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category: literaturenote citekey: poyryroadeximprovinglowtraffic title: ROADEX-IMPROVING LOW TRAFFIC VOLUME ROAD CONDITION MANAGEMENT IN THE NORTHERN PERIPHERY AREA authors: "Pöyry, T; Region, Lappi; Poyry, Tapani; Saarenketo, T" zotero_key: DHNTMTLH zotero_storage: S835LIR9 collections: imporditud folder: Liiklussageduse kaudne hindamine/05_Artiklid firstAuthor: "Pöyry, T"
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ROADEX-IMPROVING LOW TRAFFIC VOLUME ROAD CONDITION MANAGEMENT IN THE NORTHERN PERIPHERY AREA
T. Pöyry Finra, Lappi Region, Rovaniemi, Finland Tapani.Poyry@tiehallinto.fi
T. Saarenketo Roadscanners, Rovaniemi, Finland timo.saarenketo@roadscanners.com
ABSTRACT
In 1998 the road districts of Lapland in Finland, Northern Region in Sweden, Troms County in Norway, and the Highlands in Scotland initiated a technical, trans-national collaborative project named ROADEX. The aim of this collaboration was, through the exchange of experience, to identify the best practice strategies and develop procedures for dealing with common challenges associated with the maintenance of low traffic volume road networks in sparsely populated northern regions. The Roadex project was partly financed by an EU (ERDF, Article 10) funded Northern Periphery Programme.
ROADEX was divided into two sub-projects: Sub project A dealt with road condition management issues; and sub project B studied winter maintenance problems common to the partner road districts. The focus of the ROADEX sub project A (SPA) was on the low traffic volume roads of the partner districts. One of the sub project's special interests was the use of traffic restrictions in the partner districts and techniques to improve bearing capacity of these roads.
This paper presents the results of the project, a comparison study of each road district's current policies and techniques in addressing the issues, and also summarises some the results of the phase II field tests, which focused on the standard and best practise structures as well as testing the different kinds of special structures utilised in the road districts. The Roadex project identified a few common major structural problems: drainage of roads located on transversely sloping ground, permanent deformation due to freezethaw cycles, poor quality materials, and road sections resting on peat.
The results of the Roadex subproject "Road Condition management" show that each country has emphasized slightly different strategies and techniques when trying to resolve bearing capacity problems in their low traffic volume road network. A significant problem for low traffic volume road condition management, shared by all partner districts, is that almost all the structural maintenance funds and resources are allocated to main roads at the expense of medium and low traffic volume roads. As a result, the performance of main roads has been improving over the last few years, while the state of low traffic volume roads has become worse. Another aspect gaining publicity and placing pressure on road districts has been that, due to increasing logistical demands, the industries using the lower class networks for their transportation routes have increased their complaints regarding permanent or temporary load restrictions and poor quality road networks.
KEY WORDS
LOW TRAFFIC VOLUME ROADS / BEARING CAPACITY / LOAD RESTRICTIONS / BENCHMARKING
1. INTRODUCTION
The main road network's role is to provide effective transport channels for industrial products, small services, and various small and medium sized business enterprises. In the Northern Periphery region, the critical role of low and middle class roads is apparent. By estimation, one third of all transport traffic is dependent on low or middle class roads. These are typically transports that keep the local fish plants, saw mills, pulp mills, steel industry and their suppliers working. Modern logistical systems in basic industries do not tolerate interruptions in raw materials supply; economic losses quickly mount from discontinuities in production flow. Tourism is an additional regionally important user of the road network.
At present, the main inter-urban highways of Scotland, Norway, Sweden and Finland are recognized by road users to generally be in satisfactory condition. In comparison, the less frequently trafficked rural roads have suffered from financial neglect and are falling well below modern standards. They have not been designed to cope with the combination of seasonal freeze/thaw cycles of the northern climate and the heavy axle loads of modern transport. Recent development in transport and in industrial logistics have substantially increased the stress on road structures as the total weight of heavy transport has been increasing and modern super-single tires are replacing traditional twin tires on heavy transport vehicles
ROADEX sub project A (SPA) focused on low traffic volume roads in the partner districts of Lapland, the Northern Region, Troms County and the Highlands. Low traffic volume roads, roads that have less than 1000 vehicles average daily traffic (AADT), represent 85% of the total road network of the four districts and amount to approximately 32.800 km. In the NP area, gravel roads, which account for 11.000 km or 29 % of the combined road networks (Figure 1) of the four partner districts, have a critical function in local transportation networks. As such, additional consideration was given to gravel roads and their characteristics.
Figure 1 - Almost one third of the roads in the Roadex partner regions still have a gravel wearing course.
During spring, when road structures are thawing, a condition of a road can deteriorate rapidly (Figure 2). The different approaches to dealing with this critical issue, which are mainly centered around the use of traffic restrictions, were another of sub project A's special interests. The general practice of road administrations dealing with this problem has been either (a) to impose load restrictions on the sensitive road sections or (b) to upgrade the road structure. Both solutions, present a dilemma. Current finances have made it impossible to improve the road network to the point were it could withstand current demands. Traffic restrictions, however, can seriously affect the livelihood of local business and industry. In Sweden, calculations done to determine their effect indicate that load restrictions cost the national paper industry 900 million SEK (99 million Euro) annually. Within that setting Sub Project A (SPA) focused on identifying methods for 1) optimizing the implementation of traffic/load restrictions or 2) minimizing damages if restrictions are not applied.
Figure 2 - Gravel roads during the spring thaw weakening period can be almost impassible to a normal car, while in other seasons they can provide a smooth road surface with adequate bearing capacity. The photos were taken from the Roadex Seljelvnäs test section in Norway.
The SPA Road Condition Management work group collected the study data through an extensive questionnaire and work group discussions. In addition, interviews were conducted concurrently with field excursions to each partner district. A state-of-the-art report based on the questionnaire results, excursions, interviews and review of pertinent literature was published in September 2000 (Saarenketo and Saari 2000).
In each partner district, 8-9 test sections were selected for field-testing. The test sections encompassed standard structures, best practice structures and problem structures. In October – November 2000, the test sites were surveyed with a ground penetrating radar unit. They were also photographed and digital video was recorded. In the Scandinavian districts, a roughness and rutting survey unit was also used to make measurements in the test sections. In addition to the field surveys, any planning documents or other data collected from the survey sites was compiled for use in the analysis. The results of these surveys were published on a multimedia format CD.
2. LOAD RESTRICTION POLICIES IN NP DISTRICTS
The majority of load restriction and the most difficult bearing capacity problems are related to gravel roads. Especially those gravel roads, which have developed over time and as such were not constructed or designed with structures that could meet modern performance requirements. In spring, during the thawing period, many of these roads become impassable to automobiles and the road section has to be closed in order to prevent further damage (Figure 2).
An examination of the partner districts' road administrations' policies and practices regarding load restrictions reveal a number of different approaches. In contrast to the rest of the partner districts, Norway does not use temporary load restrictions, however, in Troms many roads have permanent load restrictions of 40 – 50 tonnes. Finland has only implemented permanent load restrictions on roads with weak bridges. Both Finland and Sweden permit the heaviest standard transport weights on most public roads, at 60 tonnes. Both countries also use temporary load restrictions, especially during spring thawing, to prevent severe damage during vulnerable periods. With regard to load restrictions Sweden's Region Norr is, perhaps, in the most problematic situation, as approximately 1/3 of their road network requires permanent or temporary load restrictions (Figure 3). A few roads in the Highlands have had temporary or permanent load restrictions imposed on them, however the maximum total weight permitted in Scotland is 41 – 44 tonnes.
Figure 3 - Permanent and temporarily load restricted roads in the Region Norr in Sweden.
Enforcement of load restrictions is handled differently within the districts. In Troms county, the road administration itself can order fines or other sanctions against overloaded trucks. In contrast, the police in Lapland and the Highlands handle enforcement of penalties and sanctions against load restriction violators.
Further assessment of the districts' policies reveals that Sweden and Scotland have the most protective policies with regard to preventing road damage. In Scotland, a permanent load restriction can be imposed if there is reason to believe that increasing heavy traffic may break the road. In Region Norr, temporary restrictions can be imposed if there is any evidence of defects occurring in the pavement structure and with respect to gravel roads over 1% of the road must exhibit signs of damage prior to imposing a restriction.
On a directly related topic, maximum allowed tire pressures are basically the same in all of the partner districts. There is also general agreement amongst the districts' professionals that tire pressures are too high and that especially modern super single tires are damaging pavement structures.
3. MAINTENANCE AND REHABILITATION TECHNIQUES
3.1. General
Although the project did not reveal any major breakthroughs in the area of maintenance techniques there were a number of special rehabilitation and repair techniques where their application could be transferred to other NP countries. Included among these were methods for stabilizing pavement and base course, reinforcing and insulating road structures. Surface dressing was an interesting and economical maintenance technique used regularly in both Scotland and Norway to protect pavement structures and add friction. Interestingly the field tests also revealed that some of these techniques were the source of other problems indicating that, while promising, there was still room for improving them.
3.2 . Reinforcement
Steel mesh reinforcement, in recent years, has become a common strengthening method in Region Norr and Lapland and it has also been used successfully in some test projects in the Highlands. General practice has been to install steel mesh either in the pavement or in the unbound base course. In most cases, this method has been used to prevent longitudinal cracking but it has also been used, with some success, to reinforce weak road sections resting on peat. According to interviews, steel reinforced structures functioned well if the installation instructions were followed precisely.
During the Roadex field tests, four sites with steel reinforcement were closely examined. A review of the survey results from these sites presents some interesting findings and techniques. The test section at Killimster Moss, in the Highlands, an old concrete road resting on peat was reinforced with steel mesh thus far has worked well. In Mellajärvi, Finland, the lengths of steel mesh were too short, which caused longitudinal cracking along the road shoulder. This example critically illustrates the necessity of using reinforcements with dimensions suitable for the road they are to be used on. In Region Norr, Road 398, at Lappträsk, the surveys revealed that there was much less rutting in the test sections where steel reinforcements were installed deeper in the base course instead of at the bottom of the pavement.
3.3. Stabilization
Stabilizing the top layers of pavement structures, with foam bitumen or emulsified bitumen as binder, has become popular in the Scandinavian partner districts and although its use was tested in the Highlands it has not become common practice in that region. One of the main strengths of stabilization is that it facilitates treatment and strengthening of the unbound base course. Unbound base often has a high content of fines making it susceptible to permanent deformation.
In Lapland, only emulsified bitumen is used in the stabilization process. When choosing between the emulsified bitumen or foam bitumen techniques, Norway and Sweden follow the same principles: if the fines content is low, emulsion bitumen is mainly used and when the fines content is high (>10 %) foam bitumen has obtained better results.
Figure 4 - Remix stabilization machinery is commonly used in Finnish Lapland and in the Region Norr in Sweden.
During Roadex's field test stage, bitumen stabilized sections in Norway, Sweden and Finland were surveyed. Generally, the surveys found that the stabilized sections were even and functioning well. The surveys, however, also revealed a few problems related to the stabilized sections. Based on these problems a few general recommendations can be made. Poorly performing drainage caused distress to stabilized structures. Road shoulder support plays an important role in the performance of a stabilized structure, if the shoulders were narrow and/or steep, shoulder deformation or cracking was also observed. In some recently stabilized roads, permanent deformation and cracking problems could be linked to old pavement left in the unbound base. Finally, an important factor to consider prior to stabilizing a road is that it should not have problems with uneven frost heave.
3. COMMON ROAD STRUCTURE PERFORMANCE PROBLEMS
Not surprisingly, through the results of the Roadex project several major problems, common to all of the partner districts, were identified: drainage of roads located on transversely sloping ground, permanent deformation due to freeze-thaw cycles, poor quality road materials, and road sections resting on peat. The first three problems are more or less related to water content and freeze thaw cycles. Peat roads are clearly another kind of problem that require a different approach
In the NP area, low traffic volume roads resting on peat, is a commonly encountered problem (Figure 5). A typical problem that arises from this situation occurs in sections where the road had been widened and the peat subgrade under the expansions begins to compress, resulting in severe deformation and longitudinal cracking. A number of solutions to the general problem of 'peat roads' were observed during the field test stage. Two methods were surveyed in the Highlands, the previously mentioned Road B871, which was reinforced with steel mesh, being one. The second, which was surveyed as an example of a best practice, was a special Leca lightweight fill structure used in a road at Ledbeck. Field tests were also done on road sections, in Sweden and Norway, where the road, over a peat subgrade, was strengthened and widened, through soil replacement excavations on the both road shoulders. The surveys and general experience of these structures indicate that they have functioned well.
Figure 5 - A road section from B871 in the Highlands, constructed on peat, with depression problems.
Perhaps the most complicated problem, one still without a practical or economical solution, was that of roads located on hill slopes, where the ground water table was close to the road structure, resulting in permanent deformation. In this type of setting, the road lane on the upper side of slope is especially affected by high rutting. This particular problem is related to winter conditions and the related differential frost heave and thaw settlement transverse to the direction of the road. A number of solutions were tested in the partner districts, however, they were either very expensive or produced other problems. While on the topic of drainage problems, it should be noted that the Highland region especially had a significant problem with poorly functioning drainage, which is most likely the major cause of shoulder deformation in the region.
Figure 6 - Permanent deformation problems for road located on transversely sloping ground.
5. SUMMARY AND CONCLUSIONS
Roadex project has shown that the problems of the low volume road condition management in Northern Periphery are quite similar throughout the different regions. A significant problem for low traffic condition volume road management, shared by all partner districts, is that almost all the structural maintenance funds and resources are allocated to main roads at the expense of medium and low traffic volume roads. As a result, the performance of main roads has been improving over the last few years, while the state of low traffic volume roads has become worse. Another aspect gaining more publicity and placing pressure on road districts has been that due to increasing logistical demands of the industries, fish farming and forestry especially, that are using the lower class network for their transportation routes, have increasingly raised complaints about load restrictions and poor quality road networks.
However, in spite of similar basic problems in each partner district, each country has emphasized slightly different strategies and techniques when trying to resolve bearing capacity problems in their low traffic volume road network. For instance in load restriction policies Finland only uses temporary load restrictions on the weakest roads during the spring thaw periods, at the other end of the spectrum, Norway does not apply temporary restrictions at all but uses permanent axle restrictions on its weak roads.
There were also differences in road condition monitoring systems and rehabilitation methods. Troms in Norway and Northern Region in Sweden monitor their road surface performance by measuring roughness (IRI) and rutting while Lapland also measures structural condition using FWD and GPR techniques. The Highlands Council in Scotland did not have a systematic road condition monitoring system when the project started and rehabilitation was based on visual inspections. With regard to structural solutions Norway, Sweden and Finland commonly use bitumen stabilization techniques, however, only Finland and Sweden favored steel reinforcement for dealing with longitudinal frost cracking problems and permanent deformation. The benefits of the Roadex project can already be seen in that the different road regions have now started to test best practice techniques from other countries on their own roads and at the same time the benchmarking process has confirmed for the districts that some of their current methods are the best possible.
The Roadex project showed that in the future, research should focus on the following questions: 1) How much do road closures and load restrictions affect road structure deterioration, 2) What is the lowest acceptable road standard and 3) What are the social benefits and costs, for road users and owners, of having adequate road performance and 4) How much funding is required to maintain the low traffic volume road network at a sufficient level of service?
One solution for reducing the problems could be new and 'smarter' types of restrictions such as the following: 1) optimizing (especially shortening) the duration of load restrictions, 2) regulating the time and distance between heavy load vehicles, 3) regulating the speed of transport vehicles and 4) defining truck tire pressure. In the road structure and material research field the focus should in 1) improving the drainage on hill slopes, 2) developing a better understanding of permanent deformation due to freeze-thaw cycles, 3) identifying poor quality road materials and finding better and cheaper treatments techniques and 4) finding better rehabilitation solutions for roads resting on peat
Currently, r&d co-operation amongst road districts and transportation organizations in the Northern Periphery area is continuing in the form of the Roadex II project. In this project, especially the problems of low traffic volume road performance for the forest and fishing industries are being addressed.
ACKNOWLEDGEMENTS
The Roadex project is partly financed by an EU (ERDF, Article 10) funded Northern Periphery Programme, a programme of cooperation between the northernmost regions of Finland, Scotland, Norway and Sweden.
REFERENCES
Saarenketo T. and Saari, J. (2000) Road Condition Management of Low Traffic Volume Roads in the Northern Periphery. Roadex Sub Project A Phase I state-of-the-art study report. Roadex project 1999-2001. 70 p.