Granite and concrete blocks are installed as part of Operational Projects as hardening in order to provide safety for pedestrians. Many granite blocks have been repurposed from bridge rehabilitation projects across the City. These blocks are a sustainable solution that integrates seamlessly into New York City's urban environment. NYC DOT also purchases new blocks when needed.
I recently read something about how Paris uses temporary measures before redesigning a road, selling initial changes to the public as an experiment. By not immediately going to a final design, people seem to be more accepting of the end result even if that result is exactly the same as the temporary fix was. Almost as if the drivers need some time to let go of 'their' street. Guess these kinds of blocks can easily be used to 'temporarily' change a street layout, by making a street/lane for cars inaccessible for cars.