Kitae Jang

Evaluation of Pedestrian Safety: Pedestrian Crash Hot Spots and Risk Factors for Injury Severity

Pedestrian-involved crashes that occurred in the city of San Francisco, California, over 6 years from 2002 to 2007 were analyzed to evaluate two key aspects of pedestrian safety: occurrence and severity. This analysis was done to identify locations with frequent occurrences of pedestrian-involved crashes and to examine various risk factors for the injury severity of pedestrian-involved crashes. A geographical information system analysis for hot spot identification showed that the frequency of pedestrian crashes was greater in the vicinity of the central business district but that the crash rate (the number of crashes per walking trip) was higher in the periphery of the city. For injury analysis, an ordered probit model was specified to evaluate risk factors that increased the probability of severe injury and fatality. Those factors were age (<15 and ≥65), alcohol consumption, and cell phone use among pedestrian characteristics; nighttime, weekends, and rainy weather among environmental characteristics; and, among crash characteristics, the influence of alcohol, larger vehicles (pickups, buses, and trucks), and vehicles proceeding straight and striking a pedestrian. The methods discussed are readily applicable to the evaluation of safety performance in other regions where pedestrian crash data are available.

Traffic Signal Optimization for Oversaturated Urban Networks: Queue Growth Equalization

This paper develops a signal optimization algorithm that aims to equalize queue growth rates across links in oversaturated urban roadway networks and thus postpones queue spillbacks that form at the localized sections of networks. The performance of this algorithm is evaluated by simulating traffic conditions with optimized signal settings on an idealized 3 by 3 roadway network under various oversaturated demand scenarios. The simulation experiments show that the algorithm can delay queue spillbacks by distributing queues over upstream links that would otherwise be underused. The findings from the experiments also show that the signal settings optimized by the queue growth equalization (QGE) algorithm outperform those optimized using the conventional signal optimization software, TRANSYT-7F, for all the performance measures examined in this paper, i.e., compared with TRANSYT-7F, the QGE results in higher outflows, higher vehicle miles traveled, shorter delays, less sensitivity to various demand scenarios, and delayed queue spillbacks. In addition, the algorithm is computationally light to provide a promising groundwork for large-scale signal optimization.

Traffic characteristics of high-occupancy vehicle facilities: Comparison of contiguous and buffer-separated lanes

Traffic characteristics intrinsic to contiguous and buffer-separated high-occupancy vehicle (HOV) facilities were explored by examining flow–density–speed relations and an intervening effect from the adjacent general purpose (GP) lane. Detector data were collected from multiple locations and systematically filtered to form well-defined relations between flow, density, and speed that characterize the traffic stream in the HOV lane. Analysis outcomes of the collected data indicated patterns of flow–density–speed relations for contiguous and buffer-separated HOV lanes. The data from the contiguous HOV lanes exhibited relationships as a function of the adjacent GP lane speed, whereas those in the buffer-separated HOV lanes were rather independent of the adjacent GP lane speed. Implications were drawn for capacity and speed of HOV lanes and documented in this paper. These findings were confirmed by comparative analysis of pre- and postconversion HOV configurations, from buffer-separated to contiguous, in a real freeway site.

Effects of Urban Sprawl and Vehicle Miles Traveled on Traffic Fatalities

Objective: Previous research suggests that urban sprawl increases auto-dependency and that excessive auto use increases the risk of traffic fatalities. This indirect effect of urban sprawl on traffic fatalities is compared to non–vehicle miles traveled (VMT)-related direct effect of sprawl on fatalities. Methods: We conducted a path analysis to examine the causal linkages among urban sprawl, VMT, traffic fatalities, income, and fuel cost. The path diagram includes 2 major linkages: the direct relationship between urban sprawl and traffic fatalities and the indirect effect on fatalities through increased VMT in sprawling urban areas. To measure the relative strength of these causal linkages, path coefficients are estimated using data collected nationally from 147 urbanized areas in the United States. Results: Through both direct and indirect paths, urban sprawl is associated with greater numbers of traffic fatalities, but the direct effect of sprawl on fatalities is more influential than the indirect effect. Conclusions: Enhancing traffic safety can be achieved by impeding urban sprawl and encouraging compact development. On the other hand, policy tools reducing VMT may be less effective than anticipated for traffic safety.

Heterogeneous Perception of Travelers on Greenhouse Gas Pricing in Seoul, Korea

ABSTRACT This study evaluates the effects of greenhouse gas pricing on the behavior of traveler mode choice. Based on a survey of stated travel preference, a multinomial mixed logit model was used to examine how travelers perceive the price of greenhouse gas and travel cost, and how travelers with different attributes react to them. Heterogeneous perceptions of travelers were observed: travelers were more sensitive to greenhouse gas price than travel cost. The analysis also showed significant distinctions between different traveler groups. Implications for greenhouse gas pricing and potential topics for future research are also discussed.

Logistic regression model for discretionary lane changing under congested traffic

Assessing the probability of lane-changing (LC) is essential to traffic simulation for more realistic representation of complicated traffic phenomena in congested traffic. Discretionary lane changes (DLC), which are not required for reaching a destination, are decided by drivers for the purpose of faster travel. The probability of DLC is related to the speed difference and density difference between adjacent lanes. To reveal the characteristics of DLC, we aggregated Next Generation Simulation trajectory data into a mesoscopic scale and analysed them to obtain detailed information on traffic conditions near DLC actions. We first constructed a joint probability distribution of LC in the speed difference and density difference domains. The distribution shows that speed difference and density difference significantly influence the LC rate. The constructed distribution indicates that drivers tend to change their lanes more frequently to travel faster and to have more space in the target lane. To quantify these relations, logistic regression was applied to the collected data. The outcomes of logistic regression show that the relations are statistically significant and non-linear.

How to Protect ADS-B: Confidentiality Framework and Efficient Realization Based on Staged Identity-Based Encryption

Automatic Dependent Surveillance-Broadcast (ADS-B) is one of the key technologies for future “e-Enabled” aircrafts. ADS-B uses avionics in the e-Enabled aircrafts to broadcast essential flight data such as call sign, altitude, heading, and other extra positioning information. On the one hand, ADS-B brings significant benefits to the aviation industry, but, on the other hand, it could pose security concerns as channels between ground controllers and aircrafts for the ADS-B communication are not secured, and ADS-B messages could be captured by random individuals who own ADS-B receivers. In certain situations, ADS-B messages contain sensitive information, particularly when communications occur among mission-critical civil airplanes. These messages need to be protected from any interruption and eavesdropping. The challenge here is to construct an encryption scheme that is fast enough for very frequent encryption and that is flexible enough for effective key management. In this paper, we propose a Staged Identity-Based Encryption (SIBE) scheme, which modifies Boneh and Franklins original IBE scheme to address those challenges, that is, to construct an efficient and functional encryption scheme for ADS-B system. Based on the proposed SIBE scheme, we provide a confidentiality framework for future e-Enabled aircraft with ADS-B capability.

Spatiotemporal Analysis of Macroscopic Patterns of Urbanization and Traffic Safety Case Study in Sacramento County, California

This study provides a preliminary investigation into the relationship between urbanization and traffic collisions by analyzing the spatial patterns in Sacramento County, California, from 1998 to 2008 through use of urban land classifications and traffic collision data. The ArcGIS directional distribution tool was used to create standard deviational ellipses to investigate the distributional trend of urban land and traffic collisions over time. Statistical outputs representing changes of geographical centroids, elliptical areas, and standard distances (long and short axes) were then compared. Collisions were also divided into subsets by severity level to account for inherent differences in the spatial distribution of different types of collisions. The results provided insight into the macroscopic spatial patterns of urban land and traffic safety and their relationships. The limitations of the method and the need for further research were discussed. The approach in this study would be useful for other metropolitan areas with similarly changing development patterns and can be helpful in guiding future research that compares these two phenomena.

Enforcement avoidance behavior near automated speed enforcement areas in Korean expressways

Automated speed enforcement system (ASES) has been deployed as a safety countermeasure on Korean roadways to reduce speeding-related traffic crashes; information on ASES locations is mandated to be open to the public. However, because drivers are alerted about enforcement via on-board navigation systems and roadside signs, they can avoid enforcement by momentarily reducing their speeds near ASES locations. This enforcement avoidance behavior (EAB) can induce sudden changes in speed near the enforcement locations and thereby increase risk of crash occurrence. In light of this situation, the present study evaluates the effects of ASES on traffic behavior and safety. An analysis of traffic data shows that drivers indeed diminish their speeds near enforcement locations, and accelerate shortly after passing the locations. To investigate how this behavior affects safety performance, this study, by using Empirical Bayes analysis with comparison groups, compares crash occurrences along a certain section before and after the installation of ASES. The comparative analysis shows that overall crash occurrence dropped by 7.6% on average near the enforcement locations, although the reduction was not significant. However, an average 11% non-significant increase in crash occurrence is also observed in the upstream segment, where enforcement is announced to drivers and traffic starts to diminish speed. The findings suggest that the sudden changes in traffic speed induced by EAB substantially negate the benefits of ASES. Therefore, modification of the design of current ASES is required to mitigate EAB and further improve the effectiveness of ASES.

Toward a solar city: Trade-offs between on-site solar energy potential and vehicle energy consumption in San Francisco, California

ABSTRACT This study demonstrates the trade-offs between vehicle energy consumption and on-site solar energy potential in a city landscape. While higher urban density may curb many of the problems associated with sprawl mainly by reducing vehicle travels and associated energy use, it can also limit on-site rooftop solar energy utilization due to more shade on rooftops in dense urban settings and less available rooftop area per person. Using travel survey, Geographic Information System (GIS) and Light Detection and Ranging (LiDAR) data, we estimated vehicle energy use and rooftop solar potential in the City of San Francisco as a case study and calculated possible offsetting effects between vehicle energy consumption and rooftop solar potential. Given the prevalence of gasoline-based vehicles and todays solar photovoltaic (PV) panel efficiency, vehicle energy use per capita appears to exceed energy generated by rooftop solar PVs per capita across all density ranges, especially in lower density environments. At the point when electric cars and advanced, highly efficient solar PV panels penetrate the market, the results change based on the combination of different technological options. A significant reduction of energy consumption can be achieved through the immediate and rapid spread of energy efficient technologies in vehicles and solar PVs along with the long-term effect from gradual urban densification.