A survey of literature relating to condition assessment of road equipment shows that such studies are rare. One reason for this is often lack of practical measuring methods.
Road equipment is used to improve traffic safety and traffickability on roads and also to control and guide traffic. Once an investment has been made in road equipment, it is important to ensure by appropriate maintenance measures that its function is retained. The time when these measures are to be employed can be determined by condition assessment of the function. Such assessment may be made by visual inspection or a simple physical measurement. This report gives details of a survey of literature concerning measurements used in condition assessment and methods which may be suitable for use in such measurements.
Road lighting and safety barriers
Condition assessment of the function of road equipment in most cases entails physical measurement of some relevant parameter. Since such measurement costs time and money, it is often impossible to measure all equipment of the type concerned, and it is necessary to make measurements on a sample of the population. Condition assessment therefore usually requires not only a physical measuring method but also a sampling method.
A survey of the literature relating to road equipment shows that such studies are rare. There may be a number of reasons: some equipment requires only a simple inspection and this can therefore be made for all equipment of this type at frequent intervals. There is therefore no need to sample in time, to sample equipment or to use a physical measuring method. Another reason may be that there are no easy-to-use measuring instruments available.
As far as road lighting is concerned, no reference to condition assessment of the lighting function can be found in the literature. The reason for this is obvious: the function of road lighting is best described by carriageway luminance, and this is difficult to measure. An alternative property that is easier to measure is illuminance. This measurement may however be sensitive to disturbance by nearby vehicle lights, and measurement at the time of low traffic volumes is therefore necessary in practice. There is however a Swedish study on the condition assessment of lighting columns. This study condemned 34 per cent of the columns, mostly because they were too near the carriageway in contravention of the regulations.
Condition assessments of safety barriers and noise barriers have been carried out in USA and Sweden. The American study relates to noise barriers which were visually inspected. The conclusion was that all types of noise barriers may be considered to be maintenance free for twenty years after erection. In Sweden a visual inspection was made of safety barriers on roads which had been sampled. The results showed that 7 per cent of safety barriers at the sides of Swedish roads did not comply with regulations.
Road signs and carriageway markings
Road signs are the type of road equipment which has been investigated in most studies. In several studies a relationship was sought between the age of the reflectorised surface and retroreflection. Swedish, German, American and Australian studies give similar results: ten years after the erection of the sign, the reflectorised surface has retained 70–98 per cent of retroreflectivity. Measurements were made with different types of hand-held instruments, which may be impractical; it is difficult to reach up to the sign. Vehicle mounted measuring methods are needed.
Instruments – both vehicle mounted and portable ones – are available on the market for physical measurements on carriageway markings. In spite of this, condition assessments of carriageway markings have been made only in the Nordic countries, and mainly in Sweden. These studies refer to the retroreflective properties of carriageway markings and show that most carriageway markings in Sweden do not satisfy the requirements in Swedish regulations. An American report on conditions assessment of carriageway reflectors describes measurements with a portable instrument.
It is difficult to make physical measurements of the function of traffic signals, and there are no commercial instruments available. There are consequently no references to condition assessment in the literature. The introduction of automatic monitoring of traffic signal installations has also reduced the need for condition assessment.
The conclusion of this study of the literature is that development of methods for condition assessment of road equipment should focus on
- development of a vehicle mounted method for physical measurements on lighting installations
- development of a vehicle mounted method for physical measurements of the function of carriageway markings
- development and adaptation of sampling methods for road lighting and carriageway markings.
Finally, it is emphasised that methods for condition assessment must be easy to use and suitable for personnel who have no knowledge of advanced measuring techniques.