Systematic variability in repetitious travel

The focus of this paper is the degree to which day-to-day variability in the individual's travel pattern has a systematic, or nonrandom, component. We first review the different sources of variability in travel, emphasizing the difference between between-individual and within-individual variation and the implications of this difference for travel analysis. After discussing the impact of measurement (i.e. the way in which travel behavior is measured) on the study of repetition and variability, we use the Uppsala data to examine the level of systematic variability in an individual's longitudinal travel record. The analysis focuses on two questions:

- How well does observation over one week capture longer-term (five-week) travel behavior; in other words, is behavior highly repetitive from week to week?

- How systematic is within-individual variability; in other words, are certain stops distributed over the five-week record in a nonrandom, that is either regular or clustered, fashion?

Using measures of travel that include more than one stop attribute (e.g. activity, mode, time of day, and location), we found that:

- A seven-day record of travel does not capture most of the separate behaviors exhibited by the individual over a five-week period, but it does capture, for most people, a good sampling of the person's different typical daily travel patterns.

- Whereas a considerable portion of intraindividual variability is systematic (nonrandom), clustering is a more important source of nonrandom variation than is regularity.

The results suggest that behavior does not follow a weekly cycle closely enough for a one-week travel record to measure the longer-term frequency with which the individual makes certain stops or to assess the level of day-to-day variation present in the individual's record. Because these results are likely to reflect the particular measures of behavior we used, one conclusion of this study is the need for other studies that replicate the aims of this one but use a variety of other travel measures. Only through such additional work can we truly assess the sensitivity of our findings to measurement techniques.     

低阻通风船体的远程控制测试平台开发（英文）

This paper addresses the development and testing of a remotely controlled boat platform with an innovative air-ventilated hull. The application of air cavities on the underside of ship hulls is a promising means for reducing hydrodynamic drag and pollutant emissions and increasing marine transportation efficiency. Despite this concept’s potential, design optimization and high-performance operation of novel air-cavity ships remain a challenging problem. Hull construction and sensor instrumentation of the model-scale air-cavity boat is described in the paper. The modular structure of the hull allows for easy modifications, and an electric propulsion unit enables self-propelled operation. The boat is controlled remotely via a radio transmission system. Results of initial tests are reported, including thrust, speed, and airflow rate in several loading conditions. The constructed platform can be used for optimizing air-cavity systems and testing other innovative hull designs. This system can be also developed into a high-performance unmanned boat.     

Classification issues in the analysis of complex travel behavior

Researchers have devoted considerable effort to identifying homogeneous travel-behavior groups, each of which also has distinctive sociodemographic characteristics. Interest in these efforts has been fueled by both theoretical and applied concerns. From a theoretical perspective, if such behaviorally and sociodemographically homogeneous groups cari be identified, we would have an improved understanding of the determinants of travel. From an applied perspective, because spatial choice models assume behavioral homogeneity within each sociodemographically defined subgroup, one would like to be able to identify groups that are homogeneous with respect to both behavior and sociodemographics. Most previous efforts to define such groups have classified individuals on the basis of one-day travel records. In this paper we review these efforts, note the problems inherent in using one-day travel records for identifying homogeneous travel-behavior groups, and use standard grouping procedures to classify individuals on the basis of behavior observed over a longer time period (five weeks). Using multi-day travel data means that the travel measures employed in classifying individuals are different from and more complex than those used with one-day data. We identify five travel-behavior groups, each of which has distinctive socio-demographic characteristics. Considerable intra-group variability remains, however, even though the groups are classified on the basis of longer-term behavior. The paper concludes with an examination of the implications of day-to-day variability in individual travel for classification procedures.     

The impact of married women's employment on household travel patterns: A Swedish example

As the number of married women working outside the home continues to grow, questions arise as to the impact of a wife's employment on household travel patterns. In this paper we examine the effects of a wife's employment status on her own travel activity pattern and on that of her husband. Using data from the Uppsala Household Travel Survey, in which sample-household members kept detailed travel diaries for 35 days, we first compare the travel patterns of married women employed full time with those of married women employed part time and married women not working outside the home. We then compare the travel patterns of the three corresponding groups of husbands. Measures of travel activity patterns that were used include indices of overall travel frequency for different purposes, amount of time spent and distances travelled for different purposes, indices of the level of variety in the individual's destination choice set, and measures of mode use. The results show that women employed full-time do reduce their participation in some non-work activities although their distances travelled to activity sites are not shorter than those travelled by the other women.Few significant intergroup differences distinguish the travel activity patterns of the three groups of men. The evidence suggests that a woman's full-time employment does bring significant changes to her own travel pattern but has little impact on that of her husband. The paper concludes with a discussion of policy implications and a review of several Swedish programs that could eventually result in greater similarity in the travel activity patterns of men and women.     

Safety Oriented Maneuvers for IVHS

The IVHS architecture of the California PATH program organizes traffic into platoons of closely spaced vehicles. Platoons are formed and broken up by two longitudinal control maneuvers, the merge and the split. A third longitudinal maneuver, decelerate to change lane, allows a platoon switching from one lane to another to enter its new lane at a safe spacing and speed. The maneuvers, particularly the merge, can be potentially hazardous. In a merge, the cars in the trail platoon are moving faster than those in the lead platoon, while the gap separating the two platoons is smaller than usual. A sudden deceleration by the lead platoon could cause a high-speed collision. If the relative velocities of the merging platoons can be constrained so that they are guaranteed never to collide at a high relative velocity, the merge can be considered safe. A maximum safe velocity for the trail platoon can be found for any given spacing and lead-platoon velocity. This paper presents a merge maneuver in which the velocity of the trail platoon never exceeds the maximum safe velocity. The controller switches among several feedback control laws that keep the velocity of the trail platoon inside a safe region and within comfort limits on jerk and acceleration, under normal circumstances. This merge maneuver can be considered to be the fastest merge strategy mat does not violate bounds on safety and comfort. The controller is also more robust to changes in the vehicles' acceleration capability than those that use a desired open-loop trajectory

The control approach used for the merge maneuver can be applied to the other maneuvers to ensure that they never result in a collision. The switching controllers for the split and decelerate to change lane maneuvers that are safe and yield a more comfortable ride than those that track a timed trajectory are also presented.     

The importance of the multi-purpose journey to work in urban travel behavior

This study examines the journey to work as a multiple-purpose trip (home-to-home circuit). Using disaggregate travel diary data collected over 35 consecutive days, the study shows the importance of the multi-purpose work trip in the overall travel pattern of the urban household. A large proportion of many households' total travel is undertaken in conjunction with the journey to and from work. The paper also examines the nature of these work-induced travel linkages and finds that many types of urban establishments depend heavily upon stops made in connection with the work trip. In fact, there is a group of urban functions that have stronger travel links with the workplace than with the home or with any other type of urban establishment. The study examines the implications of the multi-purpose journey to work for policies regarding mode use and the viability of centrally-located urban functions.