**1. Introduction**

The implementation of a public transport system in a city is not a usual event. This is why, before construction begins, every component and feature has to be designed to ensure its efficiency for long periods. For these reasons, both for existing mass transit systems and new ones, the perspective of maintenance and retraining appears fundamental. It is worth considering that with existing buses and a few infrastructure adjustments, like what Bus Rapid Transit (BRT) requires, an efficient service would be guaranteed, and offers a convenient solution for city administrations. The BRT public transport system was introduced in 1974 in Curitiba (Brazil). The reasons that led the administrators and technicians to make this choice were economic—reduced funds to construct a rail system—and social—because of the population increase in the city—requiring a public transport system with high capacity vehicles. After Curitiba, BRT spread worldwide, especially in Bogotà, with the implementation of "TransMilenio" in the 1990s. Such a system still represents a model for all public transport arrangements, and mostly it also showed how BRT is efficient for complex urban layouts. Before 1990, BRT operated only in eighteen cities, while, nowadays, it is active in 173 cities and serves 34,026,459 daily passengers [1] (Table 1).


**Table 1.** Global Bus Rapid Transit (BRT) data.

The benefits of a typical BRT system consist of dedicated lanes and proper vehicles and stations. Such a layout guarantees a significant advantage in terms of intermodality and interoperability. If such features are accessible to other specific vehicles, like emergency ones, then, due to reserved lanes, the congestion phenomena could be avoided for the public transport system and ordinary traffic, for instance, when users attracted by the efficiency of BRT give up using their private vehicles. Commonly BRT is considered an upgrade of existing bus mass transit systems that emulate rail systems but with reduced costs and construction times. For example, the construction costs for a single kilometer of BRT are only 52% of the costs of a light rail system and 8% of those of massive rail system construction [2]. A strategy that is commonly used to appeal to citizens consists in building stations or creating reserved lanes in places where there are parking areas for private vehicles. In this way, private vehicle users are more likely to find themselves caught up in congestion and less likely to find a parking place, thereby encouraging people to prefer the use of public transport systems. Some comparative data between BRT systems and more traditional transport systems are shown in Table 2.


**Table 2.** Comparison of the public transport systems parameters.

Generally, when a new mass transit system has been implemented, the area where it is located must be subjected to requalification works, producing a relevant cost increase. Such a case appears conveniently when the local administration decides to create so-called transit-oriented development (TOD) areas to maximize public transport use. These places are characterized by people living near transit hubs, so there would be the need to invest in activities close to these areas [3], making an essential requalification with significant consequences in terms of property value increase.

The main aim of this paper was to review some of the BRT systems operating worldwide. The following subsections will present the background, general technical features, and the correlation with autonomous vehicles. This last section represents a viable distinguishing trait of the review carried out in this paper. The discussion examines the perspectives concerning autonomous vehicles and how they can enhance and influence mass transit and, mainly, BRT systems, in a positive way, creating meaningful profits for communities.
