Forskningsområde - VTI

Low traffic volume roads - A litterature review concerning benefit, standard,
condition, operation, and maintenance
by Karin Edvardsson
VTI (Swedish National Road and Transport Research Institute)
SE-581 95 Linköping, Sweden
Summary
This research is the result of a literature study on low traffic volume roads. This report
intends to provide a basis for a project proposal with an objective to develop new tools
for creating a modern low traffic volume road network, adapted for future requirements.
Low traffic volume roads include all roads with a traffic volume of up to 1,000 vehicles
per day. In principle, only Nordic studies were considered in this report since the Nordic
climate, road construction practices, and maintenance traditions may differ to some
extent from the rest of the world.
In summary, a large amount of literature treats condition measurements and reinforcement,
particularly methods for these. However, there is not much research on the actual
road network status, degradation models and life cycle costs published.
Low traffic volume roads have low traffic intensity but it may be noted that it is the
same people who often use these roads and therefore incur increased operating costs and
reduced comfort. Often, these road users also are completely dependent on the existence
of the roads. On the paved low traffic volume roads, road users are bothered most by
potholes, unevenness and poor pavement repairs. On gravel roads, the corresponding
types of defects are potholes, corrugations and frost damages. These types of defects, on
paved as well as gravel roads, also cause most damage to vehicles.
The structural condition of the road is the most critical parameter for the asset value of
the low traffic volume road network. Road capacity affects accessibility for freight
transports and is therefore of great importance to the forest industry. Every year about
20 000 km of roads get frost restrictions, the cost of which for forestry companies solely
is estimated to be between 700 and 900 million Swedish crowns per year. Therefore, the
most viable solution, to address the problem of reduced bearing capacity, is to reinforce
weak sections. However, this requires that sufficient resources are available to take
long-term measures. Major problems have arisen when the road section has been
reinforced with a design that is too weak; problems that become particularly apparent if
the road is paved afterwards.
Degradation of low traffic volume roads is more complex than on heavily trafficked
roads where traffic is the most important parameter. At low traffic volume roads, there
is a longer time horizon as well as the fact that several parameters, such as the aging,
durability, and climate interact.
The life length of a road increases significantly when the drainage is improved.
Calculations, using PMS Object, have shown that the life length of a road construction
increases by a factor 2.2 to 2.6 when the drainage system is improved from poor to good
condition. Thus, life cycle costs (LCC) calculations show that it is profitable to keep
drainage in good condition. If the pavement's length of life can be doubled and the
discount rate is 4%, the drainage system may cost € 8,400/km every five years and life
VTI rapport 775 9