In order to ensure the safety on road, the traffic signals and streetlights play an important role in transportation. The traffic signals should light up all day and streetlights need to provide enough light at night, thus, they consume substantial energy.
The traffic signal and streetlight project conducted in Durham was intended to save electricity consumption at public area. The interview with the Traffic System Supervisor from the Department of Transportation illustrated the situation of current traffic signals and street lights in Durham. According to the supervisor, there are totally 403 signals in Durham with 95% of them using LEDs. During the last five years, a huge push initiated in 2008 and 2009 was targeting at upgrading LEDs (2-4 amps per signal), and the old signal lights (12-15 amps per signal) would be processed for recycling (Traffic System Supervisor, 2013). The data of energy usage and utility bills of these traffic signals need to be collected from North Carolina Department of Transportation (NCDOT), because among the whole 403 signals in Durham, NCDOT owns around 330-340 signals and the rest belong to the city government (Traffic System Supervisor, 2013). But the city government is in charge of maintaining all the signals in Durham. Therefore, the supervisor provided us some data of traffic signals after contacting with NCDOT.
There was a special LED streetlight project for the rail track underpass bridge in Durham. Originally, there were unmetered high pressure sodium lights, most likely 250W lamps. Duke Energy later cut the power to these lights as they were not metered, and for two years there were no lights in that section. With the LED streetlight project, the city installed 46 LED light units in this area and started metering the lights. It would be interesting to compare the LED lighting project to similar high pressure sodium lights for their efficiencies. However, the energy consumption data of these specific streetlights were not available to us (Traffic System Supervisor, 2013).
Table 10 Traffic Signals: Energy Consumption and CO2e Emission since FY 2006
|Year||Quantity (kWh)||Energy (MMBtu)||CO2e Emission (tons)|
Table 10 lists the energy consumption and CO2 equivalent emissions of all the traffic signals in Durham from FY 2006 to 2012 (Sustainability Manager, 2014a). Since the energy consumption (whether in kWh or MMBtu) and CO2e Emission, which was simply obtained by multiplying the energy with emission factor, follow the same trend, we just created a graph showing the changes of traffic signals in energy consumption. As can be seen from Figure 7, there was a significant decrease of energy consumption after upgrading most of the traffic signals with LEDs around 2009. The dashed line indicates that if the traffic signals in Durham continue the use of old light bulbs, the total energy consumption would increase steadily every year. In fact, the energy consumption dropped drastically from 1000 MMBtu level to around 700 MMBtu level due to the savings from LED lights. As for the slightly increasing consumption from FY 2011 to FY 2012, the reason is that Durham kept installing more traffic signals on road so that the total number of traffic signals increased resulting in more energy usage.