A plan to bridge this river by a road-rail bridge is under way.
Fortunately the gauge of the railways in Congo Brazzaville and Congo Kinshasa are the same 1067mm.
For details of bridge see
Brazzaville is connected to the ocean by the Congo-Ocean Railway. This railway was originally 762mm gauge but was rebuilt on an improved alignment as 1067mm gauge. As this railway bypasses rapids on the Congo River, it is classed as a "portage railway".
For details see https://www.britannica.com/place/Congo-Ocean-Railway
FYI, population figures are
* C-B 2.3m
* C-K 14m
For PARENT THREAD see https://www.railpage.com.au/f-p2189234.htm#2189234