The city of Rowlett, Texas, experienced an unauthorized wastewater ...
Work-zone intrusion alarms help protect crews; lower insurance and workers' compensation premiums may be additional benefits
The statistics tell the tale: In the U.S., workers receive an average of
over 25,000 disabling injuries annually in roadway-repair zones; between
600­p;900 workers a year die as a result of these injuries.
Of those killed, 59% die as a direct or indirect result of a vehicle entering
a work zone. Work-zone related fatalities have risen sharply over the past
several years-the increase from 1992 to 1993 alone was 20%-and the loss
of personnel is compounded by the economic loss from these accidents.
And given the current dearth of federal funding for new roads, more and
more highway- and bridge-construction workers will find themselves performing
maintenance or reconstruction work, in situations where the only barrier
between them and traffic is a thin veneer of rubber cones and arrowboards.
However, these safety devices only work if drivers are attentive and have
control of their vehicles. While such work-zone safety products do the job
they are designed to in an admirable manner, they are passive tools. What
is missing is an active tool that will warn workers that an unauthorized
vehicle has entered the work zone. With the recent advent of work-zone intrusion
alarms, this need has been filled.
The basic principle behind work-zone intrusion alarms is the same for all
products currently on the market. A work zone is either mechanically or
electronically delineated by the product, and any vehicle intrusion into
this zone sets off an aural and/or optical alarm. This gives workers time
to see where the breech of the zone has occurred and to take evasive action.
Many work-zone accidents are the result of drivers who have fallen asleep
or are operating under the influence. In these instances, the speed of the
intruding vehicle can be quite high (especially in highway work zones),
and, even with an intrusion-alarm warning, a worker may have only seconds
to flee. However, these few seconds are precious: They can make the difference
between a "near miss" and a serious injury, or a serious injury
While arrowboards, flag crews and cones can help keep attentive drivers
out of work zones, it is the in-attentive driver who poses the greatest
risk to work-zone crews. It is the latter category of drivers that intrusion
alarms guard against.
Intrusion alarms don't have a lengthy history-most of the products on the
market today are either a direct or indirect result of a 1994 Strategic
Highway Research Program (SHRP) study. They can be classified into two distinct
types: mechanical, in which a vehicle running over a pneumatic tube sets
off the alarm (like a gas station bell line); or electrical, where a vehicle
entering a work zone breaks a microwave, infrared or other electromagnetic
beam and sounds the warning.
Neither system type is inherently "better" than the other; each
has its advantages and disadvantages. Mechanical systems are, in general,
lower in cost than electronic units, but they are not as flexible. Electrical
systems can take advantage of the rapid evolution of computerized technology,
whereas mechanical systems are less intimidating to the novice. Each system
type shares many common features, such as the ability to string many individual
systems together to make a longer protection zone; both are designed to
set off an effectively loud warning siren when the work zone is breached.
Kenco International Inc., Ligonier Valley, Pa., makes the Watchdog perimeter-intrusion
alarm system. Its a mechanical system that consists of 100-ft-long lengths
of pneumatic tubing tied to a siren.
The hose-about the diameter of a garden hose-is wound off a reel that can
be mounted on the back of a pickup and placed on the pavement just inside
the cones of the work zone. At the actual work site, the junction box at
the end of the hose is wired to a siren. This siren, which can be mounted
on any metal surface-such as the top of a truck cab-with its magnetic feet,
is plugged into a standard cigarette lighter for power. (The unit also comes
with battery clips so it can be attached to any 12-volt battery.)
"The hoses are sealed tubes-there is no air going into the tubes,"
says Bill Douglas, Kenco's marketing manager. "Sensors are located
every 100 ft that detect the pressure pulses [from an encroaching vehicle],
so a worker is never more than 50 ft away from a sensor. The hose has a
nylon-braided sleeve, and a hardwire runs right with the hose that sends
the signal back to the alarm."
He says the system can be "daisy chained" with almost any number
of units; each 100-ft-length of hose is attached via its junction box to
One of the concerns of this type of system is the longevity of the pneumatic
hoses, but Douglas says this isn't an issue. "We have dragged these
hoses up and down highways; we've given them a lot of heavy use. We figure
the life expectancy of the hose is about five years."
The Watchdog system comes with 300 ft of hose, a hose reel, a siren and
100 ft of wire for hose-to-siren connection, and clips and a cigarette-lighter
adapter for power. Simple to set up, test (just stomp on each test section)
and use, the system runs for $2,295. Options include additional lengths
of hose and a strobe light that can be attached to the siren for visual
Electronic-based systems are generally higher priced-high tech often means
high prices. One of the higher-profile electronic units on the market today
is Traffic Management Systems Corp.'s Myriad Safety Sentinel2 intrusion
alarm. Jack Toman, president and CEO of the St. Louis-based company, was
a participant in the original SHRP meetings that led to the 1994 intrusion-alarm
testing. "When we were originally approached for this project by SHRP,
we designed our system to specifically address the high-speed, high-crash
risk applications. That is where the vast majority of fatalities and injuries
were taking place.
"We looked at maximum warning time as being one of the most important
factors, as well as a proactive means to get the word out to all workers
within the zone simultaneously, and tried to design it in such a way as
to eliminate every potential for falsing."
Toman came up with a system that has three basic units: a microwave transmitter,
a microwave receiver and a strobe light (known as a CORS light, for "coded
"Virtually no training is involved in setting it up," Toman explains.
"You place the receiver where you want it-by the workers-and then have
someone take the transmitter to a point back down the road. You adjust the
receiver so it catches the beam of the transmitter-there is a bar graph
on the back of the unit-and then lock it down."
This establishes the work-zone edge. Any vehicle or person who strays across
this imaginary line will set off the alarm and the CORS light. In addition,
Traffic Management's system has a CORS "slave unit" that users
can purchase and place at appropriate intervals on top of channelizers along
the work zone. When one light goes off, it sends out a digital signal that
sets off the next light up the line, which then repeats this operation.
This results in a cascade of flashing strobes that, together with the dual
130 dB sirens, clearly indicate that a vehicle has entered the protected
Toman says the basic system costs $4,000; slaves are $1,000. While Toman
has yet to have a contractor balk at such a price tag, he has a rejoinder
for those who might: "Compare the cost of our units to the loss of
even one life."
Because the systems are designed to safeguard workers, concerns about false
alarms are a very valid complaint: A system that "cries wolf"
too often will not be as effective as one that just detects what it is supposed
to. Electronic system are more prone to false alarms than mechanical systems
(workers can just step over pneumatic tubes to leave a work zone), but these
"bugs" are slowly going away.
For example, the SafetySentinel2 uses a very wide transmitting beam and
a very narrow receiver "eye," and this permits a certain degree
of "wiggle room." With this arrangement, the channelizers the
transmitter and receiver are mounted on can move in the wind or from vibration
without the receiver losing sight of the transmitter's beam, which would
set off the alarm.
The unit's receiver has a switch that can be depressed to temporarily disable
the system, allowing crew members or work vehicles to access or egress the
site. This disable button does not lock. A worker has to keep depressing
the button manually to keep the system inactive. This is a safety device
that is designed to prevent a worker from disabling the system with an "on/off"
toggle and then forgetting to activate it once crew members return to work.
This could result in just the opposite of a false alarm: a false sense of
security, which could have tragic consequences.
Active by nature, the intrusion-alarm systems are gradually integrating
other, passive features that enhance worker safety. Traffic Management's
system currently has the only fully FCC-approved "drone radar";
this system sends out radar pulses either continuously or sporadically on
both K and X bands, setting off virtually every car radar detector on the
This serves two purposes: It slows cars down before they even reach the
work zone, and drivers have already been warned that something is ahead,
so they are more likely to notice the other passive systems, such as arrowboards.
Toman says a new option the company offers is an excessive-speed module
that will measure the speed of approaching vehicles. While this may seem
like a needless frill, it is useful in that this option allows users to
set a threshold of approaching-vehicle speed to set off the system. For
example, a car traveling 85 mph in a 45 mph zone is an accident waiting
to happen; by triggering the alarm at that threshold, workers can clear
the site before the vehicle is near.
Manufacturers are learning from each other, as well. Toman says his company's
unit now includes a pneumatic tube that provides protection perpendicular
to the work zone at the taper. This component, much like the one that the
Kenco system uses, is integrated into the rest of the company's system,
so a vehicle running over the hose at the taper will set off the full warning
On the other hand, Douglas says Kenco is considering adding an optional
feature similar to drone radar for the Watchdog units. He says interest
is high for this type of device, and it will probably be available by this
fall. Another feature he expects to market is a siren that is integrated
right into a light bar, for an aural and visual warning. Again, this is
a step Traffic Management has already taken with their system.
"Keeping up with the Joneses" seems to be a big part of this rapidly
expanding market; Traffic Management has gone as far as planning a recall
of its earlier units. "I haven't actually put out the letter yet,"
Toman says, "but I plan to issue a recall of my earlier versions of
the equipment and replace them, free of charge, with the updated model.
That's going to cost a lot, but, in the long run, I believe it will be beneficial
Putting the best foot forward in this young market appears to be a wise
game plan-both Douglas and Toman expect this market to grow tremendously
in the near future. Both believe the underlying push will come from states,
which will write specifications for the intrusion alarms into contracts.
Once the states are on board, insurance companies may well follow suit.
And then there is the question of litigation. "We heard from a lawyer
who wanted to know if [intrusion-alarm systems] were out when his client
was hurt," Douglas recalls. "He said he could use something like
that against the contractor for the suit. I think this type of litigation
is something contractors are going to have to look out for in the very near
Toman recounts a similar story, and adds that he expects intrusion alarms
to be included in the Manual on Uniform Traffic Control Devices (more commonly
known as MUTCD), much as arrowboards have been, within the "next couple
of years." Since MUTCD is a document of legal standing-it is often
used as part of tort lawsuits-inclusion in the manual will all but force
contractors to use intrusion alarms.
While the use of intrusion alarms may become commonplace for the wrong reason-fear
of litigation vs. fear of personnel loss-the safety of those working in
construction zones is the real bottom line for intrusion-alarm use.
Yet even with the most elaborate series of safety devices, the average worker
is still very vulnerable. Recognizing this reality, Kenco has taken the
somewhat unprecedented step of putting aside approximately 5% of the proceeds
from the sales of its Watchdog units to establish a fund for the families
of work-zone accident victims.
"At the end of this year we will take a look as some individual cases
we have heard about and decide where to distribute the funds," Douglas
says. "There is no actual charity for work-zone accident victims; this
is it. If my competitors want to get together with me and do the same, I'll
be glad to work with them. Right now, there isn't a lot of cash in the fund-the
system is still so new-but it could be substantial if sales take off the
way I hope and expect them to."
If the makers of intrusion alarms had it their way, the alarms would be
so effective and profitable that such a fund would swell to an unbelievable
amount-but there wouldn't be anyone left who "qualified" to receive