How was the traffic scene filmed in the movie "Deep Impact"?

Question

In the film Deep Impact there is a scene where they show people evacuating major cities with long highways full of traffic. How was this scene created?

Answer 1

It was a new, unopened freeway, a mile long, filled with extras and their cars

The video explains a lot, but here are some interesting points:

• There were 2100 extras, in 1870 cars
• The extras brought their own clothing and props for their cars
• 116 cars were positioned every 15 minutes
• Many trucks contained food and drinks for the extras, as it was very hot that day
• Motor-homes were used by medics for anyone who felt faint
• Porta-loos were available every 1/8th of a mile
• Extras were recruited from local high-schools, and most were from Manassas
• An AM frequency was set up so that production could speak to the extras in their cars, using 1 walkie-talkie
• The entire scene was shot in 2 days
• No digital effects were used, apart from the comet

All from the following video:

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In anticipation of the question being split in two, I haven't addressed the spaceship question.