Technology News

No. 468 December 1997

U.S. Department of Health and Human Services

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Tests of Doppler Radar Technology for Haulage

 Truck Backup Alarms

Objective

Reduce haulage truck accidents resulting from blind spots, with a

special emphasis on reducing accidents during backing operations.

Approach

Current innovations in Doppler radar technology have led to

suggestions by several institutions and manufacturers that new

backup alarm systems are available that can replace or augment

warning systems for backing operations on large haulage vehicles.

In 1995, Spokane Research Laboratory engineers contacted

research institutions, equipment manufacturers, and vendors to

determine the availability of such systems. Only two manufacturervendors of the radar backup alarms were found. In both cases, the

units had not been tested on large, off-road mine haulage trucks.

A series of laboratory tests, controlled simulated tests on small

vehicles, and full-scale field tests on 240-ton class, end-dump

haulage trucks were conducted to evaluate the existing devices.

Field Tests

Two simple parameters were chosen as the basis for the tests: a

sensing range of 30 feet and the ability of the device to “see” both

small vehicles and human subjects. In the initial field test, the

devices were mounted on a platform on a tower placed in the bed

of a pickup truck. This test evaluated whether or not the devices

would operate in real time in near-field-type conditions. 

Only one sensor unit passed this test. This sensor was then tested

on a 250-ton mining truck at a truck manufacturer’s facility. With

the assistance of an engineer and a technician from the company,

two radar backup alarms were mounted on a plate centered over the

tail lights, backup lights, and the backup alarm at an elevation of

approximately 8 feet above the ground surface. The units were

attached with two magnetic base plates to facilitate mounting on

the truck. Mounting and wiring were accomplished in

approximately 2 hours. Since the units needed to be wired into the

24-volt system of the truck, positive connections were made on the

tail light circuit, the backup light circuit, and within the cab on the

ignition circuit. The warning lights and alarms of the radar unit

were also mounted within the cab of the truck on Velcro tape.

Initial tests to determine if the units were wired correctly and were

able to sense movement of targets were conducted while the truck

was stationary. When the truck was started, a multitude of other

alarms (air pressure, hydraulic pressure, backup alarm) were

activated, totally confusing the driver’s ability to distinguish when

the radar sensing alarms were activated. To rectify this, the ground

system on the truck’s backup alarm was disconnected, disabling

that system.

Numerous test configurations and positions of the devices were

tested. The adjustable magnetic base plates made changing the

positions of the devices easier, but aiming and adjusting gain were

time consuming. Reasonable results were obtained when two

sensors were mounted on a common base about 8 feet above the

ground surface (on the light bar) and 25 degrees off horizontal to

the ground, the gain was set at 35 percent of maximum, and the

beams were positioned to cross to the opposite footprint. This

placed the sensing beam 15 to 18 feet behind the wheels and about

10 feet on the centerline of movement. Further flattening of the

beam from the horizontal tended to make the device more sensitive

to other surrounding objects, with resulting false alarms. While

this configuration could be considered operative, it still was

problematic, since the distance over which an object was sensed

was too restricted to give a truck driver much time to react to an

alarm.

Since earlier tests at the Spokane facility suggested that better

results were achieved at higher gains when the sensors were 11 to

12 feet above the ground, researchers decided to move the sensors

higher on the truck. This new position was above the point where
Mounting sensor on light bar. Backing toward pickup truck. Note radar units mounted on top

of hinge points on truck bed.

the mining truck dump body would hinge, which was at elevation

of approximately 14 feet. Each sensor was focused over the rear tire

toward the footprint directly behind it, instead of to the opposite

side; aimed downward at 30 degrees from horizontal; and adjusted

to about 50 percent gain. Tests were then run in which the haulage

truck was backed through a parking lot where cars and other

objects had been positioned about 20 feet on either side. In this

position, the devices were able to sense a vehicle at any position

behind the truck at distances ranging from 21 to 24 feet. No false

alarms were generated at this setting.

At this point, personnel from the mining truck manufacturer and the

Spokane Research Laboratory engineer were satisfied that the

devices could operated using this configuration. However, further

efforts would be required to mount the device when the dump bed

was attached.

Recommendations

Although these devices show much promise for sensing objects

within the blind spots of vehicle drivers, they are not just bolt-onand-plug-in devices that are easy to adapt to various situations.

Mounting the units to achieve optimum sensing ability without

interference and false alarms is, at the very least, a tedious and

time-consuming job; while a magnetic mounting bracket helps

determine mounting location and aiming, the actual work of gain

adjusting, aiming and pointing, evaluating the height for the

sensor, and factoring out vibration and interference must be

established through trial and error. How the devices perform when

a truck is stationary does not indicate how well the devices work

when the truck or objects behind the truck are moving. In addition,

if a driver feels that performance does not meet expectations, all of

the effort can be negated, almost instantaneously, by

disconnecting a wire or two.

A factor that must be further evaluated is whether or not the alarms

will be noticed when the standard backup alarm is in use. It is

possible that the continuous beeping of the standard backup alarm

will mask the active Doppler radar alarm signal. These questions

will be answered only after testing in actual mining and

construction situations.

For More Information

R. Backer C. M. K. Boldt 

Spokane Research Laboratory Spokane Research Laboratory

E. 315 Montgomery E. 315 Montgomery

Spokane, WA 99207 Spokane, WA 99207

(509) 354-8017 (509) 354- 8006

Mention of any company name or product does not constitute

endorsement by the National Institute for Occupational Safety and

Health.

To receive additional information about mining issues or

other occupational safety and health problems, call 1-800-

35-NIOSH (1-800-356-4674), or visit the NIOSH Home

Page on the World Wide Web at http://www.cdc.

gov/niosh/homepage.html 

As of October 1996 the safety and health research functions

of the former U.S. Bureau of Mines are now located in the

National Institute for Occupational Safety and Health

(NIOSH).