Moshe Livneh

Relationships between road accidents and hourly traffic flow--I : Analyses and interpretation

This research extends the investigation of the relationships between measures of accidents and traffic flow, and considers the hourly flow instead of the average daily traffic (ADT), which has already been reported. The findings of this study serve as a basis for further clarification of the interactions between various levels of traffic flow and road accidents. Eight four-lane road sections were studied during an 8-year period, providing adequate data based on carefully predefined criteria. Power functions are fitted and classified according to: (1) time-sequence analysis for each roadway section; and (2) cross sectional analysis on a one year basis. The results are presented, separately for multi and single vehicle accidents, in a matrix-format. A linear dependency was observed between the power and the logarithm of the multiple constant. This was done in a similar fashion to the previously reported study of the relationships between road accidents and ADT. The results for each type of analysis and type of accident are discussed, and three examples of a practical application are given.

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.

Optimal Quality Characteristic Evaluation for Asphalt Mixing Plants

The development of a quality system for asphalt mixing plants based on original statistical development is the subject of the current investigation. Quantitative evaluation of the quality characteristic under study and distinguishing the quality level for the plant production process have been analyzed. Results for the diagnostic parameter and quality characteristic evaluations (statistical estimations) have been analyzed and compared, employing process capability indices and the control chart method. Quality evaluation of the asphalt mixture produced based on the quality mark (QM) characteristic presented during a previous analysis and corresponding statistical analysis for diagnostic parameters of the presented results and their practical application are discussed. Additional development of the QM characteristic prediction model has been fulfilled and applied in practice. Results presenting the quality mark characteristic behavior with respect to an elaborated general index have been compared with analogous behavior generated using conventional indices for quality mark evaluation. The model presented for quality mark evaluation regarding asphalt mixing plant production and its practical application provides a significant level of efficiency, but requires further development.

QUALITY ASSESSMENT DURING ROAD FORMATION AND FOUNDATION CONSTRUCTION: USE OF FALLING-WEIGHT DEFLECTOMETER AND LIGHT DROP WEIGHT

Mechanistic empirical-based specifications, which focus on the mechanical properties of materials, facilitate quantitative evaluations of alternative construction practices and materials such as reclaimed materials. Thus, to represent these mechanical properties, quality-control and-assurance testing would be expected to include stiffness along with density measurements. In two case studies, a falling-weight deflectometer (FWD) was used during the construction of two major interchanges in Israel. FWD testing was found to be very useful in identifying local spots with poor performance, thus enabling execution of the required remedy actions. The two studies also indicated that, for a given feature, both a representative central deflection at the 95 percent reliability level and a coefficient of variability of measured deflections may serve as potential quality-control indicators. The possible use of the German light dropweight (LDW) device for measuring the mechanical properties of the formation of flexible pavements was also examined. Based on the cost per test, rate of testing, and quality of the data, the German LDW can serve as a cost-effective testing device for quality control and assurance during subgrade and capping-layer compaction.

Further evaluation of the relationships between road accidents and average daily traffic

The purpose of this paper is to further improve the understanding of the relationships between measures of accidents (density and rate) and average daily traffic (ADT) on interurban road sections. The road sections studied are selected on the basis of carefully defined criteria. Power functions are fitted and classified according to: (i) a time-sequence analysis for each roadway section; and (ii) a cross sectional analysis on a one year basis. Each analysis covers both the total and individual accident types: multivehicle, single-vehicle and pedestrian involvement accidents. When the parameters of the power functions are presented in a matrix-format a linear dependency is observed between the power and the logarithm of multiple constant. The general functional form is that the total accident density which was found to increase with the increase of ADT, is the combined result of a sharp increase in multi-vehicle accidents, moderate decrease in single-vehicle accidents and a negligible effect of pedestrian accidents. The possible application of the findings is discussed and operative examples are given.

Friction Correction Equation for the Dynamic Cone Penetrometer in Subsoil Strength Testing

Extensive experience gained with the dynamic cone penetrometer (DCP) in Israel has led to some modifications in both the testing apparatus and the testing procedure. One such modification is introduction of a theoretical corrective equation when the penetration is not performed vertically in order to isolate the skin friction that develops along the penetrating rod, which significantly affects DCP values. For this purpose, the torque moment is measured at various penetration depths by the same technique applied for the well-known Vane test. This corrective equation is then modified in light of the results obtained for validating in situ DCP tests.

Comments on flow characteristics on acceleration lanes

Abstract This paper deals with driver behavior while travelling on and merging from acceleration lanes. Two possible groups of drivers were identified: drivers who always perform the merging maneuver during the second part of the acceleration lane, regardless of whether an appropriate gap or lag was available to them previously. Three components of the aggregated delay for the merging process were suggested and evaluated. A method of estimating the random delay and travel time on acceleration lane was proposed and evaluated against an aggregated empirical data obtained on three freeway acceleration lanes. An evaluation of the contribution of the ramp volume to the traffic delay was also performed and discussed and a graph which may be of practical use for road and traffic engineers in assessing the expected influence of various ramp and freeway volume combinations is presented.

THE ISRAELI EXPERIENCE WITH THE REGULAR AND EXTENDED DYNAMIC CONE PENETROMETER FOR PAVEMENT AND SUBSOIL-STRENGTH EVALUATION

One of the Israeli modifications in the dynamic cone penetrometer (DCP) apparatus is the extension of the length of the standard penetrating rod to a total of about 2.0 meters by screwing on an additional 1.0 meter rod after the original rod has completely penetrated the pavement or subgrade. Such a procedure is required when the strength profile is significant at depths exceeding 1.0 meter or when the total thickness of the pavement layers, including the relevant subgrade layers, exceeds the length of the standard penetrating rod. Through comparative in situ testing, it was found that a 20% deduction should be applied for this testing procedure to the CBR values calculated from the in situ DCP results, both for clayey and for granular subsoils, when the standard CBR-DCP equation is used. Similarly, a 10% reduction should be applied to the 1.5-meter penetration rod results.

Development of a Road Roughness Profile Delineation Procedure

There are several approaches to delineation of statistically homogeneous units for pavement response variables in a selected property, and one of them, the cumulative difference approach, is presented in the AASHTO Guide for Design of Pavement Structures (1993). This method is a relatively powerful analytical one, when the nature of the measurements involves delineating homogeneous units with different mean value levels. However, there are other cases when the delineation procedure should be applied for data with different levels of scatter characteristics, such as with standard deviation or range. This modified cumulative difference approach is fully described in this paper with application to delineating statistically homogeneous units along a road profile of roughness measurements. The suggested approach provides an advantage in delineating scattered characteristics and shows a high level of efficiency as evidenced by practical applications. The results presented are expected to serve as a basis for enhancing quality control criteria in the construction, as well as in the maintenance stages. Another goal is to serve any advanced pavement management system (PMS).