# Traffic Signs Manual/Chapter 5/2009/8

GENERAL
8.1 The general rule governing the behaviour of traffic at roundabouts is that drivers should give way to any traffic on their immediate right unless road markings indicate otherwise. This is implemented by the provision of an advisory Give Way line (see paras 8.8 and 8.15) across the entry arm of a roundabout.
8.2 At all roundabouts (except those controlled by traffic signals for 24 hours per day, see paras 8.20 and 8.21) the appropriate prescribed Give Way line should be laid at each entry and should connect the central warning line, deflection island or central reservation to the near side kerb approximately following the line of the inscribed circle. This allows vehicles in the near side lane to be positioned further into the roundabout than those in the off side lane, improving visibility to the right.
8.3 Centre lines and, where provided, lane lines on the approach to roundabouts should be replaced by warning lines (see paras 4.9, 4.24 and table [[Traffic Signs Manual/Chapter 5/2009/4|#table4.3|4-3). Where possible the number of lanes on the approach to the Give Way line should be increased. This will ensure that maximum use is made of gaps in the circulating traffic. However, care should be taken to avoid releasing too much traffic for the space available to receive it. Where the carriageway is widened on the approach to a roundabout and extra lanes provided, drivers should be made aware of this by marking the lanes as early as possible. However, no lane should be less than 2 m wide at the start of the taper, nor less than 3 m wide at the Give Way line (see figure 8-1).
8.4 It is important to provide adequate vehicular deflection through a roundabout to limit vehicle speeds. TD 16 / 93 in Volume 6 of the Design Manual for Roads and Bridges (see para 1.4) shows how vehicle paths are determined, and how they may be controlled in order to increase deflection.
8.5 The main kinds of roundabouts in use are described as conventional ("normal" in TD 16 / 93), mini, double and signalled. These are discussed in the following paragraphs:
(i) conventional roundabout (see paras 8.7 to 8.9),
(ii) mini-roundabout (see paras 8.10 to 8.17),
(iii) double roundabout (see paras 8.18 and 8.19), and
(iv) signalled roundabout (see paras 8.20 and 8.21).
8.6 Other features used include lane markings in the circulating area (see paras 8.22 to 8.29), lane destination markings and arrows (see paras 8.30 to 8.33) and segregated left turn lanes (see paras 8.34 to 8.38).
CONVENTIONAL ROUNDABOUTS
8.7 These have a one-way circulatory carriageway around a kerbed central island, often with flared approaches to allow multiple vehicle entry (see figure 8-1). Physical splitter islands are used to guide traffic and ensure adequate deflection.
8.8 The Give Way marking to diagram 1003.1 is used; the 200 mm wide line at sites where the speed limit is 40 mph or less and the 300 mm size where the limit is greater than 40 mph. The marking to diagram 1003.3 should be adopted when the roundabout has a small central island, up to approximately 4 m in diameter.
​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.
​DOUBLE ROUNDABOUTS
8.18 These junctions have two conventional or mini-roundabouts either contiguous or connected by a central link road or kerbed island (see figure 8-4). Conventional and mini-roundabouts should not be mixed at the same junction.
8.19 Double roundabouts may offer an effective means of dealing with turning movements at asymmetrical junctions, those with a stagger, or junctions with high opposing right turn flows.
SIGNALLED ROUNDABOUTS
8.20 These have traffic signals in use on one or more of the approach arms for part or all of the day.
8.21 Where signals are used, traffic signal stop lines should be laid on the main circulating carriageway, approximately at right angles to the carriageway edge. The approach road should be marked as follows:
(i) full time signals - Stop line to diagram 1001, or
(ii) part time signals - Stop line to diagram 1001 and Give Way line to diagram 1003.1. If the entry angle is such that the Stop and Give Way lines are coincident, or nearly so, the former may be omitted, but only with the written approval of the Secretary of State (see para 2.1).
LANE MARKINGS IN THE CIRCULATING AREA
8.22 Road markings may be used to channelise traffic and indicate which lane to use at and through roundabouts. Further details may be found in Advice Note TA 78 / 97 in the Design Manual for Roads and Bridges, Volume 6, (see para 1.4).
8.23 Lane markings can increase capacity by improving both the use of road space on the roundabout and the level of gap acceptance of drivers joining it. They can also reduce the following types of accidents on roundabouts:
(i) side-to-side collisions on the circulating carriageway,
(ii) drivers being forced onto the central island, and
(iii) collisions between entering and circulating vehicles.
8.24 Markings should be designed to create flowing paths around the junction for all movements, avoiding sharp turns and providing a smooth alignment between entry and exit markings. Lane markings are always provided when the roundabout is under signal control. The route through the junction should be designed to avoid lane changing on the immediate approach to a stop line.
8.25 There are four basic configurations of road markings which may be used on the circulatory carriageway, making use of diagrams 1004 / 1004.1 and 1040.4. These are summarised below:
(i) concentric markings (see para 8.26),
(ii) partial concentric markings (see para 8.27),
(iii) concentric-spiral markings (see para 8.28), and
(iv) spiral markings (see paras 8.29).
8.26 Concentric markings trace a complete path around the circulatory carriageway encouraging drivers to enter and circulate in two or more adjacent lanes.
8.27 Partial concentric markings differ from concentric markings in that their continuity around the circulatory carriageway is interrupted. They can assist on wide circulatory carriageways by presenting drivers with clearly defined lanes within which to pass around the junction, and reduce the likelihood of drivers in the off side entry lane being forced towards the central island.
​8.28 Concentric-spiral markings are similar to concentric markings except that the outermost circulating lane or lanes guide traffic to the next exit by means of a lane drop. This is effected by running the circulatory markings directly into the existing road markings on that exit. They help to reduce conflicts between vehicles at the exits where more than one exit lane is provided, and can be used with any number of circulating lanes.
8.29 Spiral markings are more appropriate on larger roundabouts and involve a series of lane-gains and lane-drops around the circulatory carriageway so that drivers enter in the lane appropriate for their desired exit and follow that lane around the roundabout to be led off at the exit.
LANE DESTINATION MARKINGS AND ARROWS
8.30 Lane destination markings and arrows to diagrams 1035 and 1038 (see paras 13.1 to 13.5), may be justified where turning flows are consistently heavy throughout the day. Careful judgement is needed to ensure that such markings are not used inappropriately, as the reduction in flexibility may adversely affect the capacity of the roundabout.
8.31 Right turn arrows are best avoided on the approach lanes to a roundabout, other than a mini-roundabout, particularly as they can mislead overseas drivers used to driving on the right. Where a right hand lane is dedicated to a specific destination, this should be associated with an ahead arrow until the vehicle is in the circulatory carriageway.
8.32 Lane destinations and arrows may be used on the approach to and in the circulating areas of multiple lane signalled roundabouts, and those with circulatory markings (see paras 8.22 to 8.29). This may increase the capacity of a roundabout or make it safer, but will be successful only if drivers are given proper advance warning either by road markings or upright signs. The latter of course must be consistent with the markings.
8.33 Lane arrows and destinations will usually be repeated on roundabout circulatory carriageways when they have been used on the entries. They help drivers to identify the correct lane as early as possible and are particularly important if the lane is dedicated to a specific exit. They should also be used on the main carriageway of gyratory systems, i.e. large roundabouts formed of a series of one-way roads. Left turn arrows should not be used on the circulatory area immediately in advance of a point where a slip road enters from the left. This can confuse some drivers into turning left prematurely and travelling the wrong way along a dual carriageway. An ahead arrow may be used at this point, followed by a left turn arrow beyond the entering road.
SEGREGATED LEFT TURN LANES
8.34 Segregated left turn lanes reduce conflict between vehicles turning left at the first exit and those already circulating (see figure 8-5). The segregation may be effected by road markings to diagram 1041.1 or 1042.1, or by a physical island, in conjunction with the marking to diagram 1041 or 1042. Left turners are channelled into the left hand lane using lane arrows and road markings, supplemented by advance direction signs to diagram 2118 or its primary route equivalent (see Chapter 7, paras 5.43 and 5.44). Left turning vehicles proceed without having to give way to others circulating on the roundabout. Segregation by road markings is more common but may be less effective because it is liable to abuse. Further guidance may be found in TD51 / 03 in Volume 6 of the Design Manual for Roads and Bridges (see para 1.4).
8.35 If the left-turners are predominantly light vehicles and there is a high proportion of cyclists or heavy goods vehicles leaving the roundabout, differential speeds in adjacent lanes could cause problems, particularly if there is an uphill gradient. This might be especially hazardous for cyclists.
8.36 The use of these lanes in urban areas where pedestrians might cross should be considered carefully. Pedestrians should never be expected to cross left turn lanes segregated only by road markings. If pedestrians are likely to be present, they should be guided to a safer crossing point using ​guard rail or suitable planting. If this is not possible, segregation should be effected by a physical island of sufficient width to accommodate the peak number of pedestrians.
8.37 Segregated left turn lanes may encourage higher speeds; any desirable speed reduction measures should be applied before entry to the lane and not within it. Where the proportion of large goods vehicles is high, it should be ensured that the lane width is sufficient to accommodate the swept paths of larger vehicles, especially where physical segregation is provided. Where few such vehicles are expected, the lane may be reduced to 3.5 m in width, or exceptionally to an absolute minimum of 3.3 m. Where road markings to diagram 1041.1 or 1042.1 are used to create the lane segregation, the overall width of the marking should normally be at least 1 m. Where reflecting road studs are used, these must be red (see para 6.9).
8.38 When segregation is achieved using road markings alone, no special allowance needs to be made for broken-down vehicles, as other traffic will not be prevented from passing. Where physical segregation is introduced, the design should not prevent vehicles from making a left turn at the roundabout in the normal way by using the non- segregated part of the approach.
YELLOW BOX MARKINGS
8.39 Direction 35 prohibits the use of yellow box markings (see section 12) at unsignalled intersections on roundabouts. This is because a circulating vehicle has priority over those entering. If it stops to avoid obstructing the box when its exit is blocked, thereby releasing the flow of entering vehicles, there is likely to be uncertainty over re-establishing right of way when the exit is clear again. Moreover, a vehicle stopped in an outer lane might obscure vehicles lawfully continuing to circulate on the inner lanes (whose exit might not be blocked) from the view of drivers entering the roundabout. Yellow box markings may however be used where traffic entering the roundabout is controlled by signals at all times.
​8.40 Although the Directions do not prohibit the use of the KEEP CLEAR marking (diagram 1026) on roundabouts, there are still the potential problems of obscuration of sight lines and re-establishing priorities. These risks should be assessed carefully when considering whether the marking might help resolve exit blocking problems.
YELLOW BAR MARKINGS
8.41 For details of the use of yellow bar markings on the approach to a roundabout see section 11.
SPECIAL CASES
8.42 It is sometimes expedient to give traffic from one arm of a roundabout priority over traffic already circulating. This might be necessary if the layout is unusual or there is a heavily dominant flow, but is likely to be more appropriate on urban roads, where speeds are lower, than in rural areas. As such a layout operates contrary to the conventional Give Way rule, it can be confusing and potentially dangerous. Traffic signal control may be a better option.
8.43 Where signalling the roundabout is not practicable, the layout in figure 8-6 may be used. The mandatory Give Way lines and triangle marking (diagrams 1003 and 1023) must be laid across the circulating area of the roundabout at the point of entry of the priority road. The Give Way markings should be reinforced by the provision of two upright GIVE WAY signs to diagram 602 as shown.
8.44 Give Way markings to diagram 1003 may also be used at conventional roundabouts (although only in conjunction with upright signs to diagram 602, see direction 34(1)), where there might otherwise be uncertainty about priorities, e.g. where drivers might be confused by a green signal at a pedestrian crossing immediately before the roundabout.
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