How many velodromes are there in the US?

Could you elaborate on the current status of velodromes in the United States? Specifically, I'm interested in understanding the approximate number of these facilities that are currently operational within the country's borders. Are there any regions that have a higher concentration of velodromes? Additionally, has there been an increase or decrease in the number of velodromes in recent years? This information would help provide a comprehensive overview of the availability and popularity of cycling tracks for both competitive and recreational purposes in the United States.