Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) dn-geo-03060
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- 8.3.2 Typical Sketch Layouts Figure 8.2
- Figure 8.5
- Figure 8.7
- Figure 8.2: Example of Compact Grade Separation for 4 Arm Junction Figure 8.3: Compact Grade Separation for 3 Arm Junction
- Figure 8.4: Single quadrant link with a ghost island junction on the single carriageway mainline
- Figure 8.6: Schematic Example of a 4 Arm Compact Grade Separation Single Carriageway
- Figure 8.7: Schematic Example of 3 Arm Compact Grade Separation on Dual Carriageways
- 8.4.2 Collisions
- 8.4.3 Traffic Signs
- 8.4.4 Road Markings
TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 156 8.3.2 Typical Sketch Layouts Figure 8.2: Detailed layout of 4 arm compact junction with compact connector roads in preferred location. Diverges and merges are to be designed in accordance with Chapter 5 for priority junctions. Layout suitable for junctions with substantial minor road through traffic. At grade junctions with a single carriageway mainline must be staggered to avoid “see through” issues. Figure 8.3: Detailed layout of 3 arm compact junction with compact connector roads in preferred location. Diverges and merges are to be designed in accordance with Chapter 5 for priority junctions. At grade junctions with a single carriageway mainline must be staggered to avoid “see through” issues. Figure 8.4: Detailed layout of a single quadrant link at single carriageway road with major road Ghost Island and roundabout (or simple priority junction) at minor road. Single quadrant links with a ghost island junction on the mainline can be considered for single carriageway roads with lower flow turning movements. The link should be located in the quadrant that will ensure the larger turning movements are left turns onto and right turns off the major road. Figure 8.5: A selection of schematic layouts indicating 4 arm compact grade separations on dual all- purpose carriageways. Figure 8.6: A schematic example layout indicating 4 arm compact grade separations on single all- purpose carriageways. Figure 8.7 A schematic example layout indicating 3 arm compact grade separations on dual all- purpose carriageways. Figure 8.8: A schematic example layout indicating 3 arm compact grade separations on single all- purpose carriageways. TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 157 Figure 8.2: Example of Compact Grade Separation for 4 Arm Junction Figure 8.3: Compact Grade Separation for 3 Arm Junction TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 158 Figure 8.4: Single quadrant link with a ghost island junction on the single carriageway mainline Figure 8.5: Schematic Examples of 4 Arm Compact Grade Separation on Dual Carriageway TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 159 Figure 8.6: Schematic Example of a 4 Arm Compact Grade Separation Single Carriageway TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 160 Figure 8.7: Schematic Example of 3 Arm Compact Grade Separation on Dual Carriageways Figure 8.8: Schematic Example of 3 Arm Compact Grade Separation on Single Carriageways TII Publications DN-GEO-03060 Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade separated and compact grade separated junctions) April 2017 Page 161 8.4 Safety 8.4.1 General One of the principal objectives of compact grade separated junction design is to improve safety by the elimination of right turn manoeuvres between the mainline and the side road, by providing left in left out turn only priority junctions and the closure of central reserve gaps. It is intended that compact grade separation shall be used to provide a safe means of crossing high speed routes for all road users. The geometrical standards for the compact connector road have been established at a level of provision intended to maintain slow vehicular speeds through their length thereby improving safety for other road users. Other positive factors which improve safety as a result of compact grade separation are; a) removing the possibility of large vehicles which cross central reserve gaps protruding into the offside lane; b) removal of U turns on the mainline. 8.4.2 Collisions Collision statistics for 3 arm priority junctions indicate that the severity of collisions is dependent upon the classification of the mainline and the mainline speed limit and that generally collision severity decreases as speed decreases. Compact grade separation will transfer the right turn manoeuvres from the higher speed, higher classification road to the lower speed, lower classification road. The effect of this should be to reduce the number of fatal and serious collisions. There may be a corresponding increase in minor injury collisions at the minor road junction, however the use of roundabouts at the junctions between the minor road and compact connector road may reduce the number of collisions at these locations also. 8.4.3 Traffic Signs On the approach to the junction from the major road, the junction must be clearly defined by means of appropriate signing indicating the junction as a priority T junction and not as a slip road. On the approach to the junction from the minor road, the junction must be clearly defined as a roundabout or priority junction appropriate to the layout used, and not as a slip road. Where normal curve widening is not provided, as described earlier in this Chapter and in Table 8.2, then regulatory signs shall be provided on the compact connector road to advise motorists in one direction that they should give way to vehicles proceeding in the opposite direction. Statutory requirements for regulatory signs are contained in the Traffic Signs Manual. Within the compact connector road it is recommended that signing be restricted to warning signs indicating the nature of the alignment, and the proximity of junctions. 8.4.4 Road Markings The application of special surface treatments may be provided as an additional means of highlighting the nature of the geometrical standards for the compact connector road. This can be achieved by the application of a contrasting surface colour (red) within the hatch markings to emphasise the nature of the curve, this should reinforce the meaning and presence of the markings to the driver. Yüklə 8,57 Mb. Dostları ilə paylaş:
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