The wiki page about the access key has a nice [transportation mode hierarchy][1]. The tree shows that the *vehicle* key both includes *motorized vehicles* and *non-motorized vehicles* but not pedestrians.
*vehicle=no* forbids *all* motorized and non-motorized vehicles *unless* specified otherwise.
*vehicle=yes* allows *all* motorized and non-motorized vehicles *unless* specified otherwise.
Examples:
* *vehicle=no*, *psv=yes* would forbid *all* motorized and non-motorized vehicles *except* those for public services (bus, taxi)
* *vehicle=yes*, *hgv=no* would allow *all* motorized and non-motorized vehicles *except* heavy goods vehicles
Update:
@Andy I'm going to reply to your comment in my question because more users might be interested in country-specific access restrictions. The wiki has a whole page about [default and country-specific implicit access restrictions][2]. But I don't know of any worldwide (online) router taking care of all these different rules. Most of them will just use the default access restrictions.
[1]: https://wiki.openstreetmap.org/wiki/Key:access#Transport_mode_restrictionshttps://wiki.openstreetmap.org/wiki/Key:access#Transport_mode_restrictions
[2]: https://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Access-Restrictions
