Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 117 of 265
9.4 SDE/SA Actions
9.4.1 SDE/SA Green Extensions
The SDE/SA facility provides green extensions that hold the associated phase(s) at
right of way until the vehicle reaches the normal detectors. Sections 9.1 and 9.2
describe the extensions provided the SDE and SA facilities.
An SDE/SA extension may be suppressed, but not the associated extra clearance,
using Special Conditioning. This would be used in an early cut-off situation where
the overlapped phase would not be required to be extended by its SDE/SA loops
during the turning movement.
9.4.2 Extra Clearance Periods
Each intersection phase which is equipped with SDE or SA can be allocated an
extra clearance period to extend the subsequent inter-green. The extra clearance
period for each phase will be introduced if any of the following conditions occur:
(a) An SDE or SA extension is active for the phase during its amber
leaving state.
(b) Any speed measurement detector does not detect a vehicle during the
associated phase green period.
(c) Optionally any extension (speed extension, green extension or Priority
extension) is active for the phase when it changes from green to amber
leaving.
The condition in (c) is not normally enabled at the time of configuration, but note that
speed extensions will still request extra clearance because of the operation of
condition (a).
An extra clearance period will be given under any mode of control, i.e. manual, VA,
fixed time, CLF, UTC, vehicle priority or hurry call. Its effect is to increase all the
inter-green timings from the phase that is being given the extra clearance, and also
to increase the phase change delay times for gaining phases (see section 11.6).
This latter increase is computed as the largest of the extra clearance times currently
applied for that stage to stage move.
Phase change delay times for individual gaining phases may be configured so that
they are not increased when a specific phase is requesting an extra inter-green due
to SDE/SA.
The range of the timing period for the extra-clearance is 0 to 50 seconds in 1-
second steps for each SDE/SA phase. The programmed value may be changed via
the handset using the SCT command.