Basically, Traffic in Beijing is hell, Traffic jam is common during rush hour, but not limited, so be carefully preparing for any trip in town, spare some free time for flexible.
I would not talk too much about the historical problem of the traffic management design. just focus on some useful tips.
Overall, see the map, the main traffic network is based on ring road plus some expressway outside beijing. In town traffic is always concentrate on the ring road, from 2nd ring road to 6th road, you may wonder where is the 1st ring? It is not clear actually, to my estimated, the moat of the forbidden city is recognized as the first ring.
2nd ring is in orange
3rd ring is in green
4th ring is in purple
5th ring is in blue
6th ring is in grey (this road is not a free road)
Here is the tips
Morning rush hour traffic has the tendency of from outer suburb to the center of the beijing(2nd ring), also traffic of south to center of beijing is stronger than the north to the center of beijing. that means more people live in outer suburb of beijing and southern suburb. Vice versa for night rush hour.
Subway is the best choice for non rush hour trip. Just buy a YIKATONG prepaid card in any of the subway station.(Not all the station can handle the deposit refund, recommend to keep it for your next beijing trip or hand over to your friend, it’s not a lot of money)
For formal or business in town trip, you can call a cab from Hotel, but for more good experience, you can also call cab by Uber or DIDI(http://www.didichuxing.com/en/), DIDI is more popular. NO tips in China just like hotel room service, just follow the taximeter. Recommend to ask for the receipt for every trip, in case any emergency, such as dropping suitcase or phone in taxi.
Do NOT drive by yourself unless you live here for years. Drive license outside China including Hong kong and Macao is illegal here except you apply a provisional license in Airport for a short term visa. Traffic in Beijing even China is awful, especially outside 4 ring road, traffic regulation violation is very common and happened all the time, also pedestrian and electric rider often neglect of the traffic light. So driving for foreigner is a little bit dangerous here.