D.E. O'Leary (1987) noted the inappropriate nature of traditional software validation techniques for expert system validation and proposed a research methods approach. R.M. O'Keefe et al. (1987) established validation as an important concern in expert system research and development and presented general descriptive methodologies for qualitative and quantitative methods of formal validation. A specific formal paradigm for prototype validation that is consistent with O'Leary's as well as O'Keefe's general guidelines for expert system development is presented. The paradigm explicitly incorporates validation into the prototype development life cycle under constrained resources, primarily time and money. The validation approach is demonstrated and evaluated relative to an expert system prototype named Signal Control at Isolated Intersections. The paradigm's strengths and weaknesses as well as its potential use with other types of expert system development projects are examined. >

Validating expert systems

What are the differences in driver injury outcomes at highway-rail grade crossings? Untangling the role of pre-crash behaviors

A methodology that quantifies potential conflicts between left-turning vehicles and opposing through vehicles and pedestrians is presented. The methodology was based on and designed to be compatible with the Highway Capacity Manual 2000. A model was developed to combine delay and safety to get a comprehensive level-of-service indicator, the delay and safety index (DS). A case study of two intersections shows that if potential conflict is not considered, the signal timing plan with permitted left turns delivers a better level of service than that with protected left turns. However, if potential conflict is considered, the level of service under protected left-turn phasing is better than that under permitted left-turn phasing, according to the DS, when the safety weight factors exceed a certain value. The proposed method models the trade-off between safety and efficiency explicitly and considers both vehicle-to-vehicle and vehicle-to-pedestrian conflicts associated with left turns.

Signalized Intersection Level of Service Incorporating Safety Risk

Facts from Figures. By M. J. Moroney. Pp. viii, 472. 5s. 1951. (Penguin Books)

Field observation of advance warning/advisory signage for passive railway crossings with restricted lateral sightline visibility: an experimental investigation.

Truck-mounted attenuator (TMA) usage varies for a number of reasons, including apathy, loss of efficiency (real or perceived), fiscal constraints, and lack of information on when and how to use the devices. Although some individual states have adopted policies, there has not been any coordinated effort to develop guidelines for the use of TMAs on a national basis. A literature review was conducted to determine the extent to which guidelines might have been developed but not widely shared. Five states were visited to solicit information regarding support for, and extent of use of, TMAs. There was a wide range in the number of TMAs presently in use. There was more consistency on other issues including the following: (a) initial support for the use of TMAs came principally from administrators; (b) field support is generally good in states using tilt-up versions of the TMA; (c) reported uses included maintenance activities, construction activities, and emergency incident management (use of TMAs on shadow vehicles was, by policy, the most common application); and (d) there seemed to be little factual basis for the existing application policies. A set of recommended guidelines was developed that included priorities for the deployment of shadow vehicles and TMAs. Two limitations on the significance and suggested use of the guidelines are acknowledged. First, the project did not involve collection and analysis of numerical data. Rather, it represented an effort at bringing together appropriate policies and procedures. Second, the guidelines are more appropriately used as a policy formation and budgeting tool.

Guidelines for the use of truck-mounted attenuators in work zones

Questionnaires were completed by 829 licensed drivers or candidates for licenses in an effort to ascertain their level of knowledge concerning highway-railroad grade-crossing information. Questions were asked concerning traffic-control devices, facts relating to grade-crossing hazards, and driver responsibilities at grade crossings. Respondents were stratified by age and elements of training and/or experience. Major findings of the study include the following: (a) Collection of Interview data at a driver's-license examining station is an effective method of determining driver knowledge, (b) more than 50 percent of all respondents believed that all grade crossings except those rarely used by trains have active warning signals, (c) most drivers have adequate knowledge concerning the hazards of grade crossings, (d) most drivers do not know the required driver response at passive grade crossings, (e) drivers perceive little law enforcement related to driver actions at grade crossings, and (f) driver knowledge and/or understanding of the traffic-control devices used to warn of grade crossings is inadequate. Recommendations are made regarding driver knowledge items that should be considered for inclusion in public information campaigns on grade-crossing safety. Future research regarding different advance warning signing for active and passive crossings and enforcement as a countermeasure is also recommended. (Author)

Driver knowledge of grade-crossing information

TWO METHODS OF ASCERTAINING THE LEVEL OF SERVICE OF SIGNALIZED INTERSECTIONS ARE ANALYZED AND A THIRD IS PROPOSED. THE 1965 HIGHWAY CAPACITY MANUAL UTILIZES VEHICLES PER HOUR OF GREEN AS AN INDICATOR OF THE LEVEL OF SERVICE, WHILE A 1962 DESIGN PROCEDURE RELIES ON THE PERCENTAGE OF CYCLE FAILURES, I.E., THE RELATIVE NUMBER OF CYCLES DURING WHICH ARRIVALS, IN A POISSON MANNER, EXCEED THE CAPACITY FOR DEPARTURES. IT IS SHOWN THAT THE TWO INDEXES HAVE A VARYING RELATIONSHIP. CONVERSION CHARTS AND TABLES ARE DEVELOPED. FOR A CONSTANT SERVICE LEVEL, A LOW APPROACH VOLUME WILL ALLOW HIGHER FAILURE RATES THAN MAY BE TOLERATED FOR HIGH VOLUMES. IN ADDITION, THE FEASIBILITY OF EMPLOYING AVERAGE INDIVIDUAL DELAY AS AN INDEX OF SERVICE LEVEL IS EXAMINED. IT IS FOUND THAT FAILURE RATE AND INDIVIDUAL DELAY ALSO HAVE A VARYING RELATIONSHIP. USING CONSTANT DELAY LINES, HIGHER FAILURE RATES WERE ALLOWED FOR HIGH VOLUMES. A COMBINED PLOT OF SERVICE LEVEL AND DELAY INDICATES AN APPARENT DIVERGENCE OF LINES, WHICH IS TAKEN TO SHOW THAT ALTHOUGH AN INTERSECTION MAY SATISFY HCM CRITERIA, INDIVIDUAL DELAY MAY VARY CONSIDERABLY DEPENDING ON ARRIVALS, CYCLE LENGTH, AND LENGTH OF GREEN TIME. A DISCUSSION OF THE PAPER BY THREE OTHER PERSONS FOCUSES ON THE APPARENT MULTIPLICITY OF CHOICES FOR EVALUATING AND DESIGNING INTERSECTIONS. /AUTHOR/

Relation of signalized intersection level of service to failure rate and average individual delay

Investigations were conducted regarding driver knowledge of grade-crossing information, the relation of driver knowledge, and techniques for advisory speed signing. A driver behavior-oriented method for evaluating passive crossings was developed. It was found that most drivers believe that all crossings regularly used by trains have active protection. Driver performance at the sites observed was not related to driver knowledge of grade-crossing facts. It was noted that drivers who looked for trains did not look a proper distance from the crossing or at an appropriate speed to be considered safe. A procedure was developed to assign safe speeds and to locate signing on the approach to the passive grade crossing. Suggestions are made for areas of future investigation. (Authors)

Improving safety at passive crossings with restricted sight distance

AN INVESTIGATION WAS MADE INTO THE EFFECT OF TRUCKS OR GRADES OR BOTH ON URBAN FREEWAY LEVEL OF SERVICE. THE PRIMARY PARAMETER USED WAS ACCELERATION NOISE, A WELL-KNOWN AND WIDELY USED TRAFFIC RESEARCH PARAMETER. A TRAFFIC STREAM COMPOSED OF BOTH CARS AND TRUCKS WAS EXAMINED. A SHORT SECTION OF THE ROADWAY WAS CONSIDERED AND THE ENTERING AND LEAVING ENERGY OF THE STREAM EQUATED. ASSUMPTIONS CONCERNING THE RESISTANCE TO BOTH MOTION AND ACCELERATION WERE ALSO DEVELOPED. FOR VERIFICATION OF THE MODEL DEVELOPED, AERIAL TIME-LAPSE PHOTOGRAPHS SUPPLIED THE BULK OF THE DATA. UTILIZING 100-FT SECTIONS MARKED OFF ON THE FREEWAY SHOULDER, SPEEDS AND ACCELERATIONS FOR EACH VEHICLE PHOTOGRAPHED WERE CALCULATED. FROM THESE, MACROSCOPIC SPEED AND ACCELERATION NOISE PROFILES WERE DETERMINED. THE RESULTS OF THE RESEARCH INDICATE THAT ACCELERATION NOISE DEFINITELY INCREASES ON A POSITIVE GRADE OF A ROLLING URBAN FREEWAY. THE AMOUNT OF CHANGE IS INDEPENDENT OF THE LANE STUDIED, HOWEVER. BECAUSE OF A WIDE VARIANCE IN THE PERCENTAGE OF TRUCKS ON THE DIFFERENT LANES, THE CONCLUSION IS THAT TRUCKS DO NOT AFFECT THE OVERALL NOISE VALUES UNDER THE CONDITIONS STUDIED. THIS CONCLUSION WAS STRENGTHENED BY MICROSCOPIC NOISE VALUES AND BY AN EXAMINATION OF TYPICAL TIME-SPACE DIAGRAMS. FINALLY, CONCLUSIONS WERE MADE CONCERNING THE TYPE OF PARAMETER NEEDED TO ASCERTAIN THE EFFECT OF TRUCKS ON THE ROAD USER. /AUTHOR/

Jack B Humphreys

Papers

Guidelines for the use of truck-mounted attenuators in work zones

Driver knowledge of grade-crossing information

Relation of signalized intersection level of service to failure rate and average individual delay

Improving safety at passive crossings with restricted sight distance

Effect of trucks on the urban freeway