Benjamin H Cottrell Jr

Analysis of Weigh-in-Motion Data for Truck Weight Grouping in Mechanistic-Empirical Pavement Design Guide

The purpose of this study was to evaluate the Virginia Department of Transportations traffic data plan for implementation of the Mechanistic–Empirical Pavement Design Guide (MEPDG) with weigh-in-motion (WIM) data from 22 sites in Virginia for 2007 and 2008. The evaluation included an assessment of the WIM data for pavement design and for enforcement of overloaded trucks and the appropriateness of the truck weight groups. Grouping the sites on the basis of average equivalent single-axle loads was notably different from the current truck weight groups and grouping results based on traffic characteristics such as truck volume. Thus, further efforts to suggest a better grouping scheme are needed. For calculating monthly traffic factors, an input to the MEPDG, volume data from WIM sites could lead to biased results. Thus, vehicle classification count data are a better source than WIM data for the factors. The enforcement sites were found to carry heavier trucks in terms of average equivalent single-axle loads than the sites installed for pavement data collection. Thus, the concern that truck weights collected at the enforcement sites might be inappropriate for pavement design because of possible avoidance of the sites by overloaded trucks seems unwarranted. However, because of several factors and limitations, a definitive conclusion regarding this result could not be drawn.

Safety and Operational Impacts of Optional Flashing Yellow Arrow Delay

Considerable debate exists over whether to delay the start of the flashing yellow arrow (FYA) signal indication (e.g., with a red arrow signal indication) during the transition from a protected movement to a permissive movement in a leading left protected–permissive left turn. The 2009 Manual on Uniform Traffic Control Devices is silent on this topic. This paper reviews the state of the practice on the use of the optional FYA delay through a literature review, a survey of state departments of transportation, and consultations with practitioners and national experts. A simulation study was also used to assess the potential impacts of the optional FYA delay on traffic safety and operations. The state-of-the-practice review indicated some preference for the use of the red arrow signal indication because of the perceived safety benefit. For example, 71% of the responding state departments of transportation that use the FYA also delayed the start of the FYA. The simulation analysis showed significant safety benefits in a delay to the start of the FYA signal indication for all scenarios except the scenario with a low opposing through traffic volume, with no significant negative impacts on average delay, average queue length, or average stopped delay for either left-turning traffic or the intersection as a whole being found.

Using All-Way Stop Control for Residential Traffic Management

All-way or multiway stop signs are perhaps the most controversial form of residential traffic control. Because stop signs are thought of as a panacea for many traffic problems, residents are likely to request all-way stop signs more frequently than any other form of control. The Virginia Department of Transportation receives requests to install all-way stop control (AWSC) on residential streets primarily to slow traffic and to reduce cut-through traffic volumes. The effectiveness of AWSC as a residential traffic management technique is evaluated. A comprehensive review of the literature and a questionnaire survey of selected traffic engineering agencies revealed how AWSC is used in Virginia and elsewhere. Most traffic engineering agencies use AWSC warrants from FHWA’s Manual on Uniform Traffic Control Devices (MUTCD). Some agencies modify the MUTCD warrants or use a rating system because the MUTCD warrants appear to be in appropriate for residential streets with lower traffic volumes. Three case studies using a series of AWSC intersections to reduce cut-through traffic on residential streets were conducted and analyzed. In these studies, AWSC when installed at a series of residential intersections effectively reduced cut-through volumes.

Safety Aspects of Line Markings on Two-Lane Low-Volume Narrow Roads in Virginia

Pavement line markings are designed to provide drivers with visual clues for safe driving, and their installation is generally determined based on roadway width, traffic volume and functional classification. In general, for two-lane roadways, the Virginia Department of Transportation currently installs a centerline pavement marking on roads that have a minimum traffic count of 500 vehicles per day and a minimum width of 18 ft. This study examined the safety aspects of line markings on low-volume (3,000 vehicles per day or less) narrow (20 ft or less) roads in Virginia. Four ways of measuring safety performance were employed. Crash frequency, density, rate and safety performance functions were used for those roads under four line marking types: no lines, a centerline only, edge lines only and both lines. Based on five years (2004~2008) of crash data on 4,797 road segments in Virginia, the study found no statistical difference between the presence and absence of a centerline and/or edge lines on the low-volume narrow roads. Omitted factors, such as curvature and speeds, might have some influence on the findings. By examining the age distributions of drivers in the crashes, it is conjectured that adding line markings can plausibly be inferred to provide safety benefits for teen drivers. Language: en