Resarch areas

Experiments show that the deep drainage system is an effective method to control the groundwater table and, concerning road construction, it is recommended as a method when the road is located in earth cut below the ground surface in combination with high groundwater table. However, it is important to maintain the drainage system.

Along route 126 near Torpsbruk, the Swedish Transport Administration for many years had problems with bearing capacity, potholes and other deterioration. The problem obviously exists due to a combination of factors such as poor construction material, and high water content in the construction.

VTI experiments show that the deep drainage system is a very effective method to control the groundwater table. This was supported by the plugging trials. The water levels increased and decreased rapidly in connection with plugging and opening of the deep drainage system. Deep drainage is also a very effective method to control the water content in the road when the groundwater table is high in the road construction. Sealing of the road verge and embankment slope affected the dynamics of water content in the road. To investigate the infiltration of rain and road water some part of the road shoulder was sealed with a plastic tarpaulin.

The results can be used to evaluate if the use of sealed road shoulders might be an appropriate maintenance action. To evaluate the long-term effect of this action on the road construction and durability the measurements have to continue for a longer period of time.

The aim of this project was to increase the knowledge of functional conflicts between the environment and the operation and maintenance of roads. Functional conflicts may arise for example, when operation and maintenance measures are interfering negatively with land owners’ use of their land.

The goal of this project was to find new, relatively unknown examples of functional conflicts through observations in the field as well as by using recorded comments and opinions received by the Swedish Transport Administration.

Following functional conflicts were identified in the field:
• Reuse of old materials may negatively affect the life-time of roads.
• Brush cutting in the roadside may enhance erosion in vulnerable areas.
• Forest clear-cutting with easily eroded soil may cause clogging of ditches and culverts.
• Culverts that end in the middle of the forest may cause the forest land to become waterlogged.

To identify more functional conflicts, opinions and comments received by the Swedish Transport Administration in three regions (central region, western region and Stockholm region) were studied.

Several functional conflicts between the operation and maintenance of the road and the surrounding environment seem to recur in the three different regions such as various
functional effects from mowing, clearing, snow removal and gravel road maintenance. There were many examples of when different types of protected objects (monuments or heritage listed items) were damaged by the operation and maintenance procedures.

It should be a prioritized issue to minimize functional conflicts since there might be serious negative effects on the environment, costs and society.

Pedestrians are the road user category that suffer most injuries caused by ice or snow surface conditions and require medical care. In a VTI study it is demonstrated that pedestrian injury costs, attributed to footway accidents caused by ice and snow, are much higher than the actual winter maintenance cost. Furthermore, approximately 85 per cent of the pedestrians were injured in urban traffic environment. As a result of this, the Swedish Association of Local Authorities and Regions (Salar) endeavours to develop a better understanding for these types of accidents.

The project’s aim was to analyse the importance of the authority or the association responsible for winter maintenance. Did it make a difference to the number of injury accidents if it was the road authority or a property association who managed the winter maintenance? SKL also wanted to know the extent of pedestrian injury costs and relate these to the cost of winter maintenance.

Injured pedestrians data from STRADA healthcare client, in the period 2003-07-01 to 2010-06-30, provided a basis for the analysis. Often, it was only the Kalmar, Skåne, Värmland, Västmanland, Västernorrland and Jämtland regions that were included in the analysis. This was because hospitals from these regions had registered injured pedestrian data in STRADA during the whole analysis period. All injured persons do not necessarily seek hospital care. Treatment may have been obtained from other health care providers. The greater the distance to the hospital, the more likely it is to seek other health care treatment. This means that there is an underestimate of the number of injured.

Winter maintenance costs were obtained for the years 2005 and 2007. The costs related to road authorities’ total winter maintenance costs. Property associations’ maintenance costs for footway surfaces are not included in road authority costs so the costs are for road maintenance. Where the road authority is also responsible for footway surfaces, the cost of maintaining these surfaces is included in the total cost. This means that road authority costs are overestimated.

Using the available data, it has not been possible to determine any differences in the number of injured pedestrians associated to winter maintenance carried out by either road authorities or property associations.

However, it has been demonstrated that pedestrian injury costs, attributed to footway accidents caused by ice and snow, are much higher than the actual winter maintenance cost. In fact, where the road authority maintains pedestrian surfaces, injury costs are at least four times larger than the total cost of winter maintenance.

This means that, in socio-economic terms, it would be worthwhile to invest more resources in footway winter maintenance.

An important question in winter road maintenance is how it can be made more energy efficient. VTI research Anna Arvidsson has made a literature review and summarized several of the factors that affect how, when and where the winter road maintenance is performed. One of the factors that account for the greatest uncertainty in terms of winter road maintenance is the weather. This is an area that has a need for more research.

First and foremost there are sensors that measure the weather on the road and close to the road. A RWIS outstation (Road Weather Information System) measures many parameters, such as road surface temperature, air temperature, relative humidity, precipitation and type of precipitation and wind speed and direction. Using the measured parameters together with weather forecasts it is possible to determine when and where the action is needed. The development of sensors is constantly moving forward, twp recent Swedish examples are BIRDS that measures the freezing point temperature on the road and RoadEye that identifies the road condition.

When you know what action to take, it is time to make a route planning to ensure that the correct action is done on the right place at the right time.

What equipment is best suited for the performance of winter road maintenance, depends on the type of action that needs to be performed. An attachment to a plough truck that is well suited for one road might be less efficient on another. There are new plough trucks that can run faster than their predecessors and therefore the fleet can be reduced and thus energy can be saved.

Spreading of salt and sand could be more efficient by using different computer programs that calculate the amount of salt/sand that is needed, but also which routes are the most suitable to drive.

The location of the salt/sand storage affects the driving distances i.e. fuel consumption, and if it is possible to place the repository at an appropriate place in the beginning of an optimally planned salt-/gritting route the energy expenditure would be reduced. If it is necessary for a replenishment of material to cover an entire route, a lot of energy could be saved by having storage along the route to avoid deadheading.

One of the factors that account for the greatest uncertainty in terms of winter road maintenance is the weather. The past two winters, 2009/2010 and 2010/2011 have been cold, with lots of snow, which has required significant resources for winter road maintenance. The Swedish climate is changing towards warmer temperatures with more precipitation as a result according to UN and IPCC. This should lead to a decreasing winter road maintenance in southern Sweden (fewer days with cold temperatures), while northern Sweden may need more maintenance on the grounds that the number of really cold days will decrease and there will be more days with risk of slippery roads. This is an area that has a need for more research.

This literature review is focused on winter road maintenance, but might as well apply to railway concerning many issues.

One of the main problems within pavement management and maintenance strategies is the relation between road surface condition and accidents, for example the relation between rut depth and accident risk. However, in a VTI study there were no results showing that deeper ruts tend to increase accident risk generally.
Efficient and cost effective maintenance and rehabilitation of roads require access to objective and reliable analysis methods and tools. Pavement management systems including road user effect models for calculating the consequences and costs for road users of different maintenance strategies have been developed over the past years. There is, however, an identified need for improvement of existing road user effect models in many countries. The road administrations in Finland, Sweden, Norway and Estonia have brought up their concern of current models not functioning adequately. The main problems in these countries are the relation between road surface condition and accidents, the effect of the main condition parameters, i.e. rut depth, to road user cost, as well as the role of road user costs/effects for a road network that is in substantially good condition. These are problems that have to be solved in order to improve justification of road maintenance budget allocations. VTI was therefore commissioned to carry out a study to determine how rut depth affects the accident risk of road users. Separate analyses were done for data from Sweden, Finland and Norway, respectively.
It was assumed that the accident risk also depends on other road condition variables, e.g. longitudinal unevenness, texture, cross fall, geographical position (country), vehicle flow, climate, weather conditions etc. All this data, in addition to rut depth, was delivered from each country providing a very good set of data for studying the effect of road condition on accident risk.
As it was assumed that the relationship between accident risk and rut depth is not necessarily a linear function, rut depth was furthermore divided into a number of categories. It was also decided that separate model variables should be inferred for speed limit and AADT classes. Rut depth categories, and speed limit and AADT classes were chosen to match each country´s maintenance management strategies.
The overall conclusion from the analysis is that the data does not support any general rules for a maintenance scheme. There are no results showing that deeper ruts tend to increase accident risk generally. Nor are there results that show that ruts have the same influence on the risk for different AADT classes at a given speed or vice versa. There appears to be an increased risk with ruts ≥ about 15 mm in the highest speed class but the results differ between AADT classes and are not similar in a neighboring speed class making the results hard to understand and less usable for stating maintenance rules.
For Norwegian data this trend cannot be seen for the highest speed class (≥90 km/h), but then this speed class is not comparable to the Swedish and Finnish highest speed classes (≥110 km/h roads and motorways, respectively).