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It starts to get a bit easier to understand and more straight forward and I will explain to you how these limits are introduced and signed.
1. 40 mph speed limits are used where there is development either of a residential or business nature or a mix of both. The development will be sporadic and will not be as dense as that found within a 30mph speed limit. 40mph speed limits can sometimes act as buffer limits before you enter a 30mph speed limit and would typically be up to 200 - 300 metres long to try and reduce vehicles speeds.
2. 50mph speed limits can be used on rural roads where the traffic flows are high, or where the mix of traffic flows and junctions are high or where there is a high Traffic Accident Injury Rate.
3. In order to create a 40 or 50mph speed limit a legal order needs to be made by the local authority or Highways Agency if it is a Trunk Road (Governments responsibility). The legal order would use section 84 of the Road Traffic Regulation Act 1984. It may be made over any section of road including street lit areas. All 40 and 50mph speed limits will require repeater signs for as long as the limits lasts at regular intervals to remind the driver.
4. If you are on a road and the speed limit changes to 40 or 50 mph, then speed limit signs need be on each side of the road. If there is a central traffic island, the signs must still be located on each side of the road and not on the nearside and traffic island only as this would be illegal. A sign may be added to the central island if the sign on the offside of the road is difficult to see. If the limit changes on a dual carriageway, then a sign is required on the nearside and on the central reservation.
5. The sizes of the signs are given in a tables - signs (1) featured on this website.
6. Repeater signs are required for 40 and 50mph speed limits, these can be mounted on metal poles or lampposts. For 40mph speed limits the first repeater sign must be erected within 250 metres of the start of the limit, thereafter at intervals of 350 metres if placed on alternate sides of the road or 500 metres if on the same side of the road. For 50 mph speed limits the first repeater must be erected within 350 metres of the start of the limit and thereafter no more than 450metres between signs on alternate sides of the carriageway or 700metres on the same side of the carriageway. These are the maximum spacings and would usually be erected closer than this. The recommended sizes for repeater signs for 30 and 40mph speed limits are 300mm while for 50mph speed limits on two way single carriageway roads the size should be 450mm - tables - signs (2)
7. If you are turning from a main road with a higher or lower limit into a side road with a 40 mph speed limit then there need be only one sign on the nearside of the carriageway within 20 metres of the junction. If the sign is over 20 metres from the junction, then a legal order needs to extend into that junction from the main road and two signs must be provided, one on each side of the carriageway. For example if you areturning from a 50mph speed limit into a 40mph speed limit and the 40mph signs were 25 metres from the junction, then a 50mph speed limit order needs making for 25 metres. If you are turning from a 30mph speed limit and the road is street lit then no order is required as the length between the junction and the 40mph signs is by virtue of the street lighting, but a 40mph speed limit order is required for the length of the 40mph speed limit.
8. If you are turning out from a side road with a lower limit than the main road then no signs are required as long as there are repeater signs on the main road either side of the junction within 100 metres. For example if you turn out of a side road with a 30mph speed limit into a 40 or 50 mph road then all that is required is 2 repeater signs on the main road on either side of the junction within 100metres, although most junctions will be signed with two signs on each side of the carriageway on the side road. In the case of turning out from a side road onto a main road with a national limit this rule does not apply and two national speed limit signs must be erected on the side road (white circle with black stripe). If the repeaters signs are more than 100 metres on either one side or the other of the junction on the major road, then the speed limit requires two signs, one on each side of the carriageway on the side road. If the main road has a national speed limit ie 60mph for a single carriageway two way road or a dual carriageway then 2 x national speed limit signs are required on each side of the carriageway despite it being a higher limit.
9. Speed limit roundels should only be marked on the road adjacent to repeater signs at the side of the road or at the start of the speed limit, if these appear where there are no repeater signs then this is illegal.
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