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RETROFITTING ROAD TRAFFIC SIGNALS WITH LED

- AN EVALUATION. BY

NITIN VAIDYA *, KRISHNA KUMAR. C. **, SURESH. P.S. ***

ABSTRACT

Road traffic signals are used as a cost effective measure for controlling traffic safely and efficiently

at intersections. Incandescent bulbs are being used as light sources in traffic signal heads for a

long time now. LED s(Light Emitting Diodes) have been used in place of incandescent lamps in

traffic signals of late due to its energy efficiency and longevity. At present there is no standards

available for LED signal faces in India. Number of standards are compared and discussed here

with the aim of providing uniformity in the standards for LED signals, especially for colour,

luminous intensity, luminous intensity distribution. Recently Surat Municipal Corporation has

embarked upon a programme of retrofitting signals with LED aspects. The evaluation of the

retrofitting with LED signal aspects are done in this paper. The investment for retrofitting LED in

traffic signals in Surat is estimated to have an IRR of 14 % compared to the use of incandescent

bulbs for an analysis period of 7 years. It was found that the power savings due to retrofitting with

LED is 88 % and the savings in maintenance cost is 51 %. It is estimated that in a city having 500

intersections approximately Rs.9.5 millions can be saved per annum, at a rate of Rs. 3/ kw. hr. of

electricity, by completely retrofitting signals with LED aspects. As an energy efficient measure, it

is suggested that the use of LED retrofit in traffic signals need to be implemented in other cities

also. At the same time proper methods need to be ensured to understand the performance of LED

retrofitted signals on its optical performance and longevity in the tropical climate prevalent in

India.

* Executive Engineer, Surat Municipal Corporation, Surat.

** General Manager, CMS Traffic systems Limited, Mumbai.

*** Manager – Traffic Engineering, CMS Traffic Systems Limited, Mumbai.

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RETROFITTING ROAD TRAFFIC SIGNALS WITH LED

- AN EVALUATION. BY

NITIN VAIDYA *, KRISHNA KUMAR. C. **, SURESH. P.S. ***

1. INTRODUCTION

Incandescent bulbs are being used as light sources in traffic signal heads for a long time now.

Conventional incandescent lamps generate light by applying voltage across a tungsten wire

filament in a glass enclosure and making it hot. Most of the energy is dissipated as heat and hence

incandescent lamps are not energy efficient. Light Emitting Diodes (LED) are semiconductor

based light sources where light is generated by an electron energy transition across a p-n junction

by passing a current through the junction. LEDs are now available in many colours including red

amber and green. LED can produce monochromatic light and hence there is no need for using

external light filters to change the colour. Incandescent lamps produce white light and require

optical filters to obtain the desired colours. LEDs are capable of operating from –40°C to 100°C

and they can withstand higher levels of shock and vibration than incandescent lamps. The life

expectancy is higher, may be 10 years or more and more than 5 years of warranty is given by the

manufacturers. LED traffic lights are made by combining number of LEDs in arrays and this

number is brought down by every passing year. The first signal lamps that were developed in 1994

had over 600 LEDs in them, the same lamp can now be built with about 100 traditional LEDs.

Now it is possible to build LED signal faces with six LEDs .( Burton,R(2003), ) LEDs can

operate with reduced power consumption. A standard 300 mm traffic signal with incandescent

lamp consumes 100 watts of power. A LED lamp having the same dimension consumes only 10

watts. This results in savings of 90 watts per lamp and a city having thousands of signal

installations can save large amounts from this. LED s have been used in place of incandescent

lamps in traffic signals of late due to its energy efficiency and longevity. India is no exception to

this and numbers of cities are having LED retrofitted traffic signals functioning now. In India,

local self governing bodies are in charge of installing and maintaining traffic signals with the

active involvement of local traffic police. One of the local self governing bodies in India, Surat

Municipal Corporation has recently embarked upon a programme of retrofitting the traffic signals

__________________________________________________________________________

* Executive Engineer, Surat Municipal Corporation, Surat.

** General Manager, CMS Traffic systems Limited, Mumbai.

*** Manager – Traffic Engineering, CMS Traffic Systems Limited, Mumbai.

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with LED. So far no effort was done to quantify the benefits due to the retrofitting with LED

signals in India. As most of the local bodies in India do not have the financial capacity to invest in

traffic control activities as necessitated by the traffic conditions, it is high time to understand the

accrued benefits from the modernization of signal systems. This paper details the standards for

LED signals along with an evaluation of the LED retrofitting done in various intersections falling

under the Surat Municipal corporation limits.

2. Standards for LED traffic signals

The visibility of traffic signal depends upon many factors, the most important of which are colour,

luminous intensity and luminous intensity distribution. Various standards are discussed here on the

basis of this here.

2.1 Indian Standards

Currently there is no specification or standards in India for LED signals and the ITE specifications

are widely accepted by the concerned authorities as a guide line for their requirement. The

guidelines given by IRC 93 -1985 “Guide lines on design and Installation of road traffic signals”

and IS 7537-1974 “ Indian Standard specification for road traffic signals” have given some

general optical requirements of traffic signals which are discussed in brief here

1. Illumination of lenses

The indication should be clearly visible from a distance of at least 400 metre under normal

atmospheric conditions

2. the intensity and distribution of light

IS 7537 -1974 specifies a minimum value of luminous intensity of 400 cd on geometrical

axis for red and green light on normal roads and 800 cd

It further stipulates that 10° below geometric axis these values are 200 cd and 375 cd

respectively on normal roads and high speed roads.

For amber signals it specifies values not less than twice the values mentioned above.

It has to be noted here that these values are for incandescent lamps and 85 % of these values

are accepted as the required value for LED traffic signals in other standards.

The minimum values for luminance on geometric axis for green arrow and red and green

pedestrian signals on geometric axis and 10º below geometric axis are 3500 cd/m2 and 2500

cd/m2 respectively.

3. Cone of vision

As per IRC 93-1985 primary signal should have a cone of vision of 30 degree on both sides of

optical axis and secondary signal should have 33.5 degree.

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2.2 Comparison of various standards for LED traffic signals

LED standards for traffic signals are varying in different countries, different specifications

dominate in USA, Japan,Europe etc. The differences are based largely on required visibility or

luminous intensity. A comparison of standards for LED traffic signals are reproduced in

Table 3.

TABLE 1 COMPARISON OF TRAFFIC SIGNAL REQUIREMENTS

ITE: Vehicle Traffic Control Signal Heads April 1985

ITE: VTCSH Part 2: LED Vehicle Traffic Signal Modules June 1998

Draft European Standard: Traffic Control Equipment - Signal Heads January 1998

Japanese Standard April 1986

CIE(Commission Internationale d’Eclairage): Suggestions from Light Signals for Traffic Control 1980

CIE: Review of the Official Recommendations for the Colors of Signal Lights 1994

Colour boundaries: Red

0.998-x<=y y<=0.308

0.998-x<=y y<=0.308

y=0.290 red y=0.980-x purple y=0.320 yellow

0.835-0.774x<=y y<=0.335

y=0.290 red y=0.980-x purple y=0.320 yellow

y=0.300 y=0.290 y=0.980-x

Colour boundaries: Yellow

0.411<=y<=0.452 0.995-x<=y

0.411<=y<=0.452 0.995-x<=y

y=0.387 red y=0.980-x white y=0.727x+0.054 green

0.932-0.918x<=y 0.036+0.611x<=y y<=0.109+0.65x

y=0.382 red y=0.790-0.667x white y=x-0.120 green

y=x-0.151 y=x-0.206 y=0.980-x

Color boundaries: Green

0.506-0.519<=y 0.150+1.068x<=y y<=0.730-x

0.506-0.519<=y 0.150+1.068x<=y y<=0.730-x[2]

y=0.726-0.726x yellow x=0.625y-0.041 white y=0.400 blue

x<=0.214 0.214<=y y<=0.499-0.474x

y=0.726-0.726x yellow x=0.625y white y=0.390-0.171x blue

y=0.726-0.726x x=0.625y-0.041 y=0.500-0.500x

Luminous intensity (cd):

Min=157 (d=200 mm) Min=399

Min=133, Max=800 (d=200 mm)

PL1: Min=100, Max1=400,

Min=240[5] Min=200, urban and daytime 50<=intensity

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Red (in the reference axis)

(d=300 mm)[1]

Min=339, Max=800 (d=300 mm)[3]

Max2=1100[4] PL2: Min=200, Max1=800, Max2=2000 PL3: Min=400, Max1=1000, Max2=2500

<=100, nighttime[6]

Luminous intensity (cd): Yellow (in the reference axis)

Min=726 (d=200 mm) Min=1848 (d=300 mm)[1]

Min=617, Max=3700 (d=200 mm) Min=1571, Max=3700 (d=300 mm)[3]

same as Red above

Min=240[5] N/A

Luminous intensity (cd): Green (in the reference axis)

Min=314 (d=200 mm) Min=798 (d=300 mm)[1]

Min=267, Max=1600 (d=200 mm) Min=678, Max=1600 (d=300 mm)[3]

same as Red above

Min=240[5] N/A

Uniformity

Intensity at each of 44 test points shall not be lower than 80% of required values. No more than 8 test points having values less than 90% of required values are allowed.

Min:Max>=1:10 (type E,W,M) Min:Max>=1:15 (type N)[7]

Min:Max>=1:5

Size 200 mm, 300 mm

200 mm, 300 mm

200 mm, 300 mm

250 mm, 300 mm

200 mm, 300 mm

Temperature

-40 to 74 C 0-100% humidity

-40 to 74 C Class A: -15 to 60 C Class B: -25 to 55 C Class C: -40 to 40 C

-20 to 60 C 40-90% humidity

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Notes

[1] The intensity value is the required value at the point where horizontal and vertical angles are 2.5 degrees from the reference axis. d indicates the diameter of the signal head. [2] The measured chromaticity coordinates of LED signal modules shall be between 500 and 650 nm. [3] The required intensity value of an LED signal is 85% of that of a corresponding incandescent signal. [4] Values are the required values in the reference axis. PL1, 2 and 3 indicate Performance Levels 1, 2 and 3. For the maximum intensity, Max1 is for Class 1 and Max2 is for Class 2. [5] Values are the required values in the reference axis. [6] Values are the required values in the reference axis. The nighttime condition excludes urban areas with bright surroundings and high-speed rural roads. [7] Type E: extra wide beam signal; Type W: wide beam signal; Type M: medium wide beam signal; Type N: narrow beam signal. Source http://www.lrc.rpi.edu/programs/lightingTransformation/led/LEDTrafficSignalComparison.asp

It can be seen that the Indian standards stipulate a luminous intensity of 400 cd for red, 800 cd

for amber and 400 cd for green light on normal roads (for incandescent lamps), ITE standards

need a minimum luminous intensities of 339 cd, 1571 cd and 678 cd for red amber and green

respectively without mentioning the type of the road.

3.Data Collection

Traffic in the city of Surat is growing at a fast pace due to its divergent and flourishing business

activities like textiles, chemicals and dyes, diamond cutting etc. The traffic here is mixed in

composition; a higher percentage is comprised by motorized two wheelers and three wheelers. A

typical junction in Surat is shown in Figure 1.

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Data were collected for various intersections where the retrofitting with LED was done. Data

related to monthly power consumption and maintenance expenses were collected from Surat

Municipal Corporation.

The list of intersections and junction wise details of the retrofitting are shown in Table 2 and

typical views of LED aspects are shown in Figure 2.

Figure 1 A typical junction in Surat.

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Junction Name

On cantilever height

On normal height

Sl. No.

Red Amber Green Red Amber Green

Pedes-trian Red

Pedes trian green

Total Aspects

1 Suryapur gate 6 6 10 22 2 Moti cinema 6 6 12 8 8 40 3 Bhagal 3 3 9 7 7 14 8 8 59 4 Chowk bazar 8 8 24 5 5 50 5 Athwa gate 6 6 12 24 6 Circuit house 2 2 4 6 6 13 6 6 45 7 Ambika niketan 2 2 4 6 6 12 9 9 50 8 Ram chowk 6 6 8 20 9 Elbee cinema 2 2 3 14 14 20 12 12 79 10 R.T.O 2 2 4 11 11 14 10 10 64 11 Majura gate 8 8 16 8 8 16 64 12 Timaliyad 12 12 24 14 14 76 13 Navsari bazaar 8 8 23 4 4 47 14 Kadiwala 3 3 9 14 14 26 14 14 97 15 Udhana darwaja 5 5 14 15 15 25 13 13 105 16 Kinnery cinema 3 3 6 8 8 10 9 9 56 17 Rushabh tower 2 2 6 14 14 28 15 15 96 18 Tarwadi 2 2 4 11 11 17 10 10 67 19 Ramnagar 2 2 6 8 8 24 10 10 70 20 Bhulka bhavan 2 2 4 7 7 11 10 10 53 21 Udipi 2 2 4 12 12 18 6 6 62 22 Daksheshwar 2 2 4 6 6 12 6 6 44 23 Dindoli 2 2 2 6 24 Sahara darwaja 3 3 6 10 10 18 10 10 70 25 Holiday inn jn. 2 2 4 10 10 22 8 8 66 Blinker aspects 123 123 47 47 107 221 344 415 187 187 1555

TABLE 2 LIST OF JUNCTIONS AND DETAILS OF

RETROFITTING

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Figure 2 Views of LED signal faces in Surat.

4. Evaluation of LED retrofit traffic signals

4.1 Cost savings

268 red signal faces, 391 amber signal faces and 522 green signal faces were replaced with

LED signals. In addition to this Pedestrian signal faces of 187 numbers each of red and green

were also retrofitted with LED signals. Considering

60 % , 35% and 5 % as the usage time of red , green and amber signal faces respectively ,

annual savings were calculated as shown in Table 4. Initially, the incandescent lamps were

having wattage of 100 each and the same was reduced to 10 for red and amber, 4 for green and

3 for pedestrian green and pedestrian red.

TABLE 3 ENERGY SAVINGS PER YEAR

Signal faces. Number

Wattage (Incandescent)

Wattage LED

Initial wattage (kwhr.)

After LED installation. (kwhr.)

Savings/yr (kwhr.)

Red 268 100 10 127166 12717 114449 Amber 391 100 10 7136 714 6422 Green 522 100 4 66686 2667 64018 Pedestrian Red 187 100 3 92144 2764 89380 Pedestrian Green 187 100 3 23889 717 23173 Blinkers 123 100 10 53874 5387 48487 Total 370895 24966 345929

Figure 3 shows the possible savings for different signal faces as per the variation of unit cost of

electricity for 25 junctions.

10

0

500000

1000000

1500000

2000000

2500000

1 2 3 4 5Cost of electricity (Rs/kwhr.)

Annu

al s

avin

gs in

Rs.

Red Amber Green Pedestrian red Pedestrian green Blinkers Total

Figure 3 Annual savings for 25 junctions.

4.2 Possible savings

Possible savings were calculated on the basis of the details available from the study in Surat. It

was found that 17 % of signal faces are red, 23 % Amber, 31% green, 11 % each pedestrian red

and pedestrian green and 7 % blinkers. These figures were used for estimating the annual savings

for different number of intersections. Possible savings with an electricity charge of Rs 3/kw.hr.

for different number of intersections are shown in Figure 3

11

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

50 100 150 200 250 300 350 400 450 500 550 600

Number of junctions

Annu

al s

avin

gs

Red Amber Green Pedestrian red Pedestrian green Blinkers Total

Figure 4 Possible savings for signalised different intersection groups at Rs 3/kwhr

It can be seen from figure 3 that there can be a savings of Rs. 9.5 millions, at an electricity

rate of Rs 3 /kwhr, for a city having 500 signalised intersections if retrofitting with LED is

done

4.3 Evaluation of retrofitting signals with LED.

An evaluation of LED signals was done by extrapolating the actual power savings accrued for one

month due to the operation of LED signals. It was found that the retrofitting with LED has

resulted in 88 % savings in power consumption and 51 % savings in maintenance costs as shown

in Table 5. The retrofitting programme has an overall Internal Rate of Return (IRR) of 14 percent

for an analysis period of 7 years, substantiating the investment done by the Municipal Corporation.

It has to be noted that the economic IRR will be higher than this value. Sensitivity analysis was

done considering the two scenarios of 10 % increase in costs and 10 % reduction in benefits. It

was found that IRR with 10 % increase in cost is 9.55 %. IRR with 10 % reduction in benefits

was found to be 8.55%. The payback period was found to be 3.31 years.

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In addition to these, there are intangible benefits like benefits accrued from the non disruption of

traffic due to 100 % utilization of the system during the warranty period, reduction in accidents ,

savings in insurance sums etc. Also it has to be noted that with the research and development in

the field of LED , the price of LEDs are going further down in the coming years , which will

improve the economical viability of retrofitting with LEDs.

TABLE 4 ACTUAL COST SAVINGS

Parameters Unit

With Led

Source

With

Incandescent

Bulbs

Savings

In Rs

%

Savings

Energy Expenses

Energy cost per Month Rs/Month

8,940 74,582

65,642

Energy cost Per Year Rs/Year

107,280 894,984

787,704 88

Maintenance Expenses

Maintenance cost per Month Rs/Month

33,000 67,235

34,235

Maintenance cost per Year Rs/Year

396,000 806,820

410,820 51

Total Expense Rs/Year

5,03,280

17,01,804

Net Savings Rs/Year

11,98,524 70

Payback Analysis

Total Initial Retrofit LED Investment

39,63,492

Payback Period Years

3.31

Life of LED Signal Years

7

Total Savings over the life of LED Rs 83,89,668

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4.4 Further use of retrofit LED in signals

Certain other details like the life span of LED signals need to be thoroughly evaluated as the

retrofitting with LED for traffic signals in India is in its initial stages. Data need to be collected in

the coming years, related to the performance of LED signals in the higher ambient temperature

prevalent in India. Various combinations of usage like use of LED aspects for red signal only etc

need to be analysed further. It is expected that use of LED retrofits are going to increase globally

as an energy efficient measure, which can also result in reasonable economical returns.

5. Conclusion

Over the past few years the use of LED retrofitting in traffic signals is growing phenomenally due

to its energy efficiency and durability. By taking into account technology explosion taking place in

the development of LED, it is expected that their efficiency will double in every two years and due

to this the number of LED in a signal can be brought down without affecting the intensity of light

output. Standards for LED signal heads are varying depending on the country. There is a need for

uniformity in the standards for LED signals, especially for colour, luminous intensity, luminous

intensity distribution.

The investment for retrofitting LED in traffic signals in Surat is estimated to have an IRR of 14 %

compared to the use of incandescent bulbs for an analysis period of 7 years. This is a conservative

value without considering many in tangible benefits and with the reduction in prices of LED in the

coming years the returns from retrofitting with LED will increase in future. It was found that the

power savings due to LED is 88 % and the savings in maintenance cost is 51 %. It is estimated that

in a city having 500 intersections approximately Rs.9.5 millions can be saved per annum, at a rate

of Rs. 3/ kw. hr. of electricity, by completely retrofitting signals with LED aspects. As an energy

efficient measure, it is suggested that the use of LED retrofit in traffic signals need to be

implemented in other cities also. At the same time, proper methods need to be ensured to

understand the performance of LED retrofitted signals on its optical performance and longevity in

the tropical climate prevalent in India.

References.

1. Burton, Roy (2003), Traffic Technology International Annual review 2003, pp 22-23.

2. IRC: 93-1985, Guide lines on design and installation of road traffic signals-. (1985). The

Indian Roads Congress, New Delhi.

3. IS 7537-1974 Indian standard specification for road traffic signals- Bureau of Indian

Standards

4. http://www.lrc.rpi.edu/programs/lightingTransformation/led/LEDTrafficSignalComparison.asp