The latest (2000) issue of the IOF Specifications for Orienteering Maps contains a section specifically for MTBO maps. However this is early days for the sport, and they are not set in concrete.
We (the NZOF MTBO Committee) think we can make the ridability symbols a little more distinct from each other, and have made a submission to the IOF MTBO Committee. Here is what we prefer, and have been using for championship maps since the first NZ Championship.
Thicknesses: Thinner lines of 0.5mm (symbols 811, 813 and 815) and 0.25mm (812, 814, 816) because we have some fairly curly tracks which are sometimes disguised by the thicker lines. Also, the thick lines need to be less dominant than symbols 501, 502 and 503 which are also used, the last of which is only 0.48mm wide. We also think the width ratio should be at least 2:1 for better discrimination.
Dash Lengths: We have retained 2.5mm (813 and 814) but use 0.5mm for 815 and 816 for better discrimination. Note that the speci gives the distance for (dash plus gap) whereas what you put into OCAD is the dash length, it is possible to misinterpret this.
Green lines: these are a NZ invention for allowable routes since off-track riding is generally not permitted; so you won't find these in the speci. They are just clones of the corresponding wide symbol, usually 813 or less commonly 815. We think their use should be restricted to situations where there is a clear handrail to follow (fence or forest edge) or else where it doesn't particularly matter where the riders go (eg short distance between two close parallel tracks). Where it is necessary to tape a route, we regard that as creating a "proper" track even if it only exists for the day, and would use the black symbols.