A 'desirable minimum' value is a design paremeter used when there is no existing constraint on a proposed or existing cycle facility.
For instance, a 'desirable minimum' width of a one-way cycleway is 2.5m.
'Desirable minimum' values should be contrasted with 'absolute minimum' values, used when there is a physical constraint present.
For Highways England schemes, designers have to record the reasons why they have had to use an absolute minimum, rather than a desirable minimum.