## 2 Literature Review  
Urban transport pricing is one of the significant factors influencing the supply quality of public transport. In particular, in emerging cities with low incomes and low car-dependency rates, public transport plays a vital role in providing access for citizens to desired destinations, such as jobs, education, and health care. Moreover, urban transport fares severely influence not only citizens' quality of life and travel options, but also the air quality. [PERSON] et al. aimed in their study to enumerate the public transport fee, changing the impact on passengers' satisfaction. However, the obtained results showed the inefficiency of recovering passenger satisfaction after a short time of the new fare policy and passengers' negative points of view toward the increase did not reduce the utilization of the service in a long term. Moreover, the high negative impact was significant in the first month after the fare increase through a slight decrease in service utilization, while after four months the utilization level rebounded back and ended up almost in the same level before changing the fare policy. Predominantly, the new fare policy did not impact the public transport utilization long term [17]. The findings of several studies demonstrated that not only the lower income citizens are significantly affected by the urban transport fare increases, but also the high income citizens, which might cause harsh damage of the environment [6; 8; 9]. For instance, more potential passengers would be attracted to get their own car in the case of more expensive public transportation. [PERSON] and [PERSON] explored the influence of the urban transport fare on the environment and they found that the urban transport fare increase negatively affected the air quality in the short term because of the immediate change of fare. However, they increased the sophistication of their results by making distinction between short and long term impacts; they found that the growth of fares had an immediate reaction by the public decreasing their public travels, thus causing more air pollution but in the long term this effect disappeared and public trips increased again [18]. Other studies have proven however, that the fare increase tends to cause the citizens to use private transportation modes even in the long term; and by that, the total vehicle usage grows significantly which has a negative impact on the environment by the higher CO\({}_{2}\) emissions [19]. Vice versa, when the citizens change their travel mode from private vehicles to public transportation, the amount of CO\({}_{2}\) emissions decreases by default, because of the previously stated reason [20]. In some small EU cities, free fare public transport exists like Hasselt, Belgium, and Templin, Germany, however, [PERSON] et al. evaluated the fare free of public transportation system in Tallinn, Estonia. The outcomes, unsurprisingly, showed that the free fare system achieved an increase in passenger numbers in all cities [12; 21]. [PERSON] investigated whether the free urban transport can attract more users and he found that the free public transport service motivated more citizens to use public transport and the increase of usage was quite significant [11]. Additionally, [PERSON] found out that free urban transport was efficient in attracting large numbers of new urban transport users or shifting drivers to utilize urban transport [12]. Moreover, [PERSON] and [PERSON] pointed out that the urban transport user numbers diminished noticeably after fare pricing increased [7]. However, [PERSON] found that use of public transport was not significantly raised after changing the urban transport fare, but the citizens appreciated the lower fares in general [10]. Another example is the Australian government, which endeavored to enhance the utilization of urban transport by providing a new fare system, which efficiently influenced the quality of life and environment quality, and to provide sustainable and functional cities.