Could a $9 toll change notorious traffic? New York became the first American city to find out.

A year ago, it began charging drivers for entering Manhattan’s busiest central neighborhoods during peak hours. Critics called it a cash grab, and President Donald Trump even vowed to kill it.

But a year in, congestion pricing has largely proved to be a success, according to new data released by the Metropolitan Transportation Authority — the agency that runs New York’s massive network of subways, buses, and commuter rails.

Since tolling began, 21 million fewer vehicles have entered the toll zone, an 11 percent drop from what was projected without it. And average vehicle speeds improved by 23 percent. That’s the difference between a one-hour crawl and a 45-minute commute.

But the real gains came at the entry points. At the Holland Tunnel, for example, morning rush hour speeds jumped from 10.8 to 16.2 miles per hour — a 51 percent improvement.

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