The Trail Ridge Road is not guaranteed to be open at any time of the year. A blizzard can close it without notice even at the height of summer. In 2001 during an August heat wave, it was closed by a blizzard when I got there. Some years later it was in a September when I was assured it would be open the next day for me to drive it. Less than two hours later it was closed due to a blizzard.
If you want to drive across the highest continuously paved road in the country, best call and check if it is open when you get to the area.... and even that is no guarantee, as I found out.
I did get to drive it a week later.
Lifey