Last year KiwiRail made the decision to replace the 16 current 30-year-old EF class electric freight trains currently in use on the North Island Main Trunk with the procurement of more DL Class Diesel Trains. These EF Class trains use the 25kvAC electrification between Te Rapa and Palmerston North that was built during the Think Big years. Their decision was based on the Better Business Case NIMT Performance Improvement Report which was heavily criticised at the time especially after leaked documents possibly showed major errors with the business case, all which was covered by GA here.

This post is not going discuss the merits of the different options of the business case, but instead, address the feasibility of a highly suggested solution to this problem which is to use dual-mode locomotives. Many people including myself asked well if KiwiRail wanted to:

Standardise the fleet;

Be environmentally friendly as possible;

Make sure of existing infrastructure;

Not have the expense of closing the electrification gap;

Then why not buy dual-mode locomotives which can use both 25kvAC traction as well as have a diesel engine. It made sense, it seemed like a real win-win option so why didn’t KiwiRail consider it? Instead of endlessly speculating I did some research which led me to believe it had something to do with the current axle load limits so I just plain asked them.

This is what they had to say to my OIA on the issue:

There are very few of these full dual mode diesel-electric locomotives in service worldwide as they require a large diesel engine, and a large electric transformer, in the same locomotive body to meet the power output requirements. This is considered an impractical proposition because of limitations on the space and weight able to be used on the New Zealand network. One example of a full dual mode diesel and electric locomotive is the Bombardier ALP-45DP. We have compared it to a DL locomotive. The DL has been used as the point of comparison because it has been designed to the maximum dimensions and weight allowable for New Zealand’s National Rail System. Bombardier ALP-45DP 21.8 metres long vs. DL 18.5m

Bombardier ALP-45DP 2.95 metres wide vs. DL is 2.7m

Bombardier ALP-45DP 4.4 metres high vs. DL 3.8m

Bombardier ALP-45DP 130.6 tonnes weight vs. DL 108t

Bombardier ALP-45DP Axle load 32.65 tonnes – Bo-Bo configuration vs. DL 18t – Co‑Co configuration

Note the large difference in the axle loads with the dual mode they referenced 32.65t with the DL at 18t. This is important because the current axle load limit on the national network is 18t which means dual mode locomotives are much too heavy to be used on the network.

Of course, you may ask what if they just put a really higher spec’d locomotive as a cover. Firstly it looks like they used the locomotive pictured in this stuff opinion article on the matter which is fair enough and secondly I managed to find a dual-mode locomotive that actually runs on 1067m gauge network like ours from South Africa to compare. However, it is still slightly over our axle load limit but not much 18.7t and it is too high at 4.1m. It also has less power than the DL’s, however, they were built in 1992-1993 so maybe an unfair comparison. If someone knows a dual-mode freight locomotive that can meet NZ Rail Specs please post in comments.

So maybe KiwiRail is correct dual-mode locomotives may not be the easy win-win solution after all.

However, I think the bigger issue here is with KiwiRail is communication. If they were a little bit more open with how they make decisions then they would face less criticism as people would understand. For example when questioned on the matter of dual-modes on RNZ’s Insight: Keeping NZ Rail on the Tracks instead of explaining the real fully understandable reason why; CEO Peter Reidy rubbished the idea by comparing it to wind powered trains. Of course, because people knew dual-modes have been around for awhile instead of addressing critics it just made it seem like KiwiRail hadn’t considered it.

But in my research on the matter, I think the really concerning thing is how poor shape our rail network is, 18t axle loads, for example, are very low compared to most countries where the standard seems to be around 25t, with many of those countries trying to increase towards 30t+. There are some lines built to 40t axle loads but are purpose built mining lines in places like Australia. Our 18t axle load limit really limits the amount of freight we can carry per wagon and thus in total. Our 1067mm gauge is not a limit either as Queensland which is also 1067mm has axle loads of 26t.

For those who may not know the axle loading of a rail network can be increased in one of a few ways

Heavier/Stronger rails (Often the rails can be recycled so replacing the rails on your most important lines can be then used to improve your minor lines) More ballast which counters to extra force from the increased weight. Stronger bridges, bridges are usually the main issue when it comes to axle load limits and your weakest point as you are only as strong as your weakest bridge.

Luckily KiwiRail seems to understand the importance of this when asked in the same OIA they said:

Making provision for future increases in axle load is a balancing act, in which we weigh the incremental cost of providing for a higher axle load against the economic cost of locking the network into a lower level of future capability by not increasing the axle-load weight. KiwiRail is taking a strategic long-term view when it renews long-life assets such as rail, sleepers and bridges. As an example of this, our Structures Code requires that all new bridges be built to 25-tonne-axle load capability (based on the low incremental cost of providing for that capability). Our infrastructure route strategy sets out that limits on most major routes will be raised to a 20-tonne maximum axle load in the medium term, and then increased to 22.5 tonnes in the long term.

Any smart future strategy for rail freight should have increasing axle loading limits are one of the highest priorities. The 22.5t KiwiRail wants should be considered a minimum with aims to at least move in line with Queensland 26t or higher. This will allow KiwiRail to carry much more freight per train dramatically increasing productivity, and who knows it just may mean we might be able to run some dual-mode freight locomotives.

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