**6. Signal priority with connected vehicles**

Some of the advanced TSPs are based on the wireless communications using Global Positioning System (GPS). These systems only report instantaneous

vehicle location data. Also, with the advances in emerging technologies, vehicles can communicate with each other (V2V) and with the infrastructure (V2I), through 5.9 GHz dedicated short-range communication (DSRC). Using this technology, each vehicle is equipped with an on-board unit (OBU) that broadcasts the vehicle speed, and acceleration at 10 times a second. A road side unit (RSU) is installed at the intersection to broadcast traffic signal status and also intersection geometry maps. The RSU can receive messages from surrounding vehicles and can provide better traffic resolution.

As soon as a transit vehicle enters the Dedicated Short-Range Communication (DSRC) range of intersection, it receives the map of the intersection and determines its location. Then, it broadcasts a request message and asks for priority. The RSU at the intersection receives the request and provides treatment. If the vehicle's speed changes dramatically, (e.g. the vehicle joins a queue) or if the transit vehicle stops at the bus stop, an updated request is broadcasted. The updated request is received by RSU and proper actions are planned. Connected vehicle technology can provide countable data because it updates vehicle dynamical traffic-related information like speed, acceleration, location, and other vehicle data in real time [57]. Such technology also provides the information about passenger counts (sitting/ standing on transit) and at stops which can be transmitted to the signal controller in real time which makes dwell time prediction more accurate.

Hu et al. [5] used TSP with connected vehicles (TSP-CV) technology and compared their logic with conventional TSP and no-TSP scenarios. Results reported that the proposed logic reduced bus delay between 9–84% as compared to conventional TSP, as well as outperforming the no-TSP scenario. Meanwhile, it was shown that as volume-to-capacity ration increases (approaching to v/c equal to 1), the difference between TSP using connected vehicle and conventional TSP decreases. Hu et al. [58] continued their studies on conditional TSP-CV and proposed a person-based optimization method along with recommending a desired speed to the bus. The conditional logic was applied only to busses that are behind schedule and it was tested on two closely spaced intersections with fixed-time control. The results revealed that conditional TSP-CV performed better, specifically when the v/c is under saturated, and again it was found that as demand increases, when it approaches capacity, the benefit of TSP decreases. Lee et al. [59] tested the application of TSP in connected vehicle technology over a smart road test bed in Blacksburg, Virginia. The experiment results confirmed that the TSP-CV logic provided bus green extension with a 100% success rate, together with reducing bus delay between 32 to 75% as compared to No TSP scenario.
