The track number is "61" for Fraizer Wells.
With the original editor (referred by jharro) I opened the file
Richard Burns Rally\track-61_M.mat
Once opened this file, on the right-down corner of the editor the different materials for this track were shown. I selected "USA 2002 standard dry new". Then on the left-up screen, as I moved the mouse I got (in the lower part of the screen) the name of the material for that part of the texture. In this case it was "Gravel Fine Shallow Dry". Looking in the list of materials (right-up part of the screen) the number for the material was 17.
Thanks jharro:wink2: