Two-Lane Highways Crest Curve Design. The Case Study of Italian Guidelines

Abstract

The main purpose of the research is to evaluate the crest vertical curves radii Rv, not considering a conventional value of the opposing vehicle height h2, but the average vehicle heights h2(m) and the value of the 15th percentile of the height distribution h2(15) of the passenger car population. The study only considered car models with more than 20,000 registered vehicles in Italy. One hundred and fifteen car models belonging to different brands were taken into consideration, for a total of over 9 million vehicles. For the statistical sample analyzed, the following vehicle heights were estimated: h2(m) = 1.48 m and h2(15) = 1.39 m. The deviations between the crest radii calculated with the Italian standard (h2 = 1.10 m), and those obtained for h2(m) = 1.48 m and h2(15) = 1.39 m are up to 12%. The differences ΔHv between the values of the visible vehicle body height Hv = Hv(t) calculated using, respectively, h2(15) = 1.39 m and h2(m) = 1.48 m are modest. The value h2(m) = 1.48 m could be adopted in order to reduce the highways construction costs. In fact, the research shows that the value h2 = 1.10 m is too conservative and leads to oversizing of the crest vertical curves. Therefore, it would be necessary to make an appropriate choice of h2 value in order to take into account the current heights of passenger cars.

A Statistically Based Model for the Characterization of Vehicle Interactions and Vehicle Platoons Formation on Two-Lane Roads

“…The phenomenon of the formation of platoons makes it possible to develop significant indicators for the analysis of service performance on two-lane roads [19].…”

“…The minimum time gap h s for passing may be considered equal to twice the average duration of an overtaking maneuver [37]. Considering for the latter a value equal to 6 s, as in Vlahogianni's studies for this type of road [38], we can assume h s = 12 s, which corresponds to the total time of the overtaking maneuver phases according to the Italian model [19], which is equal to 10 s [39,40] and which is increased by 20%. The minimum time gap h r for merging the right lane can be assumed to be equal to 8 s, in such a way as to ensure an adequate headway of approximately 4 s with respect to the previous and following vehicle when merging into the right lane.…”