Reviewing passing sight distance theory and practice in Saskatchewan.

This paper was presented at the "Geometric design and safety" session. These proceedings are available on CD-ROM. This research establishes both design passing sight distances and minimum passing zone distances considering current road demands, including heavy truck vehicle lengths and speeds. In developing a model procedure and variable input ranges, the inherent uncertainty, and therefore variability, in the input variables and solution outputs, are integrated into the solution analysis. This is accomplished by modeling the design passing sight distance and pavement markings probabilistically, which considers the statistical probability distribution of results, rather than expecting one correct distance to apply universally. The model equations used in this work combine many theories from previous papers, including the critical point concept, a probabilistic model approach, an iterative acceleration solution, and a generalized equation structure allowing for different variable inputs. This work builds on previous analyses by expanding the iterative acceleration solution to cover accelerations through the entire pass, accelerations through the critical point, as well as, accelerations completed prior to the critical point. Past work is also expanded on by proposing a theoretical and practical pavement marking distance for the minimum passing zone as a specific portion of the design passing sight distance. The results determined using the developed model, are a range of both design passing sight distance and minimum passing zone distances established using different vehicle lengths, based on current and proposed allowances on Saskatchewan two-lane, two-way highways. The results of the probabilistic analysis are for different vehicle lengths up to 30 metre long trucks being passed by passenger cars, light trucks, or vans. The impeding vehicle and initial passing vehicle speed are assumed to be 100 km/h. The results indicate that the current design passing sight distance standards set for 130 km/h design speeds roads in Saskatchewan are sufficient. In contrast, the results also indicate that the current standards set in Saskatchewan for minimum passing zones on 130 km/h design speeds may not be sufficient. (A)