Carbon Dioxide Emissions Decrease from the Onroad Sector During COVID-19 in the City of Portland, OR

Abstract:

On March 23, 2020 the Governor of Oregon's “Stay Home, Save Lives” executive order went into effect, ordering travel restrictions and closing nonessential businesses. It has been well recorded that this effort reduced onroad traffic by almost half. Then, on June 19, 2020 the city let restaurants, gyms, and barbers open with limited capacity. Even with relaxed restrictions, traffic in late July is still down 20 % from a baseline in June, 2019. This created a natural experiment for testing the impact of reduced traffic on CO2 emissions. The City plans to reduce CO₂ emissions by 80 percent by the year 2050 relative to 1990 emissions, in part by increasing the trips taken by walking from 7 to 10 %, and those by bike from 6 to 25 %, conditions similar to the lockdown period because 37 % of the regional carbon emission is from the transport sector. Here we show a drop in CO2 emissions related to the “Stay Home” order starting March 17, 2020 and relaxing in mid-June. The data are a record of automated traffic recorder activity. Before COVID, we found that restricted roads and highways carried an average of 84,000 vehicles/day, with noticeable rush hour peaks during the week and no such peaks at weekends. Weekend traffic was 78 % of the weekday traffic. We took counts in 15-minute bins at 27 sites for the first 6 months of 2020. The counts were averaged for each hour of the day. The average hourly traffic (AHT) were multiplied by the length of each segment in a GIS road map to find vehicle miles traveled (VMT). VMT were combined with local fuel formulations, fleet makeup, average speeds, and climate in the MOVES model to produce CO2 emission estimates. The estimates were compared with existing estimates from past years created by the same methodology. This work uses the natural experiment of COVID travel restrictions to estimate CO2 emissions reductions in a demonstration of a reproducible method of establishing such changes, which will support mitigation efforts.