2.Traffic Signals

An estimated 3 to 4.5 million traffic signals are presently operating in the U.S. (Hodapp, 1997; Suozzo, 1998). Each contains three 200- or 300-mm diameter signal heads, one each of red, yellow and green. Typically, each signal head contains an incandescent bulb of a wattage between 67 W and 150 W. The wattage required varies with the color: red signals require the highest wattage lamp; yellow and green signals require lower wattages. The energy demand of the average traffic signal is approximately 990 kWh/year. Thus, traffic signals use nearly 3 billion kWh/year in the U.S., of which California accounts for 310 million kWh/year and New York State accounts for 230 million kWh/year based on population estimates (Hoffman, 1990).

An increasing number of red traffic signal heads in the U.S. utilize light-emitting diode (LED) light sources. Red LED signal heads use only 10 W to 15 W, approximately 90% less than the 150 W incandescent heads they replace. Thus energy savings, as well as other perceived benefits such as the longer rated lives of solid-state LEDs (IESNA, 1993), have prompted many state and municipal transportation agencies to consider installing LED traffic signals.

Several barriers prevent more widespread use of LED traffic signals. There is a dearth of objective and accurate technical information about the performance of LED traffic signals in the field. Standard-setting bodies such as the Institute for Transportation Engineers (ITE) are presently revising decades-old and incandescent-specific performance standards. Researchers are voicing concerns about the visibility of LED signals, especially by color-deficient individuals. The first 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 replace existing traffic signals and heads is not a trivial matter for cash-strapped municipalities.

TABLE OF CONTENTS

1. INTRODUCTION
2. TRAFFIC SIGNALS
3. CODES AND SPECIFICATIONS
4. ENERGY
5. COST
6. VISIBILITY
7. OPERATION: POWER AND ENVIRONMENT
8. MARKET ISSUES: SUPPLY AND DEMAND
9. OTHER APPLICATIONS
10. PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS
11. REFERENCES