Why is the auxiliary 'avere', as opposed to 'essere', used when conjugating the verbs 'camminare' & 'viaggiare'?

Question

As a rule, transitive verbs in Italian use the auxiliary *avere* (*ho camminato, avrò camminato*) when conjugating in any of the compound tenses. However, *camminare* & *viaggiare* are intransitive and seem to be in the category as other verbs of motion: scendere, andare, cadere, etc. that use essere as a helping verb. Why are these verbs exceptions to the rule?Are there other examples of verbs that are intransitive yet use *avere* as an auxiliary verb?

Answer 1

Look at the rules is this order:

1- there are verbs that use AVERE as auxiliary 100% of the times CAMMINARE

2- there are verbs that use ESSERE as auxiliary 100% of the times ANDARE

3- there are verbs that use ESSERE or AVERE as auxiliary depending on their use as TRANSITIVE or INTRANSITIVE. SALIRE, SCENDERE etc.