Operational Analysis of the Flipped Left Diamond Interchange Design

Interchanges are critical elements of modern transportation networks. A new design called the Flipped Left-Turn Diamond Interchange (FLDI) has been proposed to enhance efficiency and increase the capacity of traditional diamond interchanges. The FLDI design features left-turn lanes in opposing directions, eliminating conflicts between opposing left-turn movements. One of the key benefits of FLDI is its ability to be easily implemented within the existing right of way, without the need for major construction or the elimination of direct connectivity between frontage roads or access to corner properties, unlike other innovative designs such as the Diverging Diamond Interchange (DDI) and Continuous Flow Intersections (CFI). The primary objective of this study is to investigate whether implementing the FLDI design can reduce vehicle delay, queue length, and the number of stops compared to a conventional diamond interchange. Additionally, the study aims to determine the applicable conditions for implementing the FLDI design and develop signal timing strategies to optimize its performance. To achieve this objective, various data types, including turning movement counts, travel time, and signal timing data, were collected at a diamond interchange in Fort Worth, Texas. Microscopic traffic models were then developed for the existing condition (conventional diamond interchange) and the FLDI design in PTV VISSIM. The base model was calibrated based on travel time and traffic count data to ensure that the developed model accurately represents the existing condition. In addition, a new signal timing plan was developed for FLDI to improve operational performance at the interchange. This phasing plan provides the traffic progression time between the two intersections at the diamond interchange and prevents the green starvation problem at the downstream intersection. The study found that FLDI is more robust than the conventional diamond interchange when subjected to heavy traffic conditions. The traffic simulation results showed that the implementation of FLDI may reduce vehicle delay, queue length, and the number of stops at the entire interchange by 30% to 40%, 30% to 50%, and 30%, respectively. The main reason for this improvement is that FLDI can allow more traffic flows to move simultaneously in one phase. Furthermore, it was found that the performance of FLDI was almost the same as the conventional diamond interchange when the interchange experiences low and medium traffic. To address traffic safety concerns, it is recommended that FLDI have a dedicated U-turn lane between the frontage roads. This study proposes that FLDI can be a viable design option for diamond interchanges with heavy traffic volume conditions due to its ability to reduce travel delays, stops, and queue lengths. Its feasibility should be evaluated carefully based on local traffic conditions and engineering judgment before implementation. This study can assist traffic engineers and transportation planners in the operational analysis of diamond interchanges

An Innovative Signal Phasing Scheme for Diverging Diamond Interchanges

This thesis presents the development of an innovative signal phasing scheme for Diverging Diamond Interchanges (DDIs) through a case study of the diverging diamond interchange at Moana Lane & Interstate-580 freeway (Moana Ln & I-580 DDI) in Reno, Nevada.An innovative phasing scheme was derived and compared against four DDI phasing schemes that had been identified through field deployment or prior publications, and subsequently evaluated in this research effort categorized by two, three, and four critical movements. The strengths and weaknesses of using phase overlaps and dummy phases were outlined to achieve operational objectives regarding if internal stops and queueing were allowed and if signal control lost time can be minimized.The effectiveness of the developed signal phasing schemes was evaluated based on a case study where Moana Ln & I-580 DDI was used as an example. A set of 30-minute vehicle volume counts were collected during the both AM and PM peak hours and interpolated into full-hour traffic counts which were used for the analysis. As the PM peak counts were substantially greater than the AM peak counts, the analysis only evaluated the PM operations. The PM peak operations were primarily studied using a VISSIM model that was built and calibrated according to real-world geometry and traffic operations.Given a fully actuated PM timing plan implemented as the base scenario, comparative phasing schemes were tested under various conditions. Modified Webster’s equations were employed to produce phase splits for the phasing schemes with trailing overlaps. Split derivation was found to share characteristics with typical diamond interchanges, though the phasing varied. The phasing schemes with their optimized splits were then modeled in VISSIM simulation. A comparative evaluation was performed based on the simulated measures of effectiveness (MOEs), such as delay time, stop delay time, and average number of stops. Simulation results indicated that the proposed phasing scheme with internal stops could allow for reductions in traffic delay as compared to other schemes. The field condition of Moana Ln & I-580 DDI do not meet all requirements for implementing the optimal proposed phasing schemes, such as the absence of detection in interior lanes that eliminate internal stops or rewiring of the controller. Thus, the recommendation of the proposed phasing scheme only applies to certain conditions, such as new or renovated interchanges, which have been presented in the thesis. The findings presented in the thesis would facilitate transportation agencies making an informed decision on the development of traffic signal timing for a DDI for use in the field or for design alternative analysis

Neurofuzzy control to address stochastic variation in actuated-coordinated systems at closely-spaced intersections

This dissertation documents a method of addressing stochastic variation at closely-spaced signalized intersections using neurofuzzy control. Developed on the conventional actuated-coordinated control system, the neurofuzzy traffic signal control keeps the advantage of the conventional control system. Beyond this, the neurofuzzy signal control coordinates the coordinated phase with one of the non-coordinated phases with no reduction of the green band assigned to the coordination along the arterial, reduces variations of traffic signal times in the cycle caused by early return to green , hence, makes more sufficient utilization of green time at closely-spaced intersections. The neurofuzzy signal control system manages a non-coordinated movement in order to manage queue spillbacks and variations of signal timings.Specifically, the neurofuzzy controller establishes a secondary coordination between the upstream coordinated phase (through phase) and the downstream non-coordinated phase (left turn phase) based on real-time traffic demand. Under the fuzzy logic signal control, the traffic from the upstream intersection can arrive and join the queue at the downstream left turn lane and be served, and hence, less possibly be blocked on the downstream left turn lane. This secondary coordination favors left turn progression and, hence, reduces the queue spillbacks. The fuzzy logic method overcomes the natural disadvantage of currently widely used actuated-coordinated traffic signal control in that the fuzzy logic method could coordinate a coordinated movement with a non-coordinated movement. The experiment was conducted and evaluated using a simulation model created using the microscopic simulation program - VISSIM.The neurofuzzy control algorithm was coded with MATLAB which interacts with the traffic simulation model via VISSIM\u27s COM interface. The membership functions in the neurofuzzy signal control system were calibrated using reinforcement learning to further the performance. Comparisons were made between the trained neurofuzzy control, the untrained neurofuzzy control, and the conventional actuated-coordinated control under five different traffic volumes. The simulation results indicated that the trained neurofuzzy signal control outperformed the other two for each traffic case. Comparing to the conventional actuated-coordinated control, the trained neurofuzzy signal control reduced the average delay by 7% and the average number of stops by 6% under the original traffic volume; as traffic volume increasing to 120%, the reductions doubled

AN INTEGRATED CONTROL MODEL FOR FREEWAY INTERCHANGES

This dissertation proposes an integrated control framework to deal with traffic congestion at freeway interchanges. In the neighborhood of freeway interchanges, there are six potential problems that could cause severe congestion, namely lane-blockage, link-blockage, green time starvation, on-ramp queue spillback to the upstream arterial, off-ramp queue spillback to the upstream freeway segments, and freeway mainline queue spillback to the upstream interchange. The congestion problem around freeway interchanges cannot be solved separately either on the freeways or on the arterials side. To eliminate this congestion, we should balance the delays of freeways and arterials and improve the overall system performance instead of individual subsystem performance. This dissertation proposes an integrated framework which handles interchange congestion according to its severity level with different models. These models can generate effective control strategies to achieve near optimal system performance by balancing the freeway and arterial delays. The following key contributions were made in this dissertation: 1. Formulated the lane-blockage problem between the movements of an arterial intersection approach as an linear program with the proposed sub-cell concept, and proposed an arterial signal optimization model under oversaturated traffic conditions; 2. Formulated the traffic dynamics of a freeway segment with cell-transmission concept, while considering the exit queue effects on its neighboring through lane traffic with the proposed capacity model, which is able to take the lateral friction into account; 3. Developed an integrated control model for multiple freeway interchanges, which can capture the off-ramp spillback, freeway mainline spillback, and arterial lane and link blockage simultaneously; 4. Explored the effectiveness of different solution algorithms (GA, SA, and SA-GA) for the proposed integrated control models, and conducted a statistical goodness check for the proposed algorithms, which has demonstrated the advantages of the proposed model; 5. Conducted intensive numerical experiments for the proposed control models, and compared the performance of the optimized signal timings from the proposed models with those from Transyt-7F by CORSIM simulations. These comparisons have demonstrated the advantages of the proposed models, especially under oversaturated traffic conditions

Integrated and adaptive traffic signal control for diamond interchange : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Mechatronics Engineering at Massey University, Albany, New Zealand

New dynamic signal control methods such as fuzzy logic and artificial intelligence developed recently mainly focused on isolated intersection. Adaptive signal control based on fuzzy logic control (FLC) determines the duration and sequence that traffic signal should stay in a certain state, before switching to the next state (Trabia et al. 1999, Pham 2013). The amount of arriving and waiting vehicles are quantized into fuzzy variables and fuzzy rules are used to determine if the duration of the current state should be extended. The fuzzy logic controller showed to be more flexible than fixed controllers and vehicle actuated controllers, allowing traffic to flow more smoothly. The FLC does not possess the ability to handle various uncertainties especially in real world traffic control. Therefore it is not best suited for stochastic nature problems such as traffic signal timing optimization. However, probabilistic logic is the best choice to handle the uncertainties containing both stochastic and fuzzy features (Pappis and Mamdani 1977) Probabilistic fuzzy logic control is developed for the signalised control of a diamond interchange, where the signal phasing, green time extension and ramp metering are decided in response to real time traffic conditions, which aim at improving traffic flows on surface streets and highways. The probabilistic fuzzy logic for diamond interchange (PFLDI) comprises three modules: probabilistic fuzzy phase timing (PFPT) that controls the green time extension process of the current running phase, phase selection (PSL) which decides the next phase based on the pre-setup phase logic by the local transport authority and, probabilistic fuzzy ramp-metering (PFRM) that determines on-ramp metering rate based on traffic conditions of the arterial streets and highways. We used Advanced Interactive Microscopic Simulator for Urban and Non-Urban Network (AIMSUN) software for diamond interchange modeling and performance measure of effectiveness for the PFLDI algorithm. PFLDI was compared with actuated diamond interchange (ADI) control based on ALINEA algorithm and conventional fuzzy logic diamond interchange algorithm (FLDI). Simulation results show that the PFLDI surpasses the traffic actuated and conventional fuzzy models with lower System Total Travel Time, Average Delay and improvements in Downstream Average Speed and Downstream Average Delay. On the other hand, little attention has been given in recent years to the delays experienced by cyclists in urban transport networks. When planning changes to traffic signals or making other network changes, the value of time for cycling trips is rarely considered. The traditional approach to road management has been to only focus on improving the carrying capacity relating to vehicles, with an emphasis on maximising the speed and volume of motorised traffic moving around the network. The problem of cyclist delay has been compounded by the fact that the travel time for cyclists have been lower than those for vehicles, which affects benefit–cost ratios and effectively provides a disincentive to invest in cycling issues compared with other modes. The issue has also been influenced by the way in which traffic signals have been set up and operated. Because the primary stresses on an intersection tend to occur during vehicle (commuter) peaks in the morning and afternoon, intersections tend to be set up and coordinated to allow maximum flow during these peaks. The result is that during off-peak periods there is often spare capacity that is underutilised. Phasing and timings set up for peaks may not provide the optimum benefits during off-peak times. This is particularly important to cyclists during lunch-time peaks, when vehicle volumes are low and cyclist volumes are high. Cyclists can end up waiting long periods of time as a result of poor signal phasing, rather than due to the demands of other road users being placed on the network. The outcome of this study will not only reduce the traffic congestion during peak hours but also improve the cyclists’ safety at a typical diamond interchange

Evaluation Of Milwaukee B And Synchronized As New Service Interchange Designs

These days, alternative interchanges are attracting the attention of transportation agencies and designers more than ever. Most of the existing interchanges in the U.S were built in the 1950s and 1960s when traffic volume was much lower, and the type of vehicles and driving habits were completely different. Moreover, the knowledge of highway design and safety is more developed now, and this provides an appropriate situation to increase the efficiency of interchanges regarding traffic operation and safety using alternative interchanges. This research evaluated the performance of two proposed service interchange designs—the synchronized design which is related to a superstreet intersection and the Milwaukee B design that is related to a parclo B design--as possible substitutes where existing interchanges are failing. Over 1700 simulation tests modeled the traffic operation, pedestrian performance, and safety of six different interchanges (two new and four existing interchanges) in different conditions of traffic volume, traffic distribution, left/right turning volume ratios, and heavy vehicle percentage. Then, a cost estimation and validation procedure were also conducted to complete the analysis. Overall, the Milwaukee B showed the best traffic operation among all the interchanges. The synchronized interchange looks promising as a substitute for a diamond interchange with dominant through traffic. The synchronized and diverging diamond interchanges (DDI) showed almost the same results while handling moderate levels of turning volume; however, the synchronized performed better than the DDI in low turning volumes while the DDI can be a better choice in high turning ratios. Regarding the safety, the DDI and Milwaukee B were the safest designs based on observed conflicting interactions in the simulation models; however, the DDI did not seem as reliable from the viewpoint of unusual maneuvers and wrong way movements. The new synchronized interchange, the parclo B, and the Milwaukee A (an existing interchange in Milwaukee, WI) showed the same rate of conflicts. The synchronized interchange may be advantageous because it was estimated to reduce the severity of crashes due to fewer crossing conflicts, a lower speed of conflicts, and a higher time to collision. The results of the pedestrian analysis indicated that a relatively safe condition is expected for pedestrians in the proposed new designs in comparison to the existing interchanges. The DDI, one of the most popular alternative interchanges, showed the worst performance in all the aspects of the pedestrian analysis

Evaluating Pedestrian Service of the New Super Diverging Diamond Interchange on Three Case Study Sites in Denver, Colorado

Ensuring safe and comfortable conditions for pedestrians necessitates specific strategies at intersections and service interchanges where traffic and pedestrians interact in complex ways with other modes of transportation. This study aims to investigate pedestrian performance at the new Super Diverging Diamond Interchange (Super DDI) using real-world locations (i.e., I-225 and Mississippi Ave, I-25 and 120th Ave, and I-25 and Hampden Ave in Denver, Colorado). Three alternative designs, typical DDI, and two versions of Super DDI were considered to make a reasonable comparison with the existing Conventional Diamond Interchange (CDI). A comprehensive series of simulation models (192 scenarios with 960 runs) were tested using VISSIM and Synchro to analyze pedestrian operation (travel time, number of stops, and waiting time) in various traffic and pedestrian distributions. As one of the primary contributions in this paper, pedestrian safety was evaluated based on a surrogate performance measure called design flag, introduced by the new National Cooperative Highway Research Program (NCHRP-948) guideline. The results indicated that the proposed new Super DDI designs are relatively safe when compared with CDI and DDI. For example, a pedestrian analysis of one of the most popular alternative interchanges, DDI, showed potential for unsafe pedestrian conditions in all aspects