In Spain, drivers have come to rely on the signing and marking of no-passing zones in two-way, two-lane highways. Therefore, their proper setup is an important issue. The present system has some deficiencies: for instance, legal and/or posted speed limits are largely ignored by a large proportion of drivers, meaning that real speeds should be considered in design. Under a contract for the Spanish State Highway Authority, the author has reviewed current models for the passing maneuver, considering two modes (flying, and delayed or trailing the passed vehicle) and two outcomes (to achieve or to abort the pass). The usual definition of the critical position, or point of no return between the two outcomes, is modified: the passing car is at such a distance from the passed car that were it to abort the maneuver, the former's nose would just get abreast of the latter's tail. The eventual opposing car is traveling at maximum speed, but can adjust its speed to avoid collision. Simple equations are derived and fitted to experimental data on passing time frequency distribution, and to actual speed distributions. The following conclusions are drawn: (1) A no-passing zone should start at some distance from the point in which sight distance (referred to as the critical position) falls below a limit corresponding to the worst combination of modes and outcomes, resulting in an earlier barrier line. "Some distance" should allow for the maneuver to be completed or aborted, as appropriate. (2) A "warning zone" should be set (by means of pavement arrows) before reaching the barrier line, to allow maneuvers already started to be achieved, and to advise that new ones should not be started. (3) The end of the no-passing zone is related to the delayed mode, and to the possibility of having enough sight distance to abort a pass started precisely at that end should an opposing car be near or fast enough. (4) The length of a passing zone should allow for a pass to be achieved within it.
Samenvatting