**3. Bus Rapid Transit (BRT) and Autonomous Vehicles**

The most important innovations that affect the transport and automotive sectors nowadays are represented by autonomous vehicles whose equipment can replace driver intervention. To highlight several autonomous vehicle types that have been implemented, it is possible to refer to the classification, depicted in Figure 3, established by SAE (Society of Automotive Engineers). There are six levels of classification: from level zero to level two, there are vehicles with full manual control (level zero) and those with some features that allow driver assistance and partial automation (level one and level two); then level three to level five indicates vehicles that are equipped with the so-called ADAS (Advanced Driver-Assistance System) that permits autonomous performances. In these cases for a third and fourth level, a driver is required. The vehicles operate autonomously only in some circumstances, while, for level five, the vehicle can achieve full autonomy [7]. Among several benefits that would be provided by autonomous vehicles, the main ones are related to safety, considering that a high-tech system would manage driving maneuvers with shorter reaction times compared to human drivers, but also to public transport services that would achieve high efficiency due to the accuracy of the IT systems. With regard to public transport, it has to be pointed out how the ADAS operation would be more relevant for road vehicles such as buses instead of rail vehicles (trains, trams) because while this one is hooked to a platform (predetermined trajectory), the trajectory of autonomous road vehicles would be utterly dependent on ADAS.

**Figure 3.** Vehicle automation levels.

Taking into account the advantages that autonomous vehicles could give to a BRT system, many companies have launched tests with autonomous buses like, for instance, the East Japan Railway Company's (JR East's) Bus Rapid Transit (BRT) lines [8], aiming to analyze self-driving technologies when applied to bus transit primarily focusing on aspects such as keeping in lane and speed control, which strongly affect BRT efficiency or the buses' decision capabilities when managing several scenarios. The cooperation of an efficient system like BRT and the technological capability of ADAS would provide an ultimate low-cost solution for critical traffic issues and emissions reduction in cities, especially considering that it is expected that in 2050, more than two-thirds of the world's population will live in cities [9]. Examples of autonomous bus services consist mainly of autonomous minibuses with a capacity of a maximum of 15 people. They operate in several contexts like hospitals, parks, universities, airports, and public roads. However, with such reduced capacity, it would be complicated to implement a BRT system that is mainly valued for its high capacity buses. Therefore, to guarantee a high capacity system, the solution would be to use a high number of minibuses that are already able to drive on a public road, and to operate them in reserved lanes, thus ensuring a significant efficiency considering that with a high quantity of vehicles, the waiting time would be decreased due to the high frequency and flexibility. Crucially, to ensure the correct operation of an autonomous BRT system, the infrastructures will need to be upgraded with ITS and sensors able to allow the following types of communications: V2I (vehicles to infrastructure), V2V (vehicle to vehicle), and V2X (vehicle to everything) [10]. In Figure 4, it is possible to see an autonomous bus that works on a street in California.

**Figure 4.** Example of an autonomous minibus.

The fact that autonomous minibuses are already operating, despite the higher capacity of autonomous buses, can be attributed to their dimensions, safety, maintenance, and other complex reasons. Moreover, there are several tests of high capacity and articulated buses equipped with ITS and sensors that allow them to operate autonomously. A test of this kind was carried out with a Volvo B10M-ART-RA-IN articulated bus [11]. One such 18 m long bus was fully equipped and tested on a 385 m long private road in Arganda del Rey (Spain). To control speed and brakes, an electronically connected I/O board was used. At the same time, the steering was equipped with a 24-volt DC motor (150 watts) that also had an incremental optical encoder (2000 ppr) and a gear reduction box (74:1). Finally, obstacle detection was allowed, thanks to two Laser Imaging Detection and Ranging (LIDAR) systems (LMS-221 and LMS-291). The average speed during the test was between 10 km/h and 25 km/h. In comparison, 60 km/h was reached only in a straight section. It has been observed that the main challenge for autonomous systems in such cases is represented by the high mass and, consequently, the greater inertia, which is why the main observations showed longitudinal and lateral maneuvers of breaking and acceleration. Test results showed that the maximum error that exceeded trajectory tracking was at least 35 cm on curves with a reduced radius, while the all trajectory error was at least 10 cm. It can be assumed that such errors are considered acceptable, taking into account the bus's elevated dimensions [12] (Figure 5).

Beyond performance, another essential benefit linked to a potential BRT autonomous system is with regard to capacity increase. This achievement is a consequence of the headway reduction between buses, which is allowed thanks to the CACC (cooperative adaptive cruise control). This system can perceive sudden changes in the speed of adjacent vehicles faster than a human driver. In this way, taking into account that vehicles will be able to brake promptly, the required safety distance while they are moving will be shorter compared to that of the human-driven vehicles. Together with shorter headway, this will form the so-called platooning, and with this asset, the BRT system will increase its capacity, emulating that of rail transit systems [13].

**Figure 5.** (**a**) Tested articulated bus, (**b**) inner road dimensions, (**c**) bus trajectory analysis.

## **4. BRT Systems Applications**

The reduced cost–benefit ratio of implementing BRT systems represents a significant turning point for several communities, not only in terms of livability, but also economic gain, since cities also consider the urban redevelopment brought by BRT systems to increase their international attractiveness with consequent positive implications from a tourist point of view. A typical example of BRT's benefits in a developing country is represented by the Lahore case in Pakistan, a city of at least eleven million inhabitants where a BRT system was activated in 2013. It operates in a reserved lane located on a 27 km long corridor with an operational speed of 26 km/h and 25 stations, and manages a quantity of 180,000 daily passengers [14,15]. With regard to performance, due to a fleet of sixty-four buses, there is a headway of three minutes. In terms of Lahore's benefits, the population density passed from 268 persons/acre to 299 persons/acre due to the increase in new construction in areas close to stations.

In conclusion, from an economic point of view, there were investments of almost \$140 million, creating 800 new employees [16,17]. In Pakistan, the city of Lahore (Figure 6) is not the only case where BRT has provided significant benefits from an economic point of view and an environmental one. For instance, Multan's BRT system was studied to evaluate the skills and performances of hybrid energy-based buses. Based on DEA (data envelopment analysis), the efficiency range of 21 stations

(except one for the hybrid bus system) was almost equal to 1, where the only exception was at a stop where the value was 0.77 [18].

**Figure 6.** Lahore BRT system.

Taking into account the data about South America, considering that it is the continent where the BRT system was first established, it is still the one in which there are more significant examples of such travel networks; moreover, it hosts and is also the often-cited system that acts as a model at an international level, for instance, the "TransMilenio" of Bogotà (Colombia) [19]. The success of TransMilenio is related to the optimal outcomes in terms of profits during the first years that covered the expenses of planning and service provision easily with privately-operated buses. Such advantages led to the implementation of other interesting BRT systems in Colombia, like the one in Barranquilla [20,21]. This metropolitan area had significant urban segregation and inequality that also affected the transportation systems (Figure 7). Due to the rapid economic and urban growth, there was a relevant increase in congestion phenomena attributed to the quantity of private vehicles. A trunk-feeder BRT service was activated to manage such a situation, connecting Barranquilla and Soledad along a 14 km corridor with exclusive right-of-way. This system, named "Transmetro", was also characterized by several feeder routes (190 km). One of the advantages of Transmetro is the free service offered for vehicles moving from the feeder to trunk route. To demonstrate how BRT systems attract private investment, this type of BRT system is characterized by a public-private partnership where the public part deals with operational and organizational aspects while private companies manage delivery service [22].

**Figure 7.** Baranquilla's BRT system.

North America has one of the most recently inaugurated BRT, for example, Albuquerque (USA), which is a city with 560,218 inhabitants. It is characterized by two priority lanes 20.2 km and 21.97 km long, respectively, each one with twenty stations and serves 8100 daily passengers. It is not the most comprehensive system in the USA. It is useful to note that its peak frequency reaches eight bus/hour [23]. Moreover, the highest use of BRT systems is not always linked to the size of continents. North America has several cities with significantly lower passenger numbers than European ones. In Europe, BRT is most widespread in France, being active in 21 cities and with a total extension of 342 km, respectively 47.72% and 39.09% of all Europe. France's most comprehensive system is in Lille (67 km), while the most recent is in Le Mans [23]. Considering its extension in Africa, BRT was not taken up as much as in other countries since it is only established in five cities. However, in Dar-es-Salaam, the most recently inaugurated system dates from 2016 and consists of just one corridor that is 21 km long, but with the highest number of daily passengers in Africa, equal to 180,000. In Oceania, BRT is mainly used in Australia, where it has an extension of 90 km and operates in three cities: Adelaide, Brisbane, and the metropolitan area of Sydney. The BRT system in Adelaide (Figure 8) is the smallest one with just one 12 km corridor. However, it is one of the first to be implemented globally, and its line is mainly characterized by the track-guided bus, a system composed of a specific platform where only the bus can drive. This type of intervention has been used to avoid the introduction of private vehicles altogether [24].

**Figure 8.** Adelaide's BRT system.
