Security is being ramped up more intensely in recent weeks, with the Games to which terrorism has been identified as the biggest threat being just weeks away.
Hundreds of check posts have been set up on expressways, national highways and town or village roads that link Beijing with other provinces or cities as part of the "defence lines", a municipal Public Security Bureau spokesman said.
The patrol posts on the second line are stationed on the major suburban roads leading to the downtown area and the third line covers all major roads in the downtown districts, state-run Xinhua news agency said.
To prevent traffic jams caused by security checks, Beijing Public Police bureau has asked the check posts to increase the personnel and take "suspicious people or vehicles" off the road and hand them over to local police stations, it said.
Safety checks take time and congestion was "sometimes inevitable", the spokesman said.
Security in Beijing and co-host cities is in top gear as China says it faced terrorist threat "unsurpassed in Olympic history".
China on Sunday renewed its pledge to ramp up security for the Games that are is expected to see a large presence of world leaders at the opening ceremony.
Anti-terror drills have been held in Beijing and co-host cities Shanghai, Tianjin, Qinhuangdao, Shenyang and Qingdao and a drive covering subways and airports is underway.
China has claimed to have busted 12 terrorist cells of overseas-based outfits this year in Kashgar in the restive Muslim-populated Xinjiang region.
