(i) STOP or GIVE WAY sign
(ii) terminal speed limit sign
(iii) other circular sign
(iv) rectangular zonal sign.
Not more than one other sign should normally be erected on the same post as a terminal speed limit sign. Where a clearway sign to diagram 642 accompanied by either a distance plate or an "End" plate is mounted below a speed limit sign, the plate should be butted up against the lower edge of the clearway sign. There should be a space equal to twice the width of the red border between the roundels to ensure that there is no ambiguity.
14.61 The most cost-effective arrangement for placing speed limit repeater signs in accordance with table 14-4 is to mount the signs back to back on alternate sides of the carriageway as illustrated in the left hand part of figure 14-19. Repeater signs may be co-located with other signs such as warning signs (see para 11.26), provided the spacing requirements specified in table 14-4 are met. The repeater sign will be mounted below the warning sign. They should not normally be co-located with directional signs, as drivers searching for a destination are likely to overlook the repeater sign.
14.62 Speed limit signs should always be mounted at heights that ensure drivers can easily see them, and where they will be free from obscuration by vegetation or other street furniture. The normal mounting height for a traffic sign, measured to its lower edge, is between 900 mm and 1500 mm above the carriageway alongside (see para 1.49 in Chapter 1). It is recommended that speed limit signs should not be mounted at heights less than 1500 mm, particularly where vehicle spray is likely to soil the sign. Where speed limit signs are erected above footways, a minimum headroom of 2300 mm is recommended, with 2100 mm as an absolute minimum. A clearance of 2300 mm should be maintained over a cycle track or shared cycleway/footway. Except where necessary to improve visibility of the sign, e.g. over the brow of a hill, or to accommodate a second sign on the same post (see para 14.60), signs should not be mounted at heights greater than this. See also paras 1.29 and 1.30.
ROAD MARKINGS
14.63 The road marking roundels shown in diagram 1065 must not be used on their own, and there is no statutory requirement to use them at all. They may be used only in conjunction with the following signs:
(i) a speed limit sign to diagram 670 (when placed to indicate the point at which a speed limit begins, or as a repeater sign in accordance with direction 11(2)),
(ii) a 20 mph zone sign to diagram 674 (but not the sign to diagram 675), or
(iii) a reminder sign to diagram 880.
Further details of the road marking roundel can be found in Chapter 5 (paras 21.4 to 21.6).
14.64 The Regulations prescribe different module lengths for hazard warning lines (diagrams 1004 and 1004.1), lane lines (diagrams 1005 and 1005.1) and centre lines (diagrams 1008 and 1008.1) depending upon the speed limit. The shorter modules (diagrams 1004, 1005 and 1008) must be used where the speed limit is 40 mph or less. The longer modules (diagrams 1004.1, 1005.1 and 1008.1) must be used where the speed limit is greater than 40 mph. Whenever an order is made to change the speed limit (e.g. from the national limit to 40 mph), care should be taken to ensure that the longitudinal road markings are correct.
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