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4.2 Goals and Their Relations to Capabilities 117

but an exit at the right is to be taken in the near future. On a state road, cruising in
the rightmost lane but having to take a turnoff to the left from the leftmost lane
yields a similar situation. So the situation is not just given by the geometric ar-
rangement of objects and subjects but also depends on the task domain and on the
intentions to be realized.
Making predictions for the behavior of other subjects is a difficult task, espe-
cially when their perceptual capabilities (Appendix A.4.7) and those for planning
and decision-making (Appendix A.4.8) are not known. This may be the case with
respect to animals in unknown environments. These topics (Appendix A.6) and the
well-known but very complex appearance and behavior of humans (Appendix A.5)
are not treated here.
Appendix A.7 is intended to clarify some notions in vehicle and traffic control
for which different professional communities have developed different terminol-
ogies. (Unfortunately, it cannot be assumed that, for example, the terms “dynamic
system” or “state” will be understood with the same meaning by one person from
the computer science and a second one from the control engineering communities.)

4.2 Goals and Their Relations to Capabilities

To perform a mission efficiently under perturbations, both the goal of the mission
together with some quality criteria for judging mission performance and the capa-
bilities needed to achieve them have to be known.
The main goal of road vehicle traffic is to transport humans or goods from point
A to point B safely and reliably, observing some side constraints and maybe some
optimization criteria. A smooth ride with low values of the time integrals of (longi-
tudinal and lateral) acceleration magnitudes (absolute values) is the normal way of
driving (avoiding hectic control inputs). For special missions, e.g., on ambulance
or touring sightseers, these integrals should be minimized.
An extreme type of mission is racing, exploiting vehicle capabilities to the ut-
most and probably reducing safety by taking more risks. Minimal fuel consumption
is the other extreme where travel time is of almost no concern.
Safety and collision avoidance even under adverse conditions and in totally un-
expected situations is the most predominant aspect of vehicle guidance. Driving at
lower speed very often increases safety; however, on high-speed roads during
heavy traffic, it can sometimes worsen safety. Going downhill, the additional thrust
from gravity has to be taken into account which may increase braking distance
considerably. When entering a crossroad or when starting a passing maneuver on a
road with two-way traffic, estimation of the speed of other vehicles has to be done
with special care, and an additional safety margin for estimation errors should be
allowed. Here, it is important that the acceleration capabilities of the subject vehi-
cle under the given conditions (actual mass, friction coefficient, power reserves)
are well known and sufficient.
When passing on high-speed roads with multiple lanes, other vehicles in the
convoy being passed sometimes start changing into your lane at short distances,