Metrics for tracking fleet progress

In the current edition of Automotive Fleet, I’ve suggested several environmental metrics for fleets to track. These are:

  • Total greenhouse gas emissions
  • Greenhouse gases per miles traveled
  • Greenhouse gases per vehicle
  • Greenhouse gases per ton of freight moved
  • Cost per metric ton of greenhouse gases reduced
  • Percentage of vehicles in the fleet that emit less than 15, 10 and 5 tons a year
  • Percentage of drivers that match or exceed EPA MPG combined rating

Given their multifaceted nature, fleets will best understand their progress by tracking a series of metrics. For example, a fleet’s total greenhouse gas emissions might be increasing because its vehicles are driving more miles, even if the vehicles themselves are becoming more efficient. Each of these data points is critical to effectively managing fleet greenhouse gas emissions.

Since it appeared last week, I’ve already heard from several fleet managers who are using these or similar metrics. I’ve also heard from some fleet managers who are struggling to collect comprehensive fleet emissions data.

If you are working with fleet environmental metrics, I like to hear from you too. What metrics are you using? What areas are most challenging to get good data?

To read more about the metrics I’ve put forward including the data need to track each, see the article on Automotive Fleet.


  • What about the coolant used in the air-conditioners in the cars? It may not be much, but any coolant that was replaced in the vehicles (happens if leaking and the unit gets 'recharged').

    I helped the University of Florida do this, and we had a decent-sized footprint for this

  • Alison,

    Good question. Vehicle air conditioners use HFC-134a, which is a very powerful greenhouse gas. As a greenhouse gas, it is actually 1,300 times more powerful than carbon dioxide. In the metrics above, refrigerants should be included as part of the greenhouse gas calculation, along with emissions of carbon dioxide, methane, and nitrous oxide. Fleets that are simply tracking carbon dioxide should note the metrics as such.

    Many fleets just track carbon dioxide, as it’s the easiest of the four vehicle gases to track. The only data that is needed is type and volume of fuel consumed. To most accurately account for methane and nitrous oxide, fleets need to track the miles traveled and pollution control technology of each unit. Refrigerants are the most difficult to track; especially for disbursed fleets, which lack the maintenance records to track a/c leakage. To help fleets account for the non-CO2 ghgs, EDF created a fleet emissions calculator ( that estimates these gases based on their relative abundance compared to co2 (on a co2E basis). The data underling the calculator is from the US EPA annual greenhouse gas inventory. The percentages for light-duty vehicles are:

    HFCs-134A 4.83%
    Methane 0.15%
    nitrous oxide 2.46%

    To fully account for vehicle HFC’s, fleets will need to know the capacity of each vehicle’s air conditioning system, its rate of leakage, any system recharges, and charge at time of disposal. For more information about tracking a/c emissions, the Minnesota Pollution Control Agency has data for model year 2009 and 2010 vehicles at The EPA's Climate Leaders Program has guidance too that recommends that fleets use default values of .5 kg of HFC-134a for the capacity of passenger sedans a/c systems and 1.5 kg for other vehicles. They also recommend a 20% annual leakage rate. EPA guidance is at:

  • Thanks for your informative and complicated reply.
    While the calculations you describe are likely very precise, it seems that the following might provide a more accurate and easily obtainable metric:
    Vendors are legally required to keep/provide very specific information on refrigerants, and I believe one of these metrics is weight sold. Thus, if the fleet manager regularly weighs the supply of refrigerants you could say that Weight supplied by vendor – current weight = total weight used to recharge air conditioners = approx. weight leaked by air conditioner since last serviced? If there is no central management of the fleet, wouldn't this information be easily obtained from the service reciept/log?

    Given how impossible the other method is, I see no reason that a simpler method couldn't do the trick, especially if the data needed is already kept by vendors.

  • Alison,

    The inventory method that you outline is definitely a good way to go when a fleet is centrally maintained. For dispersed fleets, it is more difficult than getting the information from a receipt or log. The barriers are that I see are:
    • most service receipts will only note the repaired made (i.e. A/C recharge); not the amount of materials used;
    • the technician probably doesn’t measure the exact amount of recharge put into any one vehicle; and
    • the fleet manager who gets a record of the report (and who would likely need to do the ghg calculation), likely will just see a broadly characterized repair on their service card account ( i.e. Joe’ Auto: $275), but won’t have the data or the data collection system to track actual hfcs used.

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