 |
 |
| Publications |
| Home | Press | Publications | What We Do | Who We Are | Search | Site Map | Contacts | Links | ||||
|
|
|||
| > Publications > A to Z |
< Previous | Contents | Next >
Introduction
7.1 The objective of traffic calming is to modify the behaviour of motorised users to that which is compatible with the needs of non-motorised users and the local environment. The benefits to be derived are:-
(i) Perceived and actual improvements in road safety;
(ii) Reduced severance;
(iii) Improved amenity;
(iv) Increased social activity/ decreased social exclusion, particularly among the more vulnerable; and
(v) An improved environment.
7.2 The disbenefits can be:-
(i) Capital and maintenance costs;
(ii) Increases in journey time and vehicle operating costs;
(iii) Deterioration in local and global air quality;
(iv) Public Transport and Emergency Service accessibility problems; and
(v) Increased noise and vibration.
7.3 Common features used in traffic calming schemes are as follows:-
(i) Vertical deflections;
(ii) Horizontal deflections;
(iii) Changes in surface texture;
(iv) Changes in surface colour;
(v) Reductions in carriageway width;
(vi) ‘Gateways’
(vii) Road ‘point’ closures/entry restrictions;
(viii) Landscaping/streetscaping; and
(ix) Link priority operation.
7.4 Because the implementation of traffic calming schemes is likely to have a positive impact on a wider range of road users its use can be more cost effective than providing specific facilities for individual user groups (e.g. special pedestrian or cyclist facilities).
7.5 Although traffic calming is generally aimed at reducing traffic speeds the designer should ensure that the methods employed do not have a detrimental impact on cyclists (e.g. reduced road width which creates conflicts). When preparing a scheme the designer should take into account the requirements of cycling at the outset. The implementation of the Cycle Audit Procedures introduced in Chapter 14 is regarded as a fundamental process in ensuring that cyclists are fully considered within any proposed scheme.
7.6 The following section provides details of the most common traffic calming measures and identifies treatments which will assist the cyclist.
Road Humps and Other Vertical Deflection Features
7.7 General Design Features:
7.8 The use of road humps is regulated by the Road Humps (Scotland) Regulations 1998. Humps are formed by raising the existing road level by 50-100mm and can be round or flat topped, can extend over several metres or include entire junctions. They may extend the full width of the carriageway or be attenuated with tapered ends to provide a 200mm wide drainage channel.
7.9 Road humps need to be placed at 100m intervals along the road being traffic calmed in order to reduce the 85th percentile traffic speed below 40kph. The recommended gradient for the on/off ramp of a flat top road hump is 1:15.
7.10 Impact on Cyclists:
7.11 Road humps have been found to be successful in terms of speed reduction, and flat topped humps have been used to aid vulnerable road users, such as cyclists, at special crossing facilities. However, the provision of standard road humps may have a detrimental impact on cyclists:-
(i) The ramps of some humps tend to be steep;
(ii) Changes in gradient may be abrupt;
(iii) Upstands may be created;
(iv) 200mm wide drainage channels are not wide enough to enable cyclists to bypass road humps safely, and
(v) Road humps and their associated ramps may cause problems for cyclists turning at junctions.
7.12 Recommendations:
7.13 A number of treatments have been developed which reduce the problems identified above:-
7.14 Sinusoidal Road Humps: A sinusoidal road hump has been developed by Edinburgh City Council, based on principles developed in the Netherlands. Refer to Figures 7.1b) and c).
7.15 Trials have demonstrated that sinusoidal humps, whilst being as effective as the conventional type of road hump in reducing traffic speeds, do not have a detrimental impact on cyclists. In addition, the transitional nature of the design eliminates the traffic impacts of noise, vibration and discomfort associated with flat top road humps. The successful Edinburgh trials have resulted in sinusoidal humps being approved for general use provided that design height is no greater than 100mm. Traffic Advice Leaflet 9/98 contains further information. Testing for ‘Cycling by Design’ demonstrates a maximum speed of 20mph for all motorised traffic over this type of hump.
7.16 Road Hump Bypasses: It is recommended that where sufficient carriageway width exists bypasses should be constructed to enable cyclists to avoid standard road humps. Bypasses should be designed in accordance with Figure 7.1b).
7.17 Treatment of Junctions: Where road humps are proposed at or near junctions their sloping faces should, where possible, be set back to enable cyclists to complete their turning manoeuvre before having to negotiate the road hump. Where feasible upstands should be avoided.
Speed Cushions
7.18 General Design Features:
7.19 Speed cushions are a special type of road hump which do not cover the full extent of the carriageway width. They are generally used on roads which have regular bus and emergency service activity.
7.20 Speed cushions may be placed across the carriageway in rows of 2, 3 or occasionally 4. Where roads have been narrowed a single cushion may suffice. A longitudinal distance of 60m is recommended between each cushion. (Refer to Figure 7.1a)). Cyclists may choose to bypass the cushion by using the space between kerb and cushion (as may motorcyclists).
7.21 Impact on Cyclists:
7.22 Speed cushions are likely to be shallower than road humps with gently tapering sides and by straddling the cushion, or crossing it with only two wheels, cars may reduce its traffic calming effect. As cyclists may be expected to bypass the speed cushions by using the space between kerb and cushion this potential abuse by cars is likely to have a detrimental impact on the safety of cyclists.
7.23 Recommendations:
7.24 In general careful design should enable the cyclist to bypass speed cushions whilst forcing motorists to use them. Cushions may be made more cycle friendly by:-
(i) Provision of approach and exit gradients as detailed on Figure 7.1a);
(ii) Surface materials which are skid resistant;
(iii) Avoiding upstands where feasible;
(iv) Providing adequate space (1.0m desirable, 0.75m minimum) between cushion and kerb to enable a cycle bypass to be provided;
(v) Build outs, which may be provided to protect cyclists from parking and to direct vehicles over the cushions; and
(vi) Constructing cushions away from gullies and other ironwork.
(vii) The remote use of other traffic calming features which may be applied to discourage motorcyclists from speed cushion equipped links.
Figure 7.1: Road Humps and Speed Cushions
< Previous | Contents | Next >
The information contained on this WWW site is Crown Copyright but may be reproduced without formal permission or charge for personal or in-house use. Privacy and Content Disclaimer.
For general enquiries about this web site email ceu@scotland.gov.uk or fill out our online questionnaire.
