MINI-ROUNDABOUTS
8.10 Mini-roundabouts can be very effective in improving existing urban junctions which experience safety and side road delay problems, and can often be installed with minimal alterations to kerbs etc. They have a one-way circulatory carriageway around a flush or slightly raised central disc, with or without flared approaches. Three arrows around the central disc indicate the direction of circulation. The marking (diagram 1003.4) carries no street furniture, and may be overrun by large vehicles if necessary.
8.11 The layout should be designed so that drivers are made aware in good time that they are approaching a roundabout. Mini-roundabouts should be used only when all approaches are subject to a speed limit of 30 mph or less. Their use on roads with a higher speed limit is not recommended as it is seldom possible to achieve adequate deflection and the marking may not be sufficiently conspicuous at higher speeds.
8.12 Two size ranges are prescribed for the mini roundabout marking (see figure 8-2); the choice will depend on the road space available and the need for conspicuity. The larger range should be used wherever it is needed to provide adequate deflection and deter straight through movement. The smaller range may be adequate at more constricted sites where the marking would otherwise occupy too large a part of the carriageway space and might be confusing, or where frequent overrunning would result in excessive maintenance costs.
8.13 In no circumstances may annular rings be added around the central disc. If a more conspicuous central marking is necessary, a larger disc, up to a maximum of 4 m should be used. If the junction area is very large, the diameter of the circulatory arrow marking should be increased to a maximum of 10 m, with the length of the arrows correspondingly increased to 4.45 m. Conspicuity may be further enhanced by replacing the normal central warning line on the approach with a hatched marking to diagram 1040.
8.14 The central disc of the mini-roundabout marking may be domed up to a maximum height of 125 mm (regulation 32(2)(c)), but must not exceed 6 mm at the perimeter. This will increase the conspicuity of the roundabout, particularly in wet weather. However, research evidence indicates that accident rates at domed roundabouts are slightly higher than at flush roundabouts, although the accident severity is less. The dome may be formed in bituminous or other suitable material, but the surface must be coloured white and be retroreflective.
8.15 The standard Give Way marking used at mini-roundabouts is diagram 1003.3. When used at mini-roundabouts, it must be accompanied by the upright sign to diagram 611.1 and may be accompanied by diagram 1023. In certain circumstances the Give Way marking to diagram 1003 may be used (see para 8.17 and figure 8-3). Diagram 611.1 will normally be sited about 1.5 m in advance of the Give Way marking. This might have to be increased if the sign would not otherwise be clearly visible.
8.16 Road markings or small traffic islands should be placed so as to ensure some vehicle deflection on the approaches; hatched markings to diagram 1040 can often help. Physical islands should be kept free of all furniture except the "keep left" bollards and other essential signs. Where an existing junction is being converted to a mini-roundabout, it may not be practicable to achieve the ideal amount of deflection. However, this may be acceptable if approach speeds are low.
8.17 Where suitable deflection cannot be achieved, traffic entering the roundabout might, because of its approach speed, disregard the standard advisory Give Way line (diagram 1003.3). In such cases, the mandatory GIVE WAY sign to diagram 602 may be mounted on the same post and above the sign to diagram 611.1. The GIVE WAY sign should not be used where it could confuse drivers into giving way to traffic from the left as well as from the right, e.g. on the stem of a T-junction or on any arm of a four-way junction. When diagram 602 is used, it must be accompanied by diagram 1023 and by the Give Way marking to diagram 1003 (see figure 8-3).
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