Figure 13.—Thin layer of snow on Preview

radar, which caused an alarm.

kneeling immediately behind the truck. The downward tilt of

the radar system was increased to improve detection of a

crouching person, but the system began to sense the truck itself,

which caused false alarms. The tilt angle was reset to 20°. 

Driver comments stated that the system was useful at the

beginning of the shift, when backing to the sand pile and driving

around the maintenance yard. The radar accurately detected and

displayed the distance to the sand pile, loading equipment, and

other objects. However, problems with the radar system became

evident after driving on the highway a few kilometers. On days

when it was not snowing, mud and grime from the road covered

the radar enclosure, as shown in figure 12. On days when it was

snowing, snow mixed with sand built up on the enclosure

(sometimes several centimeters thick). Snow or grime on the

radar enclosure caused the system to generate a constant false

alarm (all LED’s were lit, indicating an object immediately in

front of the radar unit). 

Initially, it was believed that removing the additional enclosure for the radar system would solve the problem. The radar

system manufacturer stated that snow or ice directly on the face

of the radar unit (with no extra enclosure) should not cause an

alarm. By adding the extra enclosure, we introduced an offset

of about 2.5 cm (1 in) between the radar unit and the snow/mud.

By removing the extra enclosure and mounting the radar as

received from the manufacturer, the snow would build up

directly on the radar unit and should be ignored. 

Tests at NIOSH were conducted to see if the radar system

would ignore snow. Figure 13 shows a simple test where a thin

layer of dirty snow was piled on top of the radar unit. This

caused a false alarm, showing that remounting an unprotected

radar system on the truck would not solve the problem. The

manufacturer indicated that software changes could be made to

ignore objects or snow build-up closer than 30 cm (1 ft) to the

radar. This change has been made, but tests results are not

available yet. 

The radar system was removed from the sanding truck after

2 months of testing. The radar antenna, alarm display, and

cabling were in good shape, but the false alarm problem from

snow/mud build-up could not be immediately solved.

Long-Term Test–Dump Truck

A 5-month test (April through August) was planned to

evaluate the effectiveness of the Preview radar system on a

dump truck used in road construction and maintenance. (A

Clarion camera system was tested in combination with the radar

system, and results for the camera system are discussed later.)

The first step in the installation of the system involved finding

a suitable mounting position on the back of the dump truck.

Several positions were tried, including the bumper area (hitch

plate) just below the dump box and the tailgate area. However,

the radar system could not be mounted in the bumper area

because (1) it would detect the nearby metal of the tailgate and

hitch and (2) the tailgate can be hinged at the bottom, which

would obstruct the radar signal. The system could not be easily

mounted on the tailgate because (1) slamming the tailgate during

unloading would cause high levels of vibration and shock

and (2) special connectors and wiring would have to be

retrofitted to the system to allow it to be disconnected quickly

when the tailgate was hinged at the bottom instead of at the top.

Therefore, it was determined that a bridge-type mounting apparatus would need to be designed to allow the radar to be

mounted above the tailgate. 

NIOSH and WSDOT personnel designed the mounting

bridge shown in figure 14. The size of material to be hauled,

such as boulders, must be considered when determining the

height of this bridge so that the bridge will not obstruct

dumping. However, if the bridge is too high, it can be easily

struck by a loader bucket or, as discussed later, it may not fit

under some material loading bins.

The radar system was mounted beside the Clarion camera

system at a height of 2.7 m (107 in) and with a downward tilt of

30°. The downward tilt was required to detect a person as close

as possible to the back of the truck. Some experimentation was

required to determine the optimum tilt angle because adjusting

the tilt to detect objects close to the truck may increase false

alarms due to the ground or truck being sensed. The radar alarm

display was mounted on the top of the video monitor in the cab

(figure 10). 

After the system was mounted, the final radar detection zone

and FOV for the camera were recorded as shown in figure 15.

Because of the mounting height of the radar, a person was not

detected immediately behind the truck. This was because a

person could walk underneath the radar beam at close distances.
8

 Figure 14.—A, Mounting bridge; B, radar and

camera mounting.

 Figure 15.—Detection zone for Preview radar system and field

of view for Clarion camera on dump truck. Figure 16.—Summer test site.

The mounting height also resulted in poor detection of a

crouching person when close to the truck, as indicated by the

dashed line inside the solid line of figure 15. A standing person

was detected at distances between 0.76 and 6.9 m (2.5 and

22.5 ft) from the back of the truck, while a crouching person

was detected at distances between 2.3 and 6.9 m (7.5 and 22.5

ft). The radar system was mounted several feet above the manufacturer’s suggested mounting height, which caused the

detection zone to be inadequate for this truck. Tests continued,

however, because the addition of the camera system provided

redundancy. 

Most of the tests were conducted at a site where the ground

was being leveled for the relocation of high-capacity power

lines in preparation for a new highway (figure 16). The haulage

road surface and material being moved consisted mostly of sand.

Moisture content of the sand varied according to weather, but a

water truck kept most of the haulage roads damp to reduce dust.

The dump truck was loaded by a front-end loader and then

driven to the dump area. Each truck traveled between 50 and 70

round trips in a workday. Truck drivers’ comments on the radar

system are summarized below.

C The radar system was useful in that it prompted the driver to

check the camera system’s video monitor, but most often the

alarms were caused by items that posed no danger, e.g., sand

piles or other equipment of which the driver was already aware.

C Very few false alarms were heard, i.e., alarms generated for

no apparent reason. 

C The radar system was reliable in detecting and displaying an

approximate distance to the sand pile when backing to the dump

point.

C The mounting bridge caused the loader operator to slow

down to avoid hitting the bridge during loading.
9

 Figure 17.—Clarion camera mounted on back of sand hopper.

C The mounting bridge was too high and would not pass under

the asphalt loading bin in later tests. This truck could not be

used for paving projects.

NIOSH personnel made additional observations while riding

in the truck.

C A short false alarm (one or two beeps) was sometimes

generated by the radar system when the truck started to move in

reverse. The cause could not be determined. No other false

alarms were generated.

C False alarms did not increase when road surface moisture

increased. 

C The width of the radar’s detection zone was wider than the

truck, and this caused some nuisance alarms, especially when

reversing near roadside berms or when loading equipment. 

C The driver did check the video monitor when the radar

generated an alarm.

While the radar system operated well on this truck, the fact

that it must be mounted high in order to avoid tailgate mounting

is a major drawback. As designed, the mounting bridge interfered with operations, and so other mounting positions are being

investigated. Based on the above observations and the fact that

this truck could not be used for paving projects, it was decided

to pursue other sensor systems that could be mounted on the

truck’s rear bumper, hitch plate, or on the side of the dump box

near the taillights.

SYSTEM 3: CLARION CAMERA SYSTEM

Distributor: Safety Vision, Houston, TX

System Description

This system consists of a Clarion camera (model CC853E),

a 15-cm (6-in) video monitor (model CJ762E) mounted in the

cab, and cables to connect the camera and monitor. The camera

has a motorized shield that covers the lens when the camera is

not in use. This can be used to protect the lens when the vehicle

is in forward gear or when the vehicle is not running.

Short-Term Test

Short-term tests were conducted on the sanding truck. The

camera was temporarily mounted at several different heights

and angles to determine the best FOV for the truck driver. The

best mounting position was high at the center of the sand

hopper. With a slight downward tilt of the camera, this location

allowed detection of a crouching person near the back of

the truck and out to 12 m (40 ft) away. Results of this initial

test showed that the camera system could be useful, so longterm tests were conducted during both winter and summer.

Long-Term Test–Sanding Truck

As mentioned earlier, this camera system was tested in

combination with the Preview radar system to determine if a

combination of radar and camera would compliment one

another. While the camera provides an actual view of the blind

area, the radar provides an alarm to prompt the driver to check

the video monitor. A 2-month test (December through January)

was planned to evaluate the effectiveness of the camera on the

sanding truck. The camera was mounted on the rear of the sand

hopper at a height of 2.2 m (87 in) (figure 17). The downward

tilt of the camera was adjusted to 35° so that a crouching person

could be seen immediately behind the truck. The video monitor

was mounted on the cab floor on a pedestal just to the right

of the gear shift, as shown in figure 10. The monitor was

positioned so that it could be easily viewed by looking slightly

downward after checking the right mirror. 

After mounting the system, the FOV for the camera was

recorded as shown by the outer dashed line in figure 11. The

FOV was adequate to show a person standing or crouching

immediately behind the truck. This view extended to 12 m

(40 ft) from the center of the hitch plate. The fisheye effects of

the wide-angle lens account for the odd shape of the FOV.

The camera system had similar problems as the radar when

driving on the road during the winter months. Ice, snow, and

mud build-up on the camera caused several problems. Initially,

the motorized lens shield on the camera was left in the open

position for forward and reverse gears. This was requested so

the driver could monitor vehicles behind the truck during

sanding and plowing operations. After the first few days of

operation, it was necessary to change this configuration so the

lens shield closed when the truck was in forward gear, allowing

the camera view to be activated only in reverse. This was

because (1) mud and snow build-up on the lens occurred
10

Figure 18.—Mud build-up on Clarion camera.

because (1) mud and snow build-up on the lens occurred

quickly in forward gear (figure 18), obstructing the camera

view, and (2) glare from headlights distracted the driver during

night operations. After this change was made, the camera

system operated reliably on warmer days. However, in snowy

conditions, ice and snow quickly covered the camera when

traveling forward. This caused the lens shield to become frozen

in the closed position, making the camera unusable even in

reverse. After a few days of operating under these conditions,

the lens shield mechanism failed and was stuck in the closed

position even after snow and ice were cleared from the camera.

A heated camera enclosure or some other method to keep snow

and ice from building up on the camera would be required

before using this system on a sanding truck.

The camera system was removed from the truck and

inspected after 2 months of use. In addition to the broken lens

shield mechanism, the glass window protecting the camera lens

was cracked. The monitor and cables appeared in good shape.

Long-Term Test–Dump Truck

Even though there were problems during the winter months,

the camera system worked well on warmer days. Long-term

tests during summer months were planned with a new camera

(same model). Again, tests were conducted in combination

with the Preview radar system. A 5-month test (April through

August) was planned to evaluate the effectiveness of the Clarion

camera and Preview radar system on a dump truck used in road

construction and maintenance. The camera was mounted on the

bridge apparatus next to the radar system as shown in figure 14.

The high mounting position provided the best FOV for the

camera and avoided the problems associated with vibration and

tailgate articulation at lower mounting positions.

The camera was mounted at a height of 2.8 m (112 in). The

downward tilt of the camera was adjusted to 50° from vertical

so that a crouching person could be detected immediately

behind the truck. The video monitor was mounted on a pedestal

on the cab floor just to the right of the gear shift, as shown in

figure 10. 

After mounting the systems, the final radar detection zone

and the FOV for the camera were recorded as shown in figure

15. The FOV for the camera (outer dashed line) was able to

show a person standing or crouching immediately behind the

truck. This view extended to 9.1 m (30 ft) from the rear of the

truck. 

Tests were conducted at an earth-moving operation for a

new highway as described earlier. Truck driver comments are

summarized below.

C The camera system is more useful than radar because an

actual view of the area behind the truck is preferred over just an

alarm.

C The camera lens did get some dust and mud on it during the

day, but not enough to obstruct the view. Wiping the lens once

a shift was usually sufficient to keep it clear.

C Using the camera at night was difficult because lighting

behind the truck was poor.

General impressions of the system by the drivers and by

NIOSH observers indicated that the camera system was useful.

However, because of the problems with the mounting bridge, it

was determined that a smaller camera that could be mounted in

a lower position, preferably on the side of the dump box, was

needed. 

The camera system was removed from the truck after 5

months of operation. The camera appeared to be in good shape,

and the lens shield operated correctly. There were a few grains

of sand between the glass window and the camera lens, which

caused some concern about the integrity of the camera enclosure. The monitor and cables appeared to be in good shape.

SYSTEM 4: INTEC CAMERA SYSTEM

Distributor: Intec, Laguna Hills, CA

System Description

The Intec camera system consists of a small camera the size

of a 5-cm (2-in) cube (model CVC210XL), an 11.4-cm (4.5-in)

video monitor (model CVM450LPP), and cables.
11

Figure 19.—Intec camera mounted for short-term test.

Figure 20.—Field of view for a person and Intec camera system. Figure 22.—Intec monitor installed in truck cab.

Figure 21.—Final installation of Intec camera on dump truck.

Short-Term Test

The camera was temporarily mounted in various positions

on the bed of a dump truck. The goal was to find a position on

the side of the box near the taillights that would be high enough

to achieve an adequate FOV, but where the camera would not

protrude too far from the side of the truck. The final position

selected was near the top of the dump box, just above the

taillights (figure 19).

The monitor was temporarily mounted in the cab of the truck

between the two seats. The FOV for the camera was tested

by recording where a person could be seen behind the truck in

both a standing and a crouching position. As seen in the graph

in figure 20, the FOV for a person in a standing position

extended from the back of the truck out to the horizon. The

right side of the FOV was blocked by the camera enclosure.

The area between the dotted line and the truck represents the

area where a crouching person could not be seen in the video

monitor because the person was beneath the camera’s FOV.

Full coverage of a crouching person behind the truck could be

achieved by tilting the camera further downward, but there is a

tradeoff between close coverage and the distance that the FOV

extends on the left side of the truck. Results of this initial test

showed that the camera system could be useful, so long-term

tests on a dump truck were conducted during the summer

months. 

Long-Term Test–Dump Truck

The Intec camera was permanently mounted on the right

side of the dump box just above the highest taillight at a height

of 2.2 m (87 in) and a downward tilt angle of 20o (figure 21).

The video monitor was mounted on a pedestal between the

seats in the cab (figure 22). Figure 20 shows the FOV of the
12

 Figure 23.—Hindsight sensors mounted on dump box for shortterm test.

 Figure 24.—Detection zone for person and Hindsight sensors

mounted on dump box corners.

camera for both a standing and a crouching person. Tests were

conducted during the summer months at patching/paving jobs

and during other various road construction and maintenance

activities. No evaluation forms were turned in, but driver

interviews were held in which the drivers commented that the

system worked well and was effective in monitoring the rear

blind area. However, they also commented that the view from

the camera was sometimes confusing because the camera did

not point in the same direction that the truck traveled when in

reverse. 

Finally, it was suggested that the camera be moved to the

other side of the dump bed to provide a better view of the larger

blind area on the right side of the truck. At the time of this

writing, the camera system had been on the truck for 5 months,

and tests were continuing with no other problems reported. 

The dump box on this truck will likely be removed in the fall

months and replaced with a sand hopper. There is a connector

on the camera, so the camera can remain with the dump box and

cables can be stored until the dump box is replaced. No winter

tests were planned for this camera. However, at the time of this

writing, designs for a heated enclosure were being considered,

and test results may be available at a later date.

SYSTEM 5: HINDSIGHT 20/20 ULTRASONIC

SENSOR SYSTEM

Distributor: Sonar Safety Systems, Santa Fe Springs, CA

System Description

Collision warning systems based on sonar or ultrasonic

sensors are popular in the automotive and delivery truck industries. The system works by transmitting high-frequency

sound waves and detecting reflections of these waves from

objects within the sound beam. The maximum range of these

systems is typically around 3 m (10 ft). Also, system sensors

must be kept clean of mud and debris for correct operation. A

Hindsight 20/20 system (model HS300) was selected for these

tests. It consisted of two sensors with rubber enclosures, an

alarm display that consisted of LED’s and an audible alarm that

changes frequency depending on distance to the detected object,

a cable junction box, and cables.

Short-Term Test

As suggested by the manufacturer, the two sensors were

temporarily mounted on the lower corners of the dump truck’s

box (just below the tailgate hinge points) as shown in figure 23.

The alarm was situated at the rear of the truck for easy viewing

for these initial tests. Several problems were seen with this

mounting configuration, including the potential for damage to

the sensors when material flowed through the tailgate and the

lack of continuous detection of a crouching person behind the

truck, as shown by the dashed lines in figure 24. 
13

Figure 25.—Final mounting position of Hindsight sensors.

 Figure 26.—Detection zone for person and Hindsight sensors

mounted on hitch plate.

An alternative mounting position for the sensors was tested

(figure 25). This placed the sensors on the hitch plate and closer

together, which resulted in a more continuous detection zone

for a person, as seen in figure 26. The total range of the system

was 2.4 m (8 ft), and detection covered most of the width of

the truck except the corners of the dump box. The system did

not generate false alarms in a clear area on asphalt, and the mud

flaps were not detected. Despite the short detection range, longterm tests on a dump truck were conducted. 

An additional short-term test was conducted on a sanding

truck. The same positions on the hitch plate were used for

sensor mounting (figure 25). Frequent false alarms were

produced, but the source of the alarms was not obvious. It was

suspected that the slightly different configuration of the mud

flaps was causing the flaps to be detected. No long-term tests

were planned on the sanding truck because it was obvious that

the sensors would be covered with snow and mud during winter

operations.

Long-Term Test–Dump Truck

The final mounting position for the sensors on a dump truck

was near the taillights, as shown in figure 25. The sensors were

mounted at a height of 76 cm (30 in) with 81 cm (32 in) spacing.

The alarm was mounted on the dashboard. The detection zones

for a standing and crouching person were the same as in the

short-term results (figure 26). The system was tested during the

summer months on road-patching and materials-hauling jobs.

No evaluation forms were turned in, but comments from drivers

were received through interviews and are summarized below.

C The system was reliable, and false alarms were rare in most

situations.

C The system produced false alarms when backing through

thick airborne dust.

C The system alarmed continuously when a trailer was pulled

behind the truck, and there was no way to temporarily turn the

system off (without disconnecting it). 

Modifications will be needed for this system to function on

trucks that pull trailers. This is true for all sensor-based systems

that do not require object motion for an alarm. Sonar Safety

Systems sells an add-on to the system that detects a trailer when

the trailer light connector is plugged into the truck. If the trailer

lights are connected, then the system is temporarily disabled.

This was not tested, but would be an acceptable solution. 

Sensing dust was a problem with this sonar system according

to the drivers, which brought up concerns about false alarms

in snow and rain. The manufacturer did acknowledge the possibility of false alarms in heavy snow. Additional tests are needed

to determine what precipitation rates would cause an alarm, if

any. Concerns were also raised regarding the short detection

range of the system. A person immediately behind a very slowmoving truck might be detected in time for the driver to react.

However, in fast-moving situations, 2.4 m (8 ft) of detection

does not give adequate time to respond (Society of Automotive

Engineers, 1999).

At the end of the summer, the system was removed and

inspected. All components were in good working order.
15

CONCLUSIONS

While many more collision warning and cameras systems are

available than were tested here, tests of the above systems did

show the challenges associated with implementing these types

of systems on trucks used in the winter or in crowded highway

work zones. The following general observations can be made

based on these test results.

C Roadway construction zones are typically crowded with

equipment and workers on foot. Sensor-based collision warning

systems, e.g., radar or sonar, will alarm often in this environment. These alarms will most often be nuisance alarms caused

from workers or objects of which the driver is already aware.

If too many alarms are associated with objects that are not in

real danger, all alarms will eventually be ignored, making the

system useless. For this reason, camera systems may be more

appropriate in this environment. 

C The alarm function of sensor-based systems provides a

warning to the driver and is a more active method of monitoring,

while camera systems are a more passive technology, much like

mirrors. Using the two systems in combination on the same

truck may have many advantages. The camera system provides

an actual view of the blind area near the truck and provides a

method to check the source of any alarms. At the same time, the

sensor provides an alarm that prompts the driver to check the

video monitor so a potential collision does not go unnoticed.

There would still be a problem with frequent nuisance alarms in

highway work zones, but they may be more tolerable if there is

a quick method of checking the source of any alarm. 

C If sensor-based systems are used to provide a warning of

an object or person near the truck, some method must be used

to eliminate false alarms from mud, dirt, or snow build-up on

the sensing portion of the system. This can be done using

processing methods that ignore object detection directly in front

of the sensor or by using some other means that prevents debris

from blocking the sensor’s signal.

C Most trucks used in construction are also used to pull trailers.

Most sensor-based collision warning systems will sense the

trailer and produce an alarm. Some method must be provided to

disable the system when a trailer is being pulled or allow quick

connection to separate sensors mounted on the trailer.

C Cameras work well during the warmer months, and daily

cleaning of the lens is usually sufficient. However, on some

types of equipment, snow and grime build up on the lens quickly

during winter. Some method of preventing snow, ice, and grime

from covering the camera must be employed. 

C It is often difficult to find a mounting position for sensors or

cameras, especially on dump trucks. Mounting these devices on

the side of the dump box was found to be an acceptable solution

if the size of the device will allow this. Durability is also an

important consideration when the device is mounted in an

exposed area.

C Many camera and sensor systems are available for automobiles and on-road trucking. The construction equipment

application is more demanding and harsher than standard

transportation applications. It is important to choose systems

made for and proven on heavy construction equipment.

FUTURE WORK

Cooperation with collision warning and camera system

manufacturers will continue so improvements can be made to

existing systems. Methods to prevent build-up of snow and

ice on cameras used on sanding trucks, plows, and other

equipment used in the winter need to be studied further. This

could include heated enclosures and air deflectors/spoilers. For

collision warning systems that use radar technology, smaller

radar antennas would make it easier to find acceptable mounting

locations. 

Evaluations of new cameras or collision warning systems

will be conducted as they come on the market. Final tests of one

or two systems will be conducted on a fleet of equipment at a

large highway construction worksite, and the results of these

tests will be available at a later date.

REFERENCES

Pratt., S.G., D.E. Fosbroke, and S.M. Marsh. 2001. Building Safer

Highway Work Zones: Measures To Prevent Worker Injuries from Vehicles and

Equipment. DHHS (NIOSH) Pub. No. 2001-128, 71 pp.

Ruff, Todd M. 2001. Monitoring Blind Spots – A Major Concern for Haul

Trucks. Engineering and Mining Journal, v. 202, no.12, Dec., pp. 17-26.

Society for Automotive Engineers [SAE]. 1999. Discriminating Back-Up

Alarm System. Surface Vehicle Standard J1741, June.

S&S Distributing. 2000. Guardian Alert Back-Up Warning System -

Warning System vs. Parking Aid. Product literature available by calling S&S

Distributing 1-800-998-0555, 1 p.
16

Appendix A.—Data Collection Form
Delivering on the Nation’s Promise:

Safety and health at work for all people

Through research and prevention

For information about occupational safety and health topics contact NIOSH at:

1-800-35-NIOSH (1-800-356-4674)

Fax: 513-533-8573

E-mail: pubstaft@cdc.gov

www.cdc.gov/niosh

DHHS (NIOSH) Publication No. 2003-113