erm, same happened when i went to a xtina concert one time, another time for a local festival in my little town. hah. plus there's always traffic on a friday. they just mentioned that it's a bit extra busy with the concert.
I live pretty next to the area where the show took place... When Rio, specially Barra da Tijuca, hosts big events, just like international shows, that's pretty common, so it's nothing really new and it had happened a thousand of times before...
HOWEVER, I can't underestimate Gaga's power. Congratulations!