Mesosimulation Transit Modeling

Transit services in the mesoscopic simulator need a transit plan defined in the Dynamic Scenario, just as in a microsimulation dynamic scenario.

The transit vehicles are modeled using the same characteristics as used in the microscopic simulator but with a different method of modeling bus stops. In the microscopic simulator, vehicles decelerate and accelerate as they arrive and depart bus stops. In the mesoscopic simulation vehicles are assumed to stop instantly and then to reach their average speed immediately. This means the waiting time at the stop is simply added to the transit vehicle's travel time. Also, all stops are considered to be at the end of the section.

Vehicle Generation Model

Transit vehicles are generated and input into the network via the first section of each transit line and they progress through the network following the transit line and serving all the corresponding stops. The arrival times into the network are obtained according to the corresponding bus schedule, defined in the Timetable. This is the same as in the microsimulation model.

Vehicle Movement Model

Transit vehicles follow a fixed route through the network. Transit vehicles normally behave like any other vehicle, according to the car-following and lane-changing models. The only difference between transit vehicles and normal vehicles is the lane choice heuristics. Transit vehicles take bus stops into account and select the entrance and exit lanes according to the next bus stop and turn connectivity (see the valid lanes section).

The turn connectivity or the valid lanes defined by turns' look-ahead model always take preference over the transit stops. This means that if a bus stop is located in the rightmost lane but the only valid lane, due to turn connectivity, is the leftmost lane, then the bus makes the stop in the leftmost lane. In other words, the dwell time is always applied in the exit lane.

Like normal vehicles, transit vehicles are assumed to stop immediately; there is no deceleration process before reaching the transit stop and there is no acceleration process once it leaves the stop.

Reserved lanes in a network can be designated for exclusive use by transit vehicles. When such a lane is available in any section of the transit line, the transit vehicles will use it. Turns and transit stops have more priority than reserved lanes, which means that a transit vehicle will leave a reserved lane whenever it needs to reach a turn lane or a transit stop.

All stops are considered to be placed at the end of the section. In terms of the internal car-following model, this assumes that all the delay is incurred at the end of the section. Bus bay stops are considered to be an extra lane, so the delay is not propagated to consecutive vehicles. It is important to consider this restriction when the stop time can influence a detector. Stops and detectors are considered to be at the end of the section, so when using an actuated control plan or transit priority we recommend cutting the section after the bus stop in order to avoid unrealistic detector-presence behavior.