It is the duty of any sheriff transporting prisoners to a correctional facility, as defined in section 17-1-102, C.R.S., or other place of confinement to convey to such facility or other place of confinement at one time all prisoners who may have been convicted and sentenced and who are ready for such transportation. If any sheriff fails or neglects to carry out the provisions of this section, the boards of county commissioners may disallow any such sheriff's bill for such extra trips as in their discretion are unnecessary. This section shall not apply to the transportation of the insane.