In our view, it is as least as important to discuss the resulting traffic flow characteristics as to discuss the details of the driving logic. For that reason, we have performed systematic validation of the various aspects of the emerging flow behavior. Since the microsimulation is composed of car-following, lane changing, unprotected turns, and protected turns, we have corresponding validations for those four aspects. Although we claim that this is a fairly systematic approach to the situation, we do not claim that our validation suite is complete. For example, weaving [40] is an important candidate for validation.
It should be noted that we do not only validate our driving logic, but we validate the implementation of it, including the parallel aspects. It is easy to add unrealistic aspects in a parallel implementation of an otherwise flawless driving logic; and the authors of this paper are sceptic about the feasibility of formal verification procedures for large-scale simulation software.
We show examples for the four categories (Fig. 4): (i) Traffic in a 1-lane circle, thus validating the traffic flow behavior of the car following implementation. (ii) Results of traffic in a 3-lane circle, thus validating the addition of lane changing. (iii) Merge flows through a stop sign, thus validating the addition of gap acceptance at unprotected turns. (iv) Flows through a traffic light where vehicles need to be in the correct lanes for their intended turns - it thus simultaneously validates ``lane changing for plan following'' and traffic light logic.
In our view, our validation results are within the range of field measurements that one finds in the literature. When going to a specific study area, and depending on the specific question, more calibration may become necessary, or in some cases additions to the driving logic may be necessary. For more information, see [27].
Figure 4: TRANSIMS macroscopic (emergent) traffic flow
characteristics. (a) 1-lane freeway. (b) 3-lane freeway.
(c) Flow through stop sign onto 2-lane roadway. (d) Flow through
traffic signal that is 30 sec red and 30 sec green, scaled to
hourly flow rates.