Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 89 of 265
6.5.3 Maximum Green (MAX, MBX etc to MHX)
A maximum green timer is provided for each ‘vehicle actuated’ phase and
commences to time upon receipt of a demand for any opposing phase. If opposing
demands are present when the phase gains ROW, the maximum green period will
commence to time off immediately.
A stage change will not take place until the maximum green times for all phases that
need to terminate have timed off, called a ‘max change’, assuming green extensions
are also present for those phases preventing a ‘gap change’.
The maximum green timer will only be effective during VA, Bus Priority and
Emergency Vehicle modes. During CLF mode it will be ignored. During UTC mode,
if it is not to be considered for special requirements, it is possible to configure it to
be held reset.
Eight sets of maximum green timings are available, referred as ‘maxsets’ ‘A’ to ‘H’,
hence the handset commands MAX, MBX, MCX, etc., to MHX. These are switched
in and out as required by the master time clock (see section 25).
The timing range is 0 to 255 seconds in 1-second steps. Up to 8 maximum green
times can be configured for each phase (one for each ‘maxset’).
It is possible to program the controller so that a specified phase has a pre-timed
maximum green (using the PTM handset command). This means that the maximum
green timer will always start whenever the phase is active, regardless of opposing
demands. Therefore, the phase at right of way will terminate after its maximum
green time has expired, even if the opposing demand does not appear until part way
through this period.
If the opposing demand does not appear until after the maximum green time has
already expired, the phase will terminate immediately, even if green extensions are
active. However, a ‘pre-timed maximum extra period’ can also be configured (using
the PTX handset command). If the pre-timed maximum green time has already
expired (or is close to expiring) the timer is restarted with this short ‘extra’ period.
Thus if green extensions are present, the phase will remain at right of way for those
few seconds or until a ‘gap change’ rather than terminating immediately the
opposing demand appears.
6.5.4 Pedestrian Clearance Period (PBT)
When a basic intersection pedestrian phase terminates, the green man is followed
by a pre-set blackout period for the U.K. (or flashing green for some countries
abroad) which in turn is followed by the red man. The blackout period is considered
as part of the inter-green, i.e. the two timers will run in parallel. Also see section
6.11 for more information on pedestrian phase types.