Near Bologna—a town great for walking with less motorcycles than…

I’ve spent time in both Parma and Ravenna and found the traffic activity to be pretty calm. Both cities have nice pedestrian only areas. My personal favorite is Parma. In Ravenna stay off the white pavers in the center of the streets. They are reserved for bicycles.

I’d choose Ravenna
It has a lot of pedestrianized areas and is pretty quiet

But mostly I’d choose for thr fantastic mosaics
All within easy walking distance to each others (Except for the few that are well out if town)

2 nights would be enough
If you wanted you could even head to the coast from Ravenna for some beach time

The historical center of Siena is largely closed to motor vehicle traffic and many streets are strictly pedestrian only. In some streets within the restricted zone, motorcycles are permitted, along with residents with permit. Some areas outside those are not restricted at all and therefore will have traffic and Siena being an ancient city many of those streets are narrow and with narrow sidewalks. Many Italians use motorcycles and mopeds because those are subject to less traffic restrictions than cars. The same situation will be true for any other city in Italy, so it really depends on the streets you are on, not on the city, actually those cities you mentioned have more cars and motorcycles than Siena, so you need to choose areas within the ZTL (Limited Traffic Zone) of any town you want to be in.

In general each of the cities you say have a wide limited traffic area: more or less the historical center. In Emilia are even pretty common the porticoes, where only pedestrian are allowed, so you can walk quite safely in Bologna, Modena, Parma. A little less porticoes are in Ferrara and much few in Ravenna.
So if you choose an hotel near one of the main square you should be fine.
In Emilia instead be careful of bicycle: cyclists never stop!

Ferrara is very pedestrian friendly. There is a bike and pedestrian path from the train station to the main piazza, with a large traffic-free area extending in various directions.

As mentioned there are LOTS of bicyclists in some of these towns.... I've especially noted in Ferrara and Ravenna so regardless of lines or paths be careful. I never experienced the non-stop cars that you have indicated in Siena.

Except for the areas outside the ZTL, in the historical center of Siena, I’ve also never seen non-stop motorcycles and cars. That would not be possible inside the ZTL so I wonder what part of town the OP was referring to. There are however lots of non-stop horses on Piazza del Campo on some specific days of the year. Of those, you must certainly be careful.

We have been here for 3 days and it has been lots of motorcycles and taxis in the historic center. Lots. Today there were less maybe because it is Sunday. We have walked all over all day long and that is what we have seen.
Glad others have had a different experience.
Still loving the incredible architecture, incredible Duomo and its wonderful museum with the climb up to a fabulous view. Lots to see.

Ferrara centre is relaxing and mostly pedestrian. A few bikes though.
https://slowtravelitalyspain.blogspot.com/2023/12/ferrara-trip-report.html?m=1

We really liked Ferrara. Are you using your chosen town as a base for seeing Bologna as well? Ferrara is only 37 minutes away. Of the towns on your list, only Modena is closer (24 minutes).

We had trouble finding a hotel to like in Modena, so in the end we did not plan to go there. In Ferrara we found a lovely family-run hotel right across from the castle. I highly recommend it—-now one of our favorites in italy.

https://www.annunziata.it/en/

Actually I never saw that TripAdvisor rating until after we stayed there and I wrote my own review (gave them 5 stars). I read about the hotel and Ferrara in some travel article, and put Ferrara on our itinerary because of that.