What is this a picture of?
UPDATE: Just about everyone guessed correctly that these are decomposing railway ties, but Frank was the first to properly guess that these are decomposing tramway ties, uncovered because of excavation work.
The city is littered with tramway rails that were merely paved over after the network was dismantled. Some are later exposed through potholes, others because of excavation work, and are slowly being removed. But much of the vast network still remains, just inches below the surface of the street.