It is estimated that there are about 250,000 signalized
traffic intersections in the U.S., which account for as many as 8-10 million
signal lamps. Due to the expansion, as well as the urbanization of the U.S. population,
the number of traffic signals will continue to grow annually.
It is well known that most of the traffic signals in North
America are based on either 8- or 12-in. diam. signal heads consisting of the
traditional red, yellow and green colors. Traffic signals that include arrow
signs also exist in red, yellow and green.
What has become more evident in recent years is that these
traditional incandescent lamp-based traffic signals are being converted to
traffic signals which incorporate light-emitting diodes (LEDs). This article
investigates the conversion of traditional traffic signals to those that
incorporate an LED-based signal system, as well as the benefits of switching to
an LED-based signal.
Old vs. new
Typically, the traditional traffic signal contains an
incandescent bulb with a power rating that operates between 65 and 150 watts
for each of the three signal colors—red/yellow/green. The energy demand
of the average traffic signal is approximately 1,000 kWh per year.
In comparison, wattage required with the LED light
colors—also red/ yellow/green—vary from each distinct color based
on the length and time each is illuminated. Contingent upon the amount of power
consumed by an LED-based traffic signal, it is possible that nearly 3.5 billion
kWh per year in the U.S. could be saved if LED signals were used to replace the
traditional incandescent traffic signals.
Digging further into the statistics, approximately 2 billion
kWh, or nearly a 60% energy savings, could be derived from switching the red
traffic signals to red LED-based signals alone. Typical red LED-based circular
signals as well as red arrows use 90-95% less power than a traditional 150-watt
incandescent light bulb.
More than 1 billion kWh could be saved by replacing the
traditional green incandescent signals with green LEDs due to a lower duty
factor.
Overall, the power ratings for LED signal modules range from
8-25 watts, depending on the color of signal and operating conditions.
When it comes to the actual bulbs within LED-based traffic
signals, LEDs last much longer than incandescent lamps—approximately 5-10
years or 100,000 hours of operation for the LEDs as compared to one year for
the traditional incandescent lamps.
This longer life span enables many departments of
transportation to re-duce their yearly maintenance schedules as well as avoid
the replace- ment costs associated with incandescent lamps.
As a result, when estimating LED-based traffic signal
project costs and benefits, a few states and municipalities have included this
routine maintenance cost savings, as well as other benefits such as reduced
emergency maintenance costs and liabilities associated with less frequent lamp
burn out, into their budgets.
Other benefits of using LED-based traffic signals include
modules that are shielded and resistant to water; ease of installation;
precision optic lenses of LED to maximize light efficiency; greater viewing
angle; and visibility.
Cost comparison
The initial cost of LED signal heads is expensive relative
to the cost of a replacement incandescent bulb. Furthermore, the initial
investment of money and personnel needed to re-place existing traffic signals
and heads is not a trivial matter for cash-strapped counties and
municipalities.
But in conjunction with the overall lower maintenance and
power costs mentioned previously, LED-based traffic signals could quickly pay
for themselves when compared to incandescent lights.
A typical incandescent bulb for a traditional traffic signal
can cost a jurisdiction approximately $2.50-$3 to purchase.
While an LED signal retrofit kit can be purchased at a
significant premium, the cost of red, green and yellow LED retrofit kits vary
considerably when considering the number of suppliers, market demand for the
signal colors, mass production and intensity requirements.
The cost has constantly been dropping over the last few
years and today, red LED retrofit kits are available for less than $100. As a
result, a single red LED pays for itself in energy savings in approximately two
to four years depending on the electricity rate.
In comparison to the red LED retrofit kit, a typical 12-in.
green LED retrofit kit costs under $170.
It must be noted that the current price ranges of LED single
signals varies dramatically due to a variety of factors which include the
signal color, size, optics used by the supplier and quantity, for example. As
mentioned above, the technological advances and the entry of many suppliers
into the LED traffic signal market has been a major factor in sharply driving
down the cost of LED-based signals within the last two years, and this trend is
expected to continue.
Additional incentive
Some other factors leading the charge toward installing
LED-based signals are the associated energy, cost, power and environmental factors.
Because of the energy savings potential, many utility
companies have programs and incentives that promote the installation of LED
traffic signals. In some cases, the incentives and rebates offered essentially cover
the cost of new modules. Power companies have played a major role in driving
the LED signal replacement programs by providing major financial rebates.
Currently, approximately 200 participants in these incentive-based utility LED
programs can be found in the U.S.
Moving ahead to LED
In the U.S., the current trend continues toward replacing
single traffic signal lamps as opposed to a complete retrofit of an integrated
fixture. Those replacing the individual lamps are multiple and independent
buyers consisting of government agencies on a federal, state, county and local
level each of which maintain the traffic signals.
LED-based traffic signal replacement programs are moving
ahead at a rapid pace in several states across the nation. Departments of transportation
in states such as California, Oregon and Pennsylvania are at the forefront of
converting their traffic signals to the LED format and have been implementing
the replacement program for more than two years. For example, Caltrans has
already replaced about 200,000 traditional traffic signals to LED-based traffic
signals.
Concurrently, almost every state in the U.S. has an LED
traffic signal retrofit program under way at least in the most initial
capacity.
Some of the states and municipalities have based their
purchasing requirements largely on the early experience, testing and
specifications developed by DOTs such as Caltrans.
The DOTs in Florida, Ohio, Michigan, New Hampshire,
Minnesota, Nevada, New York, New Jersey and Texas are among the early adopters
of major LED retrofit programs. New Hampshire has gone as far as to even
develop their own LED traffic signal purchasing requirements.
Red on top
To date, the most common LED traffic signal replacement
application has been the red signal followed by the green signal.
The reason the red signal is replaced first is because in
the typical traffic signal, the red signal will be switched on approximately
50% of the time compared to lower illumination tones for the green and
especially the yellow signal heads.
As for the yellow signal, it is not considered a priority
due to its short illumination time. Another factor contributing to the low
number of yellow signals being replaced is that they require a significantly
higher number of LEDs, according to the Institute of Transportation Engineers
specification standards.
Standardization may lower cost
An issue hindering the widespread use of LED-based signals
comes in the form of a lack of uniformity of objective and accurate technical
information about the standards and performance of LED traffic signals in the
field. Standard setting bodies such as the Institute of Transportation
Engineers provide operating and performance standards of LED signals such as
brightness, visibility, operating temperature, timing, power consumption, etc.
However, ITE standards are modified and adopted by various state DOTs based on
their own tests and operational and performance criteria.
This lack of standardization leads to the variation in
signal specification from state to state, which in turn leads to delays caused
by design modification for prequalification of vendors in every state.
With a number of different specifications in place,
manufacturers are forced to keep the cost of production high. However, the
proliferation of traffic signal specifications throughout the U.S. may have a
benefit. Because state and local jurisdictions prepare specifications, the
specs are likely to conform to any local or regional requirements, such as
weather conditions or electricity costs.
LED sources
Several companies manufacture traffic signals using LEDs and
use their own design and optics to achieve the desired performance. The usual
strategy with these signals is to package hundreds of LEDs together with
reflectors or lenses to create the high-luminance signal face that is required
by specifications of the Institute of Transportation Engineers.
Some of the leading suppliers of LED-based traffic signals
are Action Media Technologies, Actone, Cooper Lighting, Dialight, Electro
Technologies, Gelcore, LEDtronics, Leotek, Precision Solar Controls and U.S.
Traffic Corp.
More information on these companies can be obtained by
following the link in the LearnMore! box below. TME
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