EMU v. DMU
There has been a lot of focus in recent days on the technology preference for the various rail lines in the FasTracks corridors, specifically electric multiple units (EMU) v. diesel multiple units (DMU). The special attention arises from a need, in certain corridors, to make a final technology decision prior to commencing the process of soliciting potential public-private partnership (PPP) arrangements. Staff tells us it is critical to make a single technology decision in order to get the most realistic perspective on the potential cost savings associated with a PPP deal.
For those who aren’t familiar with the PPP mechanism, these arrangements entail bids by private entities to perform certain elements of transit corridor development. In certain instances, a private entity will bid to design and build a transit system, such as what occurred with the Southwest Corridor. We also have experience with private contractors who operate and maintain transit lines, just as they do with some of our existing bus routes. For FasTracks, RTD is investigating all of these options, and more, including a PPP package that entails all of the above elements, plus financing for the entire project. Without getting too detailed, the premise is that private entities are willing to engage in these PPP deals because they can secure cost savings, either through beneficial financing structures or construction and operations tools that are not always available to public entities.
Initially, staff indicated it would be necessary for the RTD Board to make the rail technology determinations at the July 24 meeting in order to move the PPP investigation forward. They argue that this is not really a final decision. The technology decision would still be subject to further public input, analysis, and decision making through the environmental assessment process. Still, it would drive a lot assumptions regarding preferences. Now, however, staff seems to be reconsidering the precise nature of the technology decision, if any, the RTD Board will need to make a our next meeting.
Regardless, the rail technology decision does loom. As a consequence, I have been hearing strong positions from proponents of both the EMU and DMU technologies, each offering compelling arguments. Significantly, the most recent staff analysis indicates that it would cost about an extra $110 million to run the power lines from Denver for the Northwest Rail line. Current predictions of the operations and maintenance costs appear to be about $2 million less for EMU in this corrdior ($19 million v. $21 million). Aside from cost, though, there are various environmental, noise, and asthetic trade-offs that need to be assessed. We also need to consider the potential future technology advances we can expect in both EMU and DMU systems and what power generation alternatives are on the horizon.
In reaching my own decision on the commuter rail technology for the Northwest Rail line, I will weigh all of the above factors. I also want to hear much more public discussion and input on this matter. For this reason, I have asked RTD staff to initiate significant public dialogue on the technology question. For sure, it will be a challenge to make much progress on this front prior to the July 24 meeting, which argues for postponing the technology decision until we are further along in the environmental assessment process. For now, though, I ask you to please pass along your own analysis on this matter.
[Note: The FasTracks web site contains the current staff analysis of the cost trade-offs between EMU and DMU systems: http://www.rtd-fastracks.com/main_1.]
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john@johntayer.org
John,
As with selecting propulsion systems for buses, RTD has to be eminently practical because, bottom-line, transit service must be reliable, on-time and as fast as practicable to support the greatest potential ridership.
In the DMU vs. EMU discussion the key relevant factor is the relative accelleration/decelleration capability of each of the two propulsion systems. Why is this important? Maximizing ridership involves achieving a balance between reaching the maximum number of potential riders with stations convenient to their home and work locations while keeping the overall run time as low as possible. Because EMUs have more low-end torque, they are able to accelerate faster and therefore, are better able to serve more stops while keeping overall run times lower.
Having only two stops, Denver and Longmont, would provide the fastest end-to-end run time but that fastest time might not attract the maximum ridership because everyone in-between Longmont and Denver would be cut out or would have to travel to one end or the other to get on. The opposite extreme would be to have one stop every half mile of urbanized area – this might result in 40 or 50 stops; I don’t know what that would do to the overall run time but you get my point.
As I recall, seven stops were approved by the FasTracks vote: Longmont, Niwot, Boulder, Louisville, Broomfield, Westminster and Denver. I believe five more have been added since the vote. At the July 9 public hearing RTD said they were likely to drop the added five stops and return to the original, voter approved list due to a failure to anticipate materials inflation rates (even for just the first three years) in their original financing plan.
The consultants involved talk about “rapid” and “exploding” population and job growth in the corridor as a part of the “purpose and need” for the expanded rapid transit lines. Whether we end up starting this rail corridor with seven or twelve stops, we can assume that, over time, as population grows in the area, new stations will need to be added to serve newly developed areas – otherwise we will miss picking up their residents and employees as riders.
Please ask staff to calculate the time savings per stop for EMU over DMU. Then see how much difference that makes for an entire 82 mile run from Denver to Longmont and back with seven stops each way. Then calculate how much difference it makes with the currently planned twelve stops each way. Then run the calculation with 15 each way and 25 each way as potential future scenarios.
There are two considerations that follow – first, how much difference will there be in an individual commuter’s travel time between the DMU and EMU with each of the different number of stations? and second, how much (if at all) will the difference influence the number of vehicles that will be needed to maintain different headways between vehicles: 30-minutes, 15-minutes, 10-minutes, 5-minutes and 3-minutes.
This should give us a clear sense of how important a consideration this is in comparing the two technologies.
We need this basic information to be able to make a rational judgement as to the most practical propulsion technology, both for the start of service and for the future of the corridor.
David Cook