Crowded Trevi Fountain
The Trevi Fountain is absolutely worth a visit if you're travelling to Rome, but you won't be alone. Steps down to the water edge mean that the fountain itself isn't particularly accessible, but it is easily viewed from standing a bit further back in the square.
Transport & Parking
I'm not sure if the area is meant to be pedestrianised but it definitely feels like it. I couldn't imagine many cars wanting to navigate through the crowds here. The streets leading to the fountain are narrow and winding like most of Rome's older districts.
In terms of viewing the fountain and hearing the roar of its water, access is okay. It's not easy to get up close enough to dip your hand in the water however, as steps lead the way down to the fountain's edge. The main difficulty is the crowds, but there's always somewhere to stand around the upper railings to get a good view of the landmark. The roads here are cobbled, but they aren't too rough at all.
I didn't see any public toilets, but the fountain is surrounded by cafes and restaurants which may have facilities.
There were some security guards around the fountain, but they don't really interact with people other than to occasionally manage the crowds.
Anything else you wish to tell us?
While a typical tourist trap, the Trevi was definitely one of the most impressive fountains we saw in Rome. Despite the crowds, it's still worth a visit.