I hadn’t realised that the downtown tunnel would still run buses through it when it reopens. According to the tunnel’s website, most of the Metro routes that went through the tunnel will be put back into it when the retro-fit is finished sometime at or before September this year. The tunnel buses, which had been electric only though the tunnel, will become diesel-electric hybrids and go wireless with in it. How this will effect air-quality in the tunnel is not mentioned. Once the train finally starts running in 2009, the tunnel’s hours of operation will increase to 18-21 hours a day which will be pretty nice.
Update: The tunnel will be ventilated by fans that have been installed.