Urban population density may influence transportation demand, e.g., as expressed through average daily vehiclekilometers traveled in private motor vehicles per capita. In turn, changes in transportation demand influence total passenger vehicle emissions to which populations are exposed. Population density can also influence the fraction of total emissions that are inhaled by the exposed urban population. Equations are presented that describe these relationships for an idealized representation of an urban area. Using analytic solutions to these equations, we investigate the effect of three changes in urban population and urban land area (infill, sprawl, and constant-density growth) on per capita inhalation intake of primary pollutants from passenger vehicles. For the system considered, the magnitude of these effects depends on density-emissions elasticity ð e Þ; a normalized derivative relating change in population density to change in vehicle emissions. For example, based on the idealized representation of the emissions-to-intake relationship presented herein, if urban population increases, then per capita intake is less with infill development than with constantdensity growth if e is oÀ0.5, while for e 4À0.5, the reverse is true. r

a b s t r a c tThis paper reports on a study of current practice in policy transfer, and ways in which its effectiveness can be increased. A literature review identifies important factors in examining the transfer of policies. Results of interviews in eleven cities in Northern Europe and North America investigate these factors further.The principal motivations for policy transfer were strategic need and curiosity. Local officials and politicians dominated the process of initiating policy transfer, and local officials were also the leading players in transferring experience.A range of information sources are used in the search process but human interaction was the most important source of learning for two main reasons. First, there is too much information available through the Internet and the search techniques are not seen to be wholly effective in identifying the necessary information. Secondly, the information available on websites, portals and even good practice guides is not seen to be of mixed quality with risks of focussing only on successful implementation and therefore subject to some bias. Officials therefore rely on their trusted networks of peers for lessons as here they can access the 'real implementation' story and the unwritten lessons. Organisations which have a culture that is supportive of learning from elsewhere had strong and broad networks of external contacts and resourced their development whilst others are more insular or inward looking and reluctant to invest in policy lessons from elsewhere. Solutions to the problems identified in the evidence base are proposed.City to city policy transfer is a very active process in the field of transport. Not enough is yet understood about its benefits or the conditions under which it is most effective. Such understandings should help to promote and accelerate the uptake of effective and well matched policies.

Reliable estimates of inhalation intake of air pollution and its distribution among a specified population are important for environmental epidemiology, health risk assessment, urban planning, and environmental policy. We computed distributional characteristics of the inhalation intake of five pollutants for a group of $25,000 people ($29,000 persondays) living in California's South Coast Air Basin. Our approach incorporates four main inputs: temporally resolved information about people's location (latitude and longitude), microenvironment, and activity level; temporally and spatially explicit model determinations of ambient concentrations; stochastically determined microenvironmental adjustment factors relating the exposure concentration to the ambient concentration; and, age-, gender-, and activityspecific breathing rates. Our study is restricted to pollutants of outdoor origin, i.e. it does not incorporate intake in a microenvironment from direct emissions into that microenvironment. Median estimated inhalation intake rates (mg d À1 ) are 53 for benzene, 5.1 for 1,3-butadiene, 8.7 Â 10 À4 for hexavalent chromium in fine particulate matter (Cr-PM 2.5 ), 30 for diesel fine particulate matter (DPM 2.5 ), and 68 for ozone. For the four primary pollutants studied, estimated median intake rates are higher for non-whites and for individuals in low-income households than for the population as a whole. For ozone, a secondary pollutant, the reverse is true. Accounting for microenvironmental adjustment factors, population mobility and temporal correlations between pollutant concentrations and breathing rates affects the estimated inhalation intake by 40% on average. The approach presented here could be extended to quantify the impact on intakes and intake distributions of proposed changes in emissions, air quality, and urban infrastructure. r

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