In Iowa.
https://cbs2iowa.com/amp/news/local/johnson-county-iowa-city-pop-up-metro-train-crandic-cedar-rapids
QuoteThe estimated startup cost of $5.7 million includes leasing battery-powered trains, remanufactured from London Underground cars, adding charging stations, and upgrading grade crossings.
Uses Lithium Iron batteries.
More details about the company Pop=up Metro:
https://www.trains.com/trn/news-reviews/news-wire/pop-up-metro-aims-to-provide-affordable-passenger-operation/
Seems like an interesting concept to provide train transit in lower population density areas.