Evaluation Of Led On Road Traffic Signals

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. 3

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 Equipmen t - Signal Heads January 1998

Japanese Standard April 1986

CIE(Commis sion International e d’Eclairage): Suggestions from Light Signals for Traffic Control 1980

CIE: Review of the Official Recommen dations for the Colors of Signal Lights 1994

Colour boundar ies: 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

0.8350.774x<=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 boundar ies: 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

0.9320.918x<=y 0.036+0.611 x<=y y<=0.109+0. 65x

y=0.382 red y=0.7900.667x white y=x-0.120 green

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

Color boundar ies: Green

0.5060.519<=y 0.150+1.06 8x<=y y<=0.730-x

0.5060.519<=y 0.150+1.06 8x<=y y<=0.730x[2]

y=0.7260.726x yellow x=0.625y0.041 white y=0.400 blue

x<=0.214 0.214<=y y<=0.4990.474x

y=0.7260.726x yellow x=0.625y white y=0.3900.171x blue

y=0.7260.726x x=0.625y0.041 y=0.5000.500x

Lumino us 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 referenc e axis)

(d=300 mm)[1]

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

Max2=110 0[4] PL2: Min=200, Max1=800 , Max2=200 0 PL3: Min=400, Max1=100 0, Max2=250 0

Lumino us intensity (cd): Yellow (in the referenc e 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

Lumino us intensity (cd): Green (in the referenc e 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

Uniform ity

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]

Size

200 mm, 300 mm

200 mm, 300 mm

200 mm, 300 mm

250 mm, 300 mm

Temper ature

-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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<=100, nighttime[6]

Min:Max>=1: 5

200 mm, 300 mm

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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Figure 1 A typical junction in Surat. 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.

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TABLE 2 LIST OF JUNCTIONS AND DETAILS OF RETROFITTING On normal height

On cantilever height Sl. No.

Junction Name Red Amber Green

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Suryapur gate Moti cinema Bhagal Chowk bazar Athwa gate Circuit house Ambika niketan Ram chowk Elbee cinema R.T.O Majura gate Timaliyad Navsari bazaar Kadiwala Udhana darwaja Kinnery cinema Rushabh tower Tarwadi Ramnagar Bhulka bhavan Udipi Daksheshwar Dindoli Sahara darwaja Holiday inn jn. Blinker aspects

3 5 3 2 2 2 2 2 2

3 5 3 2 2 2 2 2 2

9 14 6 6 4 6 4 4 4

3 2

3 2

6 4

Red 6 6 7 8 6 6 6 6 14 11 8 12 8 14 15 8 14 11 8 7 12 6 2 10 10

47

47

107

221

3

3

9

2 2

2 2

4 4

2 2 8

2 2 8

3 4 16

8

Amber 6 6 7 8 6 6 6 6 14 11 8 12 8 14 15 8 14 11 8 7 12 6 2 10 10 123 344

Green 10 12 14 24 12 13 12 8 20 14 16 24 23 26 25 10 28 17 24 11 18 12 2 18 22 415

Pedestrian Red

Pedes trian green

8 8 5

8 8 5

6 9

6 9

12 10

12 10

14 4 14 13 9 15 10 10 10 6 6

14 4 14 13 9 15 10 10 10 6 6

10 8

10 8

187

187

Total Aspects 22 40 59 50 24 45 50 20 79 64 64 76 47 97 105 56 96 67 70 53 62 44 6 70 66 123 1555

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 After LED Initial Signal installation. Savings/yr Wattage Wattage wattage faces. Number (Incandescent) LED (kwhr.) (kwhr.) (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.

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2500000

Annual savings in Rs.

2000000

1500000

1000000

500000

0 1

Red

Amber

2

Green

3 Cost of electricity (Rs/kwhr.) Pedestrian red

4

Pedestrian green

5

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

10

14000000

12000000

Annual savings

10000000

8000000

6000000

4000000

2000000

0 50

100

150

200

250

300

350

400

450

500

550

600

Number of junctions

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 With Led Incandescent

Savings

%

Source

In Rs

Savings

Bulbs

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

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

Net Savings

Rs/Year

11,98,524

70

88

Maintenance Expenses

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

12

17,01,804

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 13