PTC Ends at Tappan, Tunnel begins at Port Huron/16th St(As far as control points go)Saturnalia wrote:Distributed Power Units are not manned, they are radio-controlled from the lead locomotive. This is the distinction from the manned helper locomotives of yore. DPUs are generally intended to stay on for the entire run of the train from origin to destination, rather than just over a certain segment of the road as is typical with manned helpers.hoborich wrote:So, there is no crew or engineer on the DPUs?They dragged the DPU out at some point Monday afternoon, from what was posted on Facebook.
A few more notes on the discussion above:
As far as losing communication with the DPU, I'd imagine CN has installed repeater antennas inside the tunnel to handle DPU, EOT and PTC communications. Most tunnels of that sorta length get that treatment, and I'd imagine due to the sag in the tunnel it would be even more necessary.
It does sound like Canada will lead the investigation due to the point of derailment determined to be on the Canadian side of the border, NOT because the train hadn't made it 100% into the US yet.
As for not allowing DPUs in the tunnel due to the grade, that's kinda absurd. DPUs are usually added specifically to help longer trains tackle grades and curves. Running 12000' manifests in the tunnel would probably be more difficult without DPUs than with them.
The primary issue running long trains through the tunnel, and potential cause of the wreck, is the play in slack, whereas the train is stretched coming out of the tunnel but bunched up going in. Traditionally crews would probably have used the "stretch-braking" technique with a slight brake pipe reduction to keep the train all stretched out by slightly applying the brakes throughout the train. But with the DPU involved, they likely keep the DPU in dynamic braking until it reaches the bottom of the tunnel, thereby keeping the train stretched out, as the headend would begin pulling somewhere around the bottom of the tunnel. These are my presumptions, I should add, I have never spoken with anybody who has operated a train through this particular tunnel.
Thus, it is possible that the engineer flubbed up the coordination between the headend and DPU power. Perhaps this caused a pull-apart, and subsequent collision inside the tunnel, as the headend (going uphill) would slow down faster than the still-descending rear-end. A hit at high enough speed could cause cars to derail, and it would be on from there.
Other causes could lie in track conditions, a mechanical failure such as a broken wheel, or the aforementioned failure of DPU communication inside the tunnel.
Not sure if there are DPU Repeaters in the tunnel or not. But there is a plan B for DPUs
You cannot stretch brake in the tunnel, especially on long trains because it will not release fast enough and you either stall, or rip the train into pieces.
You cannot run a DPU engine in Dynamic brake and the head end in power, the software will not allow it, becuase it would be easy to rip the train apart with it