Combining multiple links /lines and summary an attribute.

Hi, I have multiple lines / links that each have attribute  per feuture

ID  Vehicle Load

1   0

2  300

3  250

In this case I would like all of them to create a single line with the total load, so new ID:4 and load:550. not keep the old ones.

This is the easier part however ther are intersections as well. Some times very complex ones:

Preferably this should be 2 lines with one node in the center. Maybe 2 parallell ones for the left lower part. 

I have done similar before with snapper and topologybuilder but would appreciate help. I used segment snapper.

My workspace