The article points at the importance of studying the human factor as a cause of accidents of drivers, especially in loosely structured traffic situations. The description of the experiment on the measurement of driver's accidental abilities is given. Under accidental ability is meant the capability to ensure the security of driving as a behavior that includes activities and interaction with other road users. An approach to the assessment of such component accidental abilities as a sense of danger is suggested. The experiment simulated a vehicle driving process by the movement of a scooter with the requirement to travel at the maximum possible (by the feelings of a testee) speed through the gate with varying distances between the uprights. The pilot experiment was conducted on a group of children 10-11 years old, a group of motorists (men of safe driving age (26 to 45)) and a group of students 17-18 years of age (1st year students of the Technical University). Criteria for assessing drivers' and applicants` to be drivers accidental abilities are presented in the present paper. Low level of sense of danger is associated with passing the test with a minimum distance between the posts, high speed of the route, using the brake directly at the rack or after it, testees preserving calmness and confidence on the scooter in the event of tension in standing in the racks, high level--with opposite indicators.