Private Provision of Highways: Economic Issues

This paper reviews issues raised by the use of private firms to finance, build, and/or operate highways — issues including cost of capital, level and structure of tolls, and adaptability to unforeseen changes. The public sector’s apparent advantage in cost of capital is at least partly illusory due to differences in tax liability and to constraints on the supply of public capital. The evidence for lower costs of construction or operation by private firms is slim. Private firms are likely to promote more efficient pricing. Effective private road provision depends on well-structured franchise agreements that allow pricing flexibility, restrain market power, enforce a sound debt structure, promote transparency, and foster other social goals.Privatization; Road finance; Toll road; Road pricing

Spatial Hedonics and the Willingness to Pay for Residential Amenities

Housing rents may be influenced by characteristics of nearby properties, an effect captured by spatial autoregression in a hedonic rent equation. We investigate the implications of spatial autoregression for measuring the marginal welfare effects due to a change in a residential amenity such as air quality. We show that if spatial price interdependence arises from technological spillovers, such that utility depends directly on neighboring property values, then the welfare change is given by the reduced form of the autoregressive model, effectively applying a "spatial multiplier" to the relevant implicit price. If instead spatial interdependence arises from merely pecuniary spillovers, as is commonly supposed in motivating spatial autoregression, then no spatial multiplier on implicit prices is called for in computing welfare; but it is then especially important to use the autoregressive model to measure those implicit prices.Spatial autocorrelation; spatial lag; welfare; willingness to pay; hedonic price function

Estimation of causal effects using instrumental variables with nonignorable missing covariates: Application to effect of type of delivery NICU on premature infants

Understanding how effective high-level NICUs (neonatal intensive care units that have the capacity for sustained mechanical assisted ventilation and high volume) are compared to low-level NICUs is important and valuable for both individual mothers and for public policy decisions. The goal of this paper is to estimate the effect on mortality of premature babies being delivered in a high-level NICU vs. a low-level NICU through an observational study where there are unmeasured confounders as well as nonignorable missing covariates. We consider the use of excess travel time as an instrumental variable (IV) to control for unmeasured confounders. In order for an IV to be valid, we must condition on confounders of the IV---outcome relationship, for example, month prenatal care started must be conditioned on for excess travel time to be a valid IV. However, sometimes month prenatal care started is missing, and the missingness may be nonignorable because it is related to the not fully measured mother's/infant's risk of complications. We develop a method to estimate the causal effect of a treatment using an IV when there are nonignorable missing covariates as in our data, where we allow the missingness to depend on the fully observed outcome as well as the partially observed compliance class, which is a proxy for the unmeasured risk of complications. A simulation study shows that under our nonignorable missingness assumption, the commonly used estimation methods, complete-case analysis and multiple imputation by chained equations assuming missingness at random, provide biased estimates, while our method provides approximately unbiased estimates. We apply our method to the NICU study and find evidence that high-level NICUs significantly reduce deaths for babies of small gestational age, whereas for almost mature babies like 37 weeks, the level of NICUs makes little difference. A sensitivity analysis is conducted to assess the sensitivity of our conclusions to key assumptions about the missing covariates. The method we develop in this paper may be useful for many observational studies facing similar issues of unmeasured confounders and nonignorable missing data as ours.Comment: Published in at http://dx.doi.org/10.1214/13-AOAS699 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Neuronal avalanches of a self-organized neural network with active-neuron-dominant structure

Neuronal avalanche is a spontaneous neuronal activity which obeys a power-law distribution of population event sizes with an exponent of -3/2. It has been observed in the superficial layers of cortex both \emph{in vivo} and \emph{in vitro}. In this paper we analyze the information transmission of a novel self-organized neural network with active-neuron-dominant structure. Neuronal avalanches can be observed in this network with appropriate input intensity. We find that the process of network learning via spike-timing dependent plasticity dramatically increases the complexity of network structure, which is finally self-organized to be active-neuron-dominant connectivity. Both the entropy of activity patterns and the complexity of their resulting post-synaptic inputs are maximized when the network dynamics are propagated as neuronal avalanches. This emergent topology is beneficial for information transmission with high efficiency and also could be responsible for the large information capacity of this network compared with alternative archetypal networks with different neural connectivity.Comment: Non-final version submitted to Chao

Urban Transportation Policy: A Guide and Road Map

The main transportation issues facing cities today fall into familiar categories--congestion and public transit. For congestion, there is now a far richer menu of options that are understood, technically feasible, and perhaps politically feasible. One can now contemplate offering roads of different qualities and prices. Many selected road segments are now operated by the private sector. Road pricing is routinely considered in planning exercises, and field experiments have made it more familiar to urban voters. Concerns about environmental effects of urban trucking have resulted in serious interest in tolled truck-only express highways. As for public transit, there is a need for political mechanisms to allow each type of transit to specialize where it is strongest. The spread of “bus rapid transit†has opened new possibilities for providing the advantages of rail transit at lower cost. The prospect of pricing and privatizing highway facilities could reduce the amount of subsidy needed to maintain a healthy transit system. Privately operated public transit is making a comeback in other parts of the world. The single most positive step toward better urban transportation would be to encourage the spread of road pricing. A second step, more speculative because it has not been researched, would be to use more environmentally-friendly road designs that provide needed capacity but at modest speeds, and that would not necessarily serve all vehicles.Transportation policy; Road pricing; Privatization; Product differentiation

Aerodynamic tests and analysis of a turbojet-boosted launch vehicle concept (spacejet) over a Mach number range of 1.50 to 2.86

Results from analytical and experimental studies of the aerodynamic characteristics of a turbojet-boosted launch vehicle concept through a Mach number range of 1.50 to 2.86 are presented. The vehicle consists of a winged orbiter utilizing an area-ruled axisymmetric body and two winged turbojet boosters mounted underneath the orbiter wing. Drag characteristics near zero lift were of prime interest. Force measurements and flow visualization techniques were employed. Estimates from wave drag theory, supersonic lifting surface theory, and impact theory are compared with data and indicate the ability of these theories to adequately predict the aerodynamic characteristics of the vehicle. Despite the existence of multiple wings and bodies in close proximity to each other, no large scale effects of boundary layer separation on drag or lift could be discerned. Total drag levels were, however, sensitive to booster locations