Determining the Best Method for Measuring No-Passing Zones

Abstract

The objective of this study was to develop and test a suitable method for measuring passing sight distance on two-lane, two-way highways by using one person and vehicle. A literature review and contacts with state department of transportation (DOT) engineers revealed a number of current methods, and the research team developed several new methods. However, many of the current and new methods had problems that precluded agencies from using them. Five promising methods remained for an experiment testing their accuracy relative to the slow but trust-worthy walking method: the two-vehicle method, which is the most popular method used by state DOTs, a one-vehicle method used in a few divisions of the North Carolina DOT, a new laser rangefinder method, a new optical rangefinder method, and a new speed and distance method. The experiment provided data at 20 horizontal curve sites and 20 hill sites, equally split between the piedmont and mountain regions of North Carolina. The researchers recorded the time required to perform each method and also considered equipment costs, conservatism, and training needs. On the basis of these factors, the researchers recommend that highway agencies use the one-vehicle method to measure passing sight distance in most cases. The one-vehicle method was generally more accurate than the two-vehicle method, and it was superior to the new methods in several important ways.