You are looking for a magnet equiped tube, approx 5cm long.. just above head height, no need to stand on or directly next to the actual road to find. There is room to safely stop alongside GZ.
Out in the field is what I believe to be an upside down back of an old F series ambulance, I can remember it's appearance with an advertisement for a local FM radio station when going to FM was a big deal.
If you have another theory on what it is please feel free to speculate in the log
If you have got off the hume just to grab this, there is a safe round about at the next turn left to get facing the right direction again, however I am not sure if this is socially acceptable in a heavy vehicle. At the time of posting this cache is on a B-double and 4.6m approved route..