Cars are blamed for most of the pollution in the city of 15 million people.
Last month, city officials announced plans to encourage residents to use public transportation.
But they also acknowledged that they might be losing the battle.
Olympic organisers, worried about the impact traffic and pollution might have on the Games, are drawing up plans to establish special Olympic traffic lanes and limit the number of vehicles allowed in the city.
A 10-km car trip across central Beijing can take an hour during rush hour, despite the city having highways up to 12 lanes wide.