BOB GARFIELD: We're back with On the Media. I'm Bob Garfield.

BROOKE GLADSTONE: And I'm Brooke Gladstone. This week a long-delayed and very expensive part of Boston's Big Dig just opened to the public. The new tunnel project moves miles of notoriously congested aboveground roadways underground. To try to make the journey a bit easier to navigate, the Massachusetts Turnpike Authority's Big Dig web site includes a virtual drive through the tunnels. The technology used to create this online map also helps engineers design the exit signs for what is being called "the most complicated tunnel geometry in the world." Susan Kaplan reports.

SUSAN KAPLAN: To give you an idea of just how complicated Boston's Central Artery Project is, imagine you're looking down at a table-size map of the tunnel. What you'd see would look a lot like a plate of spaghetti. To help drivers wind their way through this maze and to design the virtual Big Dig, the Massachusetts Turnpike Authority solicited help from the Human Performance Laboratory at the University of Massachusetts where inside an ordinary-looking trailer sits an unusual quarter of a million dollar high-tech driving simulator called-- an infinite reality machine.

DONALD FISHER: What the computer does is really a very fast dance between the driver and the picture on the screen. It projects at 60 hertz -- that is, 60 times a second -- a new view of the world.

SUSAN KAPLAN: Mechanical engineering professor Donald Fisher explains how the computer generates images onto three small movie-size screens that sit in front of a 1995 black Saturn. When the driver gets in the car, the computer projects a virtual roadway, and in a video-game-like fashion shows how the tunnel will appear.

DONALD FISHER: And that's one of the reasons that this was put on the web -- so that drivers who had never seen before what the signage was like in the Central Artery would have a chance to see it and hopefully not make the mistakes that would lead to incidents, crashes or other--problems in the, in the tunnel.

SUSAN KAPLAN: Fisher and his team of graduate students have clocked about 100,000 virtual miles on the test car. They use the information to get a handle on how drivers will react. Fisher says the best way to see how the tunnel design works is to put people behind the wheel. So-- I offered to give it a try. My assignment? To find the Cambridge Exit. [VIRTUALLY DRIVING] Starrow Drive --Exit 26. Okay, we're not getting off yet.

DONALD FISHER: You just missed your Cambridge Exit.

SUSAN KAPLAN: It didn't say Cambridge did it?!

DONALD FISHER: It did.

SUSAN KAPLAN: As it turned out, it took me more than a few attempts to get it right. [SEAT BELT SIGNAL PLAYS] [AHEMS] Just for the record, this is "Going to Cambridge --Take 4." [LAUGHS] [LAUGHTER] [VIRTUALLY DRIVING] Oh-- my goodness. Cambridge! I see Cambridge.

DONALD FISHER: Anything else?

SUSAN KAPLAN: I see north and I see Exit 26 in small numbers. Okay -- Exit 26. Now it says Exit 26 - Starrow Drive -- this is confusing! I'm not confused at the moment [LAUGHS] but as you know, it took quite a bit of-- took an effort.

SUSAN KAPLAN: Fisher assured me that I was not alone in my let's just say less-than-stellar performance. In fact, he thinks the Cambridge Exit illuminates one of the biggest design challenges.

DONALD FISHER: Here in the tunnels, the ceilings are 17 feet high. Trucks are 13 and a half feet high. Normally you sign two-lane exits with option-through lanes with signs who are 8 feet high. There is hardly 8 feet of height here in the tunnel, let alone 8 feet of height for a sign and a truck to pass through. There's only 3 feet--

SUSAN KAPLAN: In other words, there's not enough space in the tunnel for signs that are big enough for drivers to read! Massachusetts Turnpike Authority Chairman Matthew Amarillo acknowledges the complexity of the tunnels. He says that's exactly why the Big Dig's final hurdle will be to make sure drivers know how to get where they're going.

MATTHEW AMARILLO: One of the kind of efforts on the part of the Turnpike Authority and all of us in transportation is to provide information to motorists in real time so they can make trip plans accordingly, and because we are entering this world of tunnel-driving, it's going to require that we do provide that information. Helicopters and traffic reports are not going to be able to give you a report of what's happening underground. [SEATBELT UNFASTENED SIGNAL PLAYS]

SUSAN KAPLAN: Amarillo says state of the art roadways are merging with Internet technology to produce a new kind of super highway -- one that he says may depend heavily on the virtual world for its success. For On the Media, I'm Susan Kaplan. [MUSIC]