It's a good idea to get one if you'll be driving in

Austria, Bosnia-Herzegovina, Croatia, Greece, Hungary, Italy, Poland, Romania, Slovenia, or Spain...

这是Rick Steves的讲法。https://www.ricksteves.com/travel-tips/transportation/rental-car-requirements

我的个人经验是大部分出租车公司都不问的，被警察叫停那就是按当地要求了。

不过有了这次的经历，我会一直备着了。