Forums Forums Traffic Signals Prohibitions versus instructions at traffic signal junctions

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    Whilst it might be a compliance problem, is it a safety problem? Is there an accident problem? You also need to think about what level of enforcement will take place if you install a NRT box. I suspect you already know the answer to the question, “How much enforcement will take place?” What does the TRO for the junction say?

    The drivers are likely to be locals who make these turns already, so changing the signing is unlikely to have an effect, given that they will generally not see them due to over-familiarity with the junction – ask yourself what box signs you pass on a regular journey you make.

    Paul Clark

    I have a traffic signal site with restricted turning movements that has a compliance problem. The layout is a fully signalled urban crossroads where two, two-way, single carriageway side roads meet a dual carriageway. One of the side roads is cul-de-sac of very short length and carries little traffic movement. The other side road carries a significant volume of traffic. This arm is restricted to turning left only onto the dual carriageway, with no movement permitted ahead to the cul-de-sac or right onto the dual carriageway. Because the traffic from the dual carriageway can turn left or right under signal control into the larger side road, there must be a gap in the central reserve to allow the right turn in.

    Some drivers from the restricted side road, when given green, turn right through this gap onto the dual carriageway, in conflict with the ahead traffic they are attempting to join as this traffic has no legitimate reason to stop.

    Drivers on the restricted side road have a primary and secondary signal with left turn green arrow aspects. Just in advance of these are two road signs on their own posts to Dia. 606 turn left arrow. Thus, there are four turn left arrows in all, but some drivers still turn right.

    It has been suggested that I should add a Dia. 612 No Right Turn box sign to each signal head below the left turn arrow. The assertion is that this would reduce, or eliminate, the right turn movements because drivers do not understand green arrows at traffic signals or turn left signs. Any green on a signal head allows all movements in the minds of these drivers, it is claimed.

    My view is that those who turn right are either ignorant of the meaning of signals and signs, or do so deliberately knowing the movement is banned. My conclusion is that in the first case additional signs would be futile as they would not be understood, and in the second case also futile as they have already demonstrated their willingness to contravene a restricted movement.

    However, colleagues are adamant that signs that instruct drivers not to do something (those in a red circle) are both understood and complied with far more than signs that seek to achieve the same end by giving a positive instruction to do something. If this is accepted then many existing sites would need a proliferation of box signs as well as arrows which, to me, is an unwanted expansion of clutter.

    My question is simply, is there any convincing evidence that prohibitions against doing something are preferable to positive instructions to do something at traffic signal junctions because they are both understood and complied with more readily?

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