Traffic engineering

Automated vehicles (AVs) are becoming more common each day as car manufacturers have started to include advanced driving assistant systems (ADAS) in trendline models. The most basic level of vehicle automation includes Adaptive Cruise Control (ACC) can disrupt and change traffic flow. The current study proposes the development of controlled experiments to obtain traffic flow properties for vehicles equipped with ACC in different scenarios. As part of this dissertation, the effects of ACC on capacity are quantified at steady state conditions, meaning cruising speeds or free flow, and at bottlenecks, where speed fluctuations occur. The effects of ACC on traffic flow properties are also assessed by the construction and study of the Fundamental Diagram. Lastly, the vehicles are submitted to less predictable deceleration scenarios that involve a leading vehicle driven in ACC mode and a leading vehicle driven manually. The reaction of ACC for these cases is documented.

Macroscopic fundamental diagram is the concept of the highest importance in traffic flow theory used for development of network-wide control strategies. Previous studies showed that so called Arterial Fundamental Diagrams (AFDs) properly depict relationships between major macroscopic traffic variables on urban arterials. Most of these studies used detector’s occupancy as a surrogate measure to represent traffic density. Nevertheless, detector’s occupancy is not very often present in the field data. More frequently, field data from arterial streets provide performance metrics measured at the stop lines of traffic signals, which represent a hybrid of flow and occupancy. When such performance measures are used in lieu of density, the outcomes of the relationships between macroscopic fundamental variables can be confusing. This study investigates appropriateness of using degree of saturation, as a representative surrogate measure of traffic density, obtained from an adaptive traffic control system that utilizes stop-line detectors, for development of AFDs.

A six-degree-of-freedom model of a vehicle was simulated over different hump profiles with a computer program and the results were verified. The resulting vibration characteristics were analyzed to calculate a discomfort index. The discomfort index considered is the equivalent root mean square acceleration specified by the proposal for the revision of ISO 2631. A parametric study was conducted to find the sensitivity of different hump and vehicular parameters on the ride comfort. The optimal hump parameters were obtained for different limiting speeds. Two field humps were simulated and modification of the humps is suggested for optimum performance.

Highway Capacity Manual (HCM) 2010 methodology for freeway operations contain procedures for calculating traffic performance measures both for undersaturated and oversaturated flow conditions. However, one of the limitations regarding oversaturated freeway weaving segments is that the HCM procedures have not been extensively calibrated based on field observations on U.S. freeways. This study validates the HCM2010 methodology for oversaturated freeway weaving segment by comparing space mean speed and density obtained from HCM procedure to those generated by a microsimulation model. A VISSIM model is extensively calibrated and validated based on NGSIM field data for the US 101 Highway. Abundance of the NGSIM data is utilized to calibrate and validate the VISSIM model. Results show that HCM methodology has significant limitations and while in some cases it can reproduce density correctly, the study finds that speeds estimated by the HCM methodology significantly differ from those observed in the field.

In the last decades, population growth has been outpacing transportation infrastructure growth, and today's transportation professionals are challenged to meet the mobility needs of an increasing population. The effectiveness of the transportation system is an essential constituent of people's daily lives as they commute between different points of interest. Studies show that at many highway junctions, congestion continues to worsen, and drivers are experiencing greater delays and higher risk exposures. Engineers have very little resources to handle this increase in population. One solution to resolve and alleviate congestion due to increasing traffic volumes and travel demands relies in implementing alternative designs. This approach will help traffic engineers determine which design will be the most appropriate for a particular location. This study compares and evaluates the Diverging Diamond Interchange (DDI), which is an unconventional design, to Partial Cloverleaf (ParClo) types A4 and B4 interchange designs by evaluating different Measure of Effectiveness (MOEs). Using microsimulation platform AIMSUN, each interchange type was evaluated for low, medium and high traffic flows. The analysis revealed that the DDI with four through lanes performed better than the ParClo A4 for unbalanced conditions, the DDI with six though lanes had similar results as the ParClo B4 for very high volumes. In terms of queue, the DDI design had a much better performance. The results from the analysis help in providing guidelines to the decision makers for selecting the best alternative in terms of performance.

The rapidly and significantly growth of the population in the United States has caused expansion of the urban areas to accommodate more residential facilities.. Thus, the demand for more efficient intersection designs is a high priority, as wasted fuel and travel time increases each year. A new method to solve the congestion issue is the creation of unconventional arterial intersection designs (UAID). The objective of this study is to compare the operational and environmental performance of three UAIDs called Left-turn Bypass, Diverging Flow, and Displaced Left-turn intersections. This study will evaluate the UAIDs in the isolated manner and then compare the intersections in a network using an existing corridor in the state of Florida. The microscopic simulation platform VISSIM v. 5.10 will be used to test different scenarios. The results indicated that the Displaced Left-turn consistently reports better results for average delay of less than 20 seconds per vehicle.

In light of the growing traffic demand and the futility of the conventional solutions, many states have been considering alternative intersection designs. Researchers have demonstrated the benefits of several unconventional intersection designs and their implementation at different sites throughout the United States and abroad have delivered significant improvement in traffic compared to the conventional intersections. A signalized and un-signalized roundabout, a Continuous Flow Intersection, and a Parallel Flow Intersection have been evaluated and compared in this research as viable alternatives to the traditional single intersection. Using micro-simulation platforms, AIMSUN 6.0 and VISSIM 5.10, models of each intersection are evaluated for low, medium, and high entrance volumes. The analysis revealed that the Roundabout performs better at low entering volumes while the Continuous flow yields better results at high volumes.