I read on wikipedia:
Chaiyaphum is 337 road kilometres northeast of Bangkok.
What's the translation of “road kilometres" in French?
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The expression km de route does exist in French and Google finds many occurences but Chaiyaphum est à 337 km de route au nord-est de Bangkok is not something I would expect to hear from a native French speaker. What would be more common is: Il y a 337 km de route pour aller de Bangkok à Chaiyaphum but it is difficult to place northeast in this sentence.
Here is what I can suggest:
Chaiyaphum se trouve au nord-est de Bangkok, à 337 km par la route.
This is close to what I found here:
La distance entre Bangkok et Chaiyaphum est de 282 km. La distance par la route est de 337.5 km.
“kilomètres par la route”, as opposed to “kilomètres à vol d’oiseau” (“as the crow flies”)
https://www.google.com/search?q=%22kilom%C3%A8tres+par+la+route%22 does return a few results (but not that many).