Abishai Polus

A STUDY OF TRAVEL TIME AND RELIABILITY ON ARTERIAL ROUTES

This study is concerned with travel time and operational reliability on arterial routes. Reliability is viewed in terms of the consistency of operation of the route under investigation and defined in terms of the inverse of the standard deviation of the travel time distribution.Under certain assumptions, travel time behavior on an arterial route is seen to closely follow a gamma distribution; the reliability measure can be derived accordingly. Utilizing arterial travel time data from the Chicago area, both a regression and a statistical model are show to serve as efficient techniques in predicting reliability. The prediction models are evaluated.

PREDICTING OPERATING SPEEDS ON TANGENT SECTIONS OF TWO-LANE RURAL HIGHWAYS

Prediction and estimation of speeds on two-lane rural highways are of enormous significance to planners and designers. Estimation of speeds on curves may be easier than prediction of speeds on tangent sections because of the strong correlation of speeds with a few defined and limiting variables, such as curvature, superelevation, and the side-friction coefficients between road surface and tires. On tangent sections, however, the speed of vehicles is dependent on a wide array of roadway characteristics, such as the length of the tangent section, the radius of the curve before and after the section, cross-section elements, vertical alignment, general terrain, and available sight distance. Few studies have dealt with this issue because a considerable database is necessary to identify any significant trends and substantial modeling effort is required. Research analyzed the variability of the operating speeds on 162 tangent sections of two-lane rural highways, and models were developed for prediction of operating speed based on the geometric characteristics available. A one-model approach was used initially. Because of the low R2 values, a family of models was developed that better predicted operating speeds.

A DECISION MODEL FOR GAP ACCEPTANCE AND CAPACITY AT INTERSECTIONS

The purpose of this paper is to present a microscopic decision model for driver gap-acceptance behavior when waiting at an unsignalized intersection on the secondary road and also to estimate the resulting intersection capacity. The model is based on evaluation of the risk associated with not accepting small gaps against the potential benefit of their acceptance, which is the time saved as a result of shorter waits at the entry line. The model takes into account individual preferences by defining individual critical gap, which is different from the traditional macroscopic critical-gap approach. The latter estimates the critical gap for the entire population of drivers. The paper presents the difference between different driver populations (risk-loving vs. cautious) and shows how this difference actually results in different capacities on the minor road.

Evaluation of the Passing Process on Two-Lane Rural Highways

The main purpose of this research was to develop models to quantify the major components of the passing process. A second goal was to compare the results with existing highway-design models and to arrive at conclusions about the applicability of the existing models. Additional objectives were to evaluate several time elements of the passing process, such as the response time of drivers from the arrival of a proper gap until the start of the passing maneuver. The evaluation is based on an analysis of data that were collected by videotaping six tangent two-lane highway sections from high vantage points and from a helicopter hovering above one site. Normal driver behavior was not disturbed during the data collection process. About 1,500 passings were recorded; of these, 54 percent were characterized as “single passing,” in which one driver passed a single, slower vehicle. About half of all passing maneuvers were found to involve two cars; in the other half, at least one truck was overtaken. A model showing the relationship between the speed of the impeding vehicle and the passing distance was calibrated, and the implications for highway-design procedures were discussed. Several of the findings had unique safety implications, such as the very short headway before the start of the passing maneuver and very short driver-reaction times. The primary results of the analyses enabled determination of the required passing distances and, therefore, the sight distances needed for different design speeds and various traffic combinations. Additional safety-related aspects are evaluated and discussed.

A Passing Gap Acceptance Model for Two-lane Rural Highways

Passing manoeuvres on rural two-lane highways significantly affect highway capacity, safety and level of service. This article presents an analysis of data on drivers’ passing decisions on two-lane rural highways that were collected with an interactive driving simulator. Measurements of the speeds and positions of all vehicles in several different scenarios were collected and processed to generate observations of gap acceptance behaviour. In addition, participants responded to a questionnaire which collected information on their socio-demographic and driving styles characteristics. These data were utilised to develop a model that explains the decision whether to pass or not, using variables that capture the impact of the road geometry, traffic conditions and drivers’ characteristics. It was found that while the traffic related variables had the most important effect on passing decision, factors related to the geometric design and the driver characteristics also had a significant effect on these decisions.

A REVISED METHOD FOR THE DETERMINATION OF PASSENGER CAR EQUIVALENCIES

Abstract The operating characteristics of trucks and buses differ significantly from those of passenger cars. The former travel more slowly and occupy more space than do the latter. These are the two most prominent reasons for the need to determine the equivalencies of the large-size vehicles in terms of passenger cars, since passenger car equivalencies (PCE) are required for carrying out highway capacity calculations. This paper reviews and discusses the current approaches to such a determination, and then suggests and evaluates a revised method. A direct comparison with current practice is also presented.

An analysis of nighttime pedestrian accidents at specially illuminated crosswalks

Abstract The purpose of this research was to examine the effect of the special crosswalk illumination and signing system presently warranted for use in Israel. The study was of the before and after type and treated the fixture as an entirety, without attempting to distinguish between differential effects of the sign and of the illumination provided on the crosswalk. Ninety nine installations were studied where no other engineering changes had been made in the “after” period. It was found that a significant reduction in pedestrian night accidents was achieved where the installations were made, while the reduction in day accidents was not statistically significant. In addition to the analysis of night and day accident changes at sites where the system was installed, comparison was made between a number of these sites and a group of unlit “control crosswalks”, each of which either adjoined the lit crosswalk at the same intersection or was nearby on the same street. Accidents at these control crosswalks did not show a significant change over the period studied. Additional factors which were investigated, such as pedestrian and vehicle flow, weather and national trend of pedestrian accidents, all supported the conclusion that it was the installation of the sign and lighting system which brought about the observed reduction in accidents. It was further found that the system represents a highly worthwhile investment in terms of costs and accident reduction benefits.

Analysis and evaluation of the capacity of roundabouts

Roundabouts are replacing conventional unsignalized intersections in many parts of the world and could become more widespread in the United States, although there are some limitations as well as clear advantages. Models for entry capacity into the rotary were developed. Entry capacity depends on the geometric characteristics of the roundabout, particularly the diameter of the outside circle of the intersection. The geometric characteristics determine the speed of vehicles around the central island and, therefore, have an impact on the gap-acceptance process and consequently the capacity. Traffic conditions that impede entry capacity involve the flow around the roundabout. Flow and geometric data from six small to medium-sized roundabouts were analyzed. Individual and aggregated entry-capacity models were calibrated by using the diameter and circulating flows as explanatory variables. Very good fits to the data were obtained; the results also fit models developed in other countries. The Australian model resulted in slightly higher entry capacities for moderate to low circulating flows and lower entry capacities for high circulating flows. Very close proximity to the German model was obtained, although it does not depend on the geometric characteristics of the circle. The roundabout provides an advantage over a conventional unsignalized intersection. A faithful concurrence between the model developed and the latest Highway Capacity Manual model for right-turn capacity at an unsignalized intersection is obtained if the circulating flow is replaced by the conflicting flow. The advantage of entry capacities of the roundabout over the calculated capacities of the Highway Capacity Manual left-turn model is shown. Further research is proposed to study the effect on entry capacity of two circulating lanes rather than one and the effect of the increase in circulating flows on the gap-acceptance process, particularly the reduction in critical gap at high flows.

Impact of Infrastructure Characteristics on Road Crashes on Two-Lane Highways

Objective. The main purpose of this study is to estimate and quantify the contribution of the infrastructure to highway crashes and to develop an infrastructure coefficient, that represents the overall characteristics of the highway and could be used as an independent variable in a crash-prediction model. Methods. The infrastructure is defined in this study as the highway and its geometric features, including alignment, road-side elements, sight-distances, presence of guardrails, access-points, roadway consistency, and additional variables that measure the overall quality of the highway alignment and elements. The analysis and developments are conducted for two-lane rural highways. The approach taken is to identify the high crash-rate roads, those with crash rates above 0.25 crashes per million vehicle-km, by Smallest Space Analysis. This type of analysis allows the aggregation of higher crash-rate roads versus lower-crash-rate roads only by their infrastructure coefficients, without consideration of their crash records. Results. Crash rates that are attached by Smallest Space Analysis to the group of roads that had less desirable infrastructure features show a high correlation between the same roads and high crash rates vs. identified better infrastructures and low crash rates. Further analysis shows that low crash-rate infrastructure, as defined in this study for two-lane rural highways, can reduce the crash rate by 44% versus high crash-rate infrastructure, at the 99% confidence level, which is almost a certainty. A model for the prediction of crash rates based on a proposed infrastructure coefficient is calibrated and presented. Conclusions. It is suggested that this model be used in evaluating alternatives for new highways or in improving the alignment and road features of existing highways.

Flow Characteristics at Freeway Work Zones and Increased Deterrent Zones

Traffic-flow characteristics were studied at two work zones on suburban freeways and at a third freeway site where a police patrol car, easily noticed by drivers, was parked on the right shoulder. The purpose of the study was two-fold: (a) to estimate the speeds, headways, and capacities of sections in which some lanes were temporarily closed to traffic because of relatively short construction operations, and (b) to assess the impact of increased, visible police deterrents on traffic flow, capacity, and safety. Calculated average flow rates, obtained from 1-min observations, were similar to values suggested by the Highway Capacity Manual at Site 1 but considerably less at Site 2. The lower values at Site 2 are attributed to the transfer of vehicles from the northbound to the southbound lane and to the resulting “constrained” operation that resulted because of a temporary barrier near oncoming traffic. The presence of a police patrol car on the shoulder at Site 3 created a deterrent to drivers, resulting in reduced average headways (and therefore increased density) and reduced headway variability. Because the volumes remained about constant, the resultant space-mean speeds also dropped. The importance of the flow stability—obtained by warning and advisory signing, the gradual closure of lanes, and a visible deterrent such as a police presence—is emphasized. Further research is suggested on the optimal slope and length of lane-closure tapers on freeway work zone approaches, the capacity of other combinations of lane closures, and the safety effects of traffic deterrence caused by police presence.