Pamann
You say...
but i'm not sure what's worse in the mid-summer heat?
Assuming a flight during the hours of 0930-1630.
Unless the bus has air con, it would be extremely unpleasant. However, the windows/roof are effective UV filters, so given the choice (as a med resident, who is used to dealing with the threat of skin cancer on a daily basis), I'd be on the bus.
The cumulative effect of over exposing the skin to UV is serious and at this time of year the UV levels are very high, especially for those under 20.
So I have no doubt that holding on the steps ins the worse option, whereas holding on the bus is the less worse option.