Culoz english summary
On Monday 24 July 2006, at about 6:30 p.m., the works train 818 729 was running from the station at Culoz (its base) towards the track replacement worksite of Moirans-Grenoble. During the acceleration of the train, as it was passing through the passenger station at Culoz, the "working group" was derailed. This "working group" is the unit that removes old sleepers, lays new sleepers and levels the ballast, which is supported on the track by a deballasting axle.
The deballasting axle, after the first derailment at pk 101.747 of the Culoz - Aix-les-Bains line, jumped several times on either side of the track 1, whilst the working group broke up, after having lost the locking pin on the right hand side of the support arm of the deballasting axle. Although the derailment was observed by railway employees, the driver of the train could not be alerted, since this train was not equipped with a track to train radio. The working group collided with the lower and side clearances. At pk 103.222, at the origin of the bridge over the Rhone, whilst the front of the works train was well engaged, the out of clearance mass of the working group hit the deck of the first span of the bridge ; this span left its supports and collapsed. A certain number of parts of train P21/95 fell into the Rhone, including the deballasting axle.
One person was slightly injured, belonging to a contractor working close to the construction site of a new bridge to replace the present one.
The consequences were serious : the deck of the bridge of the track 1 was destroyed, the active part of specialised train P21/95 was destroyed. Traffic was disrupted for two days on both lines 1 and 2 between Culoz and Aix-les-Bains. Traffic was then restored on line 2, while that on line was 1 was only restored one year and 24 days later when the new bridge was commissioned.
Neither the traction conditions nor the railway infrastructure, which did not require immediate corrective measures, were the cause.
The immediate direct cause of the derailment was the weight transfer from the left wheel of the deballasting axle in presence of a left transition curve leaving a bend, which was probably the result of the combination of three factors :
a probable asymmetry of the distribution of weights of the working group of the train ;
greater torsional stiffness of the unit (working group and suspension of the deballasting axle) than originally ;
alternating weight transfers between the left and right hand wheels of the deballasting axle due to transversal shake of link supporting the working group.
A fourth factor was discarded (influence of an abnormal configuration of the lifting system of the working group) since we were not able to perform all the tests involving it.
The conditions for the certification of train P21/95, which included a complex suspended element, were insufficient to provide sufficient details as to the dynamic behaviour of the train.
The consequences of the derailment were aggravated by the absence of a track to train radio link.
A insufficient security as to the preparation of the routing of the train was revealed by the loss of the locking pin of the right arm working group (probably due to the insufficient engagement of the pin, absence of secure locking of the pin by split pin) ; furthermore, it would appear that it is necessary to reinforce the traceability of exchanges between the operators responsible for the movement of the works train.
The review of the conditions of this accident resulted in recommendations concerning the inspection of works trains before line running (coherence of the checks and role of operators).
In so far as track-to-train communications are concerned, a recommendation was made in favour of equipping such works trains with a track to train radio link.
Finally, we recommended, for future complex track maintenance vehicles, checking their ability to negotiate curve transitions and apply the complete protocol for dynamic testing on line for vehicles using new technologies.