ST750
G
ENERAL
H
ANDBOOK
667/HB/33750/000
Page 37
Issue 6
If the pedestrian phase is demanded while this period is still running, the vehicle
phase remains at green until at least this period has expired.
If the pedestrian phase is demanded after this ‘minimum’ period has expired and no
vehicles are present, then the vehicle phase loses right of way immediately.
If the vehicle detectors indicate that vehicles are present, then the vehicle phase will
remain at green until the vehicles are no longer present. This is referred to as a ‘gap
change’ since the vehicle phase loses right of way to service the pedestrian demand
when a gap in the traffic appears.
H
owever, when the pedestrian phase is demanded, the vehicle phase’s ‘maximum
green timer’ is started. If vehicles continue to be present, keeping the vehicle phase
at green, the vehicle phase will lose right of way when this timer expires, even if
vehicles
are still present. This is referred to as a ‘max change’ since the vehicle
phase loses right of way when its maximum green time expires.
The maximum green time is specified by the handset commands MAX, MBX, MCX
and MDX allowing four different times to be called up at different times of the week.
When the pedestrian phase has completed its green period and the controller has
executed the required ‘pedestrian to vehicle clearance period’ (see section 3.1), the
vehicle phase returns to green.
3.2.3 Vehicle Actuated with Pre-Timed Maximum (PTM)
This mode is very similar to normal vehicle actuated mode, except that the vehicle
phase’s maximum green timer is started as soon as the vehicle phase appears at
green, regardless of whether there is a demand for the pedestrian phase.
The option is enabled using the PTM handset command.
Therefore, if the vehicle phase has already been at green for longer than its
configured maximum green time when a push-button is pressed, the vehicle phase
loses right of way immediately subject to the pedestrian demand delay (see section
3.3.3) or the pre-timed maximum extra.
Compare this to the normal vehicle actuated mode, where the pedestrian would
have to wait for up to the maximum green time (if vehicles continue to be present)
before the vehicle phase loses right of way.
3.2.4 Linked Operation
With the controller running any of the above three modes, the operation controller
can be further modified by various ‘linking’ options.
These options hold the vehicle phase at green until a specific time when the
pedestrian phase is allowed to appear. During this ‘window’ vehicle extensions are
removed to ensure that any pending demand for the pedestrian phase is serviced.
