Eric Hildebrand

Dimensions in elderly travel behaviour: A simplified activity-based model using lifestyle clusters

The current lack of a detailed description of elderly travel characteristics and behaviours, particularly one that examines the issue at a level involving activity engagement, was a deficiency addressed by this research. Using data from the 1994/95 Portland, Oregon, Household Activity and Stated Preference Survey a simplified activity-based travel model for the elderly was developed and validated. The modelling framework makes use of lifestyle groups which are delineated through advance analyses. The final cluster solution chosen to provide a categorical basis for the modelling framework identified six distinct lifestyle groups based on socio-demographic variables. The clusters were subjectively labelled Workers, Mobile Widows, Granny Flats, Mobility Impaired, Affluent Males, and Disabled Drivers. The clusters were found to have statistically significant differences in travel behaviour and activity engagement patterns. These findings are useful to policy-makers who attempt to balance the mobility needs of the elderly with the prospect for stricter driving license policies in response to traffic safety concerns. The model framework successfully replicated all facets of the base data set used for its development. Using a sequential process, the micro-simulation model employs a bottom-up approach by stochastically developing daily activity itineraries for individuals which are subsequently assembled into trip tours. Elements of travel behaviour synthesized for individuals being modelled included total daily activities (with and without travel), activities engaged in by class (with and without travel), total daily trip tours, and mode splits.The research has shown that a categorical approach using lifestyle groups with unique activity and travel characteristics can be successfully combined within an activity-based framework. Although this approach was applied specifically to the elderly, it can be extended to other heterogeneous groups including the population as a whole. Furthermore, the study has provided a more comprehensive understanding of the varied lifestyles, activity patterns, and subsequent travel behaviour and needs of the elderly.

Are age-based licensing restrictions a meaningful way to enhance rural older driver safety? The need for exposure considerations in policy development

The stated and revealed travel behavior of a sample of 60 rural drivers aged 54–92 years provided a basis to explore the potential effectiveness of two common drivers license restrictions aimed at older drivers: time of day and road class. The potential utility and impact of these restrictions have not been explored with revealed data for jurisdictions with a large population of rural older drivers where automobile dependence is high. Data were drawn from a multiday Global Positioning System–based travel diary survey of rural older drivers in New Brunswick, Canada. Revealed travel data showed that over 50 percent of the rural drivers in the sample did not drive after dark, and 40 percent drove less than 1 percent of their total surveyed kilometers on major highways, higher rates than from participant-stated responses. The proportion of participants taking night trips and traveling on major highways decreased with age. The majority of trips taken after dark by all participants had a rural destination. The average daily kilometers driven on major highways by men and women aged 75 years and older was nearly identical (1.79 km/day). These exposure considerations suggest that restricting night travel and major highway travel for the oldest rural drivers (75 years and older) may have limited utility given that the majority of participants did not drive in these situations, and for those who did, most of their trips were in rural areas where enforcement could be expected to be limited. A better approach may be to encourage increased self-regulation through training, age-friendly upgrades to transportation infrastructure to help rural older drivers stay driving safely as long as possible, and the development of appropriate rural alternatives to help a driver transition to nondriver.

Reductions in Traffic Sign Retroreflectivity Caused by Frost and Dew

A study of in-service traffic signs was undertaken to quantify the average effects of frost and dew on their retroreflective capabilities. The results were then compared with proposed minimum retroreflectivity standards recently developed by FHWA-sponsored research for inclusion in the Manual on Uniform Traffic Control Devices. Although the effects of frost and dew were found to be variable, average reductions in retroreflectivity levels of 79% and 60%, respectively, were found. None of the different colored signs sampled with Type I (engineering grade) sheeting was found to meet the proposed minimum levels when covered in frost or dew (with the exception of signs with white backgrounds covered in dew), even though all signs were in like-new condition. Signs sampled with Type III (high intensity) sheeting had mixed results. The findings are significant enough that they should be considered in the development of the final version of the FHWA national standards. Furthermore, those jurisdictions subject to frequent cycles of frost and dew should review usage guidelines governing the grade of sign materials used, allowing for expected loss of retroreflectivity.

Impact of Wind Forces on Heavy Truck Stability

A transport truck equipped with instrumentation that measured speed, lateral acceleration, and roll angle of the vehicle was driven around a highway ramp in New Brunswick, Canada, under varying wind conditions. The rollover threshold of the truck was calculated on the basis of characteristics of the vehicle and then compared with the lateral accelerations measured on the truck. Analysis of the data indicated that there was a significant difference in lateral accelerations between different wind speeds, verifying that wind can contribute to rollover. Analysis of the rollover threshold revealed that the lateral accelerations experienced by the truck were often greater than the rollover threshold for brief periods of time, but they were not sufficiently long enough to cause rollover.

Development and Intermediate Findings of a Level III Heavy-Truck Collision Study

The development, implementation, and intermediate results of a Level III (on-scene) study of heavy freight vehicle collisions are presented. The University of New Brunswick’s Accident Research Team, under contract with Transport Canada, has conducted over 50 in-depth investigations over a 3-year period. Although the present findings are based on a relatively small sample, a number of common, and perhaps surprising issues have been identified. Many of the cases highlight the need for increased safety regulations targeted at the design and operation of these vehicles and the infrastructure over which they operate. The most common problems identified include the propensity of heavy trucks to roll over, load security, and inadequate crash protection afforded to the occupant compartment. The issues related to the establishment of an intense investigation protocol are discussed in this paper, as are the findings of the investigations that have occurred over a 3-year period. Recommendations are presented that are directed toward the refinement of a Level III protocol for further heavy-vehicle investigations. In addition, changes are proposed to existing Canadian Motor Vehicle Safety Standards as they apply to heavy trucks.

Driver tolerance of lateral accelerations on horizontal curves

There are many roadways where existing horizontal curves fail to meet minimum geometric design standards for financial or geographic reasons. Advisory speeds, typically set with a ball-bank indicator, are posted on these curves to ensure that drivers are not subjected to uncomfortable levels of lateral accelerations as they negotiate the curve. The threshold levels of lateral acceleration as estimated by ball-bank indicators vary considerably between jurisdictions with many still basing their guidelines on studies dating back to the 1930s and 1940s. This study investigated present day ball-bank indicator tolerance levels by analyzing actual driver behaviour on 30 curves posted with advisory speeds in New Brunswick. A unique method of data collection involving digital video analysis enabled the development of vehicle speed profiles approaching and throughout the curves. The results indicated that drivers tolerate higher levels of discomfort as they navigate curves than currently assumed. This finding justi...