To make the order cheaper, buy in bulk. And that bulk includes an option for 120 more. My best guess is that either Houston or San Diego is going to be exercising those options with San Diego's cars reaching the end of their 25 year life and Houston embarking on the metro solutions plan. It might also be split up into smaller orders if cities that are running low based on this most recent ridership surge.
Siemens' news release about the contract lists an option for 180 more rail cars, though UTA General Manager John Inglish said the agency most likely won't use that many. It's common practice to secure more than needed at a good bulk price, he said, then offer the excess to another transit system that needs the cars.Looks like the Siemens plant in Sacramento is going to be working overtime. Glad that these vehicles are all being built here. Imagine the economic impact if every city was building new LRVs and transit networks. Jobs Jobs Jobs.
Update: a Railway Gazette Article states that the Siemens vehicles will be a bit shorter than the Charlotte and San Diego Cars in order to accommodate 4 car trains.