Built by LORAM, this is a series of rail grinders made especially for lighter applications, such as transit systems like BART. The rail grinders can be customized to the size wanted by the buyer. This one looks to have three grind carts with four grinding stones each, plus a power car and a rear cab car. Here is a link to the manufacturer's website describing the product.
https://loram.com/maintenance-of-way/rail-maintenance/transit-r..ries/