Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) dn-geo-03060
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- Figure 7.3: Merging Diagram
- Figure 7.4.1: Merge Lane Layouts for use with Figure 7.3 (Layout A) Figure 7.4.2: Merge Lane Layouts for use with Figure 7.3 (Layout B)
- Figure 7.4.3: Merge Lane Layouts for use with Figure 7.3 (Layout C)
- Figure 7.4.4: Merge Lane Layouts for use with Figure 7.3 (Layout D)
- Figure 7.4.5: Merge Lane Layouts for use with Figure 7.3 (Departure from Standard)
TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 110 Figure 7.3 provides a number of layouts to cater for anticipated flows. Layout A (Figure 7.4.1) provides a basic parallel merge. Layout B (Figure 7.4.2), Layout C (Figure 7.4.3) and Layout D (Figure 7.4.4) are required where flows justify a lane gain arrangement. Layout E (Figure 7.4.5) may be considered as a Departure from Standard where it is not possible to use Layout C (see also Section 7.9). Ghost island road markings at merges should be designed in accordance with Chapter 7 of the Traffic Signs Manual. The minimum width of a ghost island at a merge lane is 2.0 m at its widest point and the minimum width of a chevron is 0.5m. If the ghost island marking is less than 1.2m wide it will be too narrow to mark with chevrons. The length of ghost island that is unmarked with a chevron could extend over a long distance. In order to prevent this problem, the minimum width of a ghost island must be 1.2m at a distance of 50m from the tip of the ghost island head or tail. It should be noted that ghost island layouts can require significant length to comply with the standard and this may be reflected in the land requirement especially where the layout is being provided within an existing road boundary. Gap finding is assisted when the merging traffic has the opportunity to match the speed of the mainline traffic. For all connector roads, a near straight at least equal in length to the nose length given in Table 7.1 column (3) for the appropriate Road Class must be provided upstream of the back of the merge nose. This requirement will enable merging traffic to achieve a matching speed. Platoons of traffic can enter a merge slip road if junctions upstream are signal-controlled. This traffic can have a significant effect on the mainline flow especially at peak times when available gaps in the mainline traffic flow are few. Turbulence and congestion are the result. Care should be taken to program such traffic signals with a view to reducing their impact on the mainline flow. In circumstances where traffic modelling shows significant delays incurred during peak periods as a result of high entry flows, it may be appropriate to use non-standard layouts that are not included in this Standard. Use of layouts not included in this Standard shall require a Departure from Standards. TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 111 Figure 7.3: Merging Diagram TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 112 Figure 7.4.1: Merge Lane Layouts for use with Figure 7.3 (Layout A) Figure 7.4.2: Merge Lane Layouts for use with Figure 7.3 (Layout B) Notes to Figures 7.4.1 and 7.4.2: 1. Figures in brackets refer to columns in Table 7.1. TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 113 Figure 7.4.3: Merge Lane Layouts for use with Figure 7.3 (Layout C) Notes to Figure 7.4.3: 1. Figures in brackets refer to columns in Table 7.1. 2. Option 1 is preferred due to the likely usage of Lane 1 of the connector road by the majority of large and/or slow vehicles and Lane 2 predominantly by light vehicles. Option 2 may be used in circumstances where traffic modelling indicates it is appropriate. TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 114 Figure 7.4.4: Merge Lane Layouts for use with Figure 7.3 (Layout D) Notes to Figure 7.4.4: 1. Figures in brackets refer to columns in Table 7.1. TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 115 Figure 7.4.5: Merge Lane Layouts for use with Figure 7.3 (Departure from Standard) Notes to Figure 7.4.5: 1. Figures in brackets refer to columns in Table 7.1. 2. This layout is for use where Layout C would be used but is not possible to implement because of site restraints. To use requires approval as a Departure from Standards. Yüklə 8,57 Mb. Dostları ilə paylaş:
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