EuroBillTracker

Austria
* Bad Kleinkirchheim to Tarvisio (Trbiž) 38 km

Italy
* Tarvisio (Trbiž) from Bad Kleinkirchheim 38 km

It took me no more than 15 min to find some Austria-Italy hit shortest than 52 km (Wien to Bratislava). It's really easy now that we have hit-partner lists for every country, region and town.

Even shorter:

Austria
* Feld am See to Tarvisio 32 km

Italy
* Tarvisio from Feld am See 32 km

I believe there can't be shorter than this at the moment:

Austria
* Feistritz an der Drau to Tarvisio 22 km

Italy
* Tarvisio from Feistritz an der Drau 22 km

Sorry for the multiple posts.

Here are what I believe to be the current shortest hits in Portugal (apart from the one with Spain, which seems to be correct):

Portugal
* Santa Maria da Feira from Bordeaux 772 km
* Caldas da Rainha from أوناغة (Ounagha) 874 km

Here are the shortest hits I found for Austria (apart from the first 6 km hit with Germany, which is correct):

Austria
* Kittsee to Bratislava 9 km
* Pliberk to Ravne na Koroškem 13 km

Slovakia
* Bratislava from Kittsee 9 km

Slovenia
* Ravne na Koroškem from Pliberk 13 km

OK, I'll stop now. Only now I realized this topic wasn't updated in the past 3 years…

Nieuw-Lekkerland - Gruitrode 109 km

Roetgen - Diepenbeek 61 km

Breda to Wiekevorst (53km) now already 3 times!

My contribution: From Kerpen to La Calamine - 50 km

It won't get much shorter than this!

Quite impressive!
I'm still waiting for a hit between Baarle-Hertog and Baarle-Nassau