The advertisement uses, among other tactics, the 'Question-Behaviour Effect'. The picture of a young girl with the accompanying text makes the reader think about some of the possible major consequences of getting in an unbooked taxi. Through the use of this very striking technique, it nudges the reader to question their own behaviour as to whether or not they get in unbooked taxis. Inevitably, if they do show this behaviour, the reader will be less likely to do it again as they do not want anything like this to happen to them.
In an empirical study demonstrating the 'Question-Behaviour Effect', students contacted by phone were asked to predict (yes or no) whether they would vote between the time of the call and when the voting poll shuts the next day. Those who said they were going to vote were twenty percent more like to do so than the control subjects, who made no prediction as to whether they would vote (Greenwald, Carnot, Beach & Young, 1987). This demonstrates that making a self-prediction about our intention to perform a certain behaviour, can increase the likelihood of us carrying out that behaviour.
Greenwald, A. G., Carnot, C. G., Beach, R., & Young, B. (1987). Increasing voting behavior by asking people if they expect to vote. Journal of Applied Psychology, 72, 315-318.