Maine Local Roads Center
Using
LED’s in Traffic Signals
-a note from DOT’s Traffic Engineering Division-
It has come to the DOT’s attention that many municipalities
are changing from conventional signal heads(with incandescent bulbs)
to LED signal heads. The Department recognizes the many advantages
of the LED signal heads and is more than satisfied with their performance.
However, municipalities need to be aware of potential pitfalls in
using this new technology. At many intersections, it is difficult
to really see which light is really on.
LED signals emit light in a twenty degree (20°) cone in all
directions (incandescent bulbs use a 40° cone). This makes
it absolutely imperative that the signal heads be in proper horizontal
and vertical alignment. It is for this reason that LED signal heads
should not be used on roadways with extreme grades or extreme horizontal
curvature.
Any signals on span wires must be tethered at the bottom and a
visual check of the signal head alignment must be performed in
order to verify there is no negative impact on the traveling public.
The Manual on Uniform Traffic Control Devices (MUTCD) indicates
that for an 85th percentile speed of 35 mph you would need to see
the signal head from 325 feet away. If there are signals in
your municipality, the DOT asks that you take corrective action
on any non-tethered or non-aligned LED signals.
If you have any questions on this matter, please feel free to contact
Steve Landry, Assistant MDOT Traffic Engineer at 287-3775.
Do You Have a Traffic Signal in Town?
- New L.E.D. technology can dramatically cut your electric bill
-
The future of traffic signals is changing. Light emitting diodes
(LED) are becoming an attractive alternative to standard incandescent
lamps. Energy costs in several Maine communities have been significantly
reduced by the installation of LED bulbs.
Although the initial cost of purchasing and installing LED's in
traffic signals is relatively high, the long-term cost savings makes
them an economical alternative. LED light fixtures have a life expectancy
of ten years, compared with the one-year life expectancy of standard
incandescent bulbs.
The major advantage of LED's is a dramatic reduction in power consumption
resulting in reduced energy costs. The city of Lewiston realized
a 66% reduction in electrical costs from a typical intersection
after installing LED's. The following chart, provided by Chris Branch,
Public Works Director/City Engineer for Lewiston, summarizes Lewiston's
savings for ONE of their intersections, before and after the installation
of red LED bulbs in their traffic signals.
| 157 |
1763 |
11.2 |
| 275 |
527 |
1.9 |
The Town of Yarmouth has replaced all of their red stop signals with
LED's resulting in a 31% reduction in power usage. The following chart
shows Yarmouth's actual energy savings for four signalized intersections.
These numbers are for typical red-yellow-green assemblies with a total
of 39 red bulbs replaced.
| 31 |
3006 |
97.0 |
| 31 |
2075 |
66.9 |
The
above numbers represent actual savings realized. Your savings will
be different based upon the number of bulbs replaced and the percentage
of time the light is operating.
Although comparatively expensive, the initial cost should not be
a deterrent to the use of LED bulbs. The life-cycle costs need to
be considered to evaluate the true benefit of LED bulbs. The payback
time depends upon the initial cost of the LED bulbs, the number
of lamps replaced, the electrical rates, and the annual energy savings.
Lewiston and Yarmouth paid $220-275 per installation to switch to
LED's. The following chart identifies the average payback period
as determined by the City of Lewiston.
$2,104 |
44 |
$11,680 |
5.6 |
$13,576 |
268 |
$64,320 |
4.7 |
$15,680 |
312 |
$76,000 |
4.9 |
Bill Shane, Public
Works Administrator for the Town of Yarmouth, provided the following
information concerning their use of LED light fixtures:
· LED lamp life is guaranteed for 7 years with replacement,
if the bulb should fail. The LED lamp has a life expectancy of 10
years, which significantly reduces the number of bulb changes and
therefore, the number of work zones required for these operations.
This reduces work zone liability and costs associated with traffic
signal maintenance.
· Using 1995/1996 dollars, the LED bulbs have a payback
period of 3-9 years. However, as power costs increase, the payback
period will be reduced. At $.15 per kwh, a three year payback period
can be expected.
· Yarmouth's intersections have only red LED's installed.
The walk lights, information signs, green and yellow bulbs also
draw significant energy. As the other lamps are replaced with LED's,
power consumption will be further reduced. In addition, costs will
decrease and the need for annual bulb replacement will be eliminated.
It is obvious that significant cost savings can be realized through
the installation of LED lamps. Currently, red, amber, and green
LED lamps are available. Additional information regarding LED lamp
replacement can be obtained by contacting Pete at the Center, Bill
Shane in Yarmouth, Chris Branch in Lewiston, or Ed King in MDOT's
Traffic Engineering Section at 287-3775.
WHY CONSIDER L.E.D.'s?
- Saves dramatically on power usage.
- Eliminates bulb replacement for at least 7 years.
- Reduces liability by reducing number of dead bulb changes, fewer
work zones and less traffic disruption.
- Low maintenance
- No wire filaments
- Not sensitive to mechanical shock and vibration
- Visible and bright in all weather conditions
- Available in all three colors
- Pedestrian heads are now available
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