The aim of the Bridge Road scheme is to reduce congestion on Bridge Road outbound, introducing signals with a phase for Glasshouse Lane may actually increase congestion. To discourage (via signals) the use of the estate as a short cut, the aim would be to hold the Glasshouse Lane signals on red for a reasonable time, enough to discourage through-traffic from using the estate.
However if you hold people on a red light for no reason (say if the toucan had been triggered twice in close succession) there is a risk that some will simply drive through the red signal. When the whole scheme is complete, Topsham Road, Countess Wear roundabout, Bridge Road should be a more attractive, quicker, route than Glasshouse Lane.
There has been previous consultation regarding a closure of the Glasshouse Lane junction with Bridge Road, but this was not popular with residents of the estate.