July 6th Train from Venice to Rome

There will be fast trains running
Just the portion under construction will be served by replacement bus

https://community.ricksteves.com/travel-forum/italy/train-from-rome-to-venice-end-of-july-not-available

You shouldn’t be worried at all
Just be patient

It will work this way: high speed train from Venice to Florence Rifredi. You get down there, you switch to a shuttle bus doing a couple of miles within the city of Florence, to the Florence Campo di Marte station, where a matching train will be waiting. Of course changing to a bus will be an inconvenience especially if you are loaded with baggage, and when the thing was last done in January it got somewhat chaotic, in spite of having a lot of personnel guiding people and explaining. Alternatives? Not really. A long distance bus like Flixbus would be still much slower; an internal flight would again take a lot of time going to/from both airports. The best alternative could be reworking plans and traveling on a different day.

I tried to find information on the actual engineering works on Trenitalia, Viaggiatreno and RFI, and could not find it (and I looked at the Italian versions of the site). If you have pointers towards information I'd be interested...

Tuscany page: https://www.rfi.it/it/rete/i-nostri-progetti/I-nostri-progetti-regione-per-regione/toscana.html
Lazio: https://www.rfi.it/it/rete/i-nostri-progetti/I-nostri-progetti-regione-per-regione/lazio.html
Liguria: https://www.rfi.it/it/rete/i-nostri-progetti/I-nostri-progetti-regione-per-regione/liguria.html
... and so on for 17 more pages.
Thanks to the EU Trenitalia runs the trains whereas RFI owns and takes care of the tracks.

Viaggiatreno is just a site that provides live info about the trains running on the RFI network. Not very helpful as a live-updates tool in the "Apps Era" but at least the site is multilingual and you can get an idea of the railway network by zooming in. I love the scrolling text that reads: "500 trenitalia trains are running this second". Totally pointless!

That would be a pain. I’m not surprised if it will be a royal mess. Each train carries at least 400-500 pax who have to transfer to at least 10 shuttle buses. The distance between Rifredi and Campo di Marte is probably less than 4 miles, but with traffic it will be nearly 30 min. Just multiply by the dozens of trains passing though Florence every hour in both directions and I can just imagine the gridlock on the Viali or on via Trento and via Trieste, or through the bottleneck of Piazza della Libertà area. I used to live on Via dello Steccuto as a small kid, and I don’t even know where they can fit all those buses in tha t street. That segment through the two Florence station will take just as long as the train journey from Florence to Rome.

So they are rebuilding a bridge that spans all the tracks that lead in to Campo dir Marte. I wonder if they could not have waited with that till the Passante is built...

Well, maybe they are planning on running some trains via an alternative route, and are still working it out...
That is usually what it means when "temporarily unavailable" is shown on a train.

RFI has to do the bridge work this year as it is financed with Italian funds, but complementary to PNRR European funds, so the work must be over by the end of this year.

The Passante tunnel - a long overdue project - begins just under the bridge and the north bridge pillar interferes with the underground tunnel, so the bridge has to go before the Passante is completed. BTW, passante works once caused water and mud to overflow the north end of the bridge, so something had to be done.

Ponte al Pino spans over the tracks linking Campo di Marte to SMN, Campo di Marte to Rifredi, and also the local railway between Campo di Marte and Borgo San Lorenzo. So the only alternate itinerary left is the much longer Rome-Pisa-Firenze Rifredi.

This seems that it might be similar to our travel slated for later in the month of July. In a previous question I asked about this (where tickets aren't available for purchase yet) I was told that there will likely be tickets sold closer to the date that will include a bus transfer from one station in Florence to the other station that is beyond the train bridge work). That forum post reply stated to wait until the middle of June to purchase those tickets (for the last week of July). I take solace in that, but admit it makes me a bit nervous to wait that long as the other alternative, getting a plane ticket, will certainly go up in cost in that timeframe. I am thankful to the folks who provide this first hand information--so thank you to all who do!

I'm facing a similar situation on July 29 where we're trying to go from Rome to Venice. Do I just wait or should i book flights?

Wait, the warning on trenitalia.com reads "Travel solution temporarily not available".