Daimler, Volvo, Scania and even Google are at the moment reseaching and even testing self-driving HGVs. You could then think that the lorry drivers would become even more more difficulties getting a job with self-driving HGVs making them unemployed, but that will probably not happen at all.
The lorries are not going to be all manpower-less as you know it from e.g. the metro. There is still need for lorry drivers evn in a self-driving HGV. The change will be the tasks. The lorry driver will not have to actively drive and steer anymore and would instead have to monitor the control system of the lorry. Like a technician. It will probably not be a disadvantage to be able to read a book or do other tasks during a run. It will be like a pilot in an airplane putting the system on auto-pilot. A drive will then be relaxing, but with a technician keeping an open eye and monitoring everything. The big question is: Did anybody invent an automatic loader/unloader as well?