There is good evidence from accident data that curves, especially short radius curves, are a problem for drivers. The behavioural errors that are apparent as drivers negotiate curves are discussed and it is concluded that visual perceptions are the underlying causes of such errors. How drivers perceive road curves and how this affects their steering behaviour is discussed. The visual information necessary to obviate such misperceptions is considered and suggestions are made on providing the most appropriate combinations of delineation devices (a).
The luminance of signs of two different retroreflective materials in various road situations is compared to the two performance categories dictated by driver legibility capabilities. By the use of a computer modeling program, the luminance of a sign was calculated as a function of approach distance (the supply model) for a set of parameters including sheeting type, vehicle type, headlight beam pattern, road geometry, sign position and lane position. The drivers' nighttime requirements (the demand model) were taken from the previous paper. When the demand curves are overlaid onto the supply curves, it is then apparent whether the different sheeting types can meet the requirements of the drive. From the two sheeting types that were compared, ASTM Type III (high Intensity encapsulated glass-bead material) and Type IX (very high intensity unmetalized microprismatic with high retroreflectivity at short road distances) the broad conclusions drawn are that: Type IX microprismatic sheeting has luminances that are several times that of beaded Type III sheeting over all distances and all road geometries Type IX sheeting has superior performance for vehicles that impose a large observation angle on drivers, such as trucks, buses, vans and trams. HI does not meet the minimum requirements of drivers of these types of vehicle. Consequently, it should be the sheeting of choice where there is diversity in the vehicle mix. The increased luminance provided by the Type IX sheeting over that of the beaded Type III sheeting would particularly benefit the older drivers in the legibility task.
Traffic signs are part of the road system and their general function is to display information to road users to facilitate the efficient and safe movement of goods and vehicles. If a traffic sign becomes ineffective because of the degradation in its visual properties then the efficiency and safety of the road system could suffer. The materials used on the majority of traffic signs have retroreflective properties so that they can perform adequately during the night as well as the day. Signs don't last forever; all materials will degrade with time and there will come a point at which the sign will be ineffective. Invariably this will happen to the night-time performance first. The paper describes a national daytime survey of the photometric performance of some 2400 retroreflective traffic signs in the field, and a night-time survey of the photometric performance of 200 retroreflective signs judged to be near the end of their effective life. The data were collected by all six States. The purpose of the daytime survey was to obtain population estimates of the photometric characteristics of traffic signs currently in the field over as large a spread as possible of the age of the signs. The major conclusions are: (1) The photometric performance of Class 1 white sheeting drops to about 80 per cent of its original value after 14 years. (2) The photometric performance of Class 2 sheeting (white, yellow or green) drops to 50 per cent of its original value after 10 years. (3) Cleaning signs improves their photometric performance by about 10-15 cd/lx.m2 at any time along the life-curve. (4) The night-time survey resulted in mean terminal values of 11 cd/lx.m2 for white sheeting, 6 cd/lx.m2 for yellow sheeting, 4 cd/lx.m2 for red backgrounds and 2 cd/lx.m2 for green sheeting, with some values ranging up to 68 cd/lx.m2 Because of the difficulty of making the judgement in the field, these mean estimates are likely to be low (A).
Standards Australia Committee MS/12 is currently developing a standard for Local Area Traffic Management (LATM). This report gives results of comprehensibility tests carried out on different versions of six signs for LATM applications, and visibility tests of marking patterns for road humps. Two or three versions of each sign were tested on independent groups of respondents. In the case of signs for 'One-way', 'Slow points', 'Shared zone', 'End shared zone', and 'Chicane', all versions performed about equally well, requiring that a choice be made among the alternatives on grounds other than comprehensibility. In the case of the 'Modified T-junction priority' and 'Left lane ends' signs, one version of each sign could be eliminated on the grounds of the tests, requiring a choice between the remaining alternatives on other grounds. A visibility meter was used to determine the recognition threshold for the different road hump markings, which subjects viewed monocularly at night. The tests allowed a consistent ordering of the five different patterns tested. Further testing was recommended in view of (1) possible confusion of the best-performing pattern with pedestrian crossing markings and (2) probable improvement of the performance of some of the other patterns with broader striping (A).
This paper reports a preliminary analysis of a national survey of the photometric performance of traffic signs in the field and on the photometric performance at the point where they are judged to be ineffective. The results show a good deal of consistency over most States, this preliminary analysis showing that the performance of Class 1 sheeting drops to 40 per cent of its original value after about 12 years and Class 2 sheeting drops to 50 per cent after about nine years. The mean terminal value of signs was about 10 cd m-2 /x-1 with a range up to 55 cd m-2/x-1.
The use of variable message signs (VMS) has increased considerably worldwide as an additional tool for traffic engineers to improve the efficiency and safety of the road system. They allow up-to-date information to be relayed to drivers, alleviating congestion, improving safety and aiding enforcement. There is a wide range of different kinds of VMS based on different technologies, such as optic fibre displays, light-emitting diode (LED) displays, electro-mechanical flip pixel displays and liquid cell displays.
Twenty two subjects were required to see and identify the location of coloured discs superimposed on projected colour scenes of the urban road traffic environment. The discs were 33 minute of arc in diameter and located at one of four locations 6 degrees or 14 degrees to the right and left of the centre of the scene with the aid of a fixation point on a uniform field projected between presentation of the scenes. The purpose of the study was to establish the relative contribution of the four colours (red, blue, yellow and green) to conspicuity. It was found that the coloured discs were no more conspicuous than neutral discs of the same luminances with the exception of green discs at 6 degrees eccentricity. This is a different result from that of forbes et al. (1978) And odescalchi (1960) who found red and yellow colours (but not other colours) contributed sufficiently to compensate for the loss of conspicuity due to the lower luminance of coloured objects compared to white ones. Further work is needed but it seems that at best colour does not provide any net gains to conspicuity and its role is that of identifying the object and conveying information as a colour code.
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