In the early 1990`s the first real bike path was constructed in Rome, along the embankment of the Tiber from Ponte Milvio to the GRA (*) to the north between Castel Giubileo and Labaro, and from Ponte della Magliana to the GRA to the south at the bridge of Mezzocammino.
The bike path initially was defined along its entire length by a wooden barrier, but that began to fall apart within a few years until finally it was completely removed. The surface is paved and painted red, according to a convention (red = reserved for pedestrians and cyclists) that has become quite widespread, at least in Europe.
You can start from the piazzale at Ponte Milvio, which marks the beginning of Viale di Tor di Quinto; a gentle stepped ramp leads up to the bike path which here is at the top of the river embankment; after a few hundred meters one is directed down to cross under Ponte Flaminio; immediately after you go up again to get back on the bike path and continue along the Tiber; at each point where the bike route passes under a bridge one must temporarily leave and then reenter the bike path through a constricted barrier.
In the first section one has a beautiful view of the hippodrome at Tor di Quinto which you can travel around completely; to the right is the sports complex of Acqua Acetosa; then one goes under Via Olimpica and arrives in the vicinity of the Roma Nord train station (via Vitorchiano); here you cross a bridge, which has been closed for a year with a barricade, probably due to structural problems, but with no indication that repairs are imminent: a poignant reminder of the extent of degradation and neglect in which the bike path has fallen in recent years; along the next section one follows the curves of the Tiber around a large sewage treatment plant encountering odors that are not too pleasant; one continues with decidedly more pleasant views around the area of Grottarossa near the new studios of RAI [Radiotelevisione Italiana]; finally the bike path simply ends with a gate just below the bridge that carries the GRA over the Tiber.
Underneath the bridge that carries the GRA over the Tiber, a bike path had been constructed, since 2008, that would allow bikers to cross the Tiber; in 2008 I had occasion to follow this path (after crossing a few rickety barriers ...) and I found the bike path was accessible and in excellent condition. And yet at this time (December 2009) the path is still closed to cyclists and this time with a gate secured by a heavy lock; peering through the gate, the bike path appears perfectly usable, so that one can not understand the reason for this lockout; put this together with the closing of the bridge near Via Vitorchiano, and one gets the feeling that there is a lack of caring by the current Capitoline [city hall] administration as regards bicycle paths.