Revisiting Left-Turn Waiting Areas: Optimizing Left-Turn Signal Timing to Eliminate Twice Startup, Reduce Emissions, and Improve Traffic Efficiency

Reducing urban transportation carbon emissions is a fashionable task around the globe. Electric cars, fuel cell cars, hydrogen cars, restriction policies, etc. are all aimed at this goal. But they are all expensive to make them into reality. Transportation management can also provide some contribution to this, like optimizing operation rules such as Left-turn Waiting Area Twice Startup. From the stop line to the Left-turn Waiting Area (LWA), one vehicle will start twice with more emissions due to the engine’s inefficient operating range. We proposed an Accurate Left-turn One-time Startup Model (ALOSM) based on the LWA rule, which includes the intersection geometry parameters, traffic light timing schemes, vehicle start speeds, vehicle operation speeds, and fuel vehicle ratios. Make the Left-turn Vehicle (LV) waiting behind the stop line during the through vehicle light green. Calculate the left-turn green light adjustment duration and make the LV and the last through vehicle across at one moment. With real collected data in a symbolic intersection in Xi’an, China, the simulation result shows vehicle emission would be reduced by 13% and traffic efficiency would increase by 5% in this single intersection. The whole city of 5 million vehicles would reduce 2,087.88kg CO emission in one day due to estimation.