From the Capital Airport to the National Library, the driving distance is about 35 kilometers (you didn't say which terminal), and the time should be about 50 minutes to 1 hour (in Beijing, the speed of 35 kilometers/hour is good enough without extreme traffic jams during the day, but if there is no car at night, it won't take 40 minutes). According to the normal one-hour time, the taxi fare should be 10.

But the important thing is that the road conditions are difficult to say. If you give up taking a taxi in the morning and evening rush hours, even if money is not a problem, you can't afford to hurt time.

Rail transit is actually a good choice, and most road traffic will be blocked. Because there is no charge for the airport expressway to Beijing, traffic jams occur from time to time.

Give you the best route, including subway transfer and the shortest walking route.

Capital Airport-Dongzhimen: (Airport Express /25 yuan) If it is T2, the subway station is under the terminal building. Considering the waiting time, it should arrive within half an hour. If it's T3, the subway station is also connected to the terminal, but it's a little far. The airport express from T3 should go to T2 first, and then to Dongzhimen. Considering the waiting time, it should arrive within 40 minutes. Go to 10 minutes.

Dongzhimen-Xizhimen: (Line 2 /2 yuan) 15~20 minutes, Xizhimen goes down the stairs directly, which is the platform of Line 4, and then transfer for 2 minutes.

Xizhimen-National Library: (Line 4) 10 minutes or so.

The total time should be controlled at 1 hour for about 40 minutes, and it is no problem to save 20 minutes if the bus waits smoothly.