Reaction Time

For computational reasons, the current version of MITSIM does not simulate explicitly driver's reaction time (except for vehicles at traffic signals). The acceleration rate applied for the next interval and decisions on lane changes are calculated based on the situation at the end of the previous simulation interval. Therefore, the reaction time is 0 at the beginning of a simulation interval and equals to the update simulation interval at the end. To incorporate the fact that reaction time varies among drivers and under different traffic conditions for the same driver, the update simulation interval can vary from driver to driver and from one condition to another for the same driver. When a vehicle n enters the network, it is randomly assigned a simulation interval for situation k, where indicating decelerating, accelerating, cruising at uniform speed, or stopped respectively. is drawn from a truncated normal distribution with the following parameters:

mean value;

standard deviation;

lower and upper bounds.

The step sizes determined according to the above discussion are used in refreshing a vehicle's acceleration rate and lane change maneuver in the four cases under ``normal'' conditions. To make the simulated vehicles behavior more realistically, the following exceptions are made:

(a)

When a vehicle is in the emergency regime at any time, an emergency deceleration rate (see Eq (3.10)) is applied immediately.

(b)

As a vehicle changes lanes, the car-following and event response models are invoked in the next simulation interval (i.e. seconds later) for this vehicle and the vehicle that follows in the target lane.

(c)

During the advance phase (see Figure 3.1), if the speed of a vehicle reaches the driver's desired speed or becomes zero, then the acceleration rate is immediately set to zero.

(d)

If the leading vehicle is slowing down, the following vehicle updates its acceleration rate and lane change state at the minimum of the previously scheduled update time and current clock time plus half of the driver's update step size.