It COULD be: A remote controlled boat full of mannequins, or a Ghost Ship.
If you are asking: I walk across a bridge and see a boat full of people yet there isn't a single person on the boat. How is this? The answer is, "All the people on the boat are married."
they were couples
Everyone on the boat was married
People walking down the street are known as pedestrians.
a bridge
200,000 crossed the bridge the day it was opened.
to let people across more
they visit the harbour bridge because people might want to climb it or drive or walk across it.
the science that says we are walking on the bridge to America 16,500 years ago
Thousands.
The people of London needed a new way to across the Thames. It took some people 45 minutes to get across the Thames. The Tower Bridge was built to help this problem in 1894.
Walked across a land bridge.