The supply of public transport in Sweden has been continuously increasing and as a consequence thereof, the cost for bus traffic has also increased. However, many indicators show that costs for public transports in Sweden in recent years have increased more than supply. Therefore, the aim of the present study is to test and evaluate the importance of the nine previously identified cost drivers (Camén & Lidestam, 2016) of public bus transports in Sweden. A mixed-method design, which included both focus groups and a questionnaire, was used. The questionnaire, with quantitative rating scales, was sent to representatives from the bus operators and from the Public Transport Authorities (PTAs). In the focus groups, industry associations, consultants, and politicians also participated. The results reveal what the dominating cost factors are, as well as the factors considered to be the most important, according to actors within the Swedish bus transport sector. The most important cost driver identified is peak traffic and the costs of its consequences.