EPA 'Beyond Tailpipe Emissions'. An Error Found ?

Discussion in 'Gen 3 Prius Main Forum' started by SageBrush, Oct 20, 2014.

  1. SageBrush

    SageBrush Senior Member

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    The EPA has a section on fueleconomy.gov called 'beyond tailpipe emissions' that purports to show the CO2 emissions per mile of the *EVs available. The PiP in San Diego, e.g., is rated as 200 grams CO2 per mile, of which 133 grams is from petrol and 67 grams from electricity. This presumes 29% of miles are electric. If 29% of the mile is electric, then 71% is petrol and therefore one mile of pure petrol would be 133/0.71 = 187 grams CO2 per mile.

    This is at odds with the page about the petrol Prius which discloses 179 grams CO2 per mile out of the tailpipe and 39 grams upstream, for a total of 218 grams CO2 per mile.

    Any ideas how to resolve the discrepancy ?


    EDIT: I got it.
    The upstream emissions, calculated as (total - tailpipe), includes petrol and electric upstream.

    So to figure out pure electric takes some fiddling ...
    Starting from the regular Prius, the 219 total CO2 grams per mile brakes down to 179 tailpipe and 39 upstream so 18% of total petrol emissions are upstream from petrol. This matches pretty well the numbers I have seen used before. One mile of petrol leads to 39 grams of upstream emissions, so 0.71 miles would produce 27 grams.

    The 0.29 miles of EV in a PiP is then (67-27) = 40 grams of CO2. Per mile then, 40/0.29 = 138 grams.
    And there you have it -- In San Diego by EPA, petrol use in a Prius produces about 58% more CO2 per mile than Prius EV miles.

    I think. Any corrections ?
     
  2. hybridbear

    hybridbear Member

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    Toyota ran the EPA tests separately for the PIP & the regular Prius. They likely got slightly different results which were reported to the EPA, but the results weren't different enough to change the MPG numbers on the window sticker.
     
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