what does "the concrete ribbon"mean?
[After a hundred yards all the cars slowed to a crawl. The alternative I was mayhem: people had swarmed out on the concrete ribbon of the Gulf Freeway, where people never are. Even Valenti hadn't expected this, I and John Connally was dumfounded. Lady Bird, using her homely yardstick, took note of a wizened old man holding a hand-lettered "WELCOME KENNEDY"; a dozen uniformed Girl Scouts from "Troop 1381"; a little boy with a faded American flag, standing rigidly at attention. Mrs. Kennedy pointed excitedly—on Travis Street the spectators were packed ten and twelve deep, and behind them the traffic was backed up for miles. ]
1.what does "the concrete ribbon"mean?
2.what does "packed ten and twelve deep"mean?