Olu Ashiru

Public health benefits of strategies to reduce greenhouse-gas emissions: urban land transport.

We used Comparative Risk Assessment methods to estimate the health effects of alternative urban land transport scenarios for two settings-London, UK, and Delhi, India. For each setting, we compared a business-as-usual 2030 projection (without policies for reduction of greenhouse gases) with alternative scenarios-lower-carbon-emission motor vehicles, increased active travel, and a combination of the two. We developed separate models that linked transport scenarios with physical activity, air pollution, and risk of road traffic injury. In both cities, we noted that reduction in carbon dioxide emissions through an increase in active travel and less use of motor vehicles had larger health benefits per million population (7332 disability-adjusted life-years [DALYs] in London, and 12 516 in Delhi in 1 year) than from the increased use of lower-emission motor vehicles (160 DALYs in London, and 1696 in Delhi). However, combination of active travel and lower-emission motor vehicles would give the largest benefits (7439 DALYs in London, 12 995 in Delhi), notably from a reduction in the number of years of life lost from ischaemic heart disease (10-19% in London, 11-25% in Delhi). Although uncertainties remain, climate change mitigation in transport should benefit public health substantially. Policies to increase the acceptability, appeal, and safety of active urban travel, and discourage travel in private motor vehicles would provide larger health benefits than would policies that focus solely on lower-emission motor vehicles.

Utility of Schedules: Theoretical Model of Departure-Time Choice and Activity-Time Allocation with Application to Individual Activity Schedules

The timing and duration of activities are important components of individual travel and activity behavior, affecting spatial interaction and mode choice decisions, highway and transit congestion, accessibility, and the general degree of social exclusion or inclusion experienced by the individual. The choices of timing and duration of activities are closely interrelated; however, few researchers have attempted to study this relationship. Instead strong separability assumptions have been made concerning the timing and duration dimensions. A utility theoretical model of joint activity-timing and duration choice is presented that addresses a number of the limitations of existing scheduling and time allocation models. How the theoretical model can be used to provide insight into the nature of the activity-scheduling process is outlined, and an algorithm is presented that can be used to operationalize the time allocation and activity-scheduling model. An estimable empirical form of the theoretical model is subsequently developed in which it is acknowledged that past and present activity and travel behavior decisions affect both existing and expected behavioral outcomes. How the model can be used to develop a number of disaggregate, activity-based accessibility measures is outlined, and with the aid of a simple hypothetical case study, a number of behavioral characteristics of the time-allocation and activity-scheduling model are demonstrated.

Achieving carbon-efficient transportation: Backcasting from London

Transportation is a major user of carbon-based fuels and is increasingly being highlighted as the sector that contributes the least to carbon dioxide (CO2) emission reduction targets. This paper reports on the findings of the current Visioning and Backcasting for Transport in London study, which considers the role of the transportation sector in reducing CO2 emissions in London. A backcasting study approach was used, and the likely impacts of alternative images of 2025 were tested. A transportation and carbon simulation game was also developed for London. Within this game, users are able to consider a series of potential policy packages, such as low-emission vehicles, alternative fuels, pricing regimens, public transportation, walking and cycling, strategic and local urban planning, information and communication technologies, smarter choices, ecological driving and slower speeds, long-distance travel substitution, freight transportation, and international air, and select various levels of application to help achieve headline CO2 emissions reduction targets. The roles of two external enabling measures, carbon rationing and oil pricing, were also considered. The paper considers an optimized policy package for 2025. A deep reduction in CO2 emissions from the transportation sector is theoretically possible, yet difficult to achieve. The main perceived problem is in engendering an interest in the public to change consumer purchases and behaviors. The huge challenge now is to map out and discuss a variety of policy pathways to carbon efficiency in the transportation sector and then to enable and achieve a level of consumer and behavioral change consistent with strategic aspiration.

SPACE-TIME USER BENEFIT AND UTILITY ACCESSIBILITY MEASURES FOR INDIVIDUAL ACTIVITY SCHEDULES

Accessibility is a fundamental concept in human existence, which goes to the heart of the notion of society, equity, and justice. However, despite the importance of the concept, the mathematical measures that have historically been used to quantify accessibility levels have been relatively poorly defined and have encompassed a limited range of observed forms of travel behavior. Existing space–time locational benefit measures are extended to encapsulate more realistic temporal constraints on activity participation and the associated perceived user benefit. The development of a family of space–time route benefit measures is outlined. Despite their apparent theoretical attractiveness, hitherto researchers have not used such measures. It is demonstrated how these route benefit measures can be used to develop an associated family of disaggregate activity-based space–time utility accessibility measures applicable to individual activity schedules and how income constraints can be incorporated within the space–time utility accessibility measures. Finally, the means by which stochastic frontier models can be used in conjunction with existing travel–activity diary data sets to operationalize the proposed measure of accessibility are briefly described.