United Signal AF900, fixed block CBTC) to increase the frequency of trains and reduce congestion. In October 2020, a new CASCO Tranavi (moving block CBTC, DTO) signaling system was overlaid on the existing signaling system on Line 2. The Metro line will be the first in the world to have two signal systems, the new primary one for day-to-day operations and the existing older one serving as a backup system during signal faults. Intervals of trains on Line 2 could be reduced to 90 seconds thanks to the new signal system with the backup system capable of maintaining two minute headways. For the new system, a total of 100 trains on Line 2 will have their onboard signal systems upgraded. As of 2020 upgrading work was finished on 31 trains (the new 02A05 series). Rolling stock When line 2 was opened to traffic, the AC02 train where not available. Therefore, some of the DC01 and AC01 series trains were borrowed from line 1. Former Rolling Stock When line 2 was first opened to traffic, the AC02 trains did not arrive, so some DC01 and AC01 trains were seconded from line 1. References Siemens Mobility projects Shanghai Metro lines Railway lines opened in 1999 1999 establishments in China Airport rail links in China