What I hadn't realised was that the couplers have to collapse, and in most trains are designed to do so sacrificially (i.e. to protect the body shells). Hence in this case the RAIB▸ identified that the failure of the couplers to collapse (shorten) was a primary cause of the derailment, and a design error. Exactly what should happen when the gap between the carriages has reduced to zero was not made clear (because it wasn't part of the accident). Presumably they should lock in some way, if only by being scrunched into each other.
I just wonder if the energy of the impact was below the give way point? There must be an engineering balance between being durable / reliable for every day duty and the point at which it needs to protect against impact.
Even at 15mph quite a bit of energy to redirect for a train that must be close on 300T for a 9 car hitting a stationary object
Indeed, design for crashworthiness is a complicated business - so I'm afraid you'll have to read the report! That has a lot on the subject, but is still a simplified version to support their enquiry, rather than a design guide.
And I can recommend more reading, too. Hitachi have published several articles on the
UK▸ A-trains, which mention crashworthiness:
Railway-vehicle Technologies for European RailwaysDevelopment and Maintenance of Class 395 High-speed Train for UK High Speed 1Development of Class 800/801 High-speed Rolling Stock for UK Intercity Express ProgrammeBetween them they have several pictures of the front end of the body shell and its "crush me" sections - which are surprisingly small: about the size of traditional buffers. I've added a few of those pictures below.
One point they make several times is this:
Many of the standards relating to collision, strength, fire resistance, noise, and similar were very different to those that apply in Japan.
For example, cultural factors in Europe have led to stringent collision safety rules to ensure the safety of crew, passengers, and others in the event of a collision. To comply, the front-end of the Class 395 and the vehicle-end structure of each car adopted crashworthy structures that satisfy TSI (Technical Specifications for Interoperability) and the UK?s RGS (Railway Group Standards). In the event of such an accident, the concept on which the design is based is that the crashworthy structures will crumple to absorb the crash energy and prevent the passenger and driver compartments from being crushed, thereby forming a survival space for the passengers and crew.
I can't imagine what cultural factors have led the Japanese (people, government, and railways) to think that doesn't matter.
