【正文】 s, other than those providing access to holiday areas, as, to an extent, the decline in interurban business travel during the summer is offset by tourism. The information above shows that the pattern of flow on any road can be highly variable and, in deciding when and where to undertake a traffic survey, it is important to ensure that the survey provides a fair measure of the traffic conditions that are being studied. To take the example of the road in a tourist area, a traffic survey on August bank holiday would measure peak traffic conditions. As these levels occur only one or two days a year there would be little point value in using this data as a basis for design, as the scheme would be for traffic conditions most of the time.Generally, traffic surveys should not be planned to measure the peak of the peak but to measure the39。 normal39。 peak conditions. Trunk road surveys may require a full year39。 s survey of traffic so that the 50 th(30th or 200th) highest hourly flow can be determined, and used as the basis for design.The starting point in defining a traffic survey is to decide what question has to be answered and choose the type of survey accordingly. If the survey is not adequately planned, there is a danger that wrong data will be collected and the traffic situation will not be correctly understood.The only exception to this rule occurs when one is faced with a plex situation where it may not possible, at first, to adequately understand what is going on, in terms of traffic flow and circulation. In these circumstances the traffic survey is providing evidence which will not only be used to quantify behavior, it may also be used to define it.Some surveys are adequate for measuring traffic flow and direction of movement at a single point, or at a single junction. However, if we wish to understand movement over a wider area, then other methods have to be used. Three techniques are described below, one for surveys and two covering origin and destination surveys. ( 1 ) Surveys We may wish to understand how traffic is circulating in a limited area. This could be, for example, a plex gyratory system, a residential area where we suspect that there may be ratruns, or even a town center ring road where we wish to understand if traffic uses the ring road or passes through the town center.The technique used is to record the registration mark of each vehicle as it enters and leaves the system being studied and then to match the registration marks, to establish how a vehicle traveled through the road system being studied. It is not normally necessary to record the full registration mark. (2)Origin and destination survey The alternative way to establish where drivers are traveling is to ask them, using an origin and destination (Oamp。D) survey. Various types of Oamp。D surveys are used as a part of the wider transport planning process. However, this is beyond the scope of this paper and is not explored here. The standard techniques are roadside interview surveys and selfpletion questionnaires.In most cases it will be impossible to carry out a 100% survey of drivers and so we must rely on a response from a sample of drivers in the traffic flow. Clearly, if the survey results are to be relied on, sample should be unbiased with all types of vehicles and movements represented. (3) Roadside interview surveys At a roadside interview survey, a sample of drivers are stopped at the side of the road and asked their origin and destination, plus any other data which could be of relevance, such as journey purpose.Objectives Traffic management arose from the need to maximize the capacity of existing highway networks within finite budget and, therefore, with a minimum of new construction. Methods, which were often seen as a quick fix, required innovation solutions and new technical developments. Many of the techniques devised affected traditional highway engineering and launched imaginative and cost effective junction designs. Introduction of signalcontrolled pedestrian crossings not only improved the safety of pedestrians on busy roads but improved the traffic capacity of roads by not allowing pedestrians to dominate the crossing point.More recently the emphasis has moved away from simple capacity improvements to accident reduction, demand restraint, public transport priority, environmental improvement and restoring the ability to move around safely and freely on foot and by pedal cycle. Demand management There has been a significant shift in attitudes away from supporting unrestricted growth in highway capacity. The potential destruction of towns and cities and the environmental damage to rural areas are not acceptable to a large proportion of the population. Traffic management has, largely, maximized the capacity of the highway network, yet demand and congestion continue to increase.Highway authorities accept that they do not have a mandate to provide funds for large amounts of new construction. It is clear that, for the foreseeable future, resources will not be available to provide for unrestricted growth in private vehicular traffic. Traffic engineering alone cannot provide for sufficient highway capacity even with limited amount of new construction. One method of demand management that has received considerable interest and study is congestion charging. This is where vehicles are surcharged for their use of road space depending on the prevailing levels of congestion. New technology in the form of smart cards and vehicle identification are needed to ensure that the system is practical and fair. Measures to acmodate foreign or nonlocal vehicles are also needed. Video image analysis has reached a level of sophistication that can be used for this purpose.Engineering measures The traffic engineer has a vast array of measures which can be applied to achieve his objectives. These objectives include: capacity enhancements。 accident reduction。 environmental prote