essential, they feel that on no account should the signs be deeper than the parapet and that they should preferably be less than its full height, in order not to break up the line of the bridge. We have much sympathy with this view, but it has unfortunately not proved possible to accommodate all the necessary information in a sign whose height is less than that of the parapet, particularly as the arrows have to point down into the centres of the appropriate traffic lanes. The illustration of the sign we recommend for this particular location (figure 36) will make this clear; the sign is in two parts, which will appear side by side on the parapet. We recommend that if in fact the sign does prove to spoil the line of the bridge the erection of a railing along the top of the parapet would go some way towards preserving it.
109. We do not recommend that a practice should be made of placing traffic signs on bridge parapets. As a general rule it is much preferable that overhead signs, even when they are quite close to existing bridges, should be placed on separate structures specially designed for the purpose.
Supplementary Direction Signs
110. Where the overhead signs recommended in paragraphs 105 and 106 are used there will be no need for a sign corresponding to the supplementary exit sign at ordinary junctions along the motorway, since, as explained in paragraph 106, its function is fulfilled by the second of the two overhead signs. Where the advance direction signs are roadside signs, however, we see a need for a supplementary sign in the point of land between the two arms of the junction. This sign will necessarily be large because it will have to relate to both arms. At most forks in the motorway the two arms will diverge at such a narrow angle that there will not be room for such a sign unless it is mounted high on a post and cantilevered out over the two carriageways. We recommend that this should be done. Figure 37 illustrates the two arms of the sign we recommend; where there are two or more place-names they should be aligned on the inner side of the arm.
111. The versions of this sign at present in use on the London-Yorkshire Motorway, in accordance with an earlier recommendation from us, do not incorporate arrows. We do not now consider that they give the clearest possible indication of the route to be followed, and it will be seen that the design we now recommend has an arrow at the outer edge of each arm, with the route-number next to it. In principle each arrow should point down diagonally into the respective carriageway; this means that on any one sign the angle of slope of one arrow might differ from that of the other, depending on the angle at which the carriageway to which it relates curves away from the straight. Provided that the arrows distinguish clearly between the two carriageways, however, we do not think it necessary to destroy the symmetry of the sign by having them point at different angles.
Merging Traffic
112. We have recommended at paragraph 101 that at ordinary junctions along the motorway no sign is necessary to give warning of traffic from the entry slip road merging with the main motorway traffic. Where two motorways converge, however, each of them consisting of multi-lane carriageways, the problem is obviously more serious, and we consider that appropriate warning should be given.
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