All of the listed improvements were indeed made by King Darius I to enhance the Persian Empire's administration and economy. However, if you are looking for the improvement that may not have been attributed to Darius specifically, it should be noted that while he did implement significant reforms, the specific adoption of uniform coinage, weights, and measures, along with the creation of a centralized government and improvements in road systems, were part of broader trends in the Persian Empire that included contributions from various leaders over time.
If your question is about identifying an improvement that is less directly associated with Darius compared to the others, it might be best to clarify the context or the source you are referring to. Generally, King Darius is credited with all of these advancements as part of his significant contributions to the empire. Therefore, if you are looking for a choice nearest to "EXCEPT," it could require further context as all these improvements were indeed associated with King Darius's reign.