Permitted speed decision of single-unit trucks with emergency braking maneuver on horizontal curves under rainy weather

Under adverse weather conditions, visibility and the available pavement friction are reduced. The improper selection of speed on curved road sections leads to an unreasonable distribution of longitudinal and lateral friction, which is likely to cause rear-end collisions and lateral instability accidents. This study considers the combined braking and turning maneuvers to obtain the permitted vehicle speed under rainy conditions. First, a braking distance computation model was established by simplifying the relationship curve between brake pedal force, vehicle braking deceleration, and braking time. Different from the visibility commonly used in the meteorological field, this paper defines "driver’s sight distance based on real road scenarios" as a threshold to measure the longitudinal safety of the vehicle. Furthermore, the lateral friction and rollover margin is defined to characterize the vehicle’s lateral stability. The corresponding relationship between rainfall intensity-water film thickness-road friction is established to better predict the safe speed based on the information issued by the weather station. It should be noted that since the road friction factor of the wet pavement not only determined the safe vehicle speed but also be determined by the vehicle speed, so we adopt Ferrari’s method to solve the quartic equation about permitted vehicle speed. Finally, the braking and turning maneuvers are considered comprehensively based on the principle of friction ellipse. The results of the TruckSim simulation show that for a single-unit truck, running at the computed permitted speed, both lateral and longitudinal stability meet the requirements. The proposed permitted vehicle speed model on horizontal curves can provide driving guidance for drivers on curves under rainy weather or as a decision-making basis for road managers.

Investigation of Motorcycle Trajectories in 2-lane Horizontal Curves

Most of the road design guidelines assume that the vehicles traverse a trajectory that coincides with the midline of the traffic lane. Based on this assumption the thresholds of various features are determined such as the maximum permissible side friction factor. It is therefore important to investigate the extent to which the trajectory of the vehicles is similar to the horizontal alignment of the road or substantial differences exist. To this end, a naturalistic riding study was designed and executed with the use of an instrumented motorcycle which measured the position of the motorcycle with great accuracy in a rural 2-lane road segment. The derived trajectories were then plotted against the horizontal alignment of the road and compared with the 3 consecutive elements which form a typical horizontal curve i.e., the entering spiral curve, the circular curve, and the exiting spiral curve. Linear equations were developed which correlate the traveled curvatures with the distance of each horizontal curve along the road segment under investigation. The process of the data revealed that the riders differ their trajectory compared to the alignment of the road. However, in small radius horizontal curves is more likely to observe curvatures that are similar to the geometric one. Moreover, the riders perform more abrupt maneuvres in the first part of the horizontal curves while they straighten the handlebars of the motorcycle before the end of the curve. The present paper aims to shed light on the behavior of motorcycle riders on horizontal curves and hence to contribute to the reduction of motorcycle accidents, particularly the single-vehicle ones.

Developing a Google Earth-Based Method to Measure Sight Distance for U-Turns at Unsignalized Intersections on Multilane Divided Highways

The median U-turn is one of the most popular access management techniques implemented by state transportation agencies. Sight distance (SD) is among the key elements for the safe operation of median U-turns. The traditional method of measuring SD is using sight rods in the field, which is inconvenient and unsafe; thus, it is important to develop a convenient and safer method to measure SD for U-turn movement. The objective of this study is to develop a safe and cost-effective method to measure SD for U-turn vehicles, without going into the field, using existing tools in Google Earth and a perspective grid method that can be generated by Kinovea software. The method can be used in two different road geometric conditions: (i) a straight segment with crest curves; (ii) a roadway with a combination of crest curves and horizontal curves. For Condition (i), an empirical equation was developed to estimate SD as a function of distance and elevation along the sight line measured using Google Earth. For Condition (ii), a perspective grid was first applied using Google Earth ground-level view; then the number of broken lines and gaps in each perspective grid cell was used to measure the SD. All inputs can be collected using Google Earth. Field measurements of SD for U-turns at 10 selected locations were conducted to verify the validity of the method. The results show that the differences between the model estimates and field measurements are all less than 10%.

Verification of usRAP Risk Assessments for Run-Off and Head-On Crashes Using Field Data

The United States Road Assessment Program (usRAP) provides a systemic approach to estimate the risk of severe injury and fatal crashes along roadway segments based on the expected safety performance of roadway and roadside characteristics, together with a general estimation of traffic volume. Detailed crash data are not needed for safety assessments, providing advantages over more traditional crash-driven approaches. However, experiences with usRAP are limited to the United States and to date, the program has a growing but limited number of participating states. Verification of the adequacy of usRAP assessments is therefore of significant value, not only to identify strengths and limitations of the methodology within the U.S. context, but also to potentially expand the set of tools available to agencies. This paper presents a verification of usRAP risk assessments for run-off-road and head-on crashes using over 7,000 mi of coded segments and five years of crash data collected in Utah. Comparisons between risk estimations from usRAP and actual crash rates provided insights into the expected and observed effects of roadside objects and their distances from the lanes traveled, type of median present, and horizontal curves. A spatial correlation test also confirmed the agreement between usRAP risk assessments and crash data, providing additional promising indications of the suitability of this systemic methodology for safety applications.

Assessment of Young Drivers’ Driving Behaviour and Driving Speed along Horizontal and Vertical Alignments

Young drivers are more likely to experience car crashes as they tend to have risky driving behaviours. This study aims to assess young drivers’ driving behaviour and driving speed along the horizontal and vertical alignments of roads. The 20 young drivers who participated in this study were asked to complete a self-reported assessment (Driver Behaviour Questionnaire) and then invited for an on-road driving assessment during daytime and night-time, along horizontal and vertical road alignments at a selected route in Skudai, Johor. The results from the Driver Behaviour Questionnaire revealed that distractions during driving was the most frequently reported behaviour that caused car crashes amongst young drivers, followed by error and violation. Speed profile was found to be higher during daytime when compared to night-time. A significant difference in speed between male and female drivers was noted at horizontal curves during daytime and vertical curves during night-time. The study concluded that such aberrant driving behaviours would have an impact on the driving performance, particularly on horizontal and vertical curves.

Truck stability on different types of horizontal curves combined with vertical alignments

The combination of horizontal curves with vertical alignments is commonly used in different classifications of highways; either on highway mainstream or on highway interchange ramps. The horizontal curves, combined with vertical alignments, may be single, compound or reverse horizontal curves. The current design guidelines do not adequately investigate vehicle stability on such three-dimensional (3D) alignments. Computer software that simulates vehicle behaviour on different geometrical alignments was employed to investigate vehicle stability on such 3D alignments. It was found that vehicle safety is questionable, especially for larger vehicles on reverse curves associated with vertical alignments. The critical speed, where the vehicle starts to rollover or skid, was found to be close to design speed for those 3D alignments. Design aids were then developed to address the recommended solutions to maintain the margin of safety required.