How many people live in those areas/have to commute through it?
About 53,000 year round residents in the Lake Tahoe basin, but tourists make that number swell to 300,000 during peak periods. Also lots of traffic taking I-80 over the Sierras to and from Reno and Carson City.
Oh, and this: https://www.currentresults.com/Weather/Iowa/annual-snowfall.php
Less than 40" of snow per year in most of Iowa? Pikers.