Here in Rome it ain't so bad, it IS rather hot (36°C+ temperatures with 80+% humidity, in bumper to bumper traffic)
if you ride riverside the tall trees ensure some shade.
But if you happen to take the Ring Road (in Washington, DC they call it the Beltway) then you feel like you're stepping inside an open air oven !
The humidity drops, road temperature rises as much as 20°C to well beyond "acceptable"- even cruising at 60+mph you feel the HOT air around you.
Anyway, Barstow - Kingman isn't as bad as Kingman - Seligman via Peach Springs !
...But...
...they make such wonderful burritos in Peach Springs...