published journal article
Most sensors cannot differentiate between legitimate signals and spoofing signals. Therefore, a novel research focus is required using hardware/software co-design techniques in the sensor computation domain to detect, contain, and eradicate spoofing signals in sensors.
published journal article
Abstract The equations governing the axisymmetric dynamic deformation of an elastic solid are considered as a symmetric hyperbolic system of linear first‐order partial differential equations. The characteristic properties of the system are determined and a numerical method for obtaining the solution of mixed initial and boundary value problems in elastodynamics is presented. Two examples are considered.
published journal article
Motivated by the growth of ridesourcing services and the expected advent of fully-autonomous vehicles (AVs), this paper defines, models, and compares assignment strategies for a shared-use AV mobility service (SAMS). Specifically, the paper presents the on-demand SAMS with no shared rides, defined as a fleet of AVs, controlled by a central operator, that provides direct origin-to-destination service to travelers who request rides via a mobile application and expect to be picked up within a few minutes. The underlying operational problem associated with the on-demand SAMS with no shared rides is a sequential (i.e. dynamic or time-dependent) stochastic control problem. The AV fleet operator must assign AVs to open traveler requests in real-time as traveler requests enter the system dynamically and stochastically. As there is likely no optimal policy for this sequential stochastic control problem, this paper presents and compares six AV-traveler assignment strategies (i.e. control policies). An agent-based simulation tool is employed to model the dynamic system of AVs, travelers, and the intelligent SAMS fleet operator, as well as, to compare assignment strategies across various scenarios. The results show that optimization-based AV-traveler assignment strategies, strategies that allow en-route pickup AVs to be diverted to new traveler requests, and strategies that incorporate en-route drop-off AVs in the assignment problem, reduce fleet miles and decrease traveler wait times. The more-sophisticated AV-traveler assignment strategies significantly improve operational efficiency when fleet utilization is high (e.g. during the morning or evening peak); conversely, when fleet utilization is low, simply assigning traveler requests sequentially to the nearest idle AV is comparable to more-advanced strategies. Simulation results also indicate that the spatial distribution of traveler requests significantly impacts the empty fleet miles generated by the on-demand SAMS.
published journal article
There is a pressing need to estimate the magnitude and dynamics of the behavioural effects of transportation investments and policy. This article innovates by applying an experimental-control group research design to the case of new light rail transit service in Los Angeles, California. Only a handful of previous studies use an experimental design to assess impacts of light rail transit, and this is the first to use an experimental design to measure impacts on vehicle miles travelled, a key determinant of greenhouse gas emissions from the transport sector. We administered an annual seven-day travel study to a panel of households in the vicinity of Los Angeles’ Expo light rail line before the 2012 start of rail service and twice after the line opened. We find that households living within walking distance (1 km) of the new light rail drove approximately 10 fewer miles per day relative to control households farther away. Rail transit trips among near-station households approximately tripled relative to households beyond walking distance. Such driving reductions among households within walking distance of new rail transit stations suggest that Los Angeles’ large rail transit investment, coupled with land use policy, has the potential to help achieve climate change policy goals. More broadly, experimental evaluation can provide insights into causality and patterns of travel behaviour change associated with planning policies.
published journal article
This article examines how municipal planning contexts can shape urban land use dynamics by investigating the parcel-level land use changes in a five-county Southern California metropolitan area between 1990 and 2005. An analysis, based on a multinomial logit model, shows that land use change patterns significantly vary by municipalities that were situated in heterogeneous planning contexts. More specifically, cities with limited ability to expand their jurisdictional boundaries are found to provide more recreational areas and urban open spaces, while restricting nonconventional land uses. However, no evidence of a shift from single-family to multifamily residential development is detected for such cities.
published journal article
conference paper
In the area of freight planning, particularly in commodity modeling, it is often a daunting task to identify data sources, especially data disaggregate to county or less than county levels. If one considers the case of agricultural commodities, information availability is further reduced since agricultural census data collection is infrequent and is not complete in terms of crops covered, nor does data exist below the county level in terms of geographical aggregation. Additionally, data sources such as the Freight Analysis Framework, FAF, often present annual data. Since transportation models are usually developed for peak periods and/or typical days, the traditional assumption of flat peak factors are not valid for agricultural commodities that are seasonal and that have seasonal patterns with inter-state and intra-state variations. CropScape is a tool from the United States Department of Agriculture (USDA) that provides complete coverage for the 48 contiguous states and reports all crops with a spatial resolution of less than one acre. It is in this setting that the authors tested the use of CropScape in two different analyses: FAF disaggregation and seasonality analysis. The authors present results that include models for FAF disaggregation that greatly outperform the best models currently available in the literature and a procedure for computing agricultural seasonality for any desired geographical aggregation.
published journal article
Communities near the wildland urban interface (WUI) are exposed to a mix of three interconnected hazards (wildfire, flood, and mudslide), and understanding multi-hazard perceptions is critically important for emergency preparation and hazard mitigation—particularly given the WUI’s rapid expansion and intensifying environmental hazards. Based on a survey of residents living near recent burn scars in Southern California, we document cross-over effects in hazard perceptions, where resident experience with one hazard was associated with greater hazard rankings for other hazards. Additionally, for all three hazards analyzed we document perceptions of increasing hazard levels with increasing spatial scales (home, near-home, neighborhood, and community), providing evidence of spatial optimism, or the tendency to discount proximate hazards. This study stresses the importance of using a multi-hazard and multi-scale approach for understanding and responding to local level environmental hazards.
conference paper
published journal article
Electric vehicles (EVs) have substantial potential for fleet applications as energy-efficient vehicles with fewer carbon-based emissions. However, EV utilization brings other concerns related to limited vehicle ranges and battery-charging issues, and thus the recharging infrastructure needs to be carefully designed and financially supported. This study focuses on the use of an EV fleet for an innovative transportation alternative called high-coverage point-to-point transit (HCPPT), which involves a sufficient number of deployed small vehicles that respond to real-time desires for point-to-point travel of individual travelers. As large-scale fleet operation of EVs and the HCPPT system are both envisaged only as future transportation alternatives, the benefits of combining these options have to be modeled and studied. Possible infrastructure investment benefits could result for both systems when transfer-hub locations of HCPPT are used as electric-charging locations. This paper studied the performance results from the simulation of a real-world transfer-hub system and developed certain vehicle-routing schemes to handle the specifics of EV operations. Alternative ways to schedule the charging of EVs were modeled with different insertion heuristics within vehicle-routing optimization. The results showed that the battery-charging limitations of EVs do not significantly affect the efficiency of the HCPPT system and revealed the importance of details such as the number of required charging stations at the hub locations.