**2.2 Cooperation opportunities and challenges**

The main PT service quality objective is expressed in terms of punctuality (for schedule-based operations) and/or headway regularity (for headway-based operations). Current methods are based upon in-vehicle support systems, managing holding strategies and preferential signal control (TSP) and providing PT vehicles with preferential treatment at intersections via temporary traffic signal timing adjustments [11, 12]. For schedule-based operations, holding strategies (delaying departure of a bus from a bus stop until the scheduled time) ensure punctuality by managing slack times (extra "backup time" inserted into schedules) [13]. The problem of existing methods is that they slow down busses due to the fact that they add delays to the planned trip time [14]. They also address isolated lines and ignore any disturbances observed in real-world PT operations [15]. Headway-based operations are more difficult to control, as the strategies need to account for several busses [16, 17] and multiple interacting lines [18]. Thus, additional ITS systems such as Automated Vehicle Location (AVL), Automated Passenger Count (APC) and a central coordination entity are used to control busses in real time [15, 19].

The core reliability objective is also supported by TSP strategies capable of providing conditional priority. However, since TSP influences the traffic flow reliability [20] its acceptance is limited. Future improvements of TSP exploiting AVL can be achieved. This allows previously unfeasible continuous exchange of information between vehicles and traffic signals [21], allowing cooperation bus-signal through e.g. speed advisory [22, 23]. Such systems are one of the few ITS applications that would provide benefits even at early stages of CV technology [24].

Recent advances in V2I communication enable developing a new promising efficiency-oriented class of driving support systems aiming at improving driving efficiency, comfort and reducing unnecessary stops at signals [25]. Opposite to signal control, which uses CV technology to collect information about the approaching vehicles, in V2I-based systems vehicles use signal control information to optimize their own speeds accordingly. The two SPaT-based DASs researched in literature are the Green Light Optimal Speed Advisory (GLOSA) and Green Light Optimal Dwell Time Advisory (GLODTA). GLOSA provides vehicles with speed guidance, while GLODTA advises additional holding at bus stops. Their main advantage is that these systems improve bus performance with respect to traffic signals, but, unlike TSP, they are non-intrusive (i.e. do not influence signal timings). The two V2I-based advisory systems can be combined to mutually increase their effectiveness [26] and they can be combined with traditional holding strategies. These integrated controls have been shown to meet both objectives of service regularity and reducing the number of stops, as well as they reduce the number of TSP requests [27, 28].

#### **2.3 The eCoBus integrated ecosystem**

In this work we adopt a cooperative system approach, following the C-ITS paradigm, reinforced by an energy-aware decision support system. This approach
