u/NullifyAndSecede gives the correct answer

I'd add that, the owners would likely decide to ban it if it became too costly or a problem; either customers who use the road service would be willing to pay more maybe in insurance and taking the risk (if there were more crashes that resulted from allowing it), to allow people to drive intoxicated, or if they would not the road owner might then end up banning "drunk" driving

There is a difference between choosing to take a stand for freedom regardless of costs on one's property (in which case, drunk driving might be seen as something that must be allowed, as otherwise this is taking away others' freedom) versus having the freedom to set whatever rules you think are best on your property, both of which are compatible with libertarianism (some people might argue the latter position is not, but then to prevent people from enforcing rules on their property they would have to likely use force to prevent them, which would not be libertarian)