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Cycling by Design

6.190 Large Roundabouts: Traffic speeds (particularly circulating speeds) can be significantly higher than other types of roundabout (especially on older existing roundabouts) and cyclists are therefore likely to be at greatest risk.

6.191 It is generally recommended that cyclists should be offered alternative routes away from the circulatory carriageway. The options available include:-

(i) Provision of a remote cycle track facility around the outside of the roundabout (Refer to Figure 6.16b)) with remote priority or signal controlled crossings of entry/exit arms.

(ii) Provision of a grade separated facility to enable the cyclist to bypass the roundabout. This option is likely to have a high capital cost as it is unlikely that a single grade separated facility will satisfy all movements. Refer to Paragraphs 6.128 to 6.174.

6.192 Alternatively a large roundabout may be signalised to assist cyclists and improve traffic operation generally. (Note that exits may continue to be problematic for circulating cyclists).

6.193 Continental Roundabouts: New roundabouts in mainland Europe tend to be designed for single lane entry with restricted capacity and geometry which is more suited to the needs of the cyclist. However, recent observations show that capacity considerations are leading towards UK standards in design.

6.194 Nevertheless, where they are found to be appropriate, ‘continental’ roundabouts typically employ the following design features which are different to those required by TD16/93 : Geometric Design of Roundabouts (Refer to Figure 6.16a).

(i) Entry and exit arms are perpendicular, not tangential to the centre of the roundabout.

(ii) Single lane entries and exits. Desirable width : 4.25m (lower widths are likely to leave insufficient room for cyclists and higher widths may tempt motorists to form two sub-standard entry/exit lanes again resulting in insufficient room for cyclists.

(iii) Minimal flares on entries.

(iv) An ICD range of 25-35m.

(v) A circulatory carriageway width of 5-7m.

(vi) A central island diameter range of 16-25m.

6.195 The lower standard of geometry does however result in the adverse effect of reducing the roundabout’s traffic flow capacity. A continental roundabout may only have an entry flow capacity of the order of 2,500vph and is therefore unlikely to be appropriate for busy locations.

6.196 In order to simplify the assessment process the application of the principles presented within this section have been summarised in Table 6.10.

Table 6.10: Roundabouts and Cyclists

	Type of Cycle Facility
Type of Roundabout	Within the Circulatory Carriageway	Conversion to Continental Roundabout	Remote Cycle Track	Traffic Signals	Grade Separation
Mini	Yes	N/A	N/A	N/A	N/A
Small	Yes	Where wide flares are present	Where traffic flows require	N/A	N/A
Medium	Yes up to traffic flows of 8,000 vpd	Not unless traffic flows allow	Yes where traffic flows >8,000 vpd	Yes where traffic flows >8,000 vpd	N/A
Large	No	No	Yes	Yes	Yes

Provision for Cyclists at Grade Separated Junctions

6.197 The Problem:

6.198 Grade separation is commonly used on highly trafficked all-purpose trunk and principal roads. 85^th percentile traffic speeds are likely to be in excess of 85kph for all motor vehicles whether leaving, joining or remaining on the through route. Conflicts occur over the whole length of diverging/merging slip roads between relatively slow moving cyclists wishing to continue on the main carriageway and motor vehicles wishing to leave or join the main carriageway

6.199 Merging Slip Road Treatment:

6.200 Where no alternative route for cyclists can be made available and metre wide hardstrips exist, cyclists may be encouraged to join and use the hardstrip at a point some 170m before the nosing (Refer to Figure 6.17). Approximately 55m back from the nosing a cycle track should then be provided to lead cyclists off the hardstrip. The track should turn through 90^o to meet the slip road. (Where the slip road is kerbed the kerbs should be dropped to carriageway level across the width of the cycle track). At this point cyclists should be directed to ‘give way’ before crossing the slip road at right angles. Cyclists should then use the slip road hardstrip to re-join the main carriageway.

Figure 6.17: Provision for Cyclists at Grade Separated Junctions

fig6.17

6.201 At locations where there are no hardstrips a 35m long cycle track may be provided from a point 55m from the back of the nosing (Refer to Figure 6.17d)). The track should turn through 90^o to meet the slip road. Once across the slip road cyclists would then be encouraged to use a length of advisory cycle lane to re-join the main carriageway.

6.202 Signing: A special advanced direction sign to Diagram No WBM336 (Refer to Figure 6.17) should be provided to encourage cyclists to use the facility. Approval from Scottish Ministers will be required. The sign should be erected 200m from the crossing where there is a hardstrip, and 85m when there is not. The arrow marking to Diagram No 1059 should be used to direct cyclists onto the hardstrip. The cycle symbol, Diagram No 1057, in conjunction with the advisory cycle route sign, Diagram No 815, should be used to indicate that cyclists are advised to use the hardstrip alongside the main carriageway.

6.203 The short section of cycle track should be signed using Diagram No 625 in conjunction with the cycle symbol Diagram No 1057. At the slip road crossing, cyclists should be directed to give way by the use of Diagram No 1023 and Diagram No 1003. Opposite the crossing point Diagram Nos. 1059, 1057 and 815 should be used to encourage and direct the cyclists to use the hardstrip at the edge of the carriageway slip road, or the advisory cycle lane marked on the carriageway to Diagram No 1004. Motorists using the slip road should be warned by Diagram No 544.3 that cyclists might be crossing the slip road. Staggered signs should be erected 250m from the crossing point on the off side of the carriageway and 200m on the nearside.

6.204 Diverging Slip Road Treatment: Although the majority of accidents at slip roads occur at the merging slip road, similar treatment has been considered for diverging slip roads.

6.205 However there may be difficulties in that:-

(i) effectively signing the crossing to approaching vehicles may be difficult;

(ii) cyclists may need to divert some distance along the slip road before being able to cross;

(iii) there may be possible limitations in visibility;

(iv) there may be physical difficulties in providing a link back to the main carriageway because of steep gradients (diverge slips tend to be shorter and steeper than merge slips).

6.206 Each location needs to be assessed individually and any layout designed to suit local conditions.

Treatment of Raised Rib Markings at Crossing Points

6.207 The Problem: Research has indicated that problems of handling and comfort may arise for cyclists where the previously permitted maximum height of raised rib (13mm) and the minimum spacing (250mm) have been used. Where feasible the following recommendations should be followed:

6.208 Dimensions: New sections of raised rib markings on all purpose roads should be provided in accordance with TSRGD Diagram No. 1012.3, i.e. ribs should be at 500mm centres and have a maximum height of 6mm.

6.209 Application At Crossing Points: Raised rib markings should be discontinued at defined pedestrian and cyclist crossing points, and be replaced by a non-raised rib continuous marking. The discontinuity should commence a minimum of 1m before the crossing and finish a minimum of 1m after the crossing.

6.210 Raised rib markings should be replaced with normal continuous markings in the vicinity of locations where cyclists are likely to cross the lines when riding parallel to them (e.g. at the termination of hardstrips and in the vicinity of side road junctions). In these locations the raised rib marking should be replaced by a continuous marking at least 20m in advance of the end of any hardstrip/side road junction. For merging and diverging lanes the raised rib marking should be replaced 10m in advance of the merge or diverge lane.

6.211 Where raised ribs are due to be renewed the maintenance authority should ensure that the replacement ribs have a maximum height of 6mm and a spacing of 500mm.

Access Barriers

6.212 Although it is generally desirable to avoid the use of barriers on cycle tracks and shared use facilities, particularly on unlit sections of cycle track, in some instances it may be unavoidable, for example:-

(i) Where x values for cycle track visibility splays on the approach to a junction with a road are less than 2.0m (refer to Chapter 4, Table 4.3);

(ii) Where ramp gradients on the approach to a subway are ³ 7% (refer to Paragraph 6.153 and Chapter 4, Table 4.4));

(iii) Where ramp gradients leaving a cycle/pedestrian bridge are ³ 7% (refer to Figure 6.14);

(iv) Where measures are required to discourage unauthorised use of a cycle facility by motor vehicles etc.

6.213 Typical examples of barriers are shown on Figure 6.18.

6.214 All cycle track bollards and barriers should be highly visible in order that they do not cause a hazard to the user and, for unlit facilities, be at least reflective to bicycle lights and preferably involve a minimum level of phosphorescence.

Figure 6.18: Access Barriers

fig6.18

COMMENTS : CHAPTER 6

Cycling by Design’s prime objective is to draw together and rationalise existing cycling design guidelines into a single comprehensive, coherent reference document that may be used as a source of sound technical advice. In order to achieve this objective it is imperative that Cycling by Design is developed through consultation. Please provide any comments or suggested amendments you may wish to put forward with respect to the preceding chapter.

Comments/Proposed Amendments:

Please send your comments to:

The Scottish Executive Development Department,

Standards Traffic & Environment,

Area 2-E,

Victoria Quay,

Edinburgh EH6 6QQ.

On or before 31^st December 2000.

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