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4.4. COMPONENT DESIGN
cars new location and in the SimPanels tick() method, all the cars are drawn
to a backbuffer. The last action of a tick is that the backbuffer is labeled
with the current frame number and is swapped onto the screen. This design
combines a back-buffering approach to animation with the necessesity of
clearly presenting the time dimension to the user.
The timer runs in its own thread and sleeps by x milliseconds in between
each tick. The user has direct control of the speed of the timer by controlling
x through a slider. The simulation can also be paused by suppressing the
timers ability to tick.
The vehicle movement model
The simplest mathematical car-following model is linear. This means that
as long as there’s no obstruction (another car or a red light) in front of a
vehicle, it will travel at the speed limit of k kilometres per hour. If a car
gets within a distance of L metres from an obstruction, it will reduce its
speed proportionally to that distance. If a car gets within a distance of l
metres from an obstruction, it will stop altogether.
Let x denote the distance in metres between two cars (measured from the
front of one to the back of another, or between the front of one car and a
red light ahead).
The speed v of the car is:


 k,
if x >= L
between0andk, if l < x < L
v=

 0
if x <= l
In the second case, l < x < L, we’re assuming the car changes speed proportionally to changes in distance, so that v is given by a “linear” function
of x (the graph of v as a function of x is a straight line). This means that
v = mx + c for two constants m and c. These constants can be determined
from the two conditions:
1. v=0 when x=l
2. v=k when x=L;