The 30mph speed limit that applies automatically to “restricted roads”  is triggered by there being “three or more lamps throwing light on the carriageway and placed not more than 183metres apart”.

Where there is no street lighting or inadequate spacing then in order to set a 30mph limit then the Traffic Authority needs to implement a Traffic Regulation Oder that specifically sets a 30mph limit. In addition they should also put 30mph repeater signs on such a road to remind the drivers that in the absence of the lighting or any lighting at all then a 30mph limit applies.

There may be some debate as to whether lighting that is permanently turned off is able to “throw light on the carriageway”. However Traffic Authorities are in a position to make a TRO for these so that regardless of the lighting a 30mph limit applies by virtue of the TRO rather than the lighting (or lack of it).

If the Traffic Authority sets a 20mph limit by means of a TRO then this shall apply regardless of the street lighting but will require the appropriate traffic calming or repeater signs at regular intervals.

Note that where the speed limit is 20mph or less then most warning signs no longer require their own lighting and many warning signs are not required at all.