“Traffic calming” is a specific traffic management technique with the specific objective to improve quality of life and accidents, by reducing vehicle speed, noise etc through environmentally sensitive areas. Traffic calming on main roads must be treated differently from traffic calming on lesser roads.
On main roads, it would add to accident hazards to introduce some of the more extreme physical traffic calming measures which are used to reduce traffic speeds (see below) but traffic management techniques are available to assist to slow traffic on main roads, including positive signs and road markings emphasising speed limits;
§ “rumble devices” which involve surfacing the carriageway in materials which create noise or vibration when crossed by vehicles and thus warn drivers of approaching hazards;
§ “bar markings” which comprise lateral road markings (lines at right angles to the road) on high speed approaches to urban junctions; the lines are increasingly closely spaced as the junction is approached and create a visual effect such that drivers slow;
§ road texture and colour on the approaches to critical locations (junctions, pedestrian crossings etc); and
§ linking of traffic signal timings at successive junctions to control and maintain a desired safe speed of traffic progression.
On lesser roads, a wide range of physical traffic calming measures for speed control (and in some cases, to limit traffic volumes) has been used, particularly in European cities. Typical measures include:
§ pedestrian refuges which narrow the effective road width, control vehicle overtaking and do not permit vehicles to reach high speeds road-speed control humps which reduce vehicle speed. These can take various forms including humps (i) with gradual vertical slopes which cause vehicles to slow, (ii) with sharp vertical slopes which require vehicles to more-or-less stop and (iii) which combine up and down stream slopes with a flat central area (used since they are slightly more “bus friendly” than conventional humps)
§ road narrowing such that some classes of vehicle cannot use the road (such as trucks)
§ road narrowing such that only one direction of vehicles can pass at one time – thus opposing vehicles must give way
§ chicanes such that vehicles have to following a tortuous route through a short section of road and thus must reduce speed
§ raised junctions comprising a plateau or flat topped road hump built across an entire junction
§ planting which can be used to change the perceived width of a road to cause traffic to slow
It is undoubtedly the case that most of the foregoing measures reduce traffic speeds but it is not clear if in developing cities they might:
§ introduce new hazards – for example, in developed cities, where road narrowing or chicanes have been used, there is anecdotal evidence that the measures can be hazardous;
§ result in increased environmental damage as vehicles slow or stop (in most cases as a result of the poor design of speed humps in developing cities) at humps and accelerate immediately after, thus increasing emissions; and
§ result in increased accidents due to poor design – the “absolute stop” road hump currently used in many developing cities is, again anecdotally, reported to increase the likelihood of increased “nosetail” vehicle collisions.
Inclusion in Bank traffic management projects/component – two aspects are noted:
§ traffic related environmental impact is usually mentioned as an evaluation for Bank traffic management projects although the evaluation is not often particularly convincing
§ few traffic calming measures are known
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