The most significant improvement in release 8 is that it allows modeling of networks with
oversaturated traffic conditions. Although release 7 accepted networks with these
conditions, it did not model them realistically. This is because the simulation process
applied in release 7 was not structured in such a way that spillback conditions could be
explicitly considered. Release 8 completely restructures the simulation process to address
these issues by changing from a link-wise approach to a step-wise approach.
In the link-wise approach, the simulation of the network begins at a specific link,
completes all time steps and then proceeds to the next link in turn until all links in the
network are simulated. This simulation approach does not allow the effect of spillback
occurring over time to pass from one link to another. To remedy this, release 8 introduces
a step-wise approach that allows the simulation to proceed through the complete network for every simulation time step. With this approach, the spillback effect is passed from one
link to another over time. An analogy is to imagine all links lined end-to-end in release 7,
to release 8, which resembles a bowling alley with all links being simulated in parallel—
with all link-specific interactions being more realistically modeled. In general, execution
times for release 8 will be longer than those of release 7, especially for large networks,
because of the need to use dynamic allocation of memory to accommodate the memory intensive
nature of the step-wise simulation.