Christian F Davis

Safety Benefits of Intersection Approach Realignment on Rural Two-Lane Highways

One task of traffic safety engineers is the identification of high crash locations and selection of appropriate highway treatments to reduce the number of crashes. This process relies on the availability of accurate information on crash reduction factors of various treatments. Currently, most agencies rely on information dating back to the 1960s. It is necessary to update and reassess these factors using new data and new evaluation methods. A before-and-after study is currently being conducted using empirical Bayesian methods to estimate crash reduction factors for modern conditions on two-lane rural highways. The results of the second phase of the study are reported, which aimed to evaluate the safety benefits of intersection approach realignment. Furthermore, an analysis of variance model is used to identify extra benefits of comprehensive treatments. The improvements studied appeared to reduce the total number of crashes, but the effect on type of crashes was different. Also, combining realignment with adding a left-turn lane or traffic signal does not appear to offer significant additional benefits in crash reduction.

Vehicle-based versus fixed-location measurements for traffic surveillance in IVHS

Many recent IVHS deployments feature vehicle probes as prominent sources of information about traffic conditions either in addition to or in place of traditional fixed location measurement devices such as inductive loop detectors. A number of other technologies now being considered for traffic surveillance that are deployed in fixed locations are reviewed and are found to provide the same kinds of information as more complex probe vehicle data collection systems. Recent experience with both fixed location and vehicle-based incident detection systems is summarized. Several incident detection algorithms calibrated with both fixed location and vehicle-based traffic measurements from a simulation of a signalized arterial street for a soon to be launched IVHS demonstration are introduced. The performance of these algorithms, some of which use data from only one source while others use data from both sources, is compared. While the fixed location measurements appear to be superior to the probe reports for detecting incidents when used alone, incidents detected by the respective algorithms do not completely overlap. Algorithms using both sources of data perform substantially better than either single-source algorithm, indicating that there is value in collecting information using both methods.