Testing the durability and function of road traffic management devices

Traffic management measures (vertical signs and horizontal marking, reflective elements) are used for guiding vehicles optically, indicating road mileage, marking objects in road gauge, marking vehicle and pedestrian safeguards and driver information and warning. This paper presents a synthesis of a literature study and the results of research conducted under stage one of the project LifeRoSE. The requirements for different traffic management measurements are described as well as durability and functionality tests and analysis of factors which influence durability and functionality of these measurements.


Introduction
The process of installing road safety devices on a road section has several stages.These include planning, design, construction, maintenance and removal of the devices [1].The lifecycle of a structure involves work which includes planning and design, construction (building) and repairs, maintenance and finally demolition.In addition, these activities can be delivered at different levels of management: strategic (legislation and programming), tactical (planning and design) and operational (construction, repairs and day-to-day maintenance).Decisions that are taken at the strategic and tactical levels are important for the durability, functionality, effectiveness and costs of the devices.Today, those decisions are taken in an environment of scarcity of information, a lot of uncertainty and a lack of the right methods and tools.As a result, the decisions are far from optimal [1].
Durability is defined as the ability of a device or object to maintain its utility over time.In the case of road safety devices used on the road durability means the ability (capacity) to maintain the assumed functionality during the road object's required life.Durability and life expectancy requirements for road markings are defined in standards, guidelines and recommendations which are device-specific [2].The life expectancy of road safety devices depends on the type and durability of manufacturing material [3], and how the devices are used.While this has been researched at length, it is not clear how the conditions of operation (weather, winter road maintenance, occurrence of micro vehicle impacts) affect the life expectancy of road devices.Road safety devices must meet a number of functional features such as safety, reliability, fitness, effectiveness, readiness, day and night-time visibility, adequacy and others.Some of the undesired problems that require research include a lack of methods for estimating how the type and durability of traffic management devices and operating conditions impact the functionality of the specific groups of road safety devices.Also, there are no methods for selecting the acceptability limits of how to assess the properties (functions) of devices.
The most important function of road safety devices is to protect road and roadside users from death or injury.While there has been extensive independent research into how selected factors affect the properties of road safety devices [4], this has never been a comprehensive effort.
This article describes the results of preliminary studies on the durability of horizontal and vertical marking in relation to normative requirements.The research was done in the laboratory and on test sites.This is the first stage of the research project entitled "Life cost analysis of Road Safety Elements".

Testing the durability of horizontal road markings
Horizontal markings can be divided into permanent and temporary markings, depending on their expected application.The technologies available divide the devices further into thin layer marking -with a layer of 0.30 mm to 0.90 mm, thick layer marking -with a layer of 0.90 mm to 5.00 mm, smooth (full), structural and profile marking.Their utility features fall into type I -not visible in wet conditions and during rainfall and type II -visible in wet conditions and during rainfall.In Europe two methods for testing durability are used: -assessment on an experimental section    At present, foils and signs should also be tested for foil retroreflected luminance coefficient in full geometry at night-time, resistance of plates and signs to neutral salt mist and foil durability -accelerated resistance testing of foil to weather conditions in natural and artificial conditions.Manufacturers use different service life durations for reflective foil on sign faces: for type 1 up to 3 years and for type 2 up to 5 years.Please note that in the five years of following the IBDiM Recommendations, the road sign retroreflected luminance coefficient was only tested in simplified geometry, i.e. for a single angle of observation (20') and a single angle of illumination (+5q).

Testing the life expectancy of point reflective elements
Road markings also come in the form of point reflective elements installed on the road surface as a complement to horizontal markings.They provide guidance and reflect light to warn, guide and inform road users.They can be built of one or several parts and can be stuck, anchored or inlaid.Reflective points are usually run along the shoulder, on kerbs and lines separating lanes of traffic.Their basic objective is to show how the road runs especially on bends, curves and other sites that require more driver concentration (so called light guidance).Reflective points (permanent and temporary) are tested to ensure comparability and reproducibility of test results.Tests are made on site.The standard [12] gives an exact definition of the requirements to be met by test road sections, weather conditions, traffic volume and type of surface.The standard also defines the minimal time of the test on an experimental road section: at least one year for permanent elements and at least four months for temporary elements.Road tests are conducted in five stages.

Assessment of day visibility:
-check envelope profiles of all elements for sharp edges from traffic side as a result of damage, rubbing or separation, -check the elements for integrity, if there are less than 45 elements the test is considered invalid,

Assessment of night visibility:
-check the roadway elements for luminance when lit up with headlights; permanent elements are tested from a distance of 50m ± 3m while temporary elements are tested at 20m ± 2m. 3. Photometric tests, i.e. tests of the retroreflective coefficient and luminance coefficient (for temporary elements only) using elements from experimental sections.

Figure 1
shows examples of thin and thick layer markings and of acoustic lines.

Fig. 1 .
Fig. 1.Examples of horizontal markings.To assess the durability and function of horizontal marking, the following parameters are used: -Surface coefficient of retroreflected luminance RL (in dry and wet condition), -Coefficient of diffuse luminance QD, -Coefficient of β luminance and chromaticity coordinates x, y, -Skid resistance tester SRT, -Class of traffic (number of times a wheel can drive over the marking).According to the guidelines [5] marking on specific road classes should meet the parameters listed in Table 1.

Figure 2
[6] , -assessment on a wear and tear simulator [7] Since 1995 Poland has been using experimental sections to test durability: DK 7, DK 5, DK 22, DK 16, and the street Jagiellonska in Warsaw.shows preliminary results of durability tests of horizontal marking made using thermoplastic materials on the DK 22 experimental section.Lane 1 and lane 2 denote the line number from the edge of the carriageway in the case of the longitudinal durability test pattern [6].Lane 1 (line next to edge of carriageway) is rarely driven over while lane 2 (line of wheels) is used heavily by traffic.Section 25 is thermoplastic material containing 40% of micro glass beads, section 27 is thermoplastic material containing 30% of micro glass beads.R2 and R3 requirements denote classes of surface coefficient of retroreflected luminance RL [8] at 100 mcd m -2 lx -1 and 150 mcd m -2 lx -1, respectively.

Fig. 2 .
Fig. 2. Test results of retroreflected luminance RL on DK 22 experimental section depending on how long the marking has been in use.

Figure 3 Fig. 3 .3Table 2 .ReflectiveTable 3 .
Figure 3 shows preliminary results of durability tests of horizontal marking made using thermoplastic materials on the DK 16 experimental section.Lane 2 and lane 3 denote the line number from the edge of the carriageway in the case of the longitudinal durability test pattern [6].Lane 3 (line between wheel tracks) is rarely used while lane 2 (line of wheels) is used heavily by traffic.Section 26 is thermoplastic material containing 30% of micro glass beads,

Table 1 . Minimum requirements for permanent horizontal road markings.
1.