Traffic Signs Manual/Chapter 5/2009/12
LEGAL ASPECTS
12.1 Part II of Schedule 19 to the Regulations defines two purposes for the yellow box marking to diagram 1043 or 1044 (see figure 12-1):
(i) to mark an area of carriageway conveying the prohibition that no person shall cause a vehicle to enter the box junction so that it has to stop within it due to the presence of stationary vehicles. A vehicle waiting to turn right (other than at a roundabout) may stop within the box junction for so long as it is prevented from completing the right turn by oncoming vehicles or other vehicles which are stationary whilst waiting to complete a right turn.
(ii) when placed in conjunction with diagrams 615 and 811 on an area of carriageway which is less than 4.5 m wide at its narrowest point, the road marking shall convey the prohibition that no person shall cause a vehicle to enter the box junction so that the vehicle has to stop within it due to the presence of oncoming vehicles or other stationary vehicles beyond the box.
12.2 Drivers entering the box when their exit is obstructed by stationary vehicles, whether in the road ahead or to either side, commit an offence. It is permissible, however, to enter and become stationary if turning right and prevented from leaving the junction only by oncoming traffic, or by other vehicles waiting to complete the right turn.
12.3 The Directions do not permit the use of yellow box markings at roundabouts unless traffic entering the box is controlled by signals at all times (see para 8.39 and direction 35). Nor should they be used where traffic streams merge, as it will not be clear which stream has precedence when a gap appears.
12.4 Traffic regulation orders are not needed in order to install yellow box markings, although the police should always be consulted. The marking is subject to section 36 of the Road Traffic Act 1988 (see para 2.4 and regulation 10).
SUITABILITY
12.5 Experience has shown that the marking improves traffic flows where previously there were delays due to vehicles blocking the junction and impeding the cross flow. At signal controlled junctions, the queues of traffic left at the end of a green phase have been significantly reduced and there have been marked reductions in injury accidents, especially those involving pedestrians.
12.6 Box markings are no substitute for traffic signals. They can however help to improve trafficflow at junctions where blocking back causes obstruction. Their use at pinch points controlled by priority signs and at level crossings (diagram 1045) is dealt with in paras 12.13 and 12.14 respectively.
12.7 Not all junctions are suitable for the installation of box markings, and certain criteria should be applied before deciding whether a particular site should be marked. A traffic survey should be carried out to determine the extent of the problem, not only to assess the suitability of the junction for box marking but also to establish whether any alternative measures might be effective (e.g. re-timing or linking of traffic signals at adjacent junctions). A survey will also reveal what further measures might be needed, e.g. imposition of waiting and loading restrictions or re-location of bus stops.
12.8 Factors which influence a decision to provide box markings include the following:
(i) the junction should preferably, though not necessarily, be controlled by signals (see also para 12.3),
(ii) blocking back from a junction ahead should occur under existing conditions, even if only for short periods,
(iii) there should preferably be heavy traffic flows on both opposing arms of the junction. At unsignalled junctions with minor roads where blocking of the mouth of the minor road is infrequent, a KEEP CLEAR marking (see paras 22.11 to 22.14) may be more appropriate,
(iv) opposing roads at a junction should normally be in line with each other. The markings may, however, be used exceptionally at staggered junctions, particularly where the minor roads have a right hand stagger, provided the maximum box length is not exceeded, and irregular shapes can be avoided. Two half-boxes may be a practical substitute for a single large box in such circumstances,
(v) the carriageway beyond the junction should be free from obstruction (this may necessitate the imposition of waiting or loading restrictions, or the adjustment of bus stops on the lengths concerned),
(vi) where a succession of junctions gives rise to blocking back, the establishment of a series of boxes should be considered, provided at least 20 m storage space can be maintained between successive boxes, and
(vii) there should preferably not be a high proportion of right-turning traffic, since experience has shown that the effectiveness of the marking is reduced under these conditions.
12.9 Yellow box markings may be used outside police, fire, ambulance stations or hospitals only where there is an access road forming a junction with the main road. Where vehicles exit directly onto the carriageway, a KEEP CLEAR marking to diagram 1026 or a KEEP CLEAR marking to diagram 1027.1 (varied to omit the word "SCHOOL") should be used.
12.10 Half-boxes, in which only half the area of the junction is marked (diagram 1044) are appropriate at "T" junctions and other junctions where the traffic blocks back from one direction only. Half-boxes may be used only in the position shown in the lower drawing in figure 12-1, i.e. on the minor road side of the main carriageway.
SETTING OUT
12.11 The marking consists of yellow lines forming a box enclosing cross-hatched diagonal lines (see figure 12-1). The diagonal lines are 150 mm wide and spaced 2 m apart where the shortest boundary of the box is less than 9 m long, or 2.5 m apart where the shortest boundary line of the box is 9 m or more. Yellow box markings must always have four straight sides, each being approximately transverse to the traffic flow on the approach. Up to 10% of the length of the side at any corner may be cut away as shown in the diagram to accommodate corner kerbs. The overall shape of the marking and the number of cross-hatched lines will vary to accord with the circumstances at the site.
12.12 To set out the marking:
(i) mark transverse lines across each arm of the junction approximately at right angles to the flow of traffic (see figure 12-2),
(ii) where the corners of the box have been cut away, complete the full box with construction lines; where the sides are still unequal in length, extend the short sides to X and Q using construction lines so that PX = PY = YQ,
(iii) draw a main diagonal X-Y running from corner to corner of the notional box (either pair of opposite corners may be used),
(iv) construct a diagonal line P-Q’ intersecting the first diagonal at right angles; it will not necessarily connect both corners of the yellow box,
(v) set out the intermediate lines parallel to the diagonals, at grid intervals of 2 m or 2.5 m as appropriate (see para 12.11).
Half-box markings should be designed in the same way as full box markings but with only half the box marked on the road (see lower drawing in figure 12-1).
SPECIAL CASES
12.13 Box markings are sometimes effective in combination with priority signs (diagrams 615 / 615.1 and 811 / 811.1) to break queues through an exceptionally narrow pinch point and enable an opposing flow to continue without unnecessary delay. The marking may be used for this purpose only if the carriageway width is less than 4.5 m at the narrowest point (regulation 29(2) and Part II of Schedule 19).
12.14 A different pattern of yellow box marking (diagram 1045) is used at Automatic Half Barrier level crossings (see paras 19.18 and 19.19). This may be appropriate at other forms of railway crossing if these are likely to become blocked by queuing traffic, but only with the agreement of the Railway Inspectorate. Further guidance on the use of box markings at level crossings can be found in paras 19.18 and 19.19, and at tramway crossings in paras 18.15 and 18.23.
This is NOT an official transcription, and should NOT be considered in any way a controlled copy of the work in question.
This document no longer necessarily represents current practice, as it relates to an earlier version of the regulations (TSGRD 2002 as amended at publication date) rather than the current TSRGD 2016 regulations. It should not be used for actual design or operational use without consulting a more recent edition.
This version was transcribed in May 2015, from a 2009 impression.
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