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Most models classify lane changes as either mandatory or discretionary lane
change.
This separation implies that there are no trade-offs between mandatory and
discretionary considerations.
For example, a vehicle on a freeway that intends to take on of-ramp will not
overtake a slower vehicle if the distance to the off-ramp is below a threshold,
regardless of the speed of that vehicle.
Furthermore, in order to implement MLC and DLC model separately, rules that
dictate when drivers begin to respond to MLC conditions need to be defined.
However, this point is unobservable, and so only judgment-based heuristic
rules, which often are defined by the distance from the point where the MLC
must be completed, are used.
Just like the judgement based lane changing models ,there also exist lot of
other models like general acceleration based lane changing models and gap
acceptance based lane changing models
If the gap on the target lane is not acceptable then the subject vehicle forces
the lag vehicle on the target to decelerate until the gap is acceptable.
This process is known as Forced merging.
At every discrete point in time, a driver is assumed to (a) evaluate the
traffic environment in the target lane to decide whether the driver intends to
merge in front of the lag vehicle in the target lane and (b) try to communicate
with the lag vehicle to understand whether the driver's right of way is
established.
If a driver intends to merge in front of the lag vehicle and right of way is
established, the decision process ends and the driver gradually move into the
target lane.
We characterize this instant by state M, where M denotes start forced merging.
This process may last from less than a second to a few seconds.
If right of way is not established, the subject continues the
evaluation/communication process (i.e., remains in state M) during the next
time instant.
The models discussed so far assume that lane changing is executed through gap
acceptance.
However, in congested traffic conditions acceptable gaps may not be available,
and so other mechanisms for lane changing are needed.
For example, drivers may change lanes through courtesy and cooperation of the
lag vehicles on the target lane that will slow down in order to accommodate the
lane change.
In other cases, some drivers may become impatient and decide to force in to the
target lane and compel the lag vehicle to slow down.
The discretionary lane changing process is modeled as a sequence of the
following three steps:
- Decision to consider a lane change,
- Check for the feasibility,
- Gap acceptance
Lane changing process is explained using the example which is shown in
Figure 1.
The subject vehicle in lane 2 makes a decision to consider a lane change and
then it selects a target lane which may be either lane 1 or lane 3.
Then it checks for the feasibility of lane change. Now this subject vehicle
accepts the gap in the target lane to make a lane change.
Figure 1:
Process of lane change
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![\includegraphics[height = 5cm]{qfprocessoflanechange}](img1.png)