Avoiding ZTL Zone

You devise such a thing and you will be $tinking rich.

I have never seen mention of such a thing on this forum, which gets LOTS of discussion about ZTLs

The same problem exists for all restrictions that don't ban everybody all the time: time based restrictions, certain types of vehicles only, height, width and weight restrictions. It would be very complicated as you would have to program the GPS for what your car was and was not allowed.

I think you just have to be aware of road signs (which you should be anyway if you are driving), and expect ZTL's in all town centres.

It is not just Italy, traffic-free zones exist in all European countries.
The city I live in has a restricted area, with an exception underneath the sign ("Güterumschlag gestattet Mon-Sat 05:00-11:00" = Goods Deliveries allowed Mon-Sat 05:00 to 11:00). Click here for photo of sign. That detail would need to be pre-programmed into the GPS, and you would have to tell the GPS if you were a delivery. If you don't understand the text under the sign, just stay out.

We have successfully avoided ZTL's by programming the Parking Lot into the GPS instead of the city center or even hotel. We'd rather park, then scope out the situation on foot. Reading signs in a foreign language while in a moving vehicle is challenging at best, especially when there are more than a couple of signs.

Karen has provided you with a very sensible answer. We had a car when we stayed at an agriturismo in Tuscany and had no trouble avoiding ZTLs.

In the smaller towns and cities, including Siena, ZTLs are well marked. In hill towns, it is easy to just assume everything within the city walls is ZTL.

The only tricky place in Tuscany was Florence. Our hosts at our agriturismo recommended we take the bus. I was glad we did. The bus took us right into the heart of the city. I watched the traffic as we drove in and while I think I could have managed it, I'm glad I didn't have to.

We bought the Italy/Greece map card for our Garmin and it was very helpful, especially getting us from the Rome FCO airport to the Tuscan countryside. We also took a paper map. After a few days, we found the signage so good that we were traveling all around Tuscany without the need of help from the GPS.

My wife and I drove all around in Tuscany this past summer and had no problems at all. If you are paying attention to the traffic signs and the traffic you should not have much difficulty. I did go a bit in the wrong direction near the bus station in Viterbo...and got an odd look from another driver but no tickets.
To drive in Italy get an international license, use common sense, watch the signs, park where the parking is permitted and pay for it as necessary and let the locals do the speeding....

Would be nice but no ; or I have never heard of it.

Likely the software backend is made only by a few large corporations. The interest to them of serving such a unique niche as Italian ZTL customization is likely not there. The main apps are free ; they make money on advertising so hard to see them seeing any value in creating this.

The main issue is the GPS software cannot distinguish you without legal access from someone who does have access to the ZTL. Maybe a small developer could somehow develop an add-on app that could allow for the user to input they want to avoid ZTL zones.

Google Maps will send you the right way, provided you don’t enter as destination a location inside the ZTL. If you do, Google Maps, in the route description, will say: “This route has tolls”.
To see ZTL maps of all Italian cities, you can check here. Just enter the name of the region and city in the search boxes. I entered Florence in Tuscany as an example.
https://www.accessibilitacentristorici.it/ztl/Tuscany/florence.html

However it is important that you learn the “no vehicles allowed” sign. All ZTL areas will have that sign at the entry points, like here:
https://goo.gl/images/VGrsXq

Learn also all road signs in use in the International road sign system. Most are self explanatory, some less so.
https://en.m.wikipedia.org/wiki/Road_signs_in_Italy

Karen's idea (using a parking lot as the destination) sounds good, but it didn't work for me. When we approached Siena, our Garmin kept trying to have us take the shortest route, straight through the city, to the huge parking lot that must have been on the other side. I narrowly escaped ZTLs several times. I happened to get a legal street space, although 75 feet or more below the center of the city's elevation.

I don't feel confident that selecting "Shortest Time" instead of "Shortest Route" will make this any better. Of course, some towns don't have roads all around their exterior, but it looked to me like huge Siena does.

Here’s a website that should help you plan. ZTL Maps by city. I’ve noticed that Google Maps has them highlighted on their map of Florence.

The most important thing is to be aware as you near the center of any town.