 The Rail Motor Driver departed Top Points without communicating his intention to his Guard or the Hi-Rail crew, and the Rail Motor Guard exceeded his authority by authorising the Hi-Rail to leave a worksite and proceed to Top Points.A number of other factors were found to have contributed to the collision, particularly a lack of radio communications and operational safeworking errors.Other safety issues identified during the investigation included delayed notification of the accident; poor maintenance of Train Register Books; passengers travelling in the Rail Motor driver's cab; Rail Motor Driver's fatigue; and excess speed of the Hi-Rail.