Caltrain has decided, amidst threats to cut weekend service entirely, to try a new approach to weekend service, by running express trains on the weekends. This service has been quite successful, helping considerably with a 21% increase in weekend ridership. The most probable explanation for this is quite simple: the old local service was slow, and the new express train is fast enough to be a plausible competitor to driving.
The two busiest stations outside San Francisco, on both weekdays and weekends, are Mountain View and Palo Alto, which are 36 and 30 miles away from San Francisco respectively. On weekends, it takes 77 minutes to get from Mountain View to San Francisco and 65 minutes to get from Palo Alto to San Francisco, for an average speed of 28 mph, which is no better than driving all the way on local streets. The new express train, on the other hand, does the trip in 49 minutes from Mountain View and 41 minutes from Palo Alto, for a speed of 44 mph, over 50% faster, and much closer to the speed of driving. If you manage to take the express train both ways, you save a whole hour on transportation. Even taking it in one direction and a local in the other potentially saves you half an hour, which turned out to be significant enough to increase ridership on the local trains.
This is a perfect example of the principles of normal speed rail in action. This service improvement required no new infrastructure at all, and not much extra spending on operations either. Yet it led to a significant improvement in the public perception of the service, which is reflected in the increased ridership. More ridership means more fare revenue, and in a virtuous circle, this provides more money for further service improvements. Hopefully Caltrain will learn the right lesson here, and increase the express service rather than cancelling weekend service altogether.