The TMC is located on the 37th floor of the Municipal Tower. I was given a tour by Jason Cambridge, who is a pretty cool guy.
Video Wall. (Larger version)
The most striking thing as you walk in the door is the video wall. It's composed of eight rear-projection monitors, on which are displayed video feeds from around the city. On the lower-right side is a copy of WSDOT's realtime Seatle traffic flow map, along with a chat window connected to operators in WSDOT's cd TMC. On the bottom-right is a Novell mail client; the bottom-left has general notes to TMC operators.
The video wall is controlled by a PC with a bunch of video cards. Each live video window can be resized with the mouse.
The camera feeds are live. All cameras have pan-tilt-zoom mountings, controllable by the software. A snapshot from each camera is taken frequently and FTPed to the city website. Each camera has position presets, and a snapshot isn't taken unless that particular camera is pointing at one of a its of presets. This (generally) avoids taking pictures of things which might be troublesome.
The snapshots are not archived. If they were, the TMC would be flooded with subpoenas and wouldn't have time to manage traffic.
Mini-datacenter. (Larger version)
This is the mini datacenter that lives behind the video wall. Each traffic signal in the city is connected by a wire pair to a modem in here. The system architecture dates from the 1970s. They're slowly transitioning to a newer design where each signal controller is connected to an IP network.
I have more pictures of the datacenter, but I don't know if they're worthwhile. If you want to see them, email me and I'll do what I can to post them.