BGForums

I have read in another post that roads and rails helps to get more ressources, however, the manual indicate that they help to move supplies.

Does building roads\rails near your coal or oil facilities improve their output??

I believe that building road / rails increases the supply rating of the surrounding area, which in turn increases the output of nearby factories.

Roads also let you move units quickly.

Bateman is correct.
The mechanics and mechanisms that expand and improve supply in an area are basically the same ones that increase and expand infrastructure in an area,and thru which the efficiency of facilities (which increases their production).

So if you have an area of your region which has low supply,increasing that supply by running roads and rails from a higher supplied area to it,will have all of the above effects.

As would building a land based military facility in the area.