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5. AccelerationModel

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smart-fm edited this page Nov 9, 2018 · 4 revisions

The acceleration of the subject vehicle is specified by a set of possible accelerations and decisions rules. This framework is specified in the file sim_mob::MITSIM_CF_Model In general, a vehicle accelerates or decelerates in order to:

  • react to the vehicles ahead (in the same or adjacent lane);
  • perform a lane changing or merging maneuver;
  • respond to events such that red signals and incidents; and
  • achieve its desired speed. Drivers adapt their acceleration behavior to facilitate their short term plans (i.e., target lane and gap). Different accelerations are applied depending on the current plan the driver implements: stay-in-the-lane, lane changing or target various gaps for lane-changing. The stimulus-sensitivity framework proposed within the GM model is adapted for these acceleration models. The response (acceleration or deceleration) the driver applies to a stimulus is lagged to account for reaction time as follows:


where, t is the time of observation and τ_n is the reaction time for driver n. For some of the accelerations defined in the next section, the stimulus can be the front vehicle (e.g., car-following) or vehicles in adjacent lanes (target gap). In fact, the driver reacts to acceleration behaviors, the driver is assumed to be either in a constrained or unconstrained regime. A constrained regime applies when the driver is close to the lead vehicle (the headway is smaller than the threshold) and affected by its behavior. For stay-in-lane and target gap accelerations, the lead vehicle is the front vehicle in the current lane. For lane-changing acceleration, the lead vehicle is the front vehicle iin the lane the driver is changing to. In the constrained regime, the stimulus is the relative speed of the lead vehicle and has different parameters for acceleration and deceleration. In the unconstrained regime, for the stay-in-the-lane and lane-changing cases, free-flow acceleration is applied. For target gap cases, the stimulus is determined by a desired position that would facilitate completion of the lane change. The reaction time and time headway threshold distributions account for the heterogeneity among drivers and are common to all components of the acceleration model. Besides the these plan related acceleration regimes, other "stimulus" are considered, such as the desired speed, a traffic light, an incident or lane drops. In SimMobility ST, the most constraining of all acceleration scenarios at stake determines the acceleration or deceleration rate to be implemented.

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