Vehicle emissions are a serious problem in many developed and developing urban areas. The issue is particularly severe in some of the metropolitan areas of China, which prompted researchers from Shenzhen University and the Shenzhen Nanshan Urban Planning and Land Resource Research Center to undertake an investigation on the role that transit-planning apps might have on emission sources. Such apps are primarily appealing to travelers because they allow users to avoid congestion by adjusting their route, departure time, or even mode of transportation. This has the side-effect of potentially reducing overall levels of transportation-related emissions in an urban area, depending on the market penetration of the route planner.
The authors used the AnyLogic simulation platform to combine travelor-behavior, emissions, and traffic simulation models. It was noted that this approach and the specific tools used allowed for a more realistic analysis by aggregating a wide variety of agent motivations and allowing the model's agents to interact with the model environment and each other. The models focused on a representative urban road network containing an expressway, an urban road, and a signalized intersection.
The simulation only addressed en-route changes by travelers, highlighting the effect of trip planning apps to dynamically reroute paths. Thus, there was a range of behavior—such as delaying their trips or taking an alternate mode altogether—that was not addressed by the model, which could magnify its impact findings.
The analysis found that the availability of real-time traffic information caused fluctuations in the environment's overall average speed--as one route became congested, traffic slowed to the point that it was advantageous to re-route entirely; this in turn reduced volume on the first road, resetting the cycle.
The usage of route-planning apps reduced the agents' average simulated travel time by 19 percent. This directly resulted in a simultaneous net decrease of emissions. Overall, the traffic system's total energy consumption decreased by 30 percent, with the emissions volume of individual pollutants decreasing by 24 percent or more.
The analysis also examined the impact of varying penetration rates for the trip planner. It was found that a penetration rate of approximately 30 percent was sufficient to deliver significant reductions in emissions. This figure was also somewhat dependent on the proportion of users with a high tolerance threshold, who would be unlikely to change routes even when directed to by their app.
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