TRANSYT-7F optimizes phase lengths and offsets based on an objective function called
the performance index (PI). Release 7 included four types of PI defined by disutility index
(DI) and/or progression opportunities (PROS). These objective functions were not be
suitable for optimization of oversaturated networks. Release 8 introduces four additional
objective functions that are based on traffic throughput and queuing measures. The
“throughput measure” is a ratio defined as the link vehicle departures over link vehicle
arrivals. The “queuing measure” is also a ratio and is defined as the average back of queue
on a link divided by the maximum number of vehicles that can be accommodated on the
link. The idea behind including these measures is to emphasize traffic throughput and
queue management to help links with spillback conditions. The new objective functions
are