Calculating Scope 3 Emissions: One University’s Experience

September 23rd, 2013 by

Today’s post is by guest author Mary Whitney, University Sustainability Coordinator for Chatham University in Pittsburgh, PA. It was originally offered as a response to an inquiry on GRNSCH-L, a mailing list for college and university sustainability professionals, about how to compile data for Scope 3 emissions for faculty and staff commuting distances and frequency. You can contact Mary at MWhitney At

Accounting for Scope 3 requires a lot of figuring out what are your institutional  “indicators” that can give you a sound figure, even if it is imperfect. I always try to build in assumptions that would result in over-estimating carbon burden.

Over the last 5 years I’ve refined our commuting report and would be glad to share what we’ve developed. I still have to figure out how to account for Prius vs. Hummer issues yet though, so I’d be glad of advice on that!

When we’ve compared it to surveys, it is MORE reliable. We used to have to set up the survey, then all the reminders trying to get enough responses, etc. It was a real pain and took too much time, and it wasn’t even very accurate. Then we switched to having people put in their miles when they filled out the parking permit form, but it was wildly inaccurate – people were  just guessing.

Here’s what we have worked out since:

In order to park a car on campus you have to have a permit, and so we get a list of all permit holders from the transportation office. I have the make/model and the zipcode for each person. I correlate that with a report from HR that tells me if they’re faculty or staff, 12-month or 9-month, full or part time, and another from the registrar with students full or part time.

We then assume that full time is every day, 5 days a week. This is often NOT the case, but this way we won’t undercount trips. Part-time is considered to be 3 days a week, although again, it is often less. This assumes you’re here for a MWF schedule, even though many people are only doing T/TH. I can’t tell, but again, the assumption is that it’s more trips, not less. Faculty and students are counted for 36 weeks, staff work 49.

In cases where someone is part-time but attends every day, I would undercount, but so far I haven’t found many. It would be technically possible, I suppose, to cross-tab that with more registrar data, but that would be too burdensome, and I’ve made the decision not to do that. I figure that that possibility will be evened out by the person that is counted as full-time but does one marathon day of classes, 9-9pm. So afar I’ve found one of each of those extremes, so it seems a fair way to calculate.

Then I use a site that lets me set a radius from a zipcode. I saved a list of all zipcodes in various radii from the campus. We do every mile up to 25 miles, then jump to 30, then up to 50. I calculated them at

We tested the zipcode radius with many people’s real mileage, and it was surprisingly (and happily) very close!  As a way to get a good number without putting a mileage recorder on their car, it works well. We always include the summer campers, using registration data from the camp. I assume that kids living over 50 miles are actually staying with Grandma nearby, calculated at 5 miles away, and we assume that anyone living less than 1/2 mile is driving, although in reality most of the people that live that close walk to camp each day, as we discovered! Again, overestimating so we don’t underestimate.

Then I have a spreadsheet calculate the whole mess. For example, Zipcode 11111 is 6 miles away, Jane Doe lives in 11111 , works full-time as staff on a 12-month contract. 6×2 for each day, x5 days a week, x 49 weeks = 2940 miles per year. Believe it or not, it is actually simple once you get the basic spreadsheet set up. The zipcode distances auto-populate, and so does a code for FT, PT, etc.

I do a similar thing with students and faculty who do not have parking permits, with the assumption that they are taking the bus, unless they are on the bike commuter list that get the tax credit.

If someone is getting dropped off by car and never has a permit, I cannot account for that, but they are at least captured somewhat in the bus calculations. There are also people who I KNOW walk to campus every day, but I calculate them as at least bus commuters, figuring it helps even out and reduce undercounting carbon impact. Not perfect, but everyone gets counted somewhere a little.


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