Road Network Management in an Environment of Uncertainty.
AKINYEMI E O, Institute for Infrastructural, Hydraulic and Environmental Engineering, The Netherlands
Adequate road network maintenance and development is one of the major problems currently faced by road organizations in many countries. On one hand, resources for adequate maintenance of existing roads are dwindling while the resources available are often
Adequate road network maintenance and development is one of the major problems currently faced by road organizations in many countries. On one hand, resources for adequate maintenance of existing roads are dwindling while the resources available are often much less than what is required to keep the network in desirable rideability conditions. On the other hand, there are strong pressures in many countries to expand the existing networks.
In road maintenance and rehabilitatiun(M&R), the main issue relates to decision-making. This involves providing answers to the following questions:
(1) When and where should M&R actions be applied on a network in order to make the best use of available resources?
(2) What types of M&R actions should be applied when necessary?
(3) What will be the aunual budget requirement to meet the desired M&R needs in a given planning period?
In many situations, answers to these questions are provided subjectively or on the basis of political and other criteria .One of the factors that contribute to this situation is the difficulty of obtaining objective information on M&R actions which can be deemed optimal with respect to the size of the network, available resources and desired minimum condition of a road. Another factor is that when the information is available, it is often in a form which cannot be understood or used appropriately by many agencies.To be usehd, the following questions need to be answered:
(a) What is the least desirable performance level of each road in the network ?
(b) What are the likely future traffic and other conditions on the roads in the network and what effects will they have on future performance levels?
(c) What are the possible alternative M&R actions on the network?
(d) What are the likely implications of implementing each possible action at each possible time?
Currently, these questions can be answered by using analytical decision-support systems which involve the use of pavement performance prediction models. In general, there are two possible types of performance prediction models. These are generally known deterministic and probabilistic models. Unfortunately, the two model types have a number of deficiencies. Deterministic models, which are used in many pavement management systems, have two main deficiencies. First, the outputs of the models do not seem to be realistic in many current situations as the models do not adequately consider the effects of uncertainties in future traffic loadings, in the times at which M&R actions are implemented and in the amount of resources which will be available in future etc.. Secondly, many of the models are difficult to use realistically in practice because the models often require regular network condition monitoring which needs substantial financial and manpower commitments.
Currently, stochastic models which are currently used by a number of agencies especially in the USA, are based on the assumption that pavement deterioration over time is Markovian. This implies the assumption that the probability that a pavement condition will change from one level to another in the future is only dependent on its current level and is independent of time. Undoubtedly, this approach is known to be useful in the current environment of uncertainty in many countries. However, it is not widely used probably because of two factors. Firstly, it is potentially complex to determine the relevant probabilities. Secondly, some of the assumptions may not be valid in many situations.
Association for European Transport