Search

Roadside LiDAR (light detection and ranging) is a solution to fill in the gaps for connected vehicles (CV) by detecting the status of global road users at transportation facilities. It relies greatly on the clustering algorithm for accurate and rapid data processing so as to ensure effectiveness and reliability. To contribute to better roadside LiDAR-based transportation facilities, this paper presents a fast-spherical-projection-based clustering algorithm (FSPC) for real-time LiDAR data processing with higher clustering accuracy and noise handling. The FSPC is designed to work on a spherical map which could be directly derived from the instant returns of a LiDAR sensor. A 2D-window searching strategy is specifically designed to accelerate the computation and alleviate the density variation impact in the LiDAR point cloud. The test results show the proposed algorithm can achieve a high processing efficiency with 24.4 ms per frame, satisfying the real-time requirement for most common LiDAR applications (100 ms per frame), and it also ensures a high accuracy in object clustering, with 96%. Additionally, it is observed that the proposed FSPC allows a wider detection range and is more stable, tackling the surge in foreground points that frequently occurs in roadside LiDAR applications. Finally, the generality of the proposed FSPC indicates the proposed algorithm could also be implemented in other areas such as autonomous driving and remote sensing.

Light detection and ranging (LiDAR) sensors are receiving an increasing amount of attention in traffic detection because of their powerful capacity for providing accurate trajectory data of vehicles and non-motorized road users. When installed at the roadside, LiDAR faces the same occlusion problem as other over-roadway sensors (such as video cameras)—the integrity and reliability of object detection can be reduced when occlusion occurs. Existing occlusion reasoning methods are either developed for video sensors or require sensor fusion. Fast and accurate occlusion determination is an indispensable step in the process of vehicle detection, classification, and tracking. This paper presents a novel algorithm to automatically identify the occurrence of vehicle partial occlusion and the corresponding occluding/occluded relationship from roadside LiDAR data. According to the inherent characteristics of LiDAR sensors, two specifically designed heatmaps (ClusterID heatmap and Distance heatmap) were generated and used as the basis for fast occlusion search. Using the field data collected from two testbeds, it was shown that the proposed method could achieve about 95.60% accuracy for partial occlusion identification and a processing speed of 2 ms per frame (32-laser LiDAR sensor with 0.1 s per frame).

This paper analyzes the decoupling states between CO2 emissions and transport development in China from 1994 to 2012. The results indicate that, at the aggregate level, the Chinese transport sector is far from reaching the decoupling state. Negative decoupling or non-decoupling years account for 72.2% of the study period. At the disaggregated level, the decoupling states between CO2 emissions and eight primary fuels are as follows: raw coal and coke are in the absolute decoupling state; crude oil, gasoline and diesel are in the weak negative state; and the other three types (kerosene, heavy fuel oil, and natural gas) are in the strong negative decoupling state. Policy implications underneath the identified decoupling states are also revealed to help China build a more sustainable transportation system.

The diverging diamond interchange (DDI) is an innovative alternative to the conventional diamond interchange. Its operational efficiency has proved promising because its unique geometric design allows the operation of flexible signal phasing schemes. Of all DDI phasing schemes, two-phase operations can best highlight the merit of the DDI design by using overlaps. An internal queue is allowed with different types of two-phase operations. Therefore, conventional capacity calculation methods may not be appropriate for the DDI if the effects of the internal queue need to be considered. To fill this gap, a method was developed to calculate the approach capacity of the DDI by using an analytical model that would consider the impacts of the internal queue on the traffic progression of either arterial roads or freeway ramps. The proposed model was fully calibrated with microscopic traffic simulation in Vissim; comparison of the results indicates that the model has promising accuracy and stability. One of the proposed model’s most important functions is the calculation of lost green time of traffic movements of the DDI. A similar method documented in the Highway Capacity Manual 2010 (HCM 2010), Chapter 22, was also designed to calculate the lost green time of signalized interchanges due to the impact of an internal queue. A comparison of the two methods found that the HCM 2010 method is not appropriate for DDIs because the movements feeding into the internal space of a DDI are significantly different from the movements of a conventional signalized interchange.

Motorists' probabilistic yielding behavior is often observed at unsignalized crosswalks, but its impedance on traffic capacity has not been thoroughly examined. The uniqueness of this problem, which is also the challenge, is that neither pedestrians nor motorists hold absolute priority because of uncertainty in yielding behavior. Therefore, from the perspective of queuing theory, understanding the service mechanism is key to determining system performance. In this study, based on explicit analyses of complete yielding scenarios, the distribution of service time for queuing vehicles is derived. Traffic capacity is then determined on the basis of mean service time for queuers. In the special case of drivers fully respecting the priority of pedestrian flow, the capacity model reduces to the classic formula with absolute priority. The solutions from the proposed capacity model precisely match the results from stochastic simulations. To facilitate practical applications, an approximation is also developed that greatly simplifies the capacity formula but still gives very close estimations to the exact solutions. This simplified formula is recommended for practical applications. The proposed capacity formula, as well as the service time distribution, can also be applied to develop performance measures such as traffic delay and queue length through use of sophisticated queuing formulas.

Human error is often considered the leading cause of motor vehicle crashes. Although some research has been conducted to assess the influence of human factors, full driver impacts on crashes are rarely analyzed, especially on a large scale in the United States. This study sought to identify the driver behavior and demographic factors that affected the likelihood of a multivehicle or single-vehicle fatal crash. A multinomial logistic regression framework, including odds ratios, was used to analyze the variables from several states. A tiered model approach was adopted to find the variable effects for combined, urban, rural, undivided urban, divided urban, undivided rural, and divided rural data sets. Each model produced different significant demographic or driver variables, many being unique or contradictory to the expected results of other research. Gender, often seen as a major contribution to crash outcome, was significant only for the full and urban models and likely not an important variable for determining crash outcomes in rural areas. Distracted driving and failing to make avoidance maneuvers were notably significant across various roadway types. Contrary to other studies, age, licensure, restraint use, and driving at certain times of the day were not found to be significant factors for either single- or multivehicle fatal crashes. Last, some previous conclusions about the number of occupants were refuted. These results may help safety analysts improve crash analysis and prevention methods.

Transportation planning plays a critical role in shaping economic health and quality of life. Transportation planning not only provides insight into the mobility of people and goods but also influences patterns of growth and economic activity. Metropolitan transportation planning is a challenging topic because of the lack of future traffic information, such as evaluations of capacity sufficiency on large metropolitan road networks with signalized intersections. The Highway Capacity Manual provides methods for the analysis of signalized intersections and urban streets for planning; however, these methods need detailed traffic volume inputs and lane configurations at signalized intersections, which are not normally available in metropolitan transportation planning. The conventional four-step planning process is widely used to forecast directional traffic volumes on road segments, but the projected volumes are not enough for the analysis of the capacity sufficiency of future road networks through existing methods. This paper discusses a proposed method developed through the integration of available transportation planning data and the characteristics of signalized intersections. The paper links traffic assignment results from conventional transportation planning procedures to the estimation of capacity sufficiency. With the proposed method, transportation planners can estimate the capacity sufficiency of future metropolitan road networks through the use of data that are readily available in transportation planning. This method will dramatically decrease the effort required for the capacity evaluation of large signalized metropolitan road networks.

Diverging diamond interchange (DDI) is a form of diamond interchange attracting growing interest from traffic engineers and researchers. Conventional control delay calculation models are not effective when applied to DDI because of the possible internal queue spillback. This paper describes a method to calculate control delay at DDI using a new analytical model. The model was first developed for control delay calculations of external movements at conventional diamond interchanges. Through the addition of a function to calculate delay of internal movements, the model was successfully used at a DDI to calculate control delay of both internal movements and external movements. Simulation studies are also conducted to validate the new model. This study can be used either as a stand-alone delay calculation model or as a supplement to existing simulation methods. The model also shows promise for use in other signalized interchange configurations with two or more adjacent intersections.

Although past research and experience have demonstrated the benefits of bus rapid transit (BRT) to the transportation system, implementation of BRT on congested local arterials having minimal or no rights-of-way remains a challenge. A feasible solution is to use the two-way left-turn lane (TWLTL) in the center of local streets for the purpose of BRT during peak hours. However, a TWLTL can be used in two ways for this purpose: directly as a median BRT lane and as a reversible general traffic lane (so that the curb lane is reserved for BRT). Without a clear understanding of the impacts of traffic characteristics, intersection layouts, and traffic signal control types on each of the alternatives, transit agencies usually have difficulty in determining the option that best serves transit vehicles and simultaneously minimizes impacts to the general traffic. This study evaluates the performance of a median BRT lane and a curb BRT lane and considers varying traffic conditions and physical configurations of the street and the intersections. The pros and cons of each alternative are also specified, in accordance with the simulation analysis.

Control delay is the primary measure for determination of the level of service of signalized intersections. The existing analytical delay models usually work well for isolated intersections, but are not as effective when applied to diamond interchanges. The limited storage space between the two closely spaced intersections of a diamond interchange may cause queue spillback from the internal link to the outside roads. This property would give rise to unrealistic delay calculations for diamond interchanges with high traffic volumes. This paper describes the development of a new analytical delay model that takes into account the effects of internal queue spillback at diamond interchanges. Simulation studies are conducted to compare the effectiveness of the proposed approach with existing methods. The study shows that for low-overlap time conditions, the proposed model tends to agree with the Synchro and VisSim simulations and is better than Elefteriadou's method, which tends to overpredict delay. For high overlaps, the Elefteriadou method, VisSim simulation, and the proposed model tend to agree, while Synchro diverges significantly by overestimating delay. The study contributes to the literature and practice by providing an open-source analytical model that can either be used as a stand-alone delay calculation model or as a supplement to the existing methods.

For an actuated signalized intersection, pedestrian calls are likely to affect the effective greens serving the vehicle movements, which affect the capacity and delay of the intersection. However, the current procedure in the Highway Capacity Manual 2000 (HCM) for analyzing actuated signalized intersections treats pedestrian crossing and timing statically, with either pedestrian calls at all signal cycles or no pedestrians at all. In reality, pedestrian arrivals are random events with some cycles having more pedestrians than others and other cycles having no pedestrian call at all. This paper demonstrates that the current procedure can lead to erroneous results in capacity and delay estimations. A model is introduced to overcome the shortcomings in the current procedure. The model takes into account the stochastic nature of pedestrian crossings and their effects. The model computes the probability of having pedestrian calls in a cycle and the corresponding capacities and delays for traffic movements. An implementation framework was developed to help practitioners conduct capacity analyses using the model. The model's results on a semiactuated signal-controlled intersection were comparable with the results from the SimTraffic microsimulation model. The effects of pedestrians on intersection capacity and delay were analyzed using the proposed model. Depending on the pedestrian volume and traffic conditions, the current HCM procedure could produce significant error, especially when the pedestrian volume is low, because it does not consider the stochastic nature of pedestrian arrivals.

Quantitative assessments are provided on two signal timing issues related to progression bandwidth maximization: the effectiveness of using lead–lag phasing and the effect of the number of signals on progression bandwidth. A computer program was developed to generate multiple signal system scenarios randomly and to provide maximum bandwidth solutions. The randomly generated signal system scenarios represented various signal systems likely to be seen in the real world. On the basis of these randomly generated system scenarios and their associated maximum bandwidth solutions, conclusions were drawn regarding the two issues. Lead–lag phasing had a significant advantage over the leading-left-turn and lagging-left-turn phasing schemes to provide maximum bandwidth solutions. At any signal in a system, lead–lag phasing was used in more than 70% of the cases compared, with about 20% for leading-left-turn phasing and 10% for lagging-left-turn phasing. The number of signals had a profound impact on bandwidth attainability, exhibiting a nonlinear decline in attainability and bandwidth with an increasing number of signals in a system.

A theoretical model is presented to quantitatively address the relation between bus detector location and effectiveness of transit signal priority (TSP) systems, supplemented by a sample model application and simulation experiments on a real-world arterial corridor. The simulation results agree very well with results from the theoretical model. The findings of this research contribute to a better understanding of the interaction of the various components of TSP systems, which can lead to better TSP design and implementation.