THE STATE OF THE ART OF DEICING CHEMICALS AND ABRASIVES FOR WINTER ROAD MAINTENANCE IS SUMMARIZED THROUGH A DISCUSSION OF THE FOLLOWING: PROPERTIES OF DEICING CHEMICALS; ABRASIVES; FACTORS INFLUENCING THE MELTING RATE OF SNOW AND ICE; AND THE RATE OF APPLICATION OF DEICING CHEMICALS. TABLES AND FIGURES ARE PRESENTED WHICH SHOW: (1) THE INCREASE IN THE COEFFICIENT OF SLIDING FRICTION AS ICE IS BEING MELTED BY THE ACTION OF SODIUM CHLORIDE AND CALCIUM CHLORIDE; (2) THE DECREASE IN STOPPING DISTANCE OF AN AUTOMOBILE BY SANDING THE PAVEMENT SURFACE AND BY COMPLETELY MELTING THE ICE OR SNOW (WET SURFACE); AND (3) THE SUITABILITY OF THE VARIOUS TYPES OF CHEMICALS AND ABRASIVES. ESSENTIALLY, THE ABRASIVE WILL PROVIDE IMMEDIATE TRACTION AND INCREASE SKID RESISTANCE, WHEREAS CHEMICALS WILL PRINCIPALLY ACT TO CONTROL SNOW AND ICE CONDITIONS BY (A) PREVENTING THE FORMATION OF ICE FILMS, (B) WEAKENING THE BOND BETWEEN THE SNOW AND THE ROAD SURFACE, (C) MELTING THE FRESH SNOW AS IT FALLS, AND (D) MELTING COMPACTED SNOW THAT REMAINS AFTER PLOWING.
This article reviews and evaluates three distinct approaches to modeling transit operating costs: unit cost models, four-variable regression models, and slowness regression models. Six individual operating cost models were reviewed: a four-variable unit cost model incorporating measures of annual vehicle hours, annual vehicle miles, number of peak-hour vehicles and annual revenue passengers; a four-variable regression model; a daily cost four-variable model incorporating measures of average daily vehicle miles of service, average daily vehicle hours of service, average daily passenger revenue on route and peak vehicles needed on route; two slowness function models; and an urban environment cost model that includes variables that help explain differences in operating cost such as population density, age of fleet, age of city, scheduled speed and labor costs. These models were tested on data from a number of U.S. transit agencies to determine the predictive ability of the models in terms of (1) the degree to which the model explained variation in cost and (2) the data requirements for estimating parameters using the model. Results of this analysis indicated that the simplest model in terms of data requirements is the slowness model, however it is the least desirable for general application. The four-variable unit-cost model is much better suited to generalization. Although it, too, does not encompass all factors influencing operating costs, it is well suited for short-range planning purposes and was preferable to the four-variable regression model.
THIS PAPER REPORTS THE RESULTS OF SOME EMPIRICAL PREDICTION TESTS ON DISAGGREGATE, BEHAVIORAL, STOCHASTIC MODELS OF MODAL CHOICE. IT IS DISCOVERED THAT THE EXPECTED-NUMBER CALCULATION (SUMMATION OF PROBABILITIES) YIELDS MODAL-CHOICE PREDICTIONS WITH A HIGH DEGREE OF ACCURACY, ALTHOUGH A CAVEAT IS IN ORDER REGARDING THE TRANSFERABILITY OF SUCH MODELS: THEY SHOULD BE TRANSFERRED WITH CARE AND ONLY TO SIMILAR SITUATIONS. THE STABILITY OF THE MODELS IS EVIDENCED BY THE FACT THAT THEY CAN BE BROKEN DOWN BY TRIP PURPOSE AND REAGGREGATED WITHOUT LOSS OF PREDICTIVE POWER. FINALLY, THE METHOD OF OBTAINING PREDICTIONS BY CLASSIFYING PROBABILITIES IS CONSIDERED AND REJECTED.
The author has earlier presented an improved method for the design of aggregate gradings and demonstrated its applicability to the design of dense asphaltic compositions. Subsequently, further work has been done to confirm that both continuously graded and gap-graded bituminous mixes can be satisfactorily designed according to the method and to show that, for highway and airfield pavement surfacing purposes, certain principles governing skid resistance over a practical range of speeds can be incorporated into the design method. The current study describes the application of the method to the design of concrete mixes. For gap or intermittent gradings, the relevance of studies of interparticle voids is demonstrated with respect to critical ratios of entrance and occupation (measured for typical aggregates) and a newly defined term, the critical ratio of dilation. The influence of gradings, designed according to this rational method, on concrete workability and strength is discussed. Reference is also made to the design of pavement concrete mixes to meet the different requirements of skid resistance for low-speed and high-speed conditions on roads and airfields.
THIS PAPER, WHICH DISCUSSES THE INCORPORATION OF PRACTICAL EXPERIENCE IN THE CONDUCT AND MANAGEMENT OF RESEARCH, IS DIVIDED INTO A SECTION DEALING WITH THE NECESSITY FOR THE RESEARCH, A SECTION ON THE METHODOLOGY, AND A THIRD SECTION WHICH DESCRIBES THE BENEFITS DERIVED FROM SUCH WORK. THE PAPER DEALS EXCLUSIVELY WITH APPLIED RESEARCH AND ADDRESSES PAVEMENT PROBLEMS ALTHOUGH THE CONCEPTS EXPRESSED ARE OF WIDER APPLICABILITY. THE NEED IS EXPRESSED FOR INFORMATION FROM RESEARCH AND PRACTICAL FIELD EXPERIENCE THAT CAN BE USED TO TEST HYPOTHESES FORMULATED BY INVESTIGATORS. A METHODOLOGY IS DESCRIBED HERE, WHICH UTILIZES THE CUMULATIVE EXPERIENCE OF ENGINEERS WORKING IN VARIOUS AREAS TOGETHER WITH LABORATORY DATA, DATA FROM SPECIAL TEST SECTIONS AND ANALYTICAL STUDIES; COMBINING THEM IN A FORMAT WHICH MAY BE USED BY THE PRACTICING HIGHWAY ENGINEER. THE METHODOLOGY WHICH IS BASED ON BAYESIAN DECISION STATISTICS GIVES PAST EXPERIENCE IN A STATISTICAL FORMAT. THE GENERAL FORM OF THE METHOD IS ILLUSTRATED AND THE KEY CONCEPTS ARE OUTLINED. A SERIES OF STEPS DESCRIBE THE METHODOLOGY: (1) IDENTIFY AND RANK FACTORS THAT HAVE SIGNIFICANT INFLUENCE FOR A PARTICULAR PROBLEM; (2) OBTAIN SUBJECTIVE INFORMATION OF EXPERIENCED INDIVIDUALS AN INFLUENCE OF THE SIGNIFICANT VARIABLES; (3) ASSEMBLE OBJECTIVE INFORMATION; (4) COMBINE INFORMATION TO DEVELOP STATE OF KNOWLEDGE; (5) RECOMMEND SOLUTIONS AND FORMULATE RESEARCH PROGRAMS; (6) CONTINUE EVALUATION AND MODIFICATION OF PROGRAMS AND SOLUTIONS; (7) RESEARCH SPECIAL PROBLEMS. MAJOR ADVANTAGES ACCURING TO THE METHODOLOGY ARE LISTED. THE THEORETICAL BASIS OF THE METHODOLOGY IS APPENDED.
