WWU TDM & Parking Dashboard /GHG Avoidance — How This Works
Rev. 2026-07-23 Concept mockup
How the Greenhouse Gas Calculation Works in This Dashboard
For the dashboard, non-drive trips mean avoided drive trips.
This is a big assumption. We want to call it out clearly.
Each transit boarding and each bike trip is treated as one person who chose not to drive alone. The dashboard multiplies that count by an assumed trip distance and an emissions factor, then subtracts back the emissions the bus itself produced. What's left is the estimated greenhouse gas avoided.
The calculation
One trip, traced both ways
Rider 1 boarding or bike-in
Counterfactual solo car trip assumed avoided
4 mi
Trip length × 0.404 kg/mi car factor (EPA)
if transit
Bus emits 0.25 kg/passenger-mi placeholder factor
net MT
Transit's avoided GHG added to total
if bike
net MT
Bike has no tailpipe to net back — full amount counted
Read this as: (assumed car emissions) minus (real mode's own emissions) = emissions avoided by that trip. Summed across every day in the academic year to date. Parking is not part of this calculation — it has no avoided-trip logic and is excluded entirely.
These emissions calculations we use are based on the factors below.
Car emission factor
Tailpipe CO2 per mile for a typical U.S. passenger vehicle. Applied to every avoided trip, transit or bike.
0.404 kg/mi EPA sourced
Trip length
Population-weighted blend of WWU employee (~7 mi) and student (~3 mi) one-way commute estimates, weighted ~5:1 by headcount. Cross-checked against WTA's own reported average bus trip length (~2.9 mi, all riders, all trip purposes).
4 mi Provisional
Bus emission factor
Generic mid-range U.S. transit bus estimate. WTA's actual fleet (mostly electric, hybrid, and renewable fuel as of April 2025) likely emits less than this per passenger-mile — pending WTA's own fuel and fleet data.
0.25 kg/pass-mi Placeholder
Mode-shift assumption
Each transit boarding and bike trip is assumed to displace exactly one solo car trip. Doesn't account for transfers, carpooling, walking, or trips that wouldn't have happened at all — the single biggest source of uncertainty in this estimate.
1 : 1 Assumption
What this number is not
Read the caveats before citing this
Not audited
This is a directional estimate, not a measured figure. Treat it as ±30% or wider — the mode-shift assumption above moves the number more than any emission factor does.
Combined population
Transit and parking data can't tell students and employees apart. The 4-mile trip length is a population-weighted blend, not a ridership-weighted one — the real split may differ.
Bike distance
Bike trips reuse the same 4-mile figure as transit. Bike commutes typically run shorter than the average commute distance, so this likely overstates bike's avoided distance.
Not official inventory
This is a TDM avoided-emissions estimate from named assumptions, not WWU's official campus GHG inventory. Scope and methodology have not been reconciled with official campus accounting.