John A. Deacon

Trends in highway safety: effects of an aging population on accident propensity

Aging of the United States population has a potentially adverse effect on highway safety. A key question is whether the known deterioration of driving skills with aging will be compensated by other factors, especially improved learning and attitudinal experiences of more recent cohorts. We investigate effects of driver age, cohort, and gender on accident propensity and evaluate confounding effects of year, location, and lighting. The accident propensity of different groups of drivers is measured, using a database of two-vehicle accidents, by the ratio of the number of at-fault drivers of a specific group to the corresponding number of not-at-fault drivers. Logistic regression modelling determines the statistical significance of the findings. The analysis reveals the following statistically significant effects: (a) middle-aged drivers are safer than younger drivers who, in turn, are safer than older drivers; (b) female drivers are safer on average than male drivers; (c) younger female drivers are safer than younger male drivers; (d) older male drivers are safer than older female drivers; (e) more recent cohorts of older drivers are safer than more distant cohorts; and (f) more distant cohorts of younger drivers are safer than more recent cohorts. We conclude that driver cohort provides a plausible explanation for many of the measurable, time-related accident trends that are observed. Accordingly, older drivers will be safer in the future because they will have acquired basic driving skills and attitudes in increasingly more automobile-dominated times. At the same time, the cohort effect appears small relative to other time related effects, notably aging, and older drivers will continue to be a high-risk component of the driving population and to require special consideration in driver education and licensing and in highway design and operations.

Quasi-induced exposure: methodology and insight

Even though the numerator in accident rates can be accurately determined nowadays, the denominator of these rates is an item of discussion and debate within the highway safety community. A critical examination of an induced exposure technique, based on the non-responsible driver/vehicle of a two-vehicle accident (quasi-induced exposure), is presented here. Differences in exposure for a series of accident location and time combinations are investigated, the assumption of similarities between drivers of single-vehicle accidents and the responsible driver of multiple-vehicle accidents is refuted, and the use of the non-responsible driver as a measure of exposure is tested using vehicle classification data. The results of the analyses reveal the following: (1) accident exposure is different for different location and time combinations: (2) induced exposure estimates provide an accurate reflection of exposure to multiple-vehicle accidents; (3) induced exposure estimates are acceptable surrogates for vehicle miles of travel when estimates are made for conditions during which the mix of road users is fairly constant; and (4) the propensity for involvement in single-vehicle accidents is generally different than that in multiple-vehicle accidents for a given class of road users. We concluded that the quasi-induced exposure is a powerful technique for measuring relative exposure of drivers or vehicles when real exposure data are missing.

Analytically Based Approach to Rutting Prediction

An analytically based (mechanistic-empirical) procedure was conducted to estimate the development of rutting in asphalt pavements as a function of both traffic loading and environment as defined by pavement temperatures. The procedure uses permanent strain determined for a representative asphalt concrete mix as a function of load repetitions, shear stress, and elastic shear strain. It combines multilayer elastic analysis for determining key shear stresses and strains in the asphalt concrete resulting from traffic loading to be used in the permanent strain expression with a time-hardening procedure for the accumulation of permanent strain as a function of both traffic loading and environment. The WesTrack test sections were used to calibrate the methodology, with results of rutting predictions evaluated for four different test sections from that experiment. Based on the results of the regression analyses, an expression can be used to determine coefficients for use in the permanent strain expression that reflect the permanent deformation characteristics of a specific mix as measured in repeated simple shear test at constant height. In addition to the WesTrack examples, results illustrated the use of the approach to predict rutting development in a controlled loading condition at 50°C (122°F) using the heavy vehicle simulator.

Development and Evaluation of Dynamic Flexural Beam Fatigue Test System

Although both mix variables and environmental variables are known to affect the fatigue response of asphalt-aggregate mixes, other factors—including specimen fabrication procedure and test equipment and procedures—are equally important. The development of a dynamic flexural beam fatigue test system is described, and the effects of specimen compaction method and equipment type on the precision of in situ fatigue lives of asphalt-aggregate mixes predicted by using laboratory strain-life relationships are discussed. Results indicate a coefficient of variation of 41 percent in fatigue life for the new fatigue equipment compared with one of 93 percent for an earlier electropneumatic version. The specimen compaction method was also found to influence significantly the precision of the predicted fatigue life. A 33 percent difference in coefficients of variation between the fatigue response of rolling wheel—compacted specimens and kneading-compacted specimens was observed. Consequently, twice as many specimens ar...

Accidents on rural interstate and parkway roads and their relation to pavement friction

Friction measurements were made with a skid trailer at 70 mph (31 m/s) on 770 miles (1240 km) of rural, four-lane, controlled-access routes on Interstate and parkway systems in Kentucky. Each construction project was treated as a test section. Accident experience, friction measurements, and traffic volumes were obtained for each. Various relationships between wet-weather accidents and skid resistance were analyzed. Averaging methods were used to develop trends and minimize scatter. A moving average for progressively ordered sets of five test sections yielded more definite results. The expression of accident occurrence that correlated best with skid and slip resistance was wet- weather accidents per 100 million vehicle miles (161 million vehicle km). Accidents (at 70 mph (31 m/s)) increased greatly as skid numbers decreased from 27. Analysis of peak slip numbers and accident occurrences indicated similar trends.

Traffic Volume Estimates and Growth Trends

The objective of this study was to develop a procedure to forecast highway traffic volumes through the use of growth factors representative of Kentucky highways and reflecting effects of important socioeconomic and demographic variables. A two stage modeling process was used. In the first, linear regression models were used to relate average daily travel on Kentucky roadways to personal income, price of fuel, and total miles of streets and highways. In the second, cross tabulation models were used to relate growth in volume at a specific site expressed relative to the statewide ADT to highway functional classification, rural/ urban location, county population growth, SMSA/ non SMSA designation, and volume level. The growth model yields estimates not only of the most likely rate of growth at a particular site but also of the range experienced at similar sites statewide. In collecting historical volume data for model calibration, a file was developed representing approximately 15,000 sites on the state highway system at which counts had been taken during the 1963/86 base period. On average, there were about 5.8 counts for each of these sites. Data in the file is instantly accessible by microcomputer users through dBASE software. A piecewise linear regression routine is used to provide estimates for past years during which counts were not taken. The historical volume database has been designed for continuous updating as new counts are made. Similarly, the forecasting models have been designed for convenient recalibration at annual intervals (A).

EVALUATION OF ADVANCED SURVEYING TECHNOLOGY FOR ACCIDENT INVESTIGATION

The objective was to evaluate the use of advanced technology for the investigation of traffic accidents. Substantial time and manpower are sometimes required to properly investigate serious vehicular crashes and document on-scene data. An alternative to the traditional coordinate method for on-scene data collection is the use of electronic total stations. This is a form of digital surveying equipment that can be used to obtain detailed measurements, with the option of plotting the stored data by computer. The study compared the use of advanced surveying technology with the traditional coordinate method. Detailed estimates of data collection activity were documented for a selected accident sample, and accident clearance times were documented for a much larger sample. The analysis indicated that the investigation of traffic accidents by using total-station surveys provides a substantial improvement over the traditional coordinate procedure. The number of measurements obtained at an accident scene increased by a factor of approximately 2 when the total-station equipment was used. The time to collect the data decreased by about 33%, and the man-hours decreased by about one-half. Computer plotting by the total-station procedure also resulted in a significant time savings. Decreased data collection time resulted in significant time and fuel savings to the driving public. Recommendations were made for continued use of the equipment and the purchase of more equipment when funds become available. In addition, policies for using the total-station equipment at all fatal and serious injury traffic accidents are recommended.

Integrated truck monitoring system

The primary objectives of the study are as follows: 1) Develop functional specifications for an integrated truck monitoring system for use in Kentucky, 2) Determine the extent to which KYU numbers (unique identification for large trucks operating in Kentucky) are being displayed as required, 3) Examine the impact of the KYU numbering system on motor carrier operations, and 4) Determine the magnitude of the problems related to trucks using bypass routes to avoid inspection stations. Accomplishments documented in this interim report include the following: 1) Field studies were conducted to determine the frequency of trucks bypassing inspection stations and compliance with the requirement to display a KYU number; 2) A review was made of Kentucky statutes and regulations to summarize requirements expected of trucks, truck operators, and motor carriers; 3) The current system for truck monitoring was described based on information obtained from individuals involved with truck monitoring and regulation; and 4) Estimates were made of the efficiency of collecting weight-distance and truck motor-fuel taxes (A).

Travel to Outdoor Recreation Areas in Kentucky

DURING THE SUMMER OF 1970 A LICENSE-PLATE O/D STUDY WAS CONDUCTED AT 160 SITES IN 42 MAJOR RECREATION AREAS IN KENTUCKY. MODELLING CONCENTRATED ON THE SIMULATION OF DISTRIBUTED TRAVEL FLOWS FROM EACH OF 190 ORIGIN ZONES IN THE CONTINENTAL UNITED STATES TO EACH OF THE 42 AREAS. THE PRIMARY INDEPENDENT VARIABLES EMPLOYED WERE POPULATION OF THE ORIGIN ZONE, ATTRACTIVENESS OF THE RECREATION AREA, AND SPATIAL SEPARATION OF THE ZONES AND AREAS. THE CROSS-CLASSIFICATION MODEL WAS FOUND TO BE AN ACCEPTABLE MEANS FOR SIMULATING AND PREDICTING OUTDOOR RECREATION TRAVEL FLOWS AND WAS DECIDEDLY SUPERIOR TO ANY OF THE SINGLE-EQUATION MODELS EVALUATED. WITH THIS MODEL PER-CAPITA DISTRIBUTED FLOWS WERE FLOUND TO DECREASE AT A DECREASING RATE WITH INCREASING POPULATION, INCREASE AT AN INCREASING RATE WITH INCREASING ATTRACTIVENESS OF THE TYPE OF RECREATION FACILITY, AND DECREASE AT A DECREASING RATE WITH INCREASING DISTANCE.

ALLOCATION OF HIGHWAY COSTS AND REVENUES

The highway cost allocation study is the 6th in a recent series begun in the early 1980s by the Transportation Cabinet and the Kentucky Transportation Center. Its primary objective is to determine the level of revenue contribution and cost responsibility for each class of highway user. Highway user classes, with which revenue and cost responsibility were associated, totaled 17 and included motorcycles, cars, buses, and 14 registered or declared weight classes of trucks. Primary sources of revenue allocated to the various classes of highway users include fuel taxes, registration or license fees, usage taxes, road tools, other motor carrier taxes, other Federal taxes, and miscellaneous taxes and fees. Primary expenditure categories include construction, maintenance and operation, administration and enforcement.