"Both distances are the same."
Joke? If so, you can explain the flaw in this reasoning better than I am about to.
If not, the flaw is that, taking 'average' to mean 'mean', average speed is the sum of each
speed multiplied by the TIME spent at that speed, divided by total TIME. If instead we
performed the calculation using DISTANCE instead of TIME, the result would be not the mean
speed, but the 'mean square speed' divided by the average speed. An interesting number
perhaps, but not as widely used as mean speed on its own.
If you're talking about median or modal speed, of course, those can never be higher than
30mph unless you take a detour. But that's another matter...