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    What should matter….doesn’t.

    November 10th, 2020

    Christopher Juniper
    Sustainability Economist


    It’s not rocket science, or even advanced transit science, that a key metric for transportation planning must be energy consumption per passenger/freight mile/km. This metric was rightfully suggested by the American Public Transit Assn. (APTA) 2009 “Transit Sustainability Practice Compendium.”

    If the community or nation is pursuing responsible climate chaos mitigation goals, this metric should have a twin that is also to be tightly managed: greenhouse gases per passenger/freight mile/km.

    Advanced transit systems, particularly Personal Rapid Transit, have far and away been the best option for these metrics. Yet try to find mention of them in public comparisons of travel modes. PRT is inappropriately omitted from the 2020 comparison chart of “Average Per-Passenger Fuel Economy by Travel Mode” produced by the US government’s Oak Ridge National Lab (link: None of the nine travel modes compared achieve more than 60 passenger miles per gasoline gallon equivalent (GGE). PRT could achieve 10X that maximum of 60. The worst performer: the new category called “demand response” at about 8 GGE.

    In other words, PRT systems at 200-800 GGE might achieve 100 times more energy efficiency than the money-losing, traffic-clogging “demand response” via low-paid auto driver systems created in the past decade (e.g. Uber or Lyft and their competitors). (Ultra reports 0.55 MJ per passenger mile for their Heathrow Airport system – equivalent to 0.0042 of a US gallon of gasoline or 238 passenger miles per gallon). Add solar panels to a PRT system, and only electric bikes at as much as 2000 passenger miles per gallon equivalent could compete.

    Likewise, PRT efficiencies are left out of the 2019 report by the European Environment Agency’s examination of sustainable transportation options titled “The first and last mile – the key to sustainable urban transport” (link: To their credit, they cite a 2017 lifecycle energy study (aka “well to wheel”) of CO2 emissions per passenger km of various modes in mid-size cities; well-to-wheel is the proper scope for managing climate chaos emissions since it takes energy to make and distribute energy, and we must manage for the least carbon emissions on a lifecycle basis. I’ve little doubt that PRT systems would have blown away all the 24 options of mode and fuel type examined.

    Sadly, comparisons of energy- or greenhouse-gases per unit of travel are hard to find. You can’t find one at APTA’s website. Nor the US Department of Energy or Department of Transportation. Apparently, what should matter….doesn’t.

    Its time for energy- and carbon emissions per unit of travel to take their rightful prominent place in information used by transportation planners and stakeholders. PRT makers and advocates – get moving!