The geometric features of a highway network play a significant role considering the fact that collisions occur disproportionately on horizontal curves. Based on extensive literature review, the problem mainly stems from the lack of geometric design consistency–conformance of highway geometric characteristics with drivers’ expectations. More specifically, drivers select their speeds according to their own perception of the road (referred to as the operating speed) rather than the designer’s perception (referred to as the design speed). To address operating speed consistency evaluation in Canada, two sets of models for speed behavior were examined based on speed data collected using traffic counters/classifiers on 20 curves on two-lane rural highways in Ontario. Relatively weak relationships were developed for the traditional operating speed on horizontal curves, while stronger relationships were found for the 85th percentile speed differential from a tangent to a curve. It was also shown that the nonintrus...

Achieving highway geometric design consistency is an important issue in the design and evaluation of rural highways to attain smooth and safe traffic operation. This paper presents a comprehensive literature review of highway geometric design consistency mainly on two-lane rural highways in North America and Europe. Previous research work on highway geometric design consistency is categorized into three main areas: (1) Speed considerations; (2) safety considerations; and (3) performance considerations. Speed considerations address the different effects of geometric parameters on the prediction of operating speed. Based on operating speed, design consistency of highway elements can be evaluated. Safety considerations explain the different relationships between highway safety and highway/traffic elements, vehicle stability, and low-cost improvements. Performance considerations address the different effects on driver workload, driver anticipation, highway aesthetics, and interchange design. Based on this rev...

Every year, large amounts of pavement deicing chemicals are used for snow and ice control on Canadian highways and airports. Until recently, urea had been the only pavement deicing chemical in use at Canadian airports, but due to recent concerns about the impact of this deicer on the environment, consideration has been given to replacing it with more environmentally friendly deicers. Concerns have also been expressed regarding the impact of road salts, which are used exclusively on highways but not airfields, on the environment. However, before substituting these conventional deicers with new ones, the potential deleterious effects of the new deicers on the pavement need to be quantified and compared with those of the conventional deicers. This paper presents an investigation to compare the destructive effect of newly introduced deicing chemicals such as potassium acetate and sodium formate, with urea and ordinary road salts on the durability of pavement construction aggregates and asphalt concrete when subjected to freeze-thaw cycles while submerged in solutions of different concentrations. The destructive effect of each deicer on aggregates was determined in terms of percent weight loss due to breakdown. For pavement samples, it was quantified in terms of weight and density loss, change in mechanical properties, variation in the penetration of recovered asphalt, and variation in the gradation of recovered aggregates. The test results showed that for all deicers the critical concentration, the one that caused the greatest damage to the aggregate, was in the 1–2% range, and for all deicers the quartzite aggregate suffered more damage than the limestone. It was also found that the road salt produced comparable damage to that caused by other deicers to quartzite, while the damage was significantly less for limestone aggregates. In case of asphalt concrete samples, it was found that conditioning asphalt samples using freeze-thaw cycles in the presence of a deicer solution caused a decrease in the indirect tensile strength and modulus of elasticity and an increase in the penetration values of the recovered asphalt cement. In addition, the test results showed that the maximum damage was caused by urea, while the damage due to the other deicers was comparable to that of distilled water.

Access to freeways is provided through interchanges to maintain the design concept of uninterrupted traffic flow. Therefore, provision of an appropriate entrance ramp and acceleration lane geometry that allows the entering vehicle to accelerate to a speed closer to the through lane speed is important for comfortable and safe merging maneuvers. In this paper, speed and traffic data were collected from 23 merging sites on Highway 417 located within the City of Ottawa, Canada, to study the traffic behavior at freeway merge areas. Analysis of traffic behavior showed that merging speed depends on both ramp and speed-change lane (SCL) geometrics. Lower merging speed was shown to be associated with higher collisions on the acceleration lanes. Right lane traffic volume and merging speed of entering vehicles were shown to significantly affect right lane speed along the acceleration lane. In addition, several statistically significant models were developed for the prediction of 85th percentile passenger car right l...

The perception of the driver of the road features ahead is an important human factor that can considerably affect traffic safety and design consistency, and should be addressed in road design. An erroneous perception of the road can lead to actions that may compromise traffic safety. Previous studies have shown that combined horizontal and vertical alignments can cause a wrong perception of the horizontal curvature. In this paper, the hypothesis that the perception of the driver of the horizontal curvature is affected by the overlapping vertical alignment is examined analytically. Computer animation was selected as a three-dimensional presentation method of the road perspective, and was found to produce a realistic view of the road. A sample of drivers was interviewed to determine the radius of a horizontal curve on a level grade that would look equal to a radius of a horizontal curve overlapping with a vertical curve. The statistical analysis showed that the horizontal curvature looked consistently sharp...