Not convert, but modify by adding concrete edges as in the pictures so that
both trains and buses can run on the same track. the added cost would be concrete and improved signals. The buses could run on the same power as the trains or their own power depending on which ever is more feasible.
you don't have to lose the track or modify the train track for the train
the buses have special rollers on the side to guide them along this concrete lining at maximum speed.
Its the "Duo Bus System" in the German city of Essen. while that line is used by buses and trams, we should study it between our regular trains and metro-buses. From this video you can see the tram and the bus are running on the same line.