In "Fahrenheit 451" what is the quote from Clarisse where she is talking about people driving and they don't stop to look?

The very first time that Montag meets Clarisse, she mentions how people are so rushed these days that they don't even notice the little things.  She says, "I sometimes think drivers don't know what grass is, or flowers, because they never see them slowly...if you showed a driver a green blur, Oh yes! he'd say, that's grass!  A pink blur!  That's a rose garden.  White blurs are houses.  Brown blurs are cows."  She even talks about the 200-foot long billboards, there because "cars started rushing by so quickly they had to stretch the advertising out".  Later, the last time that Montag sees her, she says that for fun, kids her age "go out in the cars and race in the streets, trying to see how close you can get to lampposts, playing 'chicken' and 'knock hubcaps."

Both of these quotes emphasize the need for thrill, entertainment, and speed in their society, which they use as a violent sort of catharsis, drowning all thought and sorrow.  I hope that one of those quotes was the one you were looking for.  Good luck!