A decade ago, when Dr. Pezhman Hourizadeh opened his optometry practice in Corona, Queens, his storefront faced a street that was only a block long and mainly served as a parking lot for vans from nearby moving companies. “Patients who came by in cars couldn’t come in,” he recalled.

The streetscape is different now. There is no street.

The city closed it as the first step in creating a plaza, a $5.4 million project that changed the look and feel of the block. Nowadays, the view from Dr. Hourizadeh’s waiting area is of people sitting at tables shaded by orange umbrellas.

What happened in Corona is urban alchemy — turning a short stretch of asphalt into a little oasis. It is alchemy that the city has performed over and over in the last 10 years, radically transforming some of the busiest corridors in New York City. The plaza outside Dr. Hourizadeh’s shop is the newest of 74 pedestrian plazas — slivers and slices here and there meant to reduce traffic congestion and pollution.