The purpose of this study is to examine the effects of the so-called 'Min-sik’s Law' that has recently become a big social issue and 'Safety Speed 5030' policy, using Difference-in-differences(DID) analysis. The results of the analysis are as follows. It was proven that the effect of the Min-sik’s Law was not successful because there was no significant effect under the DID analysis. Conversely, it is verified that the implementation of the Safety Speed 5030 policy has achieved considerable results significantly; The number of accidents, deaths, and injuries were all verified to have decreased in 10,851 case, 164 people, 18,830 people, respectively. This result proved a necessity to beware of the limitations of premature regulatory legislation in that the effect of the Safety Speed 5030 was significantly effective, while the effect of the Min-sik’s Law had no outstanding effect. The Min-sik’s Law had been passed and implemented only in three months after a sad death of an elementary school student; Low speed compliance is required in all child protection areas. In contrast, the Safety Speed 5030 had been designed over a long period of time and introduced after an adequate pilot operation; Speed limits are applied according to the characteristics of the road. In terms of procedural rationality, the Min-sik’s Law has limitations, and the Safety Speed 5030 policy is one of examples that procedural rationality leads to practical rationality. It implies that a systematic impact analysis is essential prior to the introduction of regulations. In particular, in the case of legislative legislation, unlike government legislation, legislative impact analysis is not enforced, but the results of this study indicate that it is necessary to make legislative impact analysis be compulsory if it can significantly affect the lives of the people.