On August 29, 1962, the lower level of the George Washington Bridge was opened.

When it was opened in 1931, the George Washington Bridge was the longest suspension bridge in the world, nearly twice as long as the previous record holder, the Ambassador Bridge in Detroit. It was opened with one level for six lanes but two more lanes were created in 1946 on the original upper level. The bridge’s designer, Othmar Ammann, wisely planned for a lower level to be added at a future date. Ammann’s original design included four light rail lines on the lower level but today accommodates just car traffic. On August 29, 1962, the lower level (nicknamed “Martha” after Martha Washington) opened. Today, the George Washington bridge is the world’s only 14-lane suspension bridge and the busiest motor vehicle bridge in the world, carrying over 106,000,000 vehicles a year, an average of 290,000 vehicles per day or over 12,000 vehicles per hour.
Learn more about the George Washington Bridge’s story here: http://www.northjersey.com/cm/2.1593/news/then-1.486838
Or watch this video discussing the lower level:
https://youtu.be/_DBbqcHFk2o?t=26m20s