The good thing is that the snow plows do a great job keeping most of the major arteries relatively snow free. Eisenhower tunnel on I-70 will definately be open. The only thing to consider is if the nearby Loveland Pass is closed (because of snow conditions) they meter traffic through the tunnel for hazardous cargo trucks (they are normally routed over Loveland) at the top of each hour for 15 minutes. Berthoud Pass to Winter Park is good and same for Kenosha Pass (going from Denver to Fairplay/South Park. Independence Pass (out of Aspen) and Trailridge Road (in RMNP) will be closed by mid-september (usually).

If you want a good drive, take Hwy 285 over Kenosha Pass to Fairplay and connect with Hwy 9 to Breckenridge. Then take I-70 back to Denver. Obviously, if you were doing this trip in Oct, you would see some beautiful aspen trees turning.