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Predicting the number of crashes that may occur as a result of specific highway features is critical in evaluating different treatment or design alternatives. Since different highway geometric characteristics can influence crash distribution datasets, Highway Safety Manual’s (HSM’s) predictive method encourages users to predict crashes based on their severity and collision type proportions. This study used crash data from rural two-way two-lane road segments in the Oromia region over seven years to develop Oromia’s fixed crash distribution dataset on Interactive Highway Safety Design Model (IHSDM) software. The crash distribution dataset has two parts; the crash severity proportions and the collision type percentages. The developed Oromia’s fixed crash distribution dataset was compared and validated against the default HSM crash configuration. As a result, the Crash Prediction Model (CPM) evaluation results confirmed that the developed crash severity proportion (the first part of the crash distribution dataset) estimates are more accurate and closer to the observed values. Furthermore, the findings show that crashes in the Oromia region are severer than in the states where the HSM crash configuration was developed. According to the second part of the crash distribution dataset evaluation (collision type percentage), the developed fixed crash distribution dataset outperforms the default HSM configuration in most collision type proportions, but not in all. For instance, from the ten collision type proportions developed, Right-Angle and sides-wipe collision proportions are predicted more precisely by the default HSM configuration. This points to the need for developing collision type proportion (the second part of the crash distribution dataset) as a function rather than a fixed configuration for a better result, based on the availability of complete crash data (i.e. crash location). In general, the study revealed that in order to exploit the full potential of HSM’s predictive approach, researchers must develop a jurisdiction crash distribution dataset using local crash data. The methodology demonstrated in this study to develop the jurisdiction’s crash distribution dataset has been validated as true thus, safety practitioners are encouraged to adopt it.

The knowledge about the infiltration behaviour of a dike body is an important issue in dike design and flood risk assessment. To reduce the risk of stability failures during flood events, the infiltration rate of a dike should be kept low and the elapsing time to reach the saturated steady state should be long. A number of full-scale physical flood simulation experiments on the Rostock research dike, on which different processed dredged materials were applied in the dike body (cover layers in particular) showed that the infiltration time and rate is much higher as can be expected from comprehensive laboratory test data. To obtain information about the unsaturated/saturated hydraulic soil properties of the installed dredged materials in situ, an automatic multi-objective model calibration method for a minimizing problem is used to reduce the residuals between simulated and observed time series (hydraulic head pressure, suction pressure and rate budget). The measured suction pressure time series of these physical experiments lets us suppose, that it is not possible to simulate the suction pressure behaviour of the installed dredged material using RICHARD’s unsaturated flow equation with a proper water retention function and unsaturated flow conductivity. It seems that the hysteresis effects are negligibly small and the hydraulic behaviour is governed by the inter-aggregate pore structure. In the paper, different back-calculation methods to fit the soil hydraulic parameters to the full-scale measurements are discussed and compared a proposal for the evaluation of the data is provided.

In the project DredgDikes the different research dike embankments were tested with respect to overflowing water induced erosion. Therefore, flumes were installed on the land side embankments in which the effect of overflowing water on the vegetated surface was investigated. On the Polish DredgDikes research dike near Gdansk, Poland, two parallel flumes were installed and the surface of the dike made of different mixtures of ash, silt and sand as well as clay was tested both in vegetated and unvegetated state. The results showed that the grass sods placed on the dike embankment had a comparably low erosion stability, particularly if placed directly on the hardened ash/silt dike cover with better results if placed on a clay cover, while the ash/silt mixture showed a high erosion resistance without vegetation. This results in the recommendation to use a thicker vegetation layer on top of the ash composite dike if the vegetation shall account for the erosion resistance or else, that even if the grass cover is washed away, a very solid cover made of the ash composite can withstand an overflowing event for considerable time. [ABSTRACT FROM PUBLISHER]