It would very likely get standardized similar to OTL. Italy and the Netherlands will pick a side and stick to it.How would the direction of road traffic circulation work in this world? even though most countries in the world already adopt the right side as the dominant road traffic side, some countries such as Austria, Spain, Portugal and Sweden still traveled on the left side, while in Italy and Holland the traffic side depended on which region you were in, which led to very strange situations where you had to switch sides of the street while driving constantly.
If the entirety of Austria-Hungary stays on the left side it could influence other parts of Eastern Europe to adopt left-side driving, but it is unlikely.
Sweden is surrounded by right-side driving countries, so it will likely make the switch as in OTL (though even in OTL it was quite late to do so).
Spain and Portugal will only keep left-side driving if both of them keep it. Any change from one means the other has no reason to keep left side except for being a nuisance.