Can “Diesel Multiple Units” meet Caltrain modernization needs?

The funding to electrify Caltrain was approved this past summer, with money from the High Speed Rail project, and other state and regional sources.  The High Speed Rail funding was granted because electrifying the Caltrain tracks is a pre-requisite to running High Speed trains on the Caltrain corridor.

However, the question is frequently raised at local meetings regarding whether it is possible that alternative technologies would provide the Caltrain corridor with most of the benefits of electrification for less money.   This would be relevant in the event that the High Speed Rail project was halted before Caltrain electrification was done.

At a meeting last year at Palo Alto’s Rail Committee, representatives of Caltrain and LTK consulting delivered a presentation about relative merits of “Electric Multiple Units (EMUs), the technology that Caltrain plans to use, and “Diesel Multiple Units.”

Caltrain’s current diesel trains use one locomotive per train set to draw unpowered coaches. The train set is heavy, and acceleration is proportional to train length.  This means that if Caltrain wants to stop at many stations, the local service is very slow.  To speed up the train, Caltrain needs to cut stops.  This was the tradeoff with the Baby Bullet schedule – faster end to end service, but less service to many stations. Using its current technology, Caltrain does not benefit very much from making trains longer to handle capacity, since longer trains will accelerate even more slowly.

By contrast, “Diesel Multiple Units” provide distributed traction – each train car has its own engine. These trains are of medium weight, and provide medium acceleration.  “Electric Multiple Units” also provide distributed traction.  These trains are lightweight and provide good acceleration.

This is the key slide that Caltrain used to make the argument for EMUs.  Because Caltrain has many stations fairly close together (average 2.1 mile spacing), the extra acceleration provided by the EMU provides a major benefit in allowing more stations to be served while maintaining the same or better trip times.   DMUs would not be able to provide as good a schedule.

Other transit lines where DMUs have been chosen have different characteristics – fewer stations, spaced further apart, and/or fewer train cars – so acceleration is less important to providing good service.

EMUs have other benefits, too. They emit much less pollution (particulates and greenhouse gases) and are much less expensive to run, since electricity is cheaper than diesel fuel.

Electrification and land use vision

Whether you agree that EMUs provide substantially better service for the Peninsula Corridor depends on your ideas about land use and transportation for the corridor.  Largely because of Caltrain’s presence for over a century, the corridor has a string of small, compact downtown areas.   Given concerns about sprawl, pollution, and greenhouse gas emissions, which has led to California to adopt statewide policies favoring more compact development near transit, and growing preferences among younger and older people to drive less, many cities along the corridor have transit-oriented development plans near the Caltrain line.   If you like the idea of multiple mid-sized, walkable downtown areas, connected with a frequent, BART-like schedule, then electrification provides the best results.

But if you prefer the greatest concentration of development in Downtown Palo Alto, downtown Mountain View, and Redwood City, and do not want transit-oriented development in areas with currently poor service, such as Brisbane Bayshore, Hayward Park, California Avenue, San Antonio, and Lawrence, then a service plan that visits more stations is less important. And if you believe that a peak hour commute service is best for the Peninsula, and there is little value in a transit schedule like BART, then a technology that provides lower cost of operation is less important.

Is Hybrid Diesel-Electric an option?

There are also questions asked about the possibility of using hybrid diesel electric technology.  However, current technology is not close to being able to run Caltrain, according to this report from the Caltrain-High Speed Rail Compatibility Blog. There are hybrid diesel/electric trains in use in Japan. They are used for lines whose cars seat about 45 passengers (compared to 100 for Caltrain) and travel at about 45mph max (compared to 79mph for Caltrain).  Their power output is less than a Chevy Tahoe hybrid’s.  This technology would not be able to serve the Peninsula Corridor.

Plan B if HSR implodes

Since High Speed Rail requires an electrified line, the DMU technology option would be relevant only in the event that the High Speed Rail project was halted before Caltrain electrification was done.   There are ongoing legal challenges to High Speed Rail, and the project has financial risks, so there are logical questions about whether Caltrain would have a Plan B in case High Speed Rail implodes. If that happens, and there is no other funding to electrify the line, Caltrain could be upgraded to DMUs for the cost of replacing the train set ($440 million for electric trains), and save the $785 million cost of electrification.

Meanwhile, the High Speed Rail project is moving forward, and the presentation makes a good argument that electrification is the strongest choice to modernize Caltrain with cost-effective, more frequent service.

The full presentation can be seen here: