How are traffic fines affected by the driver’s car price and the police officer’s discretion? A case study of Isfahan, Iran

Traffic violations can cause congestion and road safety risks. The two objectives of this study are (a) to study the influence of car price and (b) to investigate the influence of police discretion on the amount of fines for each driver. Car price was used as a proxy for the economic status of the driver. The fines were categorized into camera-issued or police-issued fines, and this source of issuance serves as a proxy for police discretion. A comprehensive database of 1.4 million traffic fines in Isfahan province recorded by the Iranian traffic police was analyzed. Linear regression and multinomial logistic regression models were employed to test the relationship between car price and the fine-issuing source with the amount of fine. The results indicated that the total fine amount by each driver increased by 0.183 M Rials annually with every 1000 M Rials increase in the car price. Furthermore, police stopped more expensive cars less frequently compared to cheaper ones. Both car price and police discretion had a significant effect on the total amount of fines. Therefore, as a future policy, traffic fines (especially camera-issued fines) may be set proportional to the car price. The police discretion is highlighted for further investigation.