Another statement in the TAMC fact sheet that is false is the claim of “Decreases Greenhouse Gas” with the nine roundabouts. The 9 roundabouts would actually increase Greenhouse gases! First, consider TAMC‘s own claim that the roundabouts will decrease the peak commute transit time by only five minutes (shown on TAMC’s own PowerPoint slide below) during those roughly 4 hours of peak commute each weekday. That reduction of only 5 minutes of idling emissions from a few thousand vehicles during peak commute needs to be compared to the other 20 hours each day of non-peak commute time in forcing each of the approximately 25,000 vehicles to decelerate to 15 miles an hour and then accelerate back up to 55 mph, 9 times over 8 miles.
Studies by Christopher Frey in the Department of Civil Engineering at North Carolina State University showed that vehicles emit 5 to 10 times more emissions during acceleration compared to idling. The study stated “Average emission during acceleration was found to be 5 times more than idling emission for HC and CO2 and 10 times more for NO and CO”. So do the math. Compare 5 minutes less of idling emissions from a few thousand cars during rush hour to acceleration emissions that are 5-10 times worse than idling from 25,000+ vehicles, 20 hours per day.
On-Road Measurement of Vehicle Tailpipe Emissions Using a Portable Instrument (tandfonline.com)
