Hire Car Travel from Como and Dropping Off in Split Croatia

You might find a company that will allow you to rent in Italy, drive through Austria and Slovenia, and drop in Croatia, but the additional fee for dropping in a different country will probably be very, very high. Have you tried the three major consolidators--AutoEurope, Kemwel and Gemut?

I feel like you are planning to move very fast through or near some very attractive destinations where you would benefit from spending more time. Just to give two examples, Bolzano--in addition to having a very pretty historic district and several good museums, including the one housing the Iceman--is the traditional jumping-off point for trips up into the Dolomites, where visitors are usually urged to spend multiple days. And Bled is very close to Ljubljana, a charming city worth more than a day of your time. If you try to travel through all of the places you list, even by car, you'll be giving them very short shrift; it would be more awkward by train. In addition, you might end up with three or four one-night hotel stays in a row. That tends to be really tiring, both mentally as well as physically.

Unfortunately, ground-transportation links between Italy and Slovenia/Croatia are not very convenient. You can check out some of them on Rome2Rio.com, but understand that the travel times, frequencies and costs displayed there are often unreliable. I think Rome2Rio is primarily useful for giving you hints about what modes of transportation might be possible and where you might need to switch from one to another.

When I'm interested in train schedules and don't yet need fare information, I like to use the Deutsche Bahn website.

Because of the messiness of the train/bus links, it is often suggested on this forum that travelers wishing to go from northern Italy to Ljubljana or vice versa consider a shuttle service like GoOpti. There is good rail service across northern Italy from Como or Bolzano to Venice and Trieste, where I think you could connect with a shuttle.

I'd also consider flying from Milan to Ljubljana (though there may not be any non-stops on that route) or Zagreb, which is also a worthwhile destination. Check skyscanner to see whether there's a convenient flight option. Bled is easily reached from Ljubljana by bus, and even a taxi might not be too expensive.

There is both rail and bus service between Ljubljana and Zagreb. You could pick up a Croatian rental car in Zagreb and drive by way of Plitvice Lakes National Park through Zadar to Split. I'm not aware of any direct bus service between Ljubljana and Plitvice. There are buses, at least in mid-summer, between Ljubljana and Rovinj in Croatian Istria, but that will take more time than simply heading to Zagreb and picking up a car there. I'm also not sure what the car-rental situation would be like in Rovinj; it's touristy but small.

For Plitvice, I highly recommend that you spend the night before your visit at a hotel in or near the park. Plitvice has become enormously popular and can get absolutely slammed with day-trippers. Although I hope it won't be as bad in May 2018 as it was for my visit in late August 2015, you really need to enter the park early in the morning to avoid a mob scene on the walkways. This is one of Europe's premier attractions, so be sure you can see it at its best.

You could try dropping the Italian car in Italy closer to the Slovenian border (e.g. Trieste or Goriza/Nova Goriza), taking a bus or shuttle on to Slovenia, and renting another car there. However, you'll have a similar problem returning a Slovenian car in Croatia (though probably a cheaper drop fee). You could try to get by without a car in Slovenia and take a bus/train on to Croatia (Zagreb, Rijeka, or Istria) and finally pick up your car there. Or rent three cars (Italy, Slovenia, Croatia) which could be a pain. I did find having a car in Slovenia very useful because of the little towns and great scenic drives I could enjoy. (E.g. drive between Bled and the town of Skofja Loka through the mountains via Kropa and Jamnik is very lovely.)

Another option: drop the car in Venice, ferry to Croatian Istria (e.g. Rovinj), pick up the Croatian car, and then head up to Slovenia, back down to Croatia and eventually Split. This would involve perhaps a bit more detouring than you might like, but it might simplify things a tad, and Rovinj is a lovely little town as well. Or you could just skip the detour to Slovenia, which would be a shame, but that would simplify things a lot.

But if you are in Slovenia, try not to skip Ljubljana, Slovenia - really lovely little city, one of my favorites.

One more idea, but it could mean skipping Bolzano. Fly from Milan to Zagreb - Croatia Airlines has 3 non-stop flights per week, other airlines fly more frequently with 1+ stops. Rent a car in Zagreb, first drive to Lake Bled (2-3 hours), then return to explore Croatia and drop the car off in Split. I rented a car in Lubljana and was able to drive it into Croatia and back, so the reverse might also be true. I've also had luck finding car rentals in Croatia with no drop-off fees. Another option to explore.

Frank, the drop fee is generally for short rentals or rentals dropped off in a different country. I too have done one-way rentals without drop fees but only if dropped in the same country.

You cannot universally say that there are no drop fees if dropped in the same country. I have paid fees dropping in the same country. Generally -- not always -- I find that where you drop it is the critical question. Drop it in a small, rural town where someone may have to come and get the car, you will pay a fee. Drop it in a major city - probably not. Drop fees, in country, have always been reasonable. Dropping in another country is expensive.

No, Frank #2, we can't say universally no one-way drop fees. But I can say that when I've rented twice in Croatia in major cities, with two different companies, there were no one-way drop fees for me. That's probably what the OP cares about.