I checked Wikipedia real quick:
The Los Angeles Metro Rail is an urban rail transit system serving Los Angeles County, California in the United States. It consists of six lines: four light rail lines (the A, C, E and K lines) and two rapid transit lines (the B and D lines)
Looking further, since this happened in Boyle Heights, and only Line E runs through there, it must have been a Kinki Sharyo P3010. The empty weight of one car is 45t. On pictures I can see there were three cars, so 140t (plus content) were pushing forward there. But only the first half in front of the articulation point of the first car derailed. Looking at the schema picture on the bottem here (PDF) it looks like there are three bogies. So I guess we can assume roughly 15t (plus content) would need to be bounced off the track.
I've seen the result of the same thing happening here in Zürich to our Bombardier Cobra light rail which weighs 39.2t. So I'm not that surprised anymore, but it is still impressive.
I think it would work, but it seems a little overcomplicated, you can just use the partition paths as
if
andof
ofdd
directly, as long as the output partition is not smaller than the input partition. For exampledd if=/dev/sdc1 of=/dev/sdd1 bs=4M status=progress
Your method would also copy the partition table I suppose, which might be something you want under specific circumstances, but then it would be a little harder to get the count right, just taking the size of partition 1 would be wrong, because there is some space before it (where the partition table lives) and dd would start at 0. You'd need to add up the start position and the size of partition 1 instead.
Personally I would prefer making a new partition table on the new eMCC, and create a target partition on it. Then you clone the content of the partition (i.e. the file system). This way the file system UUID will still be the same, and the fstab should still work because these days it usually refers to mounts by filesystem UUID in my experience.
If you make the target partition larger than the source partition, and you intend to use the full partition going forward you will additionally need to resize the filesystem to fit the new larger partition, for example with
resize2fs
.