Log Bridge in the interior Sarawak

In the interior Sarawak, there are many earth roads built by the logging companies to transport the logs to the major rivers. You just use the Google map and zoom down, you will see the numerous tracks criss-crossing each other in the interiors of Sarawak. There are many ravines, valleys and small rivers, and therefore bridges are required to link up the roads. 
This log bridge was built by the loggers and required hundreds of tons of logs to build it. It will not last long too. Rotting, flooding and erosion would destroy the bridges. It is also not economical. It may require hundred of tons of timber. The main adavantage is the logging companies do not need to fork out any money to build. The smaller companies prefer this method.
Bigger companies nowadays prefer to use steel bridges for the purpose. After finishing the logging area, they can dissemble and assemble in another site. 
I designed 15 steel bridges for a few timber companies. Sometimes, I used Bailey steel trusses, especially for long span bridge (maximum length 72m), but most of the time I used I-beams and trusses, length less than 40m, which can be fabricated confidently by local people.