Richard W Lyles

MOBILITY PATTERNS OF THE NEXT GENERATION OF OLDER PERSONS

Mobility patterns of the next generation of older people may be significantly different from today’s older persons. And it is likely that more older people may depend on automobiles for their daily activities. While the types of traffic safety-related problems associated with older drivers are fairly well defined, the questions that remain are about the magnitude: Will large numbers of older drivers self-test off the system? or Will many more older persons driving more often and longer distances produce even more serious safety-related problems? Differences between mobility patterns of today’s older people and those predicted for the next generation of older people are examined. The overall finding is that as the older population continues to shift to rural areas, small cities, and suburbs, there is likely to be increased per capita travel (i.e., higher exposure), even though the number of trips may be lower. It seems likely that a considerable percentage of this travel will be on the least safe parts of the highway system (i.e., local streets and roads). Although overall accident rates may remain much the same or drop slightly for the older person, the greater number of persons in the older-age cohorts and the increased mileage driven by them will likely lead to significant increases in the number of accidents experienced by this group and in general.

FREEWAY SPEED ZONES: SAFETY AND COMPLIANCE ISSUES

The effectiveness and appropriateness of establishing speed limits on freeways and the spatial extent of the zones were studied. Of particular interest were 55-mph (88-km/hr) speed zones that exist in the transition between urban and rural areas (determined according to urban area boundaries). Three types of freeway segments (urban-55, fringe-55, and rural-65) were analyzed, and although the study was of comparatively small scale, the results generally showed that higher speeds do not lead to more numerous or serious accidents. Moreover, compliance with speed limits is not necessarily a good measure of safety. On the other hand, motorists are self-policing to a certain degree in that they drive at reasonable speeds given the design of the different types of freeways. It is suggested that artificially lowered speed limits without a clear need being established from engineering and safety perspectives will not yield impressive safety benefits.

Prediction of Pavement Distress Index with Limited Data on Causal Factors: an Auto-regression Approach

Prediction of the pavement distress index (DI) for different road sections on a network scale over an extended time horizon is necessary for efficient maintenance planning and resource allocation. In many cases, however, sufficient information on causal factors of pavement distress is unavailable. Nonetheless, models with sufficient reliability have to be developed in these situations. It is shown in this research that with suitable statistical models and application, sufficient information on missing causal factors may be accounted for indirectly by incorporating preceding observed DI values as an independent variable when predicting future DI values. Among different statistical modeling approaches, autoregression models with recursive applications were shown to produce reliable DI predictions. Extended future DI values were projected recursively by first predicting DI values for the immediate future interval based on current pavement age and DI value, and then using the new predicted DI value to predict the immediate value following that, and so on. By repeating this process, DI values as far into the future as necessary were developed. Results show that current and past DI values can capture the impact of many of the causal factors and hence may be used to produce fairly reliable DI projections. The resulting predicted DI time paths generated were not S-shaped as most of the literature suggests. This, however, is operationally inconsequential since rehabilitation actions are often triggered by relatively low DI thresholds for which the simplification here is sufficient.

Self-Selection Bias in Driver Performance Studies

It is generally understood that there is some bias involved in selection of participants for driver performance studies, but little is known about the extent of this problem. To execute a National Cooperative Highway Research Program project on the effectiveness of traffic control devices, a sample of younger and older drivers was required. The purpose was to gain insight into the bias introduced through participant selection and self-selection. Of interest is whether the drivers who participate in projects for which driving or other testing is required tend to be different than the general population of licensed drivers. Results indicate that, compared with nonparticipants, participants are more active, more likely to travel and drive, less likely to avoid driving in certain circumstances, and less likely to have vision problems. The implication is that project participants represent more highly mobile and confident drivers than would be found in a random sample of the general population. However, project participants also had higher percentages of total accidents and violation points and were involved in more severe accidents than nonparticipants. These problems may be somewhat mitigated, though, by higher driving exposure for participant drivers. Such self-selection bias needs to be considered whenever research like this is undertaken.

Driver age as a factor in comprehension of left-turn signals

An experiment to measure driver comprehension of left-turn signal and sign configurations was conducted as part of a study to investigate the performance of left-turn signals used in various signal strategies. The responses of 191 individuals to 81 stimuli simulating left-turn signal phases were analyzed for the effect of signal message on driver comprehension. Stimuli included 17 left-turn signal displays used for permitted, protected, and protected/permitted left-turn strategies as well as left turns during nighttime or emergency flashing signal operations. Comprehension in the original study was based on a correct versus incorrect dichotomy: if the subject’s response agreed with a predetermined subset of possible answers, the answer was correct; all other answers were considered incorrect. These data are reanalyzed with three principal variations: (a) individuals’ answers are based on a three-level correctness concept whereby answers considered incorrect in the previous study were further categorized into minor errors and serious errors depending on whether subjects incorrectly chose to “give away” their right-of-way or to violate other drivers’ right-of-way, respectively; (b) signal message is introduced in the analysis as an explanatory variable of driver comprehension; and (c) emphasis is placed on older drivers. Youngest, oldest, and female subjects were found to drive fewer kilometers per year than middle-aged males. Comprehension was found to deteriorate with driver age in terms of both higher serious error rates and lower correct answer rates. Flashing signals were the least well understood, whereas change and red interval stimuli were understood best by all age groups.

A comprehensive review on the quasi-induced exposure technique

OBJECTIVE The goal is to comprehensively examine the state-of-the-art applications and methodological development of quasi-induced exposure and consequently pinpoint the future research directions in terms of implementation guidelines, limitations, and validity tests. METHODS The paper conducts a comprehensive review on approximately 45 published papers relevant to quasi-induced exposure regarding four key topics of interest: applications, responsibility assignment, validation of assumptions, and methodological development. RESULTS Specific findings include that: (1) there is no systematic data screening procedure in place and how the eliminated crash data will impact the responsibility assignment is generally unknown; (2) there is a lack of necessary efforts to assess the validity of assumptions prior to its application and the validation efforts are mostly restricted to the aggregated levels due to the limited availability of exposure truth; and (3) there is a deficiency of quantitative analyses to evaluate the magnitude and directions of bias as a result of injury risks and crash avoidance ability. CONCLUSIONS The paper points out the future research directions and insights in terms of the validity tests and implementation guidelines.

U.S. National Household Travel Survey Used to Validate Exposure Estimates by the Quasi-Induced Exposure Technique

Unlike exogenous estimates of exposure to risk such as vehicle miles of travel, number of registered vehicles, and number of licensed drivers, quasi-induced (Q-I) exposure has not received adequate vetting. A criticism of Q-I is that its underlying assumptions are not convincingly validated or verified, partially because the risk estimates of Q-I have not been sufficiently compared with the more conventional techniques. The 2009 National Household Travel Survey data were used to derive annual vehicle miles traveled, disaggregated by characteristics of interest (age and gender). Comparisons were developed at different disaggregation levels between the vehicle miles traveled and the relative exposure calculated with Q-I. The main findings of the exercises follow: (a) statistical results suggest that the exposure estimates for 15 age groups and driver gender are in good agreement with the corresponding annual vehicle miles traveled and thus the induced exposure estimates are deemed to be reasonably representative of the driving population and (b) the validation study revealed that data disaggregation improves the homogeneity of age and gender distributions (reduced data irregularities caused by the aggregated distributions). The comparisons confirm that Q-I is a promising and powerful tool for estimating exposure in safety analysis.

Network-Level Evaluation of Specific Pavement Study-2 Experiment: Using a Long-Term Pavement Performance Database

The research described here was conducted as a part of NCHRP Project 20–50 (10&16), LTPP (Long-Term Pavement Performance) Data Analysis: Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements. The relative effects of various design and site factors on the performance of jointed plain concrete (JPC) pavements are presented. The data used in this study were primarily drawn from Release 17 of DataPave. The Specific Pavement Study (SPS) 2 experiment was designed to investigate the effects of portland cement concrete (PCC) slab thickness, base type, drainage, PCC flexural strength, and slab width on the performance of JPC pavements. On the basis of the statistical analysis of 167 test sections, ranging in age from 5 to 12 years, it was concluded that base type was the most critical design factor affecting performance in terms of cracking and roughness as measured by the international roughness index. Pavement sections with a permeable asphalt-treated base and in-pavement drainage performed better than those with a dense-graded aggregate base or a lean concrete base. PCC slab thickness also played an important role in improving the cracking performance of the pavements. PCC flexural strength and slab width have only marginal effects on performance at this time.

Hazard Assessment of Deer–Vehicle Collisions in Michigan

ABSTRACT The relationship between deer–vehicle collision counts and vehicle miles traveled (VMT) is studied in this article using the Michigan (USA) crash database and categorized exposure data under different levels of data disaggregation. Negative binomial regression models were developed to establish the association between (human and deer) exposure and the frequency of deer–vehicle collisions. It is shown that VMT is nonlinearly correlated with the collision counts for most sets of circumstances except in rural areas. Observation of the association between the deer–vehicle collision count and the annual VMT across counties in Michigan reveals the unique characteristic of heteroskedasticity (i.e., variances of collision count are amplified with the increasing VMT). The regression results demonstrate that deer density stands out as the most significant exposure predictor in describing deer–vehicle collisions at the state level. It is recommended that differentiated exposure measurements for deer–vehicle collisions should be employed for three ecoregions in Michigan. Exposure predictors for deer–vehicle collisions appear to be more dependent on deer density in Michigans Upper Peninsula and North Lower Peninsula ecoregions, while in the South Lower Peninsula ecoregion deer and human populations are equally important.

Part 1: Rigid Pavements: Network-Level Evaluation of Specific Pavement Study-2 Experiment: Using a Long-Term Pavement Performance Database

The research described here was conducted as a part of NCHRP Project 20-50 (10&16), LTPP (Long-Term Pavement Performance) Data Analysis: Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements. The relative effects of various design and site factors on the performance of jointed plain concrete (JPC) pavements are presented. The data used in this study were primarily drawn from Release 17 of DataPave. The Specific Pavement Study (SPS) 2 experiment was designed to investigate the effects of portland cement concrete (PCC) slab thickness, base type, drainage, PCC flexural strength, and slab width on the performance of JPC pavements. On the basis of the statistical analysis of 167 test sections, ranging in age from 5 to 12 years, it was concluded that base type was the most critical design factor affecting performance in terms of cracking and roughness as measured by the international roughness index. Pavement sections with a permeable asphalt-treated b...