Families of graphs with twin pendent paths and the Braess edge

In the context of a random walk on an undirected graph, Kemeny's constant can measure the average travel time for a random walk between two randomly chosen vertices. We are interested in graphs that behave counter-intuitively in regard to Kemeny's constant: in particular, we examine graphs with a cut-vertex at which at least two branches are paths, regarding whether the insertion of a particular edge into a graph results in an increase of Kemeny's constant. We provide several tools for identifying such an edge in a family of graphs and for analysing asymptotic behaviour of the family regarding the tendency to have that edge; and classes of particular graphs are given as examples. Furthermore, asymptotic behaviours of families of trees are described.

Effects From Expanding High-Speed Railway Network on Regional Accessibility and Economic Productivity in China

This paper reviews the historical evolution of China’s high-speed railway (HSR) network, evaluates improvements in accessibility, and analyzes the associations of improved accessibility with regional economic productivity, given regional heterogeneity. Three accessibility indicators were considered: average travel time to all prefectural level regions (ATT), average travel time to important cities (ATI), and daily accessible prefectural level regions. These indicators were used to quantify the development of the HSR network during two periods, from 2007 to 2012 and 2012 to 2018. First, the results revealed that, in the first period, the accessibility indicators of the east region improved the most, whereas in the second period, the west significantly improved. We subsequently analyzed the economic productivity and -equilibrium of the urban agglomerations affected by introducing the HSR. Those results suggested that the Triangle of Central China, Chengdu-Chongqing, and Central Guizhou urban agglomerations performed well as the HSR developed. The linkages between regional economic productivity and accessibility improvement were then measured using a multivariable regression with panel data. The results showed that the reduction of ATT and ATI significantly positively contributed to economic productivity at different geographical scales in China. Furthermore, ATT had a larger effect in the northeast and central regions, whereas ATI had a larger effect on the northeast and west regions.

Instantaneous speed as a tool for defining accessibility in the road network of Ocaña, Colombia

The application of the concept of instantaneous speed to the movement of vehicles on a city’s road network made it possible to establish average operating speeds. With the help of software based on geographic information systems, it was possible to determine the minimum travel times required by vehicles to move between two points on the network. Through the above analysis of speeds and travel times, applied to the road network of the municipality Ocaña, Colombia, it was possible to establish the time required by various types of vehicles to travel between the different points of the road network, allowing to define the level of accessibility to move between different areas of the city. The analysis required the updating, characterization, georeferencing and determination of the instantaneous speeds for each trip in the different arcs of the network and the subsequent determination of the average travel time curves in the network. The urban area of the city is covered with an average travel time of 15 minutes and the operating speeds are between 5 km/h and 31 km/h, with variations depending on the type of vehicle (bus, taxi, motorcycle).

Effect of Surface Water Level Fluctuations on the Performance of Near-Bank Managed Aquifer Recharge from Injection Wells

Managed aquifer recharge operations are often conducted in near-bank areas to regulate water resources or reduce seawater intrusion. Yet little is known about the influence of surface water level fluctuations at different temporal scales on MAR performance. A generalized conceptual model was developed based on an investigation site in Western China as a basis to simulate the response surface water level fluctuations on the water table, artificially recharged water lens (formed by the artificially recharged water), groundwater flow paths and average travel times (which is an important control on how quickly contaminants are flushed out of aquifers), and the discharge of the artificially recharged aquifer during the surface water level fluctuation. The results showed a fluctuating groundwater table in the artificially recharged near-bank aquifer under the influence of surface water level fluctuations. The peak values of the increment of the groundwater table induced by artificial recharge decreased with the increase of the period and amplitude of surface water level fluctuation, but the trough values of the increment of water table increases with that. The penetration depth of surface water into the aquifer with a fluctuating surface water level leads to a decreasing increment of the groundwater table which follows a power law. The fluctuating surface water level leads to dynamic changes of artificially recharged water lens morphology and a thinner artificially recharged water lens. A mixing zone of recharged water and ambient water could be found in the artificially recharged near-bank area, which is expected to lead to modifications in the geochemical conditions in the artificially recharged near-bank aquifer. A longer period of surface water level fluctuation leads to a longer average travel time, but the larger penetration depth of surface water and amplitude lead to a shorter average travel time. The peak discharge of the near-bank aquifer was found to decrease with the period of surface water level fluctuation, but it increases with penetration depth and amplitude. This study is important in providing insights into the performance of near-bank managed aquifer recharge with respect to surface water level fluctuation.

Bi-Level Coordinated Merging of Connected and Automated Vehicles at Roundabouts

Traditional uncoordinated traffic flows in a roundabout can lead to severe traffic congestion, travel delay, and the increased fuel consumption of vehicles. An interesting way to mitigate this would be through cooperative control of connected and automated vehicles (CAVs). In this paper, we propose a novel solution, which is a roundabout control system (RCS), for CAVs to attain smooth and safe traffic flows. The RCS is essentially a bi-level framework, consisting of higher and lower levels of control, where in the higher level, vehicles in the entry lane approaching the roundabout will be made to form clusters based on traffic flow volume, and in the lower level, the vehicles’ optimal sequences and roundabout merging times are calculated by solving a combinatorial optimization problem using a receding horizon control (RHC) approach. The proposed RCS aims to minimize the total time taken for all approaching vehicles to enter the roundabout, whilst minimally affecting the movement of circulating vehicles. Our developed strategy ensures fast optimization, and can be implemented in real-time. Using microscopic simulations, we demonstrate the effectiveness of the RCS, and compare it to the current traditional roundabout system (TRS) for various traffic flow scenarios. From the results, we can conclude that the proposed RCS produces significant improvement in traffic flow performance, in particular for the average velocity, average fuel consumption, and average travel time in the roundabout.

Modeling the Impacts of Driver Income Distributions on Online Ride-Hailing Services

The online ride-hailing taxi brings new vitality into the traditional taxi market, as well as new issues and challenges. The pricing and profit distribution of online ride-hailing services is one of the major concerns. This study focuses on the pricing and income distribution in the online ride-hailing system. Queuing system model and birth and death process theory are introduced to describe the driver’s flow process in the network. The social welfare maximization model and the platform profit maximization model are constructed based on the dynamic pricing mechanism, from the government’s and platform’s standpoint, respectively. Through numerical experiments, this paper analyzes the income distribution of drivers under different settings and the influence of different factors (average travel time, psychologically expected price of drivers and passengers, and probability of driver leaving the system) on the proportion of income distribution. The results show that the drivers’ income distribution proportion is higher in the pursuit of social welfare maximization than that in the pursuit of platform profit maximization, and in different benefit pursuit models, various factors have a certain influence on the driver’s income distribution proportion. The proposed method and conclusion in this study can be considered as references for online ride-hailing market supervision and policy-making.

Optimal Deployment of Charging Stations for Aerial Surveillance by UAVs with the Assistance of Public Transportation Vehicles

To overcome the limitation in flight time and enable unmanned aerial vehicles (UAVs) to survey remote sites of interest, this paper investigates an approach involving the collaboration with public transportation vehicles (PTVs) and the deployment of charging stations. In particular, the focus of this paper is on the deployment of charging stations. In this approach, a UAV first travels with some PTVs, and then flies through some charging stations to reach remote sites. While the travel time with PTVs can be estimated by the Monte Carlo method to accommodate various uncertainties, we propose a new coverage model to compute the travel time taken for UAVs to reach the sites. With this model, we formulate the optimal deployment problem with the goal of minimising the average travel time of UAVs from the depot to the sites, which can be regarded as a reflection of the quality of surveillance (QoS) (the shorter the better). We then propose an iterative algorithm to place the charging stations. We show that this algorithm ensures that any movement of a charging station leads to a decrease in the average travel time of UAVs. To demonstrate the effectiveness of the proposed method, we make a comparison with a baseline method. The results show that the proposed model can more accurately estimate the travel time than the most commonly used model, and the proposed algorithm can relocate the charging stations to achieve a lower flight distance than the baseline method.

Assessing emergency healthcare accessibility in the Salton Sea region of Imperial County, California

The area surrounding California’s Salton Sea, which lies within Riverside and Imperial counties, has particularly negative health outcomes. Imperial County, a primarily rural region that encompasses the lake, has pediatric asthma-related emergency healthcare visits that double the state average. This paper seeks to assess the level of emergency healthcare access in the Salton Sea region of Imperial County, drawing from spatial science methods. For this study, the "Salton Sea region" is defined as all Imperial County census tracts that include the Salton Sea within its boundaries. To measure "access," this study calculated driving travel times from census tracts to hospitals within Imperial County rather than Euclidean distance to account for geography and urban infrastructures such as road networks and traffic conditions. This study also used the Rational Agent Access Model, or RAAM, to assess access. RAAM scores account for the supply and demand for hospitals in addition to travel times. Results showed that the average travel time for Salton Sea region residents to drive to Imperial County emergency healthcare facilities ranged from 50–61 minutes, compared to 14–20 minutes for other Imperial County tracts. RAAM scores, compared to other Imperial County tracts, were about 30% higher in the Salton Sea region, meaning that healthcare supply is limited in the region. State and county policy should account for spatial inaccessibility to healthcare institutions in order to address emergency healthcare access.

Equivalence of care? Accessibility and availability of dialysis services for older prisoners in Switzerland

Purpose According to the principle of equivalence of care, health care in prison has to be of the same standard and quality as in the general population. This study aims to determine the geographic accessibility of dialysis services for older prisoners and the older general population in Switzerland and whether accessibility and availability of dialysis care are equivalent. Design/methodology/approach Spatial accessibility analysis incorporated four different data types: population data, administrative data, street network data and addresses of prisons and hemodialysis services. Findings Analysis revealed that the average travel time to the nearest dialysis service was better for prisoners (11.5 min) than for the general population (14.8 min). However, dialysis service for prisoners is hampered by the necessary lead-time in correctional settings, which, ultimately, leads to longer overall access times (36.5 min). Accordingly, the equivalence of dialysis care for older Swiss prisoners is not entirely respected for availability and accessibility. Originality/value The strength of the study lies in the combination of ethical principles and the highly tangible results of a spatial accessibility analysis. The ethics-driven empirical analysis provides arguments for policy-makers to review the current practices.