The purpose of this study is to compare the visibility of various colors and patterns of retroreflective tapes and evaluate the effect of human and environmental factors on the detection of distance, perception-reaction time, and heart rate while driving behind heavy trucks with different patterns of retroreflective tapes. The Kitami Institute of Technology Driving Simulator (KITDS) was used for the experiment throughout this study. BACS Advance (TAOS Institute) is another piece of equipment used to measure heart rate and used to determine the driver's level of stress. Five patterns of retroreflective tape designs were evaluated and compared. The results of the study clearly show that the most visible retroreflective tap pattern is the fully outlined alternating red and yellow retroreflective tape following Regulation No.48 from UNECE, in comparison to the other patterns tested. Gender, driver age, the speed of the following vehicles, tape width, tape pattern, lighting conditions, and weather conditions significantly affect the detection distance. Driver age significantly affects the perception-reaction time. The perception-reaction time is significantly longer for drivers behind trucks with no retroreflective tape at the rear-end. Therefore, the selection of the most effective color and pattern of retroreflective tape is very important in order to increase the visibility of heavy trucks and reduce the chances of rear-end truck collisions, particularly at nighttime or in conditions with limited visibility. This study strongly recommends that countries which have not implemented regulations concerning the placement of retroreflective tape on the rear of large trucks, or have implemented the regulation but not in accordance with UNECE Regulation No.48, should consider revising their regulation to improve the visibility of large trucks.

In developing countries including Ethiopia, potholes are one of the most serious problems of paved roads, especially after the rainy season. Thus, a criterion that enables road administrators to prioritize the maintenance for pavements with potholes is required in addition to common indices such as the International Roughness Index (IRI). The IRI is used as a standard indicator as it can show the average deviation of a road surface. However, the use of only IRI possibly leads to misinformation when the pavement has been damaged with severe potholes, which causes traffic accidents as well as high user costs. This is due to the conditions of which a pothole develops at some locations of the pavement while no damages are observed in the rest of them. If the condition of potholes is without consideration into IRI-based pavement inspection, it brings inappropriate result and then the road users complain. In the light of this background, this study examines the impact of pothole on road user response in terms of driving safety and comfort for pavement maintenance prioritization. For this purpose, artificial pothole data at different intervals such as 10 m, 20 m, 40 m, and one pothole in a 100 m segment are considered as well as the IRI for the segment. In this study, depths of 25 mm, 50 mm, 75 mm, and 100 mm are simulated for paved roads with two layers of asphalt which is a common case in Addis Ababa City Roads. In addition to the depth and interval, the pothole diameters such as 200 mm, 500 mm, and 750 mm are also involved as a parameter. This study contributes to the establishment of a criterion for pothole conditions that are used in conjunction with the IRI for the prioritization of pavement maintenance, especially in developing countries.

世界標準の平坦性指標である国際ラフネス指数(IRI)は，局部的な路面の変状に対して，過小評価されるという課題がある．本研究では，局部変状区間の縦断プロファイルを9オクターブバンドに分割し，分割したバンドごとの最大振幅を算出する手法により，局部変状評価に適したIRIの算出延長を明らかにした．また，道路利用者が不快と感じる路面の補修推奨値を，路面評価型ドライビングシュミレータを用いた被験者評価試験により検討した．その結果，局部変状路面の補修推奨値として，10ｍ評価基準長のIRIを8mm/mとすることを提案した．また，高速道路によせられた道路利用者の意見と，その区間のIRIを照査したところ，提案した補修推奨値の妥当性が確認できた．

A lot of devices measuring the International Roughness Index (IRI) has recently been developed and applied in response to the pavement inspection purposes. Consequently, the accuracy of measured IRIs obtained with different devices on the same road surface has become a practical concern for providing a consistent inspection result. Against this background, the specified non-profit organization Pavement Diagnosis Researchers Group (PDRG) in Japan has undertaken a project regarding the experiment to harmonize and compare Test methods for surface Roughness Under actual road Environment (TRUE project) since 2014. The TRUE project has so far conducted the roughness measuring experiments three times over five years at Hokkaido, Japan. This paper introduces the features of the TRUE project such as participated devices, test site selection, and data recording and reporting procedures. A benchmark testing for obtaining reference profiles is also provided to make the project reliable. In this paper, the results of experiments conducted in the last five years are statistically described as well. Finally, this paper introduces the potential of the TRUE project such as a new device grouping and the accuracy evaluation report for device certification for contributing to further improvement of a device participated in the project.

Heart rate variability (HRV) refers to the beat-to-beat fluctuations in heart rate, which is one of the most promising physiological indicators reflecting mental stress of humans. It has different spectral components in the high and low frequency ranges that are 0.15–0.4 Hz and 0.04–0.15 Hz, respectively. One of the interesting features of HRV is that mental stress inactivates the high frequency (HF) spectral oscillations depending on its severity. The purpose of this study was to verify pavement ride quality ratings based on HRV. For this purpose, a sophisticated driving simulator (KITDS: Kitami Institute of Driving Simulator) was employed and was confirmed to be applicable to physiological testing for pavement ride quality. The result of the simulator experiment showed that the HF oscillations in the time-frequency plane analyzed by continuous wavelet transform decreased with the increase of surface roughness in terms of the international roughness index (IRI). This phenomenon was validated by the on-site experiment using an actual vehicle prior to the ride quality verification study using the KITDS. In the verification study, we observed a particular case of which the subjective ratings were inconsistent with physiological stress signs in terms of the HF oscillations. Although the traditional questionnaire-based testing allows direct measurement of the ride quality of road users, in such a case, the participants of the experiment are unconsciously exposed to mental stress regarding ride quality. The experiment result indicated that 70 % of the participants suffered the unconscious mental stress. To improve this inconsistency, we categorized subjective ratings into three categories depending on the HF oscillations of HRV. According to the result, we suggested that the IRI of 3 mm/m was reasonable as a threshold of pavement ride quality acceptance at the highway speed of 80 km/h.