Maxis is working on a patch to solve this problem, as detailed by lead designer Stone Librande on the SimCity blog. The patch will essentially force cars to choose different routes as other routes become more clogged, which should help cities to run more smoothly. Furthermore, multiple service vehicles (fire trucks, etc) will no longer crowd around a given event, addressing one of the complaints from our review.
Finally, Librande noted that many SimCity features – recently disabled to lighten the server load – are "slowly" returning. Regional achievements have been reactivated on "a select number of servers," and leaderboards are now active on the Test server. Librande asks willing players to join the Test server in order to "expedite the timeframe in which [leaderboards are] brought back to the rest of our servers."