Best Option For Reducing On-Campus Private Car-Based CO2 Emissions: Reducing VKT Or Congestion?



Reducing carbon footprint, especially from private cars, is an inevitable goal of sustainable transportation programs. Middle East Technical University (METU) in Ankara, Turkey, has a fairly large campus, for which carbon emissions are estimated to guide development of sustainable campus transportation demand management (TDM) policies. Focus is on reducing private car usage and increasing non-motorized and shared ride modes in a network. On the other hand, vehicle emissions with today’s engine technology are mostly governed by two major factors: Vehicle-km-travelled (VKT) and congestion, which slows down traffic and forces inefficiency in the engine performance. From engineering perspective, in order to evaluate real emission reduction potential of TDM scenarios, it is important to quantify its impact on these two factors and how much, which is the main focus of this study. For numerical examples, METU campus private car travel demand was used to calculate the VKT and speed levels for campus links by performing a network assignment in PTV-VISUM. The daily assignment was carried in three parts, as a morning and an evening peak, and an off-peak assignment, for a base case and 8 different scenarios.  Emission component due to congestion was determined separately, as a percentage. The results showed that METU campus emissions were primarily function of the VKT, thus, could not be reduced by congestion management alone. They could be reduced by 30% if commuters would shift to the metro service supported by a strong in-campus shuttle services.

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