The Rocky Mountain Institute (RMI) debuted the SHIFT Calculator in October 2021: https://shift.rmi.org/
“The SHIFT Calculator provides new insight into the travel and environmental impacts of highway expansions. Created in partnership with NRDC, Transportation for America, and UC Davis, this tool uses highway lane mile data collected through the US Department of Transportation and enables users to estimate the amount of vehicle-miles traveled that a widening project will incur on a highway or arterial road. For the Austin example, the Calculator projects that TxDOT’s plans [for expanding I-35] would generate 255 million to 382 million additional vehicle miles traveled (VMT) per year—the emissions equivalent of adding approximately 32,500 passenger cars to roads or burning an additional 17 million gallons of gasoline per year.
Why does this happen? Through the heavily studied effect of “induced demand,” widening a highway only encourages nearby residents and drivers to use that highway even more. This is due to the real but short-term gains in time savings temporarily generated by highway expansions. But as research shows, these time savings are typically wiped out within 5–10 years, after which the highway returns to or surpasses its previous state of congestion.”
Read Community Impact’s coverage of the Calculator in the context of I-35 in Austin.