The passenger experience is very important to us, it's an overall package ranging from the human element of the train staff through to you getting a comfortable seat on a train which has suitable light, heat and air-conditioning. Somewhere in the mix is the comfort of the train, does it shake? does it rattle?
The Vomit Comet
Long standing rumours about the poor ride of the new Cork Dublin Express coaches emerged from within Iarnród Éireann in November 2005. While on the first day of service in May 2006, the Rail Users Ireland crew were most impressed with the ride and where assured that it would be made even better. Well in fact it got worse much worse so much so that passengers started contacting us complaining of feeling nauseous and suffering from vertigo, some even reported being thrown from their feet.
Rail Users Ireland discussed the ride issue on numerous occasions with various managers within Iarnród Éireann, all agreed that the ride was not right, few were willing to admit to the serious nature of the problems which led to the extensive program of modifications undertaken in late 2006. Despite these modifications the ride remains poor and is so bad that it is not unknown for trains to make unscheduled stops so the driver can inspect the train to ensure nothing is amiss, of course drivers actually have found broken bolts in the suspension so every funny noise is taken very seriously. Of course Iarnród Éireann claimed the problem was sorted.
However Iarnród Éireann have now tendered for assistance in carrying out ride comfort modifications following passenger feedback. While this work will be carried out under warranty and paid for by CAF the manufacturer. It should have been performed long ago as by Irish Rail's own admission "the vehicle ride is unacceptable and has never achieved the standard required".
The question remains is it the track or the train? The ride of the Mk4 train varies between coaches, the direction of travel and the position of the coach in the train. However in the years following the introduction of the Mk4 fleet many miles of new track has been laid, the Mk4 rides smoothly on this track without any of the vibration or swaying seen on the older track.
Time To Get Scientific
A comparison was needed, the older Mk3 coach was compared to the new Mk4 coach. The Mk3 coach has long been recognised as having an exceptionally smooth ride and is used as a reference in contract documents as the standard for a new train to meet.
We selected Dublin Thurles as the test section. We justified this as follows:
- It's a fast section of track and both Mk3 and Mk4 trains operate non stop.
- Journey times are fairly consistent which is essential for what we have planned.
- The Rail Users Ireland committee frequently travels the line and are familiar with the bumps.
- All trains run in hauled mode when leaving Dublin, so we could discount issues due to push pull operation, which are noticeable.
To ensure a level playing field we always travelled in coach C in the centre seats, which typically gives the smoothest ride, the laptop was positioned on the table, and we sat at a window seat facing Dublin. We travelled the line on both train types only two weeks apart ensuring the track condition was similar. As both trips took where within 2 minutes of each other in length it was considered the trains where travelling at a similar speed throughout the journey.
So the rail industry shell out €50,000 a go on autonomous under floor GPS/GSM kit we went with the economy solution, simple equipment and a human. The equipment consists of a 2 axis accelerometer attached to the back of a laptop screen connected via USB to the laptop.
Some custom written software logs the data to disk. Excel can then plot the graphs dynamically resulting in almost instant feedback. We record both the lateral, the side to side and the vertical, the up and down accelerations.
The main interest to passengers is the side to side motion as this makes it difficult to walk though the train, type on a laptop and indeed throws your tea or coffee around. The data we have collected shows that lateral acceleration is both stronger and several times more frequent in occurrence than up and down.
Ride quality has always been a very personal matter, so we need to determine thresholds. We ignore any all lateral acceleration less 0.1 m/s^2 as these are not generally noticeable. Indeed the vibration of a underfloor engine creates false triggers. So the rules are:
any lateral acceleration greater than 0.2 m/s^2 was considered undesirable
any lateral acceleration greater than 0.3 m/s^2 was considered unacceptable.
The CAF Cork Dublin Express/Mk4
These coaches were specially designed for Iarnród Éireann in 2003 by CAF with interiors by the Design Triangle Derby. Outwardly a standard UK 23m long coach but is slightly wider at 2.85m. They are 200km/h capable weighing in at 41-42 tons. Heavily computerised.
The suspension is typical European design used in many trains elsewhere, it assumes a high quality stiff track is provided, as is the case in Europe.
The BREL Mk3
Design concept dates from 1969 by British Rail primarily as evolution of Mk2f and chosen for the HST project. A 22.7m long 2.7m wide 200km/h capable coach weighing in at 34.5 tons with automatic doors. Remains the lightest 23m air conditioned 200km/h coach ever built. Special production run to suit CIE requirements with power doors and sundry electrical improvements in 1984. No computers.
The suspension was designed specifically for UK track, which similar to Ireland is not as heavy as that on mainland Europe.
The Cork Dublin Express Train, Mk4
The old train but still the smoothest, Mk3
It instantly clear from the graphs that the BREL Mk3 is the unquestioned winner, but how can a coach built in the mid 1980's based on a 1969 design beat a 21st century train with the benefit of fancy computers, 30 years of experience and technical advancement?
A key noticeable trait of the Mk4 is a side to side sway, its not terribly objectionable but shows a possible issue with the secondary suspension not being stiff enough, it could also be a issue with the wheel profiles which steer the train around corners, on straight sections the wheels may hunt around if the profile is wrong giving a side to side motion which can become increasingly violent as speed increases.
It has become clear that the Mk4 suspension was never designed to cope with Irish conditions, serious problems have been encountered with bolts working loose. The same bolts would on occasion snap while being retightened. As the train swayed from side to side bolts in the suspension occasionally were sliced in two. However following an extensive rebuild in 2006 these problems were resolved