Santa Rosa to Larkspur is 41 miles. That would be about an hour or so via light rail with a maximum speed of 55 mph and stops, so something a little faster might be in order. Rather than a light rail vehicle, something off the shelf like a Siemens Desiro (used in San Diego County and many European countries), might be more appropriate. If the trains stay on the NWP ROW, there will be no need for interurban style street running requiring something that can turn like an LRV. Desiros are available as DMUs or EMUs, and as 2 to 4 car sets.

Remember that an NWP passenger system would not just be taking people to the ferry at Larkspur to connect to SF, although that would be part of the market. There would be people using it for Santa Rose to Petaluma or Novoto to San Raphael trips. The SF commuter business would be a big part of it, but not the only part.

The downside of using Desiros, or light rail cars, for that matter, would be that freight and passenger service would have to be separated by time or track, but designing and building a US crashworthy DMU might not be worth it. If the line is electrified, perhaps SMART could add onto a SEPTA, NJ Transit or MTA order for cars that would be FRA compliant.