2. Indicators and Research Methodology
2.2. Analysis of the Technical Condition of Roads
Standard technical indicators for road maintenance refer
to the technical parameters of the road and its surface and describe the condition of roads and thereby the technical effectiveness of maintenance. These are:
• pavement roughness – the skid resistance properties of the surface.
Pavement roughness is one of the main factors improving traffic safety: the higher the roughness, the higher the adherence between the wheel tyres and the rolling surface, and as a result the risk of skidding is lower and the braking distance is shorter;
• longitudinal and transverse road evenness – road parameters that are most clearly perceptible by road users. The longitudinal evenness is a quality, which is perceived by the user as the capacity of the road to not trigger quivers and vibrations of the vehicle.
Transverse evenness is determined by geometrical deviations of the actual surface in relation to the ideal surface. The evener the road, the higher the riding comfort and the lower the risk of damaging the vehicle. On the other hand, an uneven road provokes an effect of wheels “bouncing” on the surface (in other words – dynamic load effect), which further results in a variable adherence between the wheels and the surface. Improper parameters of transverse road evenness may cause poor stormwater drainage contributing to higher water skid. Moreover, water that fills ruts accelerates deterioration of the surface;
• load capacity – thickness of individual pavement layers, which is appropriate for the traffic structure, as well as well-selected building materials, which should have the properties ensuring the durability of layers during the intended period of pavement exploitation.
Load capacity is not perceived by road users, but it determines the weight of goods vehicles allowed to the road. Surfaces of roads constructed for higher category of traffic (heavy or very heavy Technical Indicators
Indicators and Methodology of Research
vehicle traffic) are, in most cases, made of many layers. The higher the load capacity, the higher “resistance” of the road to the traffic of heavy vehicles, which indeed is the major factor contributing to road deterioration. Static axle loads admissible in Poland are 80, 100 or 115 kN depending on the public road category. As vehicles roll on the surface, the dynamic load on the surface is in fact significantly higher than the static load. The dynamic impact of the vehicle on the surface results in a surface-vehicle interaction.
The most recent research shows that the impact of heavy vehicles on the surface is of a more aggressive influence than it has been assumed so far (ELLPAG 2009; OECD/ITF 2010);
• depth of ruts and potholes – depressions, cracks and potholes in the road surface. The more of them and the bigger they are, the lower the riding comfort and the higher the risk of an accident or damage to the vehicle and – similarly as in the case of unevenness – the higher the risk of accelerated road deterioration (both due to the impact of water and the interaction between vehicles and the “bad” surface).
In case of routine maintenance there are also less complicated APIs, for example the cleanness of the road, and indicators relating to other elements of the right-of-way (e.g. maximum height
of grass on shoulders). Well-defined APIs for routine maintenance in connection with performance to target indicators constitute a basis for Performance Based Contracts (PBCs). They are also crucial for controlling the maintenance works performance.
In the context of road infrastructure maintenance management we must bear in mind that the technical condition of the road and its durability before deterioration are hardly predictable. The condition of roads also depends on many factors (cf. Figure 1), on which the road authority has limited influence, e.g. professionalism and due care on the part of designers and constructors, weather and water
conditions, as well as parameters of road traffic and drivers’ compliance with the road code. The ability to limit the unpredictability of those factors is of key influence for planning and scheduling repavements, including the chance to elaborate stable financial plans.
Indicators and Methodology of Research
Table 2. Road condition parameters from the perspective of road users and the road authority
ROUGHNESS EVENNESS LOAD
CAPACITY and riskier the travel travelling on the road
mean unpleasant travel and increase the risk of vehicle damage
For the road AUTHORITY
is getting lower in proportion
the longer the road preserves its evenness, the lower the risk of accelerated deterioration and increased repavement needs
traffic of too heavy vehicles
Thus the effectiveness of the road condition management in view of the technical road properties depends on at least three key factors:
• qualitative control of design, building materials and workmanship;
• preventing structural maintenance delays, as from a certain critical condition point the deterioration of pavement and other construction elements accelerate. Therefore, the road authority should care to ensure, on an annual basis, appropriate funds in the budget for maintenance works in line with the principle that new investment projects are admissible only after satisfying the need for road repairs and renewals, and not the other way round;
• enforcement of traffic bans on too heavy vehicles (in comparison to the road axle load standard), which however, is beyond the road authority’s control as vehicle inspection usually does not belong to his responsibilities. Whether bans are observed or not depends on drivers themselves, the police, Road Transport Inspection Service and other services authorised to carry out inspections.
Indicators and Methodology of Research
Figure 1. Factors decisive for the condition of road infrastructure
LIFESPAN OF A ROAD
Each element of road infrastructure is subject to wear during use.
Roads must be repaired on a regular basis so that they do not lose their use value.
The lifespan of a road is determined by its original technical design.
The better the design is adjusted to natural conditions and traffic forecasts, the slower the road deterioration.
Good quality of the materials used, as well as good workmanship quality are the condition for preserving the use value of the road in the planned period.
Low quality speeds up deterioration and repair needs.
DESIGN AND WORKMANSHIP
WEATHER AND CLIMATE
The most dangerous natural enemy of roads is water, which not only seeps through the construction elements of the road, but also - by changing the states of matter - causes mechanical damage to the pavement and its foundation.
Blobs of water gathering under the surface, by freezing, blast out the surface, which then cracks under the pressure of wheels. Thus, minor damage to the surface becomes the reason for faster technical deterioration of the road. Therefore delays in repairs lead to a more than proportional increase of repair needs.
The warmed-up pavement on the road is pressed down by the wheels which causes rutting.
WATER
TRAFFIC FLOW
The more vehicles roll on the road, the faster the pavement wear i.e.
pavement loses on thickness and it becomes smoother. Another effect is the pavement spalling.
Heavy vehicles traffic weakens individual pavement layers, causes rutting, unevenness and other pavement failure. The larger the flow of heavy vehicles, the faster the wear and more frequent repair or renewal needs.
AXLE LOADS AND TRAFFIC STRUCTURE Source: own description.