Report of Investigations 9654

Test Results of Collision Warning Systems 

on Off-Highway Dump Trucks: Phase 2

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

November 2000
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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DHHS (NIOSH) Publication No. 2001-100
CONTENTS

Page

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

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

Test description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Test results, Komatsu 210M ....................................................................... 4

System: Sensor Vision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

System: Preview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

System: Ultrawide-band radar prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

System: Buddy System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

System: Rear Guard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Test results, Caterpillar 793B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

System: Ogden Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

System: Guardian Alert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

ILLUSTRATIONS

1. Side view of Komatsu 210M ................................................................ 2

2. Rear view of Komatsu 210M ................................................................ 3

3. Determining detection zone for a person . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4. Determining detection zone for a pickup truck .................................................. 4

5. Detecting a cinder block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

6. Sensor Vision system mounted on rear of dump truck ............................................. 4

7. Two types of monitors mounted in cab of dump truck ............................................ 5

8. Detection zone of Ogden radar system and a person at rear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

9. Detection zone of Ogden radar system and a pickup at rear ........................................ 5

10. Field of view of two different cameras monitoring rear of truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

11. Ogden radar system mounted on front bumper .................................................. 6

12. Detection zone of Ogden radar system and a person in front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

13. Detection zone of Ogden radar system and a pickup in front ....................................... 7

14. Detection zone of Ogden radar system on a Caterpillar 793 truck and a person ......................... 7

15. Detection zone of Ogden radar system mounted high on Komatsu truck and a person ................... 7

16. Trihedral corner reflectors for determining beam dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

17. Comparison of detection zones for (A) a large reflector and a pickup truck and (B) a small reflector and 

a person . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

18. Preview radar system antenna and electronics enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

19. Preview radar system display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

20. Detection zone of Preview radar system and a person at rear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

21. Detection zone of Preview radar system and a pickup at rear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

22. Preview radar system mounted on front bumper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

23. Detection zone of Preview radar system and a person in front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

24. Detection zone of Preview radar system and a pickup in front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

25. Detection zone of Preview radar system mounted high on Komatsu truck and a person . . . . . . . . . . . . . . . . . . 11

26. Multispectral ultrawide-band radar system and alarm display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

27. Detection zone of ultrawide-band radar system and a person at rear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

28. Detection zone of ultrawide-band radar system and a pickup at rear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

29. Ultrawide-band radar system mounted on front grill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

30. Detection zone of ultrawide-band radar system and a person in front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

31. Detection zone of ultrawide-band radar system and a pickup in front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

32. Detection zone of ultrawide-band radar system mounted high on Komatsu truck and a person . . . . . . . . . . . . . 14
CONTENTS–Continued

Page

33. Installation of Buddy system components on front deck of dump truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

34. Buddy system prototype tag on worker’s belt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

35. Buddy system alarm display with no tag detected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

36. Determining detection zone of Buddy system and a person . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

37. Detection zone of Buddy system and a person . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

38. Rear Guard sensors mounted on rear of dump truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

39. Detection zone of Rear Guard system and a person at rear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

40. Detection zones of Rear Guard system with sensors at ends of front bumper . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

41. Detection zones of Rear Guard system with sensors at center of front bumper . . . . . . . . . . . . . . . . . . . . . . . . . . 17

42. Rear Guard system’s ultrasonic sensors mounted close together on front bumper . . . . . . . . . . . . . . . . . . . . . . . 17

43. Radar unit mounting position on Caterpillar 793B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

44. Detection zone of Ogden radar system on Caterpillar 793B with a pickup at rear . . . . . . . . . . . . . . . . . . . . . . . 18

45. Determining detection zone for a pickup behind Caterpillar 793B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

46. Detection zone of Guardian Alert radar system on Caterpillar 793B with a person at rear . . . . . . . . . . . . . . . . . 19

47. Detection zone of Guardian Alert radar system on Caterpillar 793B with a pickup at rear . . . . . . . . . . . . . . . . . 19

TABLES

1. Dump truck specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Summary of test results for collision warning systems on a Komatsu 210M . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

cm centimeter mm millimeter

GHz gigahertz ms millisecond

km kilometer ft foot

km/h kilometer per hour in inch

m meter mph mile per hour
TEST RESULTS OF COLLISION WARNING SYSTEMS

ON OFF-HIGHWAY DUMP TRUCKS: PHASE 2

By Todd M. Ruff1

ABSTRACT

This report summarizes ongoing research at the National Institute for Occupational Safety and Health,

Spokane Research Laboratory, in which collision warning systems for surface mining dump trucks are being

evaluated. Common accidents involve these large trucks running over smaller vehicles or pedestrian workers.

Collision warning systems currently use one of several methods, including radar, radio-frequency-signal

detection, or ultrasonic signals, to detect and warn of the presence of an object or person in the blind spots of

the mining equipment. Most available systems have not been tested on large off-highway dump trucks. This

report evaluates several systems on two sizes of trucks, a 50-ton-capacity truck commonly used in quarries and

construction and a 240-ton-capacity truck commonly used in open-pit mines. Tests were conducted to

determine false alarm rates, alarm effectiveness, and reliable detection zones for a person and a pickup truck.

The results indicate that radar and radio-frequency identification systems show promise for this application and

that several of the improved systems are ready for extensive field tests. However, challenges still exist in

applying these technologies to large trucks.

1

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

Figure 1.—Side view of Komatsu 210M.

INTRODUCTION

This report summarizes the results of continuing tests on

collision warning systems for surface mining equipment at the

National Institute for Occupational Safety and Health (NIOSH),

Spokane Research Laboratory (SRL). Collision warning

systems currently use one of several methods, including radar,

radio-frequency-signal detection, or ultrasonic signals, to detect

and warn of the presence of an object or person in the blind

spots of the mining equipment. Phase 1 tests are described in a

NIOSH Report of Investigations (RI) entitled “Test Results of

Collision Warning Systems for Surface Mining Dump Trucks”

[Ruff 2000]. Detailed descriptions of the technologies and other

background information are presented in that report. 

One goal of the phase 1 tests was to narrow the number of

collision warning systems to be tested in an operating surface

mine because time constraints would not allow all systems to be

tested. The final selection was based on whether or not the 

system (1) was available off the shelf, (2) had positive test

results and adequate detection areas, and (3) was packaged for

the mining environment. Two radar systems and one radiofrequency identification (RFID) system were selected for further

tests at a surface mine (phase 2). The radar systems were tested

by NIOSH personnel, and only these results are discussed in this

RI.2

The second phase involved (1) retesting three of the collision

warning systems on a 240-ton-capacity truck at a surface mine,

(2) testing three phase 1 systems that had undergone improvements on a 50-ton-capacity truck, and (3) testing two new

systems on the 50-ton-capacity truck. Tests on the 50-toncapacity dump truck are discussed under the section “Test

Results, Komatsu 210M.” The results of tests on the larger

truck are discussed under the section “Test Results, Caterpillar

793B.”

 2

The Buddy System by Nautilus International was tested on a Komatsu 930E

at the Phelps Dodge Morenci mine by Jason Hart, president of Nautilus

International. Test results are not recorded here but are available through

Nautilus.

TEST DESCRIPTION3

Tests of the collision warning systems were designed based

on experience gained from previous tests, some aspects of SAE

J1741 Discriminating Backup Alarm Standard [Society for

Automotive Engineers (SAE) 1999], and input from the Mine

Safety and Health Administration (MSHA). The systems were

tested on a rigid-frame, off-highway dump truck that represented

those used in industry as closely as possible. 

Because of the number of systems and the amount of time

required, only two radar systems and one RFID system were

tested on a large dump truck at the Phelps Dodge Morenci Mine

in Arizona. Specifications for this truck are shown in table 1. 

For the other systems, a smaller dump truck was rented, and the

tests were conducted at a remote auxiliary site of SRL.

The largest dump truck available for rental in the Spokane

area was a 50-ton-capacity Komatsu 210M Haulpak4

 (figures 1

and 2). Although this truck has similar features and is commonly used in sand and gravel operations, it is smaller than most

trucks used in surface mining. While not an ideal representation

of the larger trucks, the 50-ton truck did provide an adequate

platform for initial tests. Specifications for this truck are also

shown in table 1.

Each collision warning system was mounted on the truck

according to the manufacturer’s suggestions and with the

3

This section has been updated from RI 9652 [Ruff 2000]. For a full

description of the test procedure, see the earlier RI. 4

Mention of specific products or manufacturers does not imply endorsement

by the National Institute for Occupational Safety and Health.

requirement that the sensor be accessible and not interfere with

the truck’s operation. To monitor the rear blind spot of the truck,

the sensor was mounted near the light bar above the rear axle.

To monitor the front blind spot, the sensor was mounted near the

front bumper or on the grill. 

The test area at SRL was approximately 60 m (200 ft) long

by 30 m (100 ft) wide, while the test area at the Morenci Mine

was approximately 30 m (100 ft) long by 30 m (100 ft) wide. 
3

Figure 3.—Determining detection zone for a person.

Figure 2.—Rear view of Komatsu 210M.

Table 1.—Dump truck specifications

Truck make and model Komatsu 210M, 50-ton capacity Caterpillar 793B, 240-ton capacity

Meters Feet Meters Feet

Overall length . . . . . . . . . . . . . . . . . . . . . . . . 9.2 30 ft 3 in 12.9 42 ft 3 in

Overall width . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 14 ft 7 in 7.4 24 ft 4 in

Tire diameter . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 ft 6 in 3.6 11 ft 10 in

Distance, axle to tire edge . . . . . . . . . . . . . . . 0.61 2 ft 1.1 3 ft 6 in

Distance between inner dual tires . . . . . . . . 1.4 4 ft 7 in 2.5 8 ft 2 in

Height to light bar . . . . . . . . . . . . . . . . . . . . . 1.7 5 ft 8 in 3 10 ft

Distance, truck bed extended past axle . . . . 2.7 9 ft 4.6 15 ft

Height of front bumper . . . . . . . . . . . . . . . . . 0.76 2 ft 6 in 1.2 4 ft

Maximum speed forward . . . . . . . . . . . . . . . 64.4 km/h 40 mph 54.7 km/h 34 mph

Maximum speed reverse . . . . . . . . . . . . . . . . NA NA 11.2 km/h 7 mph

Both sites were cleared of debris and graded flat. The surfaces

of the test areas were dirt and gravel with no large rocks or ruts.

This gave researchers a clear field for testing the collision

warning systems under ideal conditions. Obstacles and other

debris were then added as each test progressed. 

The obstacles to be detected by the collision warning system

consisted of either a person or a three-quarter-ton, four-wheeldrive pickup truck with an extended cab (figures 3 and 4). The

person for these tests was a man between 178 and 191 cm (70

and 75 in) tall, wearing a hard hat, cotton shirt, and jeans.

The reliable detection zone for an obstacle was recorded by

standing or parking the truck on the points of a grid with 0.76-m

(2.5-ft) spacings marked in the sensor’s potential detection area.

For the rear blind spot, the dump truck was moved slowly

(< 8 km/h [5 mph]) in reverse, and the state of the alarm was

monitored. If the alarm turned on immediately (< 200 ms) and

consistently after the truck moved, then that point was recorded

as a “reliable” detection point. The recorded points on the grid

were then joined to form an outline of the reliable detection

zone. A second zone was recorded as needed and labeled

“sporadic” if an obstacle was detected some of the time, but not

always (less than 100% detection, but more than 10%). Note

that in certain areas near the dump truck, it would not be safe to

move the truck toward a stationary person or pickup. In these

cases, the dump truck was kept stationary and the person or

pickup moved toward the sensor. 

The alarm display for each system was mounted near the

sensor or antennas. This allowed researchers to monitor the

alarm easily. Normally the alarm display would be mounted in

the cab with the operator. Each alarm display was temporarily

taken inside the cab and tested to see if the lights were visible

and the audible alarm could be heard above engine noise.

According to SAE J1741, it is desirable that a collision

warning system ignore an object the size of a cinder block in the

blind spot of the dump truck (figure 5). While this may or may

not be important to a mine implementing a collision warning

system, researchers at SRL tested each radar system to see how

it reacted to a cinder block placed at various distances along the

truck’s centerline.
4

Figure 4.—Determining detect Figure 5.—Detecting a cinder block. ion zone for a pickup truck.

 Figure 6.—Sensor Vision system mounted on rear of dump truck.

Cameras are on top and radar unit is on the bottom.

TEST RESULTS, KOMATSU 210M

SYSTEM: SENSOR VISION

Manufacturer: Vision Techniques and Ogden Safety Systems,

U.K. www.visiontechniques.co.uk

Description: 

This system combines radar technology with cameras to

provide a vision system with alarm functions. A Mitsubishi

camera was placed near the light bar on the rear of the truck to

monitor the rear blind spot. Figure 6 shows three cameras

mounted on the truck for testing purposes. Either a cathode ray

tube (CRT) or liquid crystal display (LCD) monitor is mounted

in the cab to provide the driver with a view of the blind spot.

Figure 7 shows both types of monitors temporarily mounted in

the cab. 

The radar unit is mounted near the camera and detects

moving objects in the radar’s beam (figure 6). An alarm that

consists of a light-emitting diode (LED) and an audible warning

is activated in the cab of the truck when an object is detected by

the radar unit. This prompts the driver to check the video

monitor. Multiple radar systems and cameras can be installed

to monitor the front or sides of the truck. While the camera

system is available for purchase, the radar system has not yet

been approved by the Federal Communications Commission

(FCC) for use in the United States.

The radar system uses frequency-modulated continuous wave

(FMCW) technology and operates between 13 and 14 GHz. It

transmits a low-power signal and measures any return signals

reflected from objects within its transmit beam. The

characteristics of the reflected signal contain information on

distance and movement. Using this principle, it is possible to

determine the speed at which the object is approaching the radar

unit and the distance to the object.

The radar beam can be configured to meet the requirements

of different mining equipment. The width and depth of four

zones within the beam can be adjusted to accommodate unique

shapes for the detection zone. For example, on larger trucks,

it is important to detect objects near the radar unit and inside the

rear dual tires. At the same time, it is also important to detect

objects immediately behind the rear dual tires, requiring a

widening of the beam after it clears the tires.

Test Results:

For the rear blind spot of the truck, the radar unit was

mounted level at 1.35 m (53 in) high, near the light bar. The

cameras were mounted just above the radar unit at 1.65 m

(65 in) high (figure 6). The video monitors and radar alarm
5

Figure 7.—Two types of monitors mounted in cab of dump truck.

 Figure 8.—Detection zone of Ogden radar system and a person

at rear.

 Figure 9.—Detection zone of Ogden radar sysem and a pickup at

rear.

were mounted inside the truck’s cab. In these tests, the radar’s

beam configuration was optimized for this particular truck. As

mentioned, the beam widths can be adjusted to accommodate

larger trucks. However, the overall length of the detection zone

is limited to approximately 12.2 m (40 ft).

The first test evaluated the radar’s false alarm rate in a totally

clear zone behind the truck. No false alarms were activated

when the dump truck was moved in reverse. The truck was also

backed into an area with low foliage (under 30 cm [1 ft] high),

which was not detected.

The next test was to determine if a cinder block was detected

behind the vehicle. When the radar unit was mounted level and

at a height of 1.35 m (53 in), a cinder block was not detected at

any position behind the truck. Lower mounting positions may

allow the block to be detected; this will be discussed later.

The detection zone for a pedestrian worker was then recorded

as shown in figure 8. The test was conducted primarily by

having a person walk toward the stationary dump truck. Several

positions behind the truck were also tested with the person

remaining stationary while the dump truck moved. This was

necessary to verify that the detection zone was consistent when

the truck was moving. The detection zone extended out to 12.2

m (40 ft) and adequately covered the width of the truck. Some

small adjustments to the detection zone may be needed to ensure

that coverage extends as close to the tires as possible.

The detection zone for a pickup truck was recorded as shown

in figure 9. The zone adequately covered the width of the dump

truck and extended for 12.2 m (40 ft). The pickup truck was

reliably detected as long as its entire front bumper was within

the zone indicated. The detection zone was verified by moving

the dump truck toward the stationary pickup at several test

points.

The field of view of the cameras was also tested by walking

through each camera’s field and recording where a person could
6

 Figure 10.—Field of view of two different cameras monitoring

rear of truck.

Figure 11.—Ogden radar system mounted on front bumper. Figure 12.—Detection zone of Ogden radar system and a person

in front.

no longer be seen in the monitor. Figure 10 shows the field of

view for two different lenses. Generally, a wide field of view is

preferred so that an object can be seen out by the rear dual tires.

A separate radar unit was mounted on the front bumper of the

dump truck at 89 cm (35 in) high and with no cameras (figure

11). This radar unit’s beam was configured differently to

accommodate the detection zone needed at the front of the truck.

The front detection zone differs from the rear in that it is

important to have a wide beam beginning immediately in front

of the radar unit to cover the width of the front bumper. Also,

a shorter length for the front detection zone is sufficient for this

truck because of improved visibility. This is not true for larger

trucks, however, where front blind spots can extend beyond

12 m (40 ft).

The system was tested for false alarms in a clear zone

in front of the truck. No false alarms were activated when

the truck was moved forward at slow-to-moderate speeds

(< 32 km/h [20 mph]). 

The cinder block was then placed in front of the truck. At

some locations, the block was detected because of the lower

mounting position. 

The reliable detection zone was then recorded for a person

(figure 12). Detection extended from immediately next to the

bumper out to 7.6 m (25 ft) and adequately covered the entire

width of the truck. A shorter detection zone was determined to

be better for the front of this truck because of the lesser extent

of the blind spot. This zone could be adjusted for larger trucks.

Again, the detection zone was verified by moving the dump

truck toward a stationary person, and similar results were seen.

The front detection zone for a pickup truck is shown in figure

13. The zone extended from the bumper out to 9.1 m

(30 ft) and adequately covered the width of the dump truck.

Discussion:

The radar system works well on trucks that have mounting

positions below 1.8 m (6 ft). The detection zones are ideal for

the Komatsu 50-ton truck. However, larger trucks with high

mounting positions may present a problem for this radar system.

Initial tests with the Ogden radar system at the Phelps Dodge

Morenci Mine on larger trucks showed that the detection zones

decreased in size as a result of the high mounting position and

the antennas had to be tilted. Figure 14 shows an example of

the rear detection zone of a person and a Caterpillar 793
7

 Figure 13.—Detection zone of Ogden radar system and a pickup

in front.

 Figure 14.—Detection zone of Ogden radar system on Caterpillar

793 truck and a person.

 Figure 15.—Detection zone of Ogden radar system mounted high

on Komatsu truck and a person.

240-ton truck. These tests are discussed in more detail later.

Installing this system on large trucks where the mounting

positions will be over 2.5 m (8 ft) above the ground may require

a different antenna design. Figure 15 shows the test results of

mounting the system high on the front deck of the Komatsu

truck.

It was suggested by an Ogden Safety Systems engineer that

a trihedral corner reflector should be used to determine the

outermost edges of the radar beams. This is useful for

determining the area detected by a corner reflector, but one

should use caution when trying to equate this area with the

actual detection zone for a person or pickup. 

Two sizes of reflectors were tested at NIOSH. A small

reflector meant to represent a person and a large reflector meant

to represent a pickup were constructed from cardboard and

covered with metal tape (figure 16). The large reflector is 380

mm (15 in) long on each side, and the small reflector is 140 mm

(5.5 in) long. The large reflector was tested first, and its

detection zone was compared to the actual detection zone of a

pickup truck. Figure 17A shows the results. The detection zone

for the reflector was significantly wider and slightly longer than

that for the actual truck. There was some question on how
8

 Figure 16.—Trihedral corner reflectors for determining beam

dimensions.

 Figure 17.—Comparison of detection zones for (A) a large

reflector and a pickup truck and (B) a small reflector and a person.

to hold the reflector and what effect the person holding the

reflector had on the results.

 The small reflector was then tested, and its detection zone

compared to the detection zone for a person. For this test, the

radar unit was taken off the truck and mounted to a test stand

1.14 m (45 in) high. The small reflector must be mounted to a

3-m (10-ft) plastic pole so that the person holding the reflector

remains outside the detection zone while the reflector is inside

of it. Figure 17B shows the results. The detection zone for the

reflector is significantly smaller in this case. It was difficult to

determine whether the radar unit was detecting only the reflector

and not the person holding it. Also, detection of the reflector

depended on height and orientation. This made it difficult to

obtain consistent results.

It is known that mud flung from the tires of a dump truck can

cause false alarms from the rear-mounted radar unit. This is

probably true for all radar systems. This problem could be

solved by deactivating the rear unit or decreasing sensitivity

when traveling forward. There were no other false alarm

sources seen during the limited tests conducted. However,

testing the system on a large truck under actual working

conditions will be required before further conclusions can be

drawn. 

The cameras and monitors appeared to be built sturdily

enough to withstand a mining environment. Again, further tests

will need to be conducted at a surface mine before conclusions

can be made. The manufacturer has had camera systems in

mines and quarries in England for several years, and the systems

have held up well under mining conditions. 

The camera view with the wider angle had the best coverage

for showing objects near the truck; however, the lens did distort

the image, making it difficult to judge distance. The narrowangle lens did not show objects near the tires of the truck. Both

color and black-and-white cameras were tested. The black-andwhite cameras operated better under low-light conditions and

are best suited for locations that operate in both daylight and at

night.

SYSTEM: PREVIEW

Manufacturer: Preco, Inc. Boise, ID www.preco.com

Description:

The Preview system is a pulsed time-domain radar operating

at 5.8 GHz. The radar signal is pulsed 40 times per second and

detects both stationary and moving targets. The system consists

of a radar antenna and processing electronics (figure 18), an
9

 Figure 18.—Preview radar system antenna and electronics

enclosure.

Figure 19.—Preview radar system display.

 Figure 20.—Detection zone of Preview radar system and a

person at rear.

alarm display (figure 19), and wiring. An optional external

backup alarm is also available. The system can be activated

using the reverse gear input so that the alarm is activated only

when moving in reverse and an obstacle is detected.

The radar system can determine distance to an object within

its detection zone. This information is displayed on the alarm

using eight LED’s that indicate distances under 1 m (3 ft) out

to 7 m (24 ft). An LED is lit if an object is detected at the

corresponding distance. A four-tone audible alarm also

indicates distance by changing frequency according to where the

object is detected. The radar antenna determines the Preview

system's area of coverage and thus is not adjustable

by the user.

Test Results: 

For the rear blind spot of the truck, the Preview system was

mounted level near the light bar at a height of 1.3 m (51 in)

(figure 18). The mounting height was critical for this radar

system. If the system were mounted higher than 1.3 m (51 in)

from the ground, the radar would constantly detect the bed of

the dump truck, causing false alarms. After determining the best

mounting position, the system was tested for false alarms in a

clear field by moving the truck in reverse. No false alarms

occurred. The system did detect low foliage (< 30 cm [1 ft]

high) at the edge of the test area.

The cinder block was detected by this radar unit at distances

of 7.6 to 9.1 m (25 to 30 ft). The block was not detected if it

was closer than 7.6 m (25 ft) to the truck. The reliable detection

zone for a person standing behind the truck extended from the

radar unit out to 9.1 m (30 ft) (figure 20). The radar unit did

detect a person standing near the inner dual tires, but not near

the outer dual tires. Small areas were detected sporadically on

the fringes of the detection zone. The detection zone was

verified at several positions when a person remained stationary

while the dump truck moved. Range information shown on the

display was correct when a person was detected. 

The rear detection zone for a pickup truck was recorded as

shown in figure 21. The zone adequately covered the width of

the dump truck and extended out to 8.4 m (27.5 ft). The pickup

truck was reliably detected as long as its entire front bumper

was within the zone indicated. The detection zone was verified

by moving the dump truck toward the stationary pickup. The

alarm display did not always show the correct range information

for the pickup truck. At some test points, all the LED’s came on

as if the pickup truck were very close to the radar unit, even

when the pickup was at the far edges of the detection zone. 

The system was then mounted on the front of the dump truck

at a height of 94 cm (37 in) (figure 22). Mounting height was

not as critical on the front of the truck because no part of the

truck extended beyond the bumper. There were no false alarms

when the truck was moved forward in a clear field. 
10

 Figure 21.—Detection zone of Preview radar system and a

pickup at rear.

Figure 22.—Preview radar system mounted on front bumper.

 Figure 23.—Detection zone of Preview radar system and a

person in front.

 Figure 24.—Detection zone of Preview radar system and a pickup

in front.

Cinder block detection occurred from 4.6 to 9.1 m (15 to

30 ft) away from the sensor. The lower mounting height caused

the system to be more sensitive to low-lying objects. The

detection zone for a person extended from the radar unit out to

8.4 m (27.5 ft) (figure 23). However, areas on either side of the

radar unit and near the bumper were not covered by the beam.

The detection zone for a pickup truck is shown in figure 24.

The zone adequately covered the width of the dump truck and

extended out to 9.1 m (30 ft). The pickup truck was reliably

detected as long as its entire front bumper was within the zone

indicated. The detection zone was verified by moving the dump

truck toward the stationary pickup.
11

 Figure 25.—Detection zone of Preview radar system mounted

high on Komatsu truck and a person.

Discussion:

This system seemed adequate for this size of dump truck,

although a wider beam near the bumper would provide better

coverage for the front blind spot. The system needs to be tested

on a larger truck to verify that it can be used for such trucks. To

simulate a higher mounting position on a larger truck, the radar

unit was mounted at a height of 2.6 m (103 in) on the front of

the Komatsu dump truck. The radar unit had to be tilted

downward 30° to ensure detection of a person near the truck

when this configuration was used (Figure 25). The detection

zone was then decreased in length to 7.6 m (25 ft), and a person

could walk very near the truck and not be detected. Additional

tests on larger trucks need to be conducted to determine the

effect of the overhanging steel from the bed and false alarm

rates from tilting the radar unit downward.

The manufacturer has designed this radar system to meet

SAE standard J1741 [SAE 1999]. However, at certain mounting

heights, the system did detect a cinder block in the center of the

detection zone, which should not have occurred according to the

standard. However, it is up to each individual mine to

determine if this is important or not. 

The alarm display has eight LED’s and four different audible

alarms to indicate the distance to a detected object. When

detecting a person, this range information is reliable, and the

audible alarms are effective. The audible alarms may need to be

louder on certain vehicles, and a volume control may need to be

added. When detecting a pickup truck, however, the range

information is not always correct. The sensitivity may need to

be adjusted to correct this situation, but the adjustment must be

done at the factory.

SYSTEM: ULTRAWIDE-BAND RADAR PROTOTYPE

Manufacturer: Multispectral Solutions, Inc. (MSSI), 

 Gaithersburg, MD www.multispectral.com

Description:

MSSI’s radar system is based on ultrawide-band technology

that uses nanosecond radar signal pulses to produce a wide,

instantaneous bandwidth waveform. It transmits at a center

frequency of 5.65 GHz. The radio frequency circuitry for a

ultrawide-band system is minimal, consisting of a low-noise

amplifier and a broadband tunnel detector. In addition, digital

signal processing is employed, further lending to a low-cost

modular design and a potentially small-sized package.

A transmitter module emits ultrawide-band radar pulses at a

fixed repetition rate from the transmitting antenna. A receiver

antenna picks up both transmitted pulses and pulses reflected

from the environment and/or targets of interest. A radiofrequency module amplifies and filters the pulses and sends

them to a processing board. The transmitted pulses are picked

up by one detector of a dual, short-pulse detector (initialization

pulse), while the second detector picks up target and clutter

information. A high-speed time-detector circuit measures the

relative positions of the two pulses and passes this information

to a digital signal processor. The digital signal processor then

performs calculations to control detector sensitivity and to

convert the time difference to a precise measurement of distance

for display as a target. 

The first version of this radar system had difficulty detecting

objects close to the antennas and was only reliable from 9.1 to

13.7 m (30 to 45 ft). Modifications were made over the past

year to remedy this problem. 

• The receiver-processor board was replaced with an improved

design. The new processor board is capable of much finer

adjustments in the minimum detection distance. Receiver

circuitry was also updated and improved on the new board.

• The radio-frequency transmitter and receiver sections were

moved to separate boards and shielded from each other.

Previously, energy from the transmitter circuit was coupling into

the receiver circuit. This caused the initial pulse coming into the

receiver to stretch, limiting detections at close range. When the

transmitter and receiver were separated and shielded, the initial

pulse length was reduced to less than one-third of its original

length. 

• A digitally controlled variable attenuator was added to the

radio-frequency receiver circuitry. The variable attenuator

allows increased sensitivity adjustments and gives optimum

attenuation settings over the detection range of interest. 

• A new, three-LED range display with audio alarm was built.

Modifications were made to the processor board code and

field programmable gate array design to set detection ranges

and for LED drivers. The system cable was also rebuilt to

accommodate the new display.
12

 Figure 26.—Multispectral ultrawide-band radar system and

alarm display (right). Figure 27.—Detection zone of ultrawide-band radar system and

a person at rear.

• The power supply board was redesigned to meet the new

system power requirements. LED driver circuitry was installed

on this board for the LED range display.

Test Results:

For the rear blind spot of the truck, the ultrawide-band

radar system was mounted level near the light bar at a height of

1.37 m (54 in) (figure 26). At the initial sensitivity setting, an

occasional false alarm occurred when the dump truck was

moved in reverse in a clear field. After the sensitivity was

decreased, no false alarms occurred. The cinder block was not

detected except sporadically when the block was 6.1 m (20 ft)

away from the radar unit. 

The reliable detection zone for a person standing behind the

truck is shown in figure 27. This zone extended 15.2 m (50 ft)

from the radar unit. The radar detected a person standing near

the outer dual tires with small areas detected sporadically on the

fringes of the detection zone. The detection zone was verified

at several positions with the person remaining stationary while

the dump truck was moved. Range information shown on the

display was accurate and corresponded to the correct distance to

the person.

The rear detection zone for a pickup truck was recorded as

shown in figure 28. The zone adequately covered the width of

the dump truck and extended out to 15.2 m (50 ft). The pickup

truck was reliably detected as long as its entire front bumper

was within the zone indicated. The detection zone was verified

by moving the dump truck toward the stationary pickup. The

range information on the display was also correct for the pickup.

The system was then mounted level on the front of the dump

truck at a height of 1.32 m (52 in) (figure 29). Lower mounting

heights may cause an increase in false alarms due to detection

of the ground. There were no false alarms when the truck was

moved forward in a clear field. Cinder block detection again

occurred sporadically at a distance of 6.1 m (20 ft). 

The detection zone for a person extended from the radar unit

out to 13.7 m (45 ft) (figure 30). An area about 4.6 m (15 ft)

farther was detected sporadically. The width of the detection

zone was adequate beyond the bumper, but a person standing

right next to the bumper was detected only sporadically. 

The detection zone for a pickup truck is shown in figure 31.

The zone adequately covered the width of the dump truck and

extended out to 16.8 m (55 ft). The pickup truck was reliably

detected as long as its entire front bumper was within the zone

indicated. The detection zone was also verified by moving the

dump truck toward the stationary pickup.

Discussion:

The improvements made to this system greatly increased its

reliability, and the system shows good potential. Additional

improvements are being made. While the size of the detection

zones for people and pickup trucks may have been too large for

a 50-ton-capacity dump truck, they would be adequate for larger

trucks. The antenna is being redesigned to cover areas close to

the truck when high mounting positions are required. Figure 32

shows the detection zone for a person when the radar unit was

mounted 3 m (10 ft) high on the front of the Komatsu truck. 

Currently, a person close to the radar unit would not be detected

and the detection zone is decreased to 7.6 m (25 ft) in length due

to the downward tilt of the radar unit. It is anticipated that

further improvements to the antennas will
13

 Figure 28.—Detection zone of ultrawide-band radar system and

a pickup at rear.

Figure 29.—Ultrawide-band radar system mounted on front grill.

 Figure 30.—Detection zone of ultrawide-band radar system and

a person in front.

alleviate the problems seen with higher mounting positions.

Also, the temporary enclosure for the radar antennas is now

being redesigned, and packaging will be improved for mine

environments. 

The alarm display has three range gates with LED’s to

indicate the distance to an object. Although these gates were

reliable, the audible alarm might be difficult to hear inside the

equipment cab. A volume adjustment will be added to the

display.

SYSTEM: BUDDY SYSTEM

Manufacturer: Nautilus International, Burnaby, B.C., Canada

www.nautilusinternational.com

Description: 

This system is classified as an RFID-based system. It consists of a tag reader mounted on the mining equipment and
14

 Figure 33.—Installation of Buddy system components on front

deck of dump truck.

 Figure 31.—Detection zone of ultrawide-band radar system and

a pickup in front.

 Figure 32.—Detection zone of ultrawide-band radar system

mounted high on the Komatsu truck and a person.

tags attached to pedestrian workers or smaller vehicles to be

protected. The tag reader consists of processing electronics and

a loop antenna (figure 33). It is mounted on the front deck of

the dump truck, where it continuously transmits a low-frequency

signal that encompasses the entire truck. The processing

electronics also contain a separate high-frequency transceiver to

communicate with the tags.

Each tag contains a transceiver to communicate with the

reader=s processing electronics. The tag measures the field

strength of the low-frequency signal generated by the loop

antenna. The field strength increases as the distance between

the tag and the loop antenna decreases. If the field strength

exceeds a user-defined limit, this information is sent to the tag

reader and an alarm is generated at both the tag and at the alarm

display in the dump truck’s cab.

Modifications to this system over the last year included

a simpler antenna design and enclosure, stand-alone tags, and an

LCD monitor for displaying alarm information. The current tag

was a prototype for test purposes (figure 34), and smaller

versions are being designed. The tags provide an audible

alarm if they come within the detection zone of a truck; a

distance display is optional. The tags can be worn on a belt and

must have the battery recharged at the end of each day. The

tags also have an override switch that allows a worker to

approach a truck without activating the alarm on either the tag

or in the truck’s cab.

The alarm display shown in figure 35 is an LCD screen that

shows an identification and the distance to the tag. The tag ID

is programmable and must be configured on a personal

computer. The display also acts as a video monitor when the

optional camera system is installed.
15

Figure 35.—Buddy system alarm display with no tag detected.

Figure 34.—Buddy system prototype tag on worker’s belt. Figure 36.—Determining detection zone of Buddy system and a

person.

Figure 37.—Detection zone of Buddy system and a person

Test Results:

This system was tested by attaching the tag to the belt of a

person who then walked around the truck and noted when an

alarm was sounded in the cab and on the tag (figure 36). The

loop antenna was placed on the front deck of the dump truck and

attached to the railing in a near-vertical position (figure 33).

The communications antenna was also placed on the front deck

of the truck. The alarm display was monitored by the truck

driver.

Figure 37 shows the reliable detection zone for a person and

a 15-m (50-ft) detection radius. All blind areas are monitored

simultaneously with this system. As shown in figure 37, the

detection zone extends farther in front of the truck than to the

rear because of the position of the loop antenna. The tag was

detected at all locations and orientations within the zone shown,

even in the engine compartment and wheel wells. Additional

tests need to be conducted with the tag mounted on a pickup

truck to determine the best mounting position. Tests with a

cinder block were not conducted because the block would not be

detected unless a tag was attached to it.
16

Figure 38.—Rear Guard sensors mounted on rear of dump truck.

 Figure 39.—Detection zone of Rear Guard system and a person

at rear.

Discussion:

Mounting the loop antenna at the rear of the truck would

solve the problem of the longer detection distance in front.

However, two antennas, one at the front and one at the rear, may

be required to establish detection zones with more equally sized

areas and to allow each zone to be adjusted independently. This

arrangement would also provide information on whether the tag

was at the rear or the front of the truck.

A desirable feature of this system is that the tag generates an

audible alarm so that the pedestrian worker is also alerted when

in the detection zone of a dump truck. An optional display on

the tag also provides a distance readout. 

An override switch allows the tag to be ignored by the

system when the worker holds down a button. This cuts down

on annoyance alarms when the worker and the driver are

mutually aware of each other’s presence and activities close to

the truck are required.

The alarm display was effective in the cab and displayed

both the distance and the unique identification of the tag.

Additional tests need to be conducted to determine the effects of

multiple tags in the detection zone of a truck.

A disadvantage of this system is that each small vehicle and

pedestrian worker must be outfitted with a tag in order to be

detected. This makes the system more expensive than radar

systems, but its added functionality, size of detection zone, and

lack of false alarms may be worth the added cost. 

System: Rear Guard

Manufacturer: Castleton, Inc., Westminster, CA

www.rearguard.com

Description:

This system operates by transmitting an ultrasonic signal and

detecting echoes from nearby objects. An ultrasonic pulse is

transmitted every twentieth of a second from each sensor to

provide continuous coverage out to about 2.4 m (8 ft). The

sensor beam is wide both horizontally and vertically and is

teardrop shaped.

The system consists of sensors mounted on the bumper of the

vehicle, an alarm display that provides an audible alarm, and a

visual alarm that uses LED’s. Two or more sensors can be

mounted on the vehicle to cover front and rear blind spots.

Wide vehicles may require three or four sensors to cover a blind

spot adequately.

Test Results:

The system was mounted on the rear of the truck at a height

of 1.37 m (54 in). Sensors were separated by a distance of

36 cm (14 in) (figure 38). It was difficult to find a mounting

position at the rear because of the limited space near the light

bar, which could result in false alarms set off by the tires and

truck bed. The sensitivity of the system had to be reduced to

25% to eliminate such false alarms, presumably as a result of

detecting the tires. 

The detection area (figure 39) for a person was very limited

because of the close mounting of the sensors and the low

sensitivity setting. No other mounting position could be found

that increased the detection area without also increasing the

number of false alarms. The pickup and cinder block were not

tested because of the limited size of the detection zone.

Mounting the system was much easier on the front of the

dump truck. The sensors were mounted on the front bumper at

a height of 1.07 m (42 in). Two separation distances were tried

to adjust the detection zone, and sensitivity was increased to

60%.

Figure 40 shows the detection zone for a person with the

sensors at the extremes of the bumper and pointing slightly

inward (the sensor housing is manufactured this way). The

reliable detection zone extended in front of each sensor to about

2.4 m (8 ft). However, a large null space existed in the center

of the truck as a result of the configuration of the beams. A

third sensor may be required to cover the entire front of the

truck, but this was not provided with the system. 
17

 Figure 40.—Detection zones of Rear Guard system with sensors

at ends of front bumper. A person is being detected.

 Figure 41.—Detection zones of Rear Guard system with sensors

at center of front bumper. A person is being detected.

 Figure 42.—Rear Guard system’s ultrasonic sensors mounted

close together on front bumper.

Figure 41 shows the detection zone for a person when the

sensors were mounted next to each other at the center of the

bumper and pointed outward (figure 42). The reliable detection

zone extended to about 1.8 m (6 ft) in front of the truck, but only

covered the center area. Areas near the bumper at the corners

of the truck were not covered.

Because of the limited sized of the detection zones, the

cinder block and the pickup truck were not tested.

Discussion:

While this system may be adequate for smaller vehicles, it

will not work on the large trucks used in mining. The coverage

area of the sensors is too limited to detect objects at the

distances needed. Also, because of the beam shape, null spaces

in the coverage area near the truck will exist. 

There was also some concern about the reliability of this

system in harsh weather. False alarms may be caused when the

system is exposed to heavy rain or snow. False alarms were

also generated when the sensitivity settings were above

approximately 60%.

TEST RESULTS – CATERPILLAR 793B

System: Ogden Radar

Manufacturer: Ogden Safety Systems 

www.visiontechniques.co.uk

Description: 

This radar system is the same used in the Sensor Vision

system described above. While an older version of the radar

system was used in these tests, the general description found in

that section still applies. This radar system is not yet available

in the United States.

Test Results:

The radar unit was mounted on a Caterpillar 793B 240-toncapacity dump truck near the light bar on the steel beam that

runs above the axle (figure 43). The mounting height was

2.7 m (9 ft) to the bottom of the radar unit. No suitable

mounting position was found lower than this. Because of the

mounting height, the radar unit was tilted downward 15°. The

alarm display was mounted near the axle for easy monitoring

during the tests.

First, the radar system was tested for false alarms in a clear

field while the truck was slowly moved in reverse. The system
18

Figure 43.—Radar unit mounting position on Caterpillar 793B.

 Figure 44.—Detection zone of Ogden radar system on Caterpillar

793B with a pickup at rear.

 Figure 45.—Determining detection zone for a pickup Caterpillar

793B.

did not detect the movement of the tires and did not generate

false alarms. Also, no false alarms from the ground were

generated as the truck moved in reverse.

Figure 14 shows the detection zone for a person. The person

walked toward the stationary truck because it was unsafe to

move the truck toward a stationary person at grid points close to

the truck. At maximum settings, the range of the radar unit was

6.1 m (20 ft) directly behind the truck. There was no detection

from 0 to 2.4 m (8 ft) because of the required mounting height,

which means that someone near the wheels

of the truck would not be detected. Because it is critical to

detect a person near the tires of the truck, the radar unit was

tilted to 20° using spacers. The person was still not detected

from 0 to 1.8 m (6 ft), and the overall range of the system

decreased to 5.2 m (17 ft).

Figure 44 shows the detection zone for a pickup truck. The

tilt was reset to 15°. The truck was oriented to face the back of

the dump truck and slowly driven toward the stationary dump

truck (figure 45). The pickup truck was detected from near the

rear tires out to 7.6 m (25 ft). 

Discussion:

As seen in figure 14, the detection zone was significantly

narrower and shorter because of the higher mounting position

and tilt. Also, the critical areas near the tires of the truck were

not within the detection zone because a person could walk

underneath the radar beam. This is consistent with the high

mounting positions on the front of the Komatsu truck (figure 15), although the radar settings were adjusted to improve the

width of the detection zone. 

The detection zone for a pickup truck was also smaller

because of the mounting height. However, a pickup was

detected when it was near the tires (probably because the back

of the pickup remained in the beam even though the front did

not). It was concluded that, for high mounting positions,

redesign of the antenna would be required in order to detect

objects both near the tires and 6.1 to 9.1 m (20 to 30 ft) beyond

the end of the dump truck’s bed.

The front detection zones for this truck were not determined

because lower mounting positions were available and their use

would have given data that corresponded to data collected on

the Komatsu truck at SRL. Also, tests on cinder blocks were
19

 Figure 46.—Detection zone of Guardian Alert radar system on

Caterpillar 793B with a person at rear.

 Figure 47.—Detection zone of Guardian Alert radar system on

Caterpillar 793B with a pickup at rear.

not conducted because of time constraints.

The radar and alarm display enclosures appeared well built

and suitable for mining applications. Wiring could be improved

to ensure that it could withstand high temperatures and impacts

from flying rock, etc. The alarm display was intuitive and could

be heard above engine noise in the cab; however, more thorough

tests would need to be conducted to determine its effectiveness

under actual operating conditions.

System: Guardian Alert

Manufacturer: Sense Technologies, Inc. Vancouver, B.C.

Canada http://guardianalert.com/warning.htm

Description [Ruff 2000]: 

This motion-sensing radar unit operates at 10.525 GHz. The

radar unit does not require on-site licensing and is protected

under U.S. patents 4803488 and 5028920. 

The radar unit uses frequency modulation of microwave

signals to determine the distance to an obstruction. The sensor

is also pulse modulated so that it will not activate radar detectors

or interfere with other similar devices. In fact, multiple sensors

may be used on the same vehicle. The sensor will alert the

operator to the nearest obstruction and, rather than requiring a

fixed time between the moment it first detects an obstruction, it

requires a fixed distance (12 cm [5 in]) in order to react. This

makes the sensor insensitive to the velocity of the vehicle and

simplifies the analysis.

The system consists of a radar antenna and an electronics

enclosure, an alarm display, and wiring. The alarm display is

mounted in the cab and provides range gates that indicate

distance to the obstacle. Red, yellow, and green LED’s flash to

indicate an obstacle in a particular range gate, and a beeper

increases in frequency as the obstacle gets closer to the

equipment. This particular model was configured for three

range gates: 0 to 3, 3 to 6, and 6 to 12 m (0 to 10, 10 to 20, and

20 to 40 ft). The total range, beam width, and range gates can

be configured at the factory.

Test Results:

The Guardian Alert system was mounted in the same position

as the Ogden system at 2.7 m (9 ft) high with a 10° downward

tilt (figure 43). The zone behind the dump truck was cleared,

and the dump truck was moved in reverse to test for false

alarms. The radar unit generated an alarm with a single or

double chirp whenever the truck lurched, e.g., when putting the

truck into gear or braking suddenly. However, after the truck

began moving smoothly in reverse, the Guardian Alert system

did not detect tire rotation and did not generate a false alarm.

A person walked toward the stationary dump truck to define

the detection zone (figure 46). The range of this system

extended from near the tires to 6.1 m (20 ft). The width of the

zone extended only 3 m (10 ft), slightly wider than the distance

between the tires.

A pickup was then used to define the detection zone (figure 47). The pickup was slowly driven toward the rear of the

stationary dump truck. The range of the Guardian Alert system

extended from near the tires out to 10.7 m (35 ft) from the truck.

The width of the detection zone improved to around

9.1 m (30 ft).

Discussion:

The detection zone for a person was significantly narrower
20

on the Caterpillar 793B than on the Komatsu 210M [Ruff 2000].

It appears that the recessed mounting position behind the tires

and the mounting height reduced detection zone dimensions.

An alternative mounting position or antenna design would be

needed if the system were to be used on the rear of this truck.

It is anticipated that the system would be effective on the front

of the truck. 

The detection zone for a pickup truck was better than that for

a person; however, a longer distance for the detection zone

would be preferred. The pickup was detected near the tires and

the entire width of the dump truck was covered as long as the

pickup was within 6.1 m (20 ft).

Occasional false alarms occurred when the truck lurched

while shifting gears or braking. This could probably be

remedied in the radar’s processing algorithms and will be

suggested to the manufacturer.

The enclosure for the radar antenna appeared to be adequate

for a mining application. The wiring would need to be

improved to withstand high temperatures and impacts from

flying debris, and the enclosure for the alarm display would

need to be made more robust. The audible alarm might not be

heard above other noises in the cab, and a volume control

should be added. Also, a more intuitive scheme for lighting the

LED’s would be preferred. Simply lighting one of a series of

LED’s all labeled with the correct distance information would

be easier to interpret. 

CONCLUSIONS

Results from these tests have supported the conclusions and

recommendations made in a previous report [Ruff 2000], which

are summarized and updated in the current report.

Collision warning systems must be tested on the actual

equipment on which they are to be used to ensure that the

detection zones are adequate for that particular piece of

equipment. The distances to components on the truck, such as

the truck bed or tires, do affect the characteristics of radio

frequency transmissions and radar reflections. Beam widths and

distances that are effective for smaller trucks may not be

sufficient for larger trucks or other types of equipment, such as

front-end loaders. Mounting height also has an effect on the

size of the detection zone. 

Detection zones must be verified using actual objects, such

as a person or a pickup truck, that must be detected in actual

practice. Initial determination of detection zones can be

accomplished using corner reflectors when radar systems are

used; however, detection zones need to be verified using a

person and a pickup truck to ensure accuracy. It is understood

that repeatability is difficult because of different body types and

pickup truck models, but sufficient accuracy can be obtained

using a person falling in the range of average height and weight

and any common full-sized pickup truck.

The ideal detection zone depends on the type of mining

equipment and where the collision warning system is mounted

on that equipment. It is important that the detection zone cover

the entire width of the equipment and be as close as possible to

either the bumper at the front or the tires at the rear. The length

of the zone should extend approximately 12 to 15 m (40 to 50 ft)

to prevent accidents involving large, slow-moving dump trucks.

Higher speeds would require longer detection distances to give

the truck driver enough time to react to an alarm; however,

accident reports show that most accidents occur shortly after the

truck starts moving from a parked position.

It is important to verify the reliability of a collision warning

system by actually moving the dump truck toward the obstacle

at several points in the detection area where it is safe to do so.

Earlier tests showed that equipment vibration and other moving

parts, such as tires, can affect the operation of a system when

the equipment is in motion. These effects have ranged from

total system failure to occasional false alarms. 

A problem seen with radar systems is their susceptibility to

false alarms or nuisance alarms from objects that pose no

danger, such as rocks or ruts in the roadway. There are also

alarms from objects of which the equipment operator is already

aware, such as shovels or pit walls. Too many alarms are a

major concern because an equipment operator may become

frustrated and start ignoring them. It is very difficult to climb

out of the truck to verify the source of every alarm. Because of

this problem, it is recommended that radar systems be used in

conjunction with another secondary system, such as video

cameras. This will allow an operator to verify the source of an

alarm without leaving the cab. It also improves the reliability of

a collision warning system by providing a method of verifying

the location of an obstacle and the number of obstacles in a

blind area. As the functionality and reliability of radar-based

collision warning systems improve, a secondary system may

become optional. 

RFID systems are not prone to false alarms, but a secondary

system, such as a camera, may be helpful in locating the source

of an alarm or avoiding collisions with untagged objects. The

disadvantage of RFID systems is the requirement that all objects

or people that need to be protected must have a tag attached.

This could require a large amount of tags at a mine site. Tag

reliability must be high, and maintenance kept to a minimum.

Cameras by themselves do not generate an alarm that alerts

an operator to an impending collision. It is recommended that

a secondary system be used with cameras to provide such an

alarm. Such a secondary system would be an effective means

of prompting an operator to check his/her video monitor when

necessary. Several mine safety managers have expressed a

concern over this problem and have had first-hand experience

with camera systems that did not help prevent a collision.
21

Table 2.—Summary of test results for collision warning systems on a Komatsu 210M

System Buddy

System

Body

Guard

Knapp Guardian

Alert

Preview Ogden Rear Guard MSSI

*

Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RFID RFID Doppler

radar

Doppler

radar

Pulsed

radar

FMCW

radar

Ultrasonic UWB

radar

User-adjustable zones . . . . . . . . . . . . . . . . . . . . . . Yes Yes Yes No No Yes Yes Yes

Motion required for detection . . . . . . . . . . . . . . . . No No Yes Yes No Yes No No

Maximum length of rear detection zone as

 tested (person/pickup in feet) . . . . . . . . . . . . . . 50/50 50/50 22.5/65 25/45 30/27.5 40/40 8/NA 50/50

Total coverage near outer dual tires . . . . . . . . . . . Yes Yes Yes Yes No No No Yes

Maximum length of front detection zone as

 tested (person/pickup in feet) . . . . . . . . . . . . . . 50/50 50/50 22.5/65 30/37.5 27.5/30 25/30 8/NA 45/55

Total coverage near bumper . . . . . . . . . . . . . . . . . Yes Yes Yes Yes No Yes No No

Sporadic detection at zone edges . . . . . . . . . . . . No Yes No No Yes No Yes Yes

For use in all weather . . . . . . . . . . . . . . . . . . . . . . Yes Yes Yes Yes Yes Yes No Yes

False-alarm rate in clear field . . . . . . . . . . . . . . . . None None Infreq. Frequent None None Infreq. None

Cinder block detection . . . . . . . . . . . . . . . . . . . . . No No Yes Yes Yes Yes NA Yes

Level of effort in mounting . . . . . . . . . . . . . . . . . . High High Med. Low Med. Low Med. Low

Multiple units needed for entire coverage

 (front/back) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . No Yes Yes Yes Yes Yes Yes Yes

Cost (H = above $8000, M = $2000-

 $8000, L = below $2000) . . . . . . . . . . . . . . . . . . High High Low Low Low Low Low Med.

NOTE: Some system information taken from Ruff 2000.

* Still under development.

RFID = Radio-frequency identification. FMCW = Frequency-modulated continuous wave. UWB = Ultrawide band.

Table 2 summarizes the results from the phase 1 and 2 tests

of available collision warning systems on a Komatsu 210M

dump truck. These tests were useful in showing the potential for

the use of this technology on large trucks, but an actual test 

program over an extended time is needed to verify that these

systems will be effective in an operating mine and on other

types of equipment. This will be the focus of the next phase of

testing. 

REFERENCES

Ruff, Todd M., Test Results of Collision Warning Systems for Surface

Mining Dump Trucks. NIOSH Report of Investigations 9652, 2000, 44 pp.

Society for Automotive Engineers (SAE). Discriminating Back-Up Alarm

System Standard J1741. June 1999, 9 pp. 
Delivering on the Nation’s Promise:

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

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DHHS-(NIOSH) Publication No. 2001-100