This sort of race can't have an escort car because it's not going to be a single peloton. It'll be a whole bunch of cyclists riding solo or in groups of 2–20+ spread out all across the course as they go at their own pace. From the article it seems like they did have signs up warning drivers about it.

You're right that mixing a cycling race with cars is a bad idea. The road really should have just been closed. Unfortunately the amount that would have cost (a cost that is entirely up to how much the government decides to make it cost) would almost certainly have been prohibitive and never would have been possible. It needs to be made much more affordable.

But that doesn't really change the underlying behavioural problems. Education is never a solution to road safety; that's something we know very well. But to some extent, we know that drivers in this country have a behaviour issue. They get very aggressive. And in part, this is because they know they can be. Better education, along with stronger enforcement of rules against aggressive road behaviours (making a public show of that enforcement so word spreads about it), both in rural and urban locations, could help shift people's behaviour.