|Used for different types of information for mountainbikes, actual use unclear. Can regard both practical suitability or legal access both for bicycles in general or specifically for mountain bikes. For general legal access use bicycle=* instead|
|Used on these elements|
|Status: in use|
|Tools for this tag|
The key mtb=* has been used for different to types of information regarding since 2009. This key was not documented until April 2020 and it's actual use is not very clear, but points more towards practical suitability then legal access-restrictions as meant in Key:access.
Current usage: mainly practical suitability
mtb=* often appears to have been used to describe whether a path or road is suitable for mountain bikes, rather than describing the formal legal accessibility different from the legal access for bicycle=* in general.
The key mtb=* is also used in combination with tourism=information and information=* to signify that these have something to do with mountain biking. E.g. a map with mountain bike routes of the region information=map or a guidepost for mountain bikers information=guidepost or bicycle shop specialising in mountain bikes shop=bicycle.
Current usage on roads and paths Key:highway also points towards practical suitability instead of formal legal accessibility specifically for mountainbikes (instead of bicycles in general) as meant in Key:access:
Another indication that mtb=* is not used in the sense of access=* is that a legal nuance like mtb=permissive -which might be expected on outback trails- is only used very rarely compared to mtb=yes: ratio 1:1.000 (Taginfo). In comparison bicycle=permissive is used in a much larger proportion of cases: ratio compared to bicycle=yes about 1:50 (Taginfo).
Although current usage on roads and paths seems to describe practical suitability, a better alternative to describe this would be the keys mtb:scale=* and/or tracktype=* sac_scale=* smoothness=*, since it would not only indicate whether a path or road is suitable, but also specify how difficult it is for mountain bikes of different levels.
Furthermore usage to describe legal access specifically for mountainbikes (as opposed to bicycles in general) would be also expected to be rare, since in most countries and situations all types of (non-motorised) bicycles are treated equally in regards to legal access.
Besides the lack of relevance for a legal distinction between mountainbikes and other types of bicycles, it would be very hard to legally accurately define the difference between a "mountainbike" (example 1 / 2) and for instance a "hybrid bike", (example), "cross bike" (example) or "monstercross gravelbike" (examples)
In line with the approved proposal for Key:electric_bicycle, a separate tag for legal access for mountainbikes should only be used if legal access for mountainbikes is different from legal access for bicycles in general. If local law treats mountainbikes identically to bicycles in general, the key bicycle=* should used instead to document legal access restrictions for all kinds of bicycles.