Safety and Operational Impacts of Alternative Intersections

As the degradation of service at some conventional intersections increases, there becomes a need for alternative solutions other than expensive interchanges. Many alternative intersections have been proposed in the past. Under certain traffic and local conditions some solutions are more promising than other. In some cases, the conventional intersection may still be the optimal choice. The presented research focused on developing guidelines that would help planners and designers identify the most promising solutions for further analysis. This objective has been addresses in two ways. Firstly, the existing knowledge on alternative intersections has been identified. Secondly, the performance of conventional and alternative intersections under a range of Indiana traffic conditions has been evaluated using micro-simulation model - VISSIM. Although a large number of sources could be found on the research subject, the existing knowledge about performance of alternative intersection design is incomplete. Only a few designs proposed in the past have been applied at a considerable number of locations including roundabouts, median U-turns, and jag-handle intersections. Other types still await implementation. The available sources are not comprehensive and deal with conditions that might be different from Indiana. The knowledge of the safety impact of these intersections is very limited. A large number of more than 1,300 scenarios were simulated runs performed with VISSIM calibrated to Indiana conditions. The simulated types of intersections included: conventional, roundabouts, jag-handle near-sided and far-sided, median U-turns, and continuous-flow intersection. Except roundabouts, all other intersections were signalized to test their capacity limits and delay-based performance. Although the roundabouts were the lowest delays at low volumes they also reached the capacity before other did. The most promising solutions for heavy volumes are median U-turns and continuous-flow intersections. The presented research developed guidelines for using alternative intersection designs. The guidelines compile the existing knowledge found in existing publications and research reports with the simulation experiments performed with VISSIM. The guidelines are ready to use and will help planners and designers determine which intersection types are the most promising under considered conditions and should be considered in a detailed way. The simulation results have been summarized in an easy to use format of graphs

Improving the sustainability of transportation: environmental and functional benefits of right-turn by pass lanes at roundabouts

The functional performances of conventional roundabouts (single-lane and multi-lane) and innovative roundabouts (spiral, flower, C and turbo) can be improved through right-turn bypass lanes controlled by stop, yield or free-flow signs. The article presents evaluations of the emissions of air pollutants (carbon dioxide, nitrogen oxides, particle pollution (PM10 and PM2.5)), fuel consumption and construction, management, energetic and environmental costs in roundabouts without or with bypass lanes (controlled by stop, yield or free-flow). The suggested methodology has a general character and can be applied as a multi-parametric criterion for choosing road intersections, although, in the present paper, it has been employed only for a case study. For the aims of this research, we employed recent closed-form formulations to determine roundabout performances; moreover, we used the Copert IV® software to estimate air emissions in nine different types of vehicles. Numerous traffic simulations were carried out. The variation in the maximum hourly traffic Qmax and annual traffic QTOT provided the appropriate domains of the examined geometric layouts, both in functional and environmental terms and with regard to generalized costs, estimated for a 10-year period. It resulted that the introduction of right-turn bypasses in all arms of conventional roundabouts with a one ring lane and one lane at the entries (single-lane roundabouts) is the most cost-effective when the flows entering the roundabout are higher than Qmax = 2000 veh/h. Moreover, free-flow bypass lanes always provide greater capacity and lower delays than stop- or yield-signaled bypasses. However, with extremely high Qmax values, stop-controlled bypasses guarantee lower fuel consumption, while those with a yield sign lower total costs

Broadening Understanding of Roundabout Operation Analysis: Planning-Level Tools and Signal Application

In United States, roundabouts have recently emerged as an effective and efficient alternative to conventional signalized intersections for the control of traffic at junctions. This thesis includes two investigations related to the operations of roundabouts. The first investigation examines the ability of a planning-level tool (the critical sum method) to serve as an indicator variable for the results of the Highway Capacity Manual’s average delay per vehicle measure for a roundabout facility; to what extent do the results of one predict the results of the other? The critical sum method was found to accurately predict the HCM average delay per vehicle for low-volume conditions, approximately up to an average delay of 15 seconds per vehicle, but the tool was found to provide inaccurate predictions for higher volume conditions. The second investigation looks at the potential of metering signals on a roundabout facility to transfer excess capacity from a low-volume approach to an adjacent higher-volume approach. The analysis indicated positive results for the theoretical benefits of the metering signal when only placing simulated traffic on two of the approaches, but the results were not duplicated when analyzing more-realistic volume scenarios with traffic on all four approaches. Advisor: John Sangster

Upgrading of Milner and Klipfontein Road Southbound Approach to alleviate traffic issues

Introduction The population of the world is increasing at a rate of 1.07% each year. In order to accommodate this growth, quality and efficiency of services need to be improved. This includes improving the quality and efficiency of the transportation services, as a country's sustainability is reliant upon these systems. In many countries, the increase in population has congested the CBD areas, forcing people to migrate outside of the CBD. This has resulted in urban sprawl. However, the apartheid era has resulted in urban sprawl in South Africa, which left many people living along the periphery, close to the industrial areas and a distance away from the CBD. One of the biggest challenges people living outside of the CBD area experience, is a poor and unreliable public transport system. It is difficult for people to access other areas and this has increased the number of private vehicles on the road. According to a list of the top 10 countries with the highest public transport ridership, that was developed by Worldatlas.com (2019), Kenya has the highest public transport ridership. Of the total population, 63% of the people use public transport. Furthermore, the other 9 countries mentioned have ridership volumes ranging from 53% to 57%. This proves that 40% to 50% of the population in other countries is still using private vehicles above public transport and this is still considered high. Research Problem The use of private vehicles in South Africa has been on the rise. As a result, the congestion levels on the roads have increased. This has resulted in longer travel times, busier roads and an increase in road accidents as drivers spend more time travelling to and from destinations. Milner and Klipfontein Road is located in Mowbray. The intersection is surrounded by a shopping mall, a hospital, a clinic, a school and a number of other amenities. Therefore, the traffic travelling through this intersection daily is relatively high. The southbound approach of Milner and Klipfontein Road intersection, however, has the highest volume of traffic operating through the intersection daily, as it connects the M5 highway (Class 2) and Raapenberg Road (Class 3) to Klipfontein Road (Class 3). The southbound approach is a three-lane approach, of which one lane is a short turning lane. With high volumes of traffic operating through this approach daily, the road tends to get very congested, especially during the peak period. The high congestion levels have resulted in a number of other issues, which include longer travel times from Alexandra and Raapenberg Road intersection to Milner and Klipfontein Road intersection, vehicles struggling to change lanes due to limited gap length available and spilling of traffic onto Raapenberg Road. This study will, therefore, focus on finding suitable measures to assist with alleviating the congestion as well the other issues currently being experienced along the southbound approach of Milner and Klipfontein Road. Literature Review It is important to manage the transport system as this affects the economy of the country. There are two types of traffic congestion and they are either recurrent or non-recurrent. Traffic congestion is a result of having too many vehicles on the road i.e. when the demand is larger than the supply. It is, therefore, necessary to improve the quality of a road or an intersection. There are three types of intersection designs and they include: priority control, traffic signals and rotary movement control. It is important to determine the most efficient way for an intersection to operate by determining the way in which conflicting volumes will be served. To avoid undesirable delays and deal with large volumes of traffic, signalised or rotary movement is often preferred. At signalised intersections, it is important to measure the effectiveness of an intersection by evaluating its performance and the design of the signal process as this can affect the time of travel, choice of route, mode of transport and If the route will be completed. To measure the effectiveness of the signalised intersection, the following elements must be assessed: the capacity, the volume to capacity ratio, the delay and the queue length. The Level of Service (LOS) also plays an important role in determining the operation of the intersection and provides the engineer or designer with information related to the type of flow or movement at each approach and intersection. The signal design plays an important role in the operation of the intersection too. It is important to ensure that the signal timing is correct as this can affect the flow of traffic. There are different signal controls that can be implemented, and they include, semi actuated, fully actuated and fixed timing. To retime a signalised intersection is considered the most cost-effective method of redesign. Phasing of the intersection is important as this can affect the level of service of operation of the intersection. To determine which phasing is necessary, the following must be assessed: the number of road accidents, the sight distance available, the geometry of the road, speeds of vehicles, the total volumes and the operation of the intersection. Unsignalised intersections are generally not preferred as volumes and speeds differ at each approach. High accident statistics are expected. This affects the overall capacity and operation of an intersection. Rotary movement control which refers to roundabouts or traffic circles, can handle larger volumes of traffic and reduce conflicting movements. They are therefore, considered much safer than other forms of at-grade intersections. The literature review will provide more detail regarding traffic congestion, intersection design and measuring the effectiveness of an intersection. Data collection and Analysis The site investigation was undertaken on 20 February 2019 between the AM peak (6:00 and 8:30) and the PM peak (16:00 and 18:30), to determine the extent of the traffic congestion currently being experienced, along the southbound approach of Milner and Klipfontein Road. Based on the findings, the PM peak period was considered the “worst case scenario”. A traffic count was not required; as previous traffic count data was available from the City of Cape Town records. A full traffic count was completed in 2017 for the entire intersection. A travel time survey was undertaken on Wednesday, 24 July 2019 between 16:00 and 18:00. The runs were calculated at 10-minute intervals. The data obtained from this survey was validated against the traffic count survey to determine whether the data obtained from City of Cape Town records, was indeed correct. It should be noted that the travel time survey was only completed during the PM peak, as the majority of traffic travel along that approach (direction towards home), during the PM peak. It was also confirmed to be the time of day when traffic was the worst. During the process of the travel time survey, a separate survey was completed to determine the direction in which vehicles were travelling. The vehicles were monitored from where they entered the southbound approach (M5 highway or Raapenberg Road), whether they stayed in the lane they entered the approach or whether they changed lanes. This survey would determine the destination of travel. Furthermore, vehicles changing lanes, were also further monitored, to determine if they were undertaking this movement legally or illegally. A solid white line, located approximately 200m away from the signalized Milner and Klipfontein intersection, separates the two lanes entering from M5 highway and Raapenberg Road. It prevents vehicles from changing lanes when unsafe to do so. The data was captured in Sidra and Junction to assess the delay and level of service at the intersection and specifically along the southbound approach of Milner and Klipfontein Road intersection. Results and findings The southbound approach is a three-lane approach. It comprises of a left lane, which is used for straight ahead movements and left turning movements, a middle lane used for straight ahead movements and a short right turn lane. The traffic count data that was obtained from the City of Cape Town records for 2017, established that a high volume of traffic passed through Milner and Klipfontein Road intersection daily. The peak periods of the day had a variation in the volumes of traffic along each approach, except for the southbound approach, which had high volumes of traffic at both peak periods. Majority of the traffic enters from either M5 highway or Raapenberg Road and exits onto Milner or Klipfontein Road eastbound. The signal phasing at the intersection comprises 4 phases, with no priority given to the southbound approach eastbound movements, even though the highest traffic volumes travelling in that direction. This has resulted in traffic congestion and a backlog of traffic onto Raapenberg Road. As a result, vehicles take longer than necessary to reach the intersection. The travel time survey investigated vehicles travelling from Alexandra and Raapenberg Road towards Milner and Klipfontein Road. The total distance is 1.2km in length. On average, a driver driving at a speed of 60km/hr. (length of road is short, and it bends), should take 3 minutes and 20 seconds to complete this stretch of road. This total time is inclusive of the signal system. It took vehicles more than 7 minutes to complete the 1.2km distance. The road accident statistics also indicate that a high number of accidents take place at Milner and Klipfontein Road intersection. Over the latest five-year period, a total of 256 accidents took place at the intersection. Of the 256 accidents, 53% of the accidents took place along the southbound approach. Furthermore, the directional survey also established that majority of the vehicles entering from both Raapenberg and the M5 highway, were travelling eastbound along Klipfontein Road. Majority of the vehicles changing lanes, have however, done this legally (not crossing the solid line). As a result, many vehicles were merged between two lanes, obstructing oncoming vehicles. It is evident from the results that there is a need for mitigating measures. High volumes of traffic are experienced along the southbound approach, with a high portion of this traffic wanting to make use of the left lane. Limited gaps are available for changing lanes, travel time is longer than expected and spilling of traffic is occurring on Raapenberg Road all due to high congestion levels along the southbound approach. It is therefore proposed that a roundabout be constructed at Milner and Klipfontein Road intersection to reduce conflicting movements, improve the delay and LOS of the intersection and reduce the issues currently being experienced along the southbound approach. Recommendations It is recommended that a proper design be completed to understand the proper effects in terms of operation of the intersection by implementation of a roundabout. Further research should be undertaken to determine the effect of the roundabout on the AM peak

Modelação interpretativa da segurança e emissões em corredores de rotundas e semáforos

Scientific research has demonstrated that the operational, environmental and safety performance for pedestrians depend on the geometric and traffic stream characteristics of the roundabout. However, the implementation of roundabouts may result in a trade-off among capacity, environmental, and safety variables. Also, little is known about the potential impacts for traffic from the use of functionally interdependent roundabouts in series along corridors. Thus, this doctoral thesis stresses the importance of understanding in how roundabout corridors affect traffic performance, vehicular emissions and safety for vulnerable users as pedestrians. The development of a methodology capable of integrating corridor’s geometric and operational elements is a contribution of this work. The main objectives of the thesis are as follows: 1) to analyze the effect of corridor’s design features in the acceleration patterns and emissions; 2) to understand the differences in the spatial distribution of emissions between roundabouts in isolation and along corridors; 3) to compare corridors with different forms of intersections such as conventional roundabouts, turbo-roundabouts, traffic lights and stop-controlled intersections; and 4) to design corridor-specific characteristics to optimize vehicle delay, and global (carbon dioxide – CO2) and local (carbon monoxide – CO, nitrogen oxides – NOX and hydrocarbons – HC) pollutant emissions. Vehicle dynamics along with traffic and pedestrian flow data were collected from 12 corridors with conventional roundabouts located in Portugal, Spain and in the United States, 3 turbo-roundabout corridors in the Netherlands, and 1 mixed roundabout/traffic-lights/stop-controlled corridor in Portugal. Data for approximately 2,000 km of road coverage over the course of 50 h have been collected. Subsequently, a microscopic platform of traffic (VISSIM), emissions (Vehicle Specific Power – VSP) and safety (Surrogate Safety Assessment Model – SSAM) was introduced to faithful reproduce site-specific operations and to examine different alternative scenarios. The main research findings showed that the spacing between intersections influenced vehicles acceleration-deceleration patterns and emissions. In contrast, the deflection angle at the entrances (element that impacts emissions on isolated roundabouts) impacted slightly on the spatial distribution of emissions. It was also found that the optimal crosswalk locations along mid-block sections in roundabout corridor was generally controlled by spacing, especially in the case of short spacing between intersections (< 200 m). The implementation of turbo-roundabout in series along corridors increased emissions compared to conventional two-lane roundabout corridors (1-5%, depending on the pollutant). By changing the location of a roundabout or turbo-roundabout to increase spacing in relation to upstream/downstream intersection resulted in an improvement of corridor emissions. Under conditions of high through traffic and unbalanced traffic flows between main roads and minor roads, vehicles along roundabout corridors produced fewer emissions (~5%) than did vehicles along signalized corridors, but they emitted more gases (~12%) compared to a corridor with stop-controlled intersections. This research contributed to the current state-of-art by proving a full comprehension about the operational and geometric benefits and limitations of roundabout corridors. It also established correlations between geometric variable of corridors (spacing), crosswalk locations or traffic streams, and delay, and CO2, CO, NOX or HC variables. With this research, it has been demonstrated that the implementation of a given intersection form within a corridor focused on minimizing CO2 may not be translated to other variables such as CO or NOX. Therefore, the develop methodology is a decision supporting tool capable of assessing and selecting suitable traffic controls according the site-specific needs.Estudos anteriores demonstram que os desempenhos operacional, ambiental e ao nível da segurança para os peões de uma rotunda dependem das suas características geométricas e dos fluxos de tráfego e de peões. Porém, a implementação de uma rotunda pode traduzir-se numa avaliação de compromisso entre as variáveis da capacidade, emissões de poluentes e segurança. Para além disso, a informação relativa às potencialidades de rotundas interdependentes ao longo de corredores é diminuta. Assim, esta tese de doutoramento centra-se na compreensão dos impactos no desempenho do tráfego, emissões e segurança dos peões inerentes ao funcionamento de corredores de rotundas. Uma das contribuições deste trabalho é o desenvolvimento de uma metodologia capaz de avaliar as características geométricas e operacionais dos corredores de forma integrada. Os principais objetivos desta tese são: 1) analisar o impacto dos elementos geométricos dos corredores de rotundas em termos dos perfis de aceleração e das emissões; 2) investigar as principais diferenças na distribuição espacial das emissões entre rotundas isoladas e em corredores; 3) comparar os desempenhos operacional e ambiental de corredores com diferentes tipos de interseções tais como rotundas convencionais, turbo-rotundas, cruzamentos semaforizados e interseções prioritárias; e 4) dimensionar um corredor de modo a otimizar o atraso dos veículos, e emissões de poluentes globais (dióxido de carbono – CO2) e locais (monóxido de carbono – CO, óxidos de azoto – NOx e hidrocarbonetos – HC). O trabalho de monitorização experimental consistiu na recolha de dados da dinâmica do veículo, e volumes de tráfego e pedonais. Para tal, foram selecionados 12 corredores com rotundas convencionais em Portugal, Espanha e Estados Unidos da América, 3 corredores com turbo-rotundas na Holanda e ainda um corredor misto com rotundas, sinais luminosos e interseções prioritárias em Portugal. No total foram recolhidos aproximadamente 2000 km de dados da dinâmica do veículo, num total de 50 h. Foi utilizada uma plataforma de modelação microscópica de tráfego (VISSIM), emissões (Vehicle Specific Power – VSP) e segurança (Surrogate Safety Assessment Model – SSAM) de modo a replicar as condições de tráfego locais e avaliar cenários alternativos. Os resultados mostraram que o espaçamento entre interseções teve um impacto significativo nos perfis de aceleração e emissões. No entanto, tal não se verificou para o ângulo de deflexão de entrada (elemento fulcral nos níveis de emissões em rotundas isoladas), nomeadamente nos casos em que as rotundas adjacentes estavam próximas (< 200 m). A implementação de corredores de turbo-rotundas conduziu ao aumento das emissões face a um corredor convencional de rotundas com duas vias (1-5%, dependendo do poluente). A relocalização de uma rotunda ou turbo-rotunda no interior do corredor, de modo a aumentar o espaçamento em relação a uma interseção a jusante e/ou a montante, levou a uma melhoria das emissões do corredor. Conclui-se também que em condições de elevado tráfego de atravessamento e não uniformemente distribuído entre as vias principais e secundárias, os veículos ao longo de um corredor com rotundas produziram menos emissões (~5%) face a um corredor com semáforos, mas emitiram mais gases (~12%) comparativamente a um corredor de interseções prioritárias. Esta investigação contribuiu para o estado de arte através da análise detalhada dos benefícios e limitações dos corredores de rotundas tanto ao nível geométrico como ao nível operacional. Adicionalmente, estabeleceram-se várias correlações entre variáveis geométricas do corredor (espaçamento), localização das passadeiras e volume de tráfego, o atraso, e emissões de CO2, CO, NOX e HC. Demonstrou-se ainda que a implementação de uma interseção ao longo do corredor com a finalidade de minimizar o CO2 pode não resultar na melhoria de outras variáveis tais como o CO ou NOX. Esta metodologia serve como apoio à decisão e, portanto, permite avaliar o tipo de interseção mais adequado de acordo com as especificidades de cada local.Programa Doutoral em Engenharia Mecânic

Potential of Connected Fully Autonomous Vehicles in Reducing Congestion and Associated Carbon Emissions

Congestion is an ongoing problem for many urban centres worldwide (such as London), leading to excessive delays, noise and air pollution, frustrated drivers, and high energy consumption. The carbon footprint of conventional transport systems can be high as a result and transport is among the highest contributors of greenhouse gas emissions. Therefore, with the growing interest in developing connected fully autonomous vehicles (ConFAVs), there is a pressing need to consider their effects within the congested urban setting. To address this, the current research study was designed to investigate the potential for ConFAVs in providing a sustainable transport solution. During this research, a simulation model was developed, calibrated, and validated using field data collected from several sites in East London, using the graphical user interface (GUI) simulation software PTV VISSIM to simulate the proposed driving and car following behaviour, which included the platooning of these ConFAVs, to assess how they could improve the level of service of the roads. Using the new model, this research addresses the shortcomings of two other adaptations of the Wiedemann 99 car-following models by changing the ConFAV’s behaviour to be more cautious when travelling behind a human driven vehicle, and less cautious when behind another ConFAV. As little is known about the transitional period from zero autonomy to full autonomy on the already congested road network, due to the fact that these vehicles are typically tested in small numbers (often one at a time in a controlled environment), the present research study introduced ConFAVs to the simulated network gradually and in large numbers at 20% intervals (namely 0% where there are no ConFAVs, 20%, 40%, 60%, 80%, and finally 100% where all vehicles within the network were ConFAVs). The average delays and subsequent level of service for the roads within the networks were then assessed against each ConFAV penetration level. This helped understand how the network’s efficiency changes when the number of ConFAVs increases, and the potential benefits for these self-driving vehicles on congestion and the ensuing greenhouse gas emissions. The model showed that a reduction in delay of up to 100% can be achieved by introducing ConFAVs, which translates to a significant reduction in greenhouse gas emissions. This, coupled with the fact that ConFAVs are predominantly electric, points to a future sustainable road transport system. The primary purpose of this research would be to investigate the potential of ConFAVs in reducing traffic congestion and, as a result, greenhouse gas emissions

Real-time Traffic Flow Detection and Prediction Algorithm: Data-Driven Analyses on Spatio-Temporal Traffic Dynamics

Traffic flows over time and space. This spatio-temporal dependency of traffic flow should be considered and used to enhance the performance of real-time traffic detection and prediction capabilities. This characteristic has been widely studied and various applications have been developed and enhanced. During the last decade, great attention has been paid to the increases in the number of traffic data sources, the amount of data, and the data-driven analysis methods. There is still room to improve the traffic detection and prediction capabilities through studies on the emerging resources. To this end, this dissertation presents a series of studies on real-time traffic operation for highway facilities focusing on detection and prediction.First, a spatio-temporal traffic data imputation approach was studied to exploit multi-source data. Different types of kriging methods were evaluated to utilize the spatio-temporal characteristic of traffic data with respect to two factors, including missing patterns and use of secondary data. Second, a short-term traffic speed prediction algorithm was proposed that provides accurate prediction results and is scalable for a large road network analysis in real time. The proposed algorithm consists of a data dimension reduction module and a nonparametric multivariate time-series analysis module. Third, a real-time traffic queue detection algorithm was developed based on traffic fundamentals combined with a statistical pattern recognition procedure. This algorithm was designed to detect dynamic queueing conditions in a spatio-temporal domain rather than detect a queue and congestion directly from traffic flow variables. The algorithm was evaluated by using various real congested traffic flow data. Lastly, gray areas in a decision-making process based on quantifiable measures were addressed to cope with uncertainties in modeling outputs. For intersection control type selection, the gray areas were identified and visualized