What are we trying to achieve?

Our public are worried about the volume, speed and weight of traffic through their road, town or village. It is causing accidents and is ruining the environment. Traffic calming is talked about loosely as a general "all-purpose" solution to the problem. But all too often I find that the problem is rarely identified clearly so the aims and objectives are also not defined properly. Our public have high expectations of traffic calming but are often disappointed. Traffic calming is expensive, so it must be got as nearly right as possible first time every time.

So exactly what are you trying to achieve?

Identify the problems, do they include:-

• excessive speed?
• too much traffic?
• too many heavy vehicles?

In other words make sure everyone agrees what the problems are so that you are tackling them correctly. Let’s look at these three aspects first:

1. Excessive speed. Dealing with this is probably the main thrust of traffic calming, so first define the speed which is acceptable for each road or length of road in the area concerned. This is the process of "speed capping" - ensuring that those who would drive above a certain identified speed are physically prevented from doing so. There has been much written about the reduction of speed attributable to the various traffic calming devices used, but we now need to think in absolute speed control for a given stretch of road then using a given device that works for that speed and further subdivide that for a given vehicle type i.e. car, bus, fire engine, ambulance etc.

2. Volume. Traffic calming may divert traffic onto other roads more or less suitable to take the traffic. So if you expect to reduce traffic flow you will have to study the network carefully; in any event you will have to take some diversion of traffic into account. But there will be times when there is no noticeable difference in traffic flow, where calming does not divert traffic but merely constrains speed. This will probably be the case in small villages where there is little alternative network available locally.

3. Heavy vehicles. Pedestrians perceive that HGVs travel at excessive speeds mainly because of the "momentum" factor associated with such large vehicles. There is a case for large vehicles to be forced to travel more slowly than cars and light vehicles in some environments. This is especially true in historic villages where main roads carry significant volumes of HGVs causing serious problems of damage and vibration. But most vertical deflections are so severe on larger vehicles that they are hardly used on roads which carry them. New traffic calming devices specifically intended to differentiate between cars and larger vehicles favouring the latter show considerable promise.

Transport Policy

Traffic calming is just a part of the implementation of your authority’s policies on transport as a whole. It will be part of the framework in which you will have developed your traffic and travel policies in your area. This will relate to public transport provision, cycling facilities, pedestrian facilities, safer routes to school and many other aspects of transport and local land use policies. Traffic calming is not normally expected to affect levels of traffic flow significantly but there can be local variations when schemes are implemented.

Traffic calming can be successful in improving life for residents and businesses in the area affected. But this needs careful thought, planning, consultation and execution of a quality product which must be expected to have a long life.

Often a measure of the success of a scheme will be the apparent lack of interest or concern. Newspaper articles are made up of things that have gone wrong not those that are working; I have installed a number of mini-roundabouts away from where I now live and I occasionally enquire of some of them to be advised that they just continue to tick over. That is good news. A good traffic calming scheme will blend well into the environment, and will continue to operate with little fuss or concern. Make sure your scheme ends up that way; try to do even better; make sure your scheme is recognised as good of its type and is pleasing to the senses – remember there is always somebody that has to live it!

Bringing speeds down

As a driver I am all too aware that whatever my intentions my speed may gradually rise over time so that where I might have been happy to drive at say 50mph, after some 20 minutes my speed has risen nearer to 60mph. This problem is associated with perception and becoming used to travelling at that speed and the reverse is true when slowing down. I have learnt to check my speedometer carefully when changing to a lower speed environment to ensure that the reduction in speed that I feel I am achieving is being realised. So the problem of getting speeds down in villages is often associated with the problem of drivers’ failure to realise that they are going faster than they think, and this needs to be borne in mind when introducing traffic calming at the interface between higher and lower speed roads.

What works?

As I reported in my book on mini-roundabouts, traffic calming arrived with the first introduction of mini-roundabouts at junctions in urban areas where previous forms of control were not working well, and at sites considered too small for conventional roundabouts. Although the expression "traffic calming" was not used then, the availability of a tool to restrain speeds at a node in a network, while generally improving capacity, was bound to be exploited, and many authorities in the UK and abroad have done this successfully.

If the business of getting speeds down is to be effective it is worth looking at some devices that we know work well. Table 1 illustrates the various traffic calming devices in use and summarises how their effectiveness is derived and identifies other factors which must be taken into account in their use.

Keeping speeds down

From the outset it has been assumed that the use of humps or other vertical deflections might be dangerous if drivers attempted to traverse them at speed. So they had to be associated with other speed controlling devices first and this was included in the legislation. In England and Wales this was revoked in 1996 when it ceased to be mandatory to introduce vertical deflections using some other specific speed controlling device, usually involving a sharp turn, a mini-roundabout, other yield feature or the closed end of a cul-de-sac. The essence was that humps could be repeated as often as necessary once speeds were already under control along a length of road, and to this end they have been very successful. A string of mini-roundabouts cannot usually be achieved because of the lack of junctions with sufficient turning movement to justify their provision although there are some schemes where they have been effective.

Humps

Above all humps work! They have been around in one form or another on the roads in the UK for some 10-15 years but after all this time I remain disappointed at their performance considering their potential. In particular most humps are poorly and inaccurately constructed. I believe that they could be used quite safely to introduce areas or forms of control where it is important for drivers to reduce speed. I am now recommending their use on the immediate approach to certain mini-roundabout layouts and at some gateways. The humps in these circumstances will be very visible but are often not seen just after a bend or other speed controlling device. Such placement may justify the expensive provision of the hump warning sign, whereas we have spent £millions in the UK just signing humps from every possible direction because it seemed the right thing to do.

Chicanes

A chicane is in essence a bend or double bend; used as a stand alone device it can be relatively ineffective and has a much more serious effect on long vehicles such as buses and fire engines; there is only one reason for drivers to reduce speed and therefore from time to time chicanes go wrong. Combined with shuttle working (pinch-points), drivers would now have to consider the possible need to yield to the opposing stream and this is where more than one reason to slow down, as at roundabouts, starts to come into play. Lateral deflection devices may develop into useful traffic calming features, but on quiet roads the yield effect may be of limited value especially if drivers can see some distance along the road and so "size up" the situation well before negotiating the physical feature.

Signing, Road Markings & Audible Warning Devices

These rely on drivers’ co-operation, and evidence so far of visual indications of the special need to reduce speed in one place may be counter-balanced by the gradual reduction in drivers’ compliance with speed limits signed only by the usual pairs of speed limit signs elsewhere. Drivers will need to be made aware of the special need as in The New Forest and parts of Dartmoor National Park where 40mph speed limits have been introduced to apparently good effect with reasonable compliance by the tourist traffic anyway. The signs have been designed with considerable thought for the environment too.

On their own the plethora of signs and carriageway markings available and used in the UK has had relatively little influence on drivers bearing in mind their huge and intrusive visual effect. One particular exception has been the use of the yellow bar markings on the approaches to large roundabouts which work relatively well. We need to do better here. In many instances the garish designs of gateways in particular is quite unacceptable for the relatively little effect that they have. But smart signs too are showing some promise. These illuminate to warn individual drivers that they are exceeding a preset speed (usually the speed limit if there is one), by some amount. If speeding has become a habit rather than a deliberate driving error, these signs, directed specifically at individuals on a continuous basis, will have a good long term effect; they will not however deter the determined speeder.

The use of raised markings on approaches to hazards may be helpful in rural areas, but avoid using these near residential properties because noise levels, although not high, are sufficient to be irritating. Changes of surface texture and colour, as used on approaches to pedestrian crossings, mini-roundabouts and traffic signals may be helpful. But, none of these force lower speeds.

Landscaping

What I am concerned about here is the potential benefit of a complete multi-disciplinary design for the streetscape. Only occasionally do we seem to get this right in the UK – our continental neighbours seem to have more style than we do. Their much simpler road layouts, carriageway markings and the absence of the sign lighting requirements (which we seem to be stuck with in the UK) all help to create a cleaner, tidier and more beautiful environment where driving is more of a delight than a hassle. The lighting requirement for so many traffic signs and the continued use of 250 volts AC mean that electrical equipment has to be mounted at a height relatively difficult to access by vandals. The signs in the UK and their mounting systems are arguably among the worst in the world.

Enforcement

Often by speed cameras, enforcement can help greatly in controlling wayward drivers; but it is a tool to be used carefully and is not a satisfactory alternative to correct engineering measures in urban areas but should be used in tandem. Neither should enforcement be used by the authorities as a revenue raising device; if used at locations where the speed limit is clearly unrealistic it will not help the cause of road safety, rather it will annoy drivers who honestly considered that they were travelling at a reasonable speed. Thankfully these devices are currently being used to target known accident problem sites which is their best use, particularly where the current speed limit would preclude the use of physical devices. The "trip" speed will necessarily be well above that desired for the stretch of road concerned; so the use of enforcement cameras alone to effect a scheme will be very limited.

Summary

I opened this chapter by posing the question "What are we trying to achieve?" It has been my experience that, although volume of traffic is often a main source of complaint, it is speed and perhaps traffic domination over the environment that upsets people so much. How often do we hear of parents who will no longer allow their children to cycle to school for example, because of the traffic? As a result those same parents add to the traffic volume by driving their children to school, precipitating a downward spiral of increased volume, worsening environment for pedestrians and so even more take to their cars. Traffic calming can redress the balance by allowing pedestrians and cyclists to mix more safely with the traffic as a whole, and restraining speed has to be a key aspect of this. Other aspects such as reduced flows will follow if the main road network is performing properly or alternative provision (public transport, pedestrian ways and cycle facilities) is made available. In examining traffic calming proposals I have come across a lot of muddled thinking about these and other aspects of the subject so let’s look at the first crucial aspect of traffic calming and that is network management.