This article deals with the border effect phenomenon affecting the mobility of inhabitants in border regions. It aims to identify the determinants of the border effect in transport at the municipal level, considering the distance from the border, the populations and the characteristics of the closest bordering country. The survey in the Czech Republic eventually involved 675 representatives of municipalities who answered questions on inter-municipal mobility. The results confirmed that the most substantial handicap was population size, with small populations corresponding to the limited use of public transport when travelling beyond a given border. The results confirmed that the characteristics of the state or region that shares the border must be considered when assessing border regions. Therefore, the solution to the problems of individual border regions cannot be viewed with a single instrument. It is necessary to consider substantial differences resulting from the economic level of neighbouring countries.