Introduction

This is a summary of my findings whilst trying to understand how speed limits are set in a village and in particular how the decision is made between 40mph and 30mph. I hope the information will help others and provide some pointers to a few useful documents. This is work in progress and will be updated….

Richard

Notes and extracts

The speed limit for a village is 30mph, so what defines a village? According to Ref [2] (which is a must read!) there needs to be at least 20 houses and be at least 600m long to define a village. Looking at Station Road a 40mph road in Alburgh, then this is approx. 500m long and has 11 houses so I presume this lower density is why this has a higher speed limit?

There’s a tool to help decide on limits which I haven’t tried but may be worth a look? https://www.gov.uk/government/publications/speed-limit-appraisal-tool

Ref [3] Section 3 Key points states:

“The Highways Agency is responsible for determining speed limits on the trunk road network. Local traffic authorities are responsible for determining speed limits on the local road network”

So who is the Local Traffic Authority for South Norfolk, is the Highways Dept. the right place to send queries for Alburgh?

Ref [3] Para 40 states that

Speed limits should not be used to attempt to solve the problem of isolated hazards, for example a single road junction or reduced forward visibility such as at a bend…

I understand this to mean that a speed limit shouldn’t be reduced in order to make a sharp bend safer or a difficult junction. Instead a specific warning sign should be used.

Ref [3] Para 35 and 36 states

“35. Mean speed and 85th percentile speed (the speed at or below which 85% of vehicles are travelling) are the most commonly used measures of actual traffic speed. Traffic authorities should continue to routinely collect and assess both, but mean speeds should be used as the basis for determining local speed limits“

“36. For the majority of roads there is a consistent relationship between mean speed and 85th percentile speed. Where this is not the case, it will usually indicate that drivers have difficulty in deciding the appropriate speed for the road, suggesting that a better match between road design and speed limit is required. It may be necessary to consider additional measures to reduce the larger than normal difference between mean and 85th percentile speeds or to bring the speed distribution more in line with typical distributions. The aim for local speed limits should be to align the speed limit to the conditions of the road and road environment.”

I have now calculated the mean speed and 85th percentile using the data gathered by the mobile speed monitors. Using the data from Station road we have.

Mean Speed	85th Percentile Speed
31	35
34.7	40
31	40
32.5	40
33.6	40

Following the guidance from para 35 above the mean speed should be used to set the speed limit which is closer to 30 mph that 40mph in most instances.

Ref [3] Para 131 – 140 is for villages and worth a read.

131. Fear of traffic can affect people’s quality of life in villages and it is self- evident that villages should have comparable speed limits to similar roads in urban areas. It is therefore government policy that a 30 mph speed limit should be the norm through villages.

132. It may also be appropriate to consider 20 mph limits or zones in built- up village streets which are primarily residential in nature, or where pedestrian and cyclist movements are high. Such limits should not, however, be considered on roads with a strategic function or where the movement of motor vehicles is the primary function.

133. Traffic Advisory Leaflet 01/04 (DfT, 2004) sets out policy on achieving lower speed limits in villages. It suggests that reasonable minimum criteria for the definition of what constitutes a village, for the purpose of applying a village speed limit of 30 mph, would be that there were:
* 20 or more houses (on one or both sides of the road); and
* a minimum length of 600 metres

134. If there are just fewer than 20 houses, traffic authorities should make extra allowance for any other key buildings, such as a church, shop or school. Where the character of a village falls outside this definition, local authorities are encouraged to use their discretion in deciding whether a lower speed limit is appropriate.

135. The criteria above should give adequate visual messages to drivers to reduce their speed. It is recommended that the minimum length for the new limit is at least 600 metres to avoid too many changes in speed limits along a route, and to aid compliance. Traffic authorities may, however, lower this to 400 metres when the level of development density over this shorter length exceeds the 20 or more houses criterion and, in exceptional circumstances, to 300 metres.

136. In some circumstances it might be appropriate to consider an intermediate speed limit of 40 mph prior to the 30 mph terminal speed limit signs at the entrance to a village, in particular where there are outlying houses beyond the village boundary or roads with high approach speeds. For the latter, traffic authorities might also need to consider other speed management measures to support the message of the speed limit and help encourage compliance so that no enforcement difficulties are created for the local police force. Where appropriate, such measures might include a vehicle-activated sign, centre hatching or other measures that would have the effect of narrowing or changing the nature and appearance of the road.

137. Where the speed limit commences at the village boundary, the village nameplate sign (prescribed in diagram 2402.1 of TSRGD 2002) and speed limit roundel may be mounted together. The combined sign should be located at the point where the speed limit starts, and it may be helpful if drivers can see housing at the same time as the signs, reinforcing the visual message for reduced speed.

138. If there are high approach speeds to a village, or the start of the village is not obvious, village gateway treatments can also be an effective way to slow drivers down. Advice can be found in Local Transport Note 1/07 Traffic Calming (DfT, 2007) and Traffic Advisory Leaflets 01/94 VISP – A Summary (DoT, 1994a) and 01/04 Village Speed Limits (DfT, 2004).

139. In situations where the above criteria for a village are not met and there is a lesser degree of development, or where engineering measures are not practicable or cost-effective to achieve a 30 mph limit, but a reduction from the national 60 mph speed limit is considered appropriate, traffic authorities should consider alternative lower limits of 40 or 50 mph.

140. A recommendation to use the framework for the assessment of speed limit options on rural single carriageway roads, in place since the publication of the previous Speed Limit Circular (01/2006), is withdrawn.