Unconventional Intersection Designs Research Articles

The Integrated optimization of intermittent lane intersection design and dynamic signal control: efficiency, safety, and fuel consumption

ABSTRACT Existing unconventional intersection designs can enhance the capacity of intersections to deal with repaid pressure on urban commuting, whereas they force vehicles to multi-stop and reorganize, resulting in safety risks and high fuel consumption. This paper proposes the Intermittent Lane Intersection (ILI) that combines the advantages of variable lane intersection and CTE (Combining the tandem control and exit lanes for left-turn control). An integrated optimization model is established to obtain the optimal geometric and signal control parameters, and a homothermic genetic algorithm is used to solve the model. Then, the application of ILI in different traffic demands of the Tianfu Third Street intersection is analyzed. Compared with the benchmark design (TI, CTE, and CTE with signal coordinated control), ILI can effectively reduce intersection delay, fuel consumption, and parking times. Additionally, ILI has great application superiority when the traffic arrival rate is [1500,1700] and the left-turn ratio is [0.40,0.60].

Evaluation of Driving Behavior and Traffic Safety at a Shifting Movements Intersection

Unconventional intersection designs have been proposed for their theoretical potential to enhance traffic safety and operation simultaneously as a result of reducing the number of conflict points and signal phases. However, this has only been achieved with a very limited range of intersection designs which have a very low number of conflict points and under certain traffic conditions. For example, restricted crossing U-turn (RCUT) intersection, which has the lowest number of conflict points among other proposed intersection designs, has operational advantages at extremely unbalanced traffic volumes. Shifting movements (SM) intersection design, which has the same number of conflict points as the RCUT intersection, has been proposed to replace the RCUT implementation at intersections with medium to high minor traffic volumes. It was proven that SM outperforms an RCUT intersection which has medium to high minor traffic volumes in average delay and throughputs. This study aimed to investigate the safety aspects of this intersection design by utilizing the driving simulator. The effectiveness of using infrastructure-to-vehicle (I2V) communication for mitigating confusion at unconventional intersections was also investigated in the study. The results indicated that RCUT and SM intersections have similar safety performance and crossing them is completed with less risk than crossing the conventional intersection. However, there is a need to improve drivers’ knowledge about the SM intersection, especially with regard to the major left-turn movement. Most participants found that using I2V communication was helpful in understanding unconventional movement patterns.

Unconventional Intersection Designs for Improving Traffic Operation Along Arterial Roads

The main objective of this paper is to evaluate the effect of implementing four Unconventional Arterial Intersection Designs (UAIDs) including median U-Turn, Superstreet, Jughandle and Single Quadrant Intersection on a major arterial road using SYNCHRO microscopic simulation software. For this purpose, Wadi Saqra Signalized Intersection on Shaker Bin Zaid major arterial road in Amman, Jordan was selected. The simulation results showed that only the Jughandle improved the intersection Level of Service (LOS) slightly, F–E. Nevertheless, the intersection delay was significantly reduced by 64.81%, 76.6%, 91.28% and 75.60% on the proposed Median U-Turn, Superstreet, Jughandle and Single Quadrant unconventional intersection design, respectively. This indicated that these UAIDs don't perform well under heavy traffic volumes. Also, since the Jughandle was the only UAID which improved the LOS on the main intersection, the operational performance of Prince Shaker Bin Zaid arterial after implementing the Jughandle at the main intersection was evaluated including the main intersection: Wadi Saqra intersection, one prior to the main intersection and one after the main intersection. It was found that the use of the Jughandle increased the average travel speed by 35% and decreased the average stopped delay by 28.68% on the arterial road. Also, this paper evaluated the current transportation system and road user's attitude towards UAIDs' implementation through a questionnaire survey. The results indicated high acceptance of UAIDs. Finally, the construction cost for each UAID type was estimated. It was found that the Jughandle had the highest construction cost due to its high acquisition cost.

Implementation of a Double Continuous Flow Intersection in Riyadh

The continuous growth of population in the capital, coupled with increased auto ownership and dependence has worsened traffic conditions on Riyadh's road network. Conventional methods to address this increased demand could be costly and insufficient. There has been greater interest in using alternative measures to improve the performance and safety characteristics on main corridors, particularly those that arrive at signalized intersections. Heavy left turning traffic at these intersections is one of the main causes for delays. Previous research has investigated several types of alternative designs termed "unconventional" arterial intersection designs that could minimize the effect of left turning traffic. This paper provides decision makers with an objective assessment on the efficiency of implementing an unconventional intersection design, the Double Continuous Flow Intersection (DCFI) configuration, to improve the operational and safety characteristics of an existing major signalized arterial intersection in Saudi Arabia. In this study, the Kingdom Hospital Intersection in Riyadh was selected, as it is one of the most congested intersections in Riyadh. Using the collected traffic data, the micro-simulation program VISSIM was used to analyze and compare the efficiency of both configurations. When compared to the existing conventional signalized intersection design, it was found that the proposed Double Continuous Flow Intersection (DCFI) unconventional intersection design decreased the average delay per vehicle by 99 seconds. The proposed Double Continuous Flow Intersection configuration also improved the Level of Service at the intersection from level F (152 sec/veh average delay) to level D (53 sec/veh average delay).

Feasibility and Operational Analysis of Unconventional Intersection Designs in Dense Urban Areas

The increasing populations in major urban areas and the complexities associated with living in those communities have fuelled the increasing demands for mobility in most of the major metropolitan areas. This high demand coupled with the limited resources and restrictions on the available right of way in urban areas has motivated transportation engineers in different agencies around the world to test and apply unconventional solutions in an attempt to improve the level of service on the major roadway network. This paper combines both theoretical and real-life operational performance comparison for the before and the after of the construction of unconventional designs on two major intersections in the city of Riyadh, KSA. It provides the results of VISSIM micro-simulation model calibration and the performance analysis for the case study intersections. In addition, it presents the comparison of the existing conditions following the actual construction of the unconventional intersection designs and it and provides a feasibility analysis for a double continuous flow intersection that was used in the study. The results have showed an improved intersection performance from the simulation models and the actual data collected for the case study intersections. In addition, they have showed that it has been feasible to apply those designs in urban areas.

Evaluation of Transit Signal Priority on Arterial Performance - A Comparison between Conventional and Unconventional Intersection Operation

Transit Signal Priority (TSP) shows capability to improve traffic operations through providing transit vehicles a higher priority to cross intersections. However, implementing TSP could impose extra delays to the adjacent traffic. Specifically, TSP imposes extra delay on turning traffic that could be solved by converting the intersections to unconventional intersection. To do so, this paper models assesses and evaluates the possibility for implementing a TSP in arterial roadway in Amman, capital of Jordan, by using real traffic data under different scenarios including conventional and unconventional intersection designs. The evaluation was done using simulation. Simulation results show that the TSP implementation reduces system travel time and improves the overall system delay. Specifically, implementing the combination of TSP with unconventional intersection design reduces corridor travel time, system delay, and queue length. Moreover, simulation results indicated that applying TSP improves individual movements travel time and delay up to 35% per vehicle.

An Alternative Design for the Intersections With Limited Traffic Lanes and Queuing Space

Existing unconventional intersection designs mainly apply to large intersections, such as the intersection of two major roads, in which there are numerous lanes on each leg and the allowed queue length is long. This paper presents a new unconventional intersection design to improve the operational efficiency of the intersections with limited traffic lanes and short distance for vehicular queuing, such as the intersections on collector roads. The new design combines the advantage of the tandem control and exit-lanes for left-turn control (CTE). An optimization model is established to maximize the capacity of the intersection under the CTE design in which the allocation of the mixed-usage lane, lane markings, and signal timings are integrated. A case study and extensive numerical analysis are conducted to evaluate the performance of the proposed model. Comparisons are made between the proposed CTE design and the other three designs, namely the tandem design, exit-lanes for left-turn design, and conventional design, under different geometric and traffic demand cases. The results show that CTE design has promising property when the left turn ratio is low to medium (<; 50%), and the queue length is limited (<; 200m).

Modelling the operation of vehicles at signalised intersections with special width approach lane based on field data

The intersection with special width approach lane (SWAL) is a newly proposed unconventional intersection design. A microscopic traffic flow model was proposed for describing the operation of vehicles at signalised intersections with SWAL. The operation process of driving on the SWAL was divided into four segments, including entering segment, transition segment, special width lane segment, and exiting segment. The car-following and lane selection behaviours of vehicles in these segments are analysed. The parameters used in the model were calibrated using the field data collected in Germany. The proposed model was realised in a time-discretised simulation. The sensitivity analyses of geometric, traffic, and signal factors were conducted. The results show that for the car-following behaviour, the passenger cars on the narrowed lanes cannot drive as efficient as on the normal width lane. For lane selection behaviour, it mainly depends on the distance between the two nearest vehicles in front of the two narrow lanes. The effectiveness of the SWAL depends on whether it is long enough to accommodate the queuing vehicles, which is a combined result of the layout design and the signal timing.

Modelling the saturation flow rate for continuous flow intersections based on field collected data.

The continuous flow intersection [CFI) is an unconventional intersection design which has been used in many cities all over the world. However, as an important parameter for the geometric design, signal timing, and operation evaluation, the saturation flow rate at CFI has not been carefully examined. In this paper, a saturation flow rate adjustment model for CFI intersections is established based on field data under the calculation framework of the HCM2016. Four movements related with CFI, namely the left-turn at the CFI approach, through movement at the CFI approach, left-turn at the pre-signal, and exit movement at the pre-signal, are discussed. The proposed model is validated and the relative error is less than 10%. The treatments to mitigate the negative impact on the saturation flow rate at the CFI are also recommended. The results show the saturation flow rate of the first three movements are decreased due to the CFI control. For the left-turn, through movement, and left-turn at the pre-signal, the degree of the reduction of the saturation flow rate are mainly related to the heavy vehicle ratio, the proportion of lane changing vehicles, and the length of displaced left-turn lanes, respectively.

Saturation Flow Models of Exit Lanes for Left-Turn Intersections

AbstractA newly proposed unconventional intersection design, exit lanes for left-turn (EFL) intersections, has been demonstrated to be very promising for capacity improvement. However, the differen...

Optimal Timing Model for Continuous-Flow Intersection

Continuous flow intersection (CFI) is one of the most important unconventional intersection design (UID) modes. This kind of intersection transfers left-turn movements to secondary intersections to obtain a 2-phase signal control scheme at main intersection, so the traffic efficiency at main intersection is greatly improved. To further exploit the traffic efficiency of continuous flow intersection, the coordination of main and secondary intersection signals is theoretically studied, and an optimal timing model for general use is proposed. The optimal timing model can effectively coordinate primary and secondary intersection signal timings and produce the most effective signal timing schemes for main and secondary intersections to great extent reduce vehicle delay and improve intersection capacity, and can ensure reliable operation of primary and secondary intersections in practical application. Based on the delay compositions and their characteristics of CFI, the delay and queue process evolution with the signal offset of main and secondary intersections and the corresponding scene are analysed. Then, the method for solving optimal offset between main and secondary intersections is given by optimal analysis to simplify the solving procedure of the model. In the end, an arterial intersection in Nanchang is studied as a case of how to apply the CFI channelization design to a conventional intersection and how to apply the optimal timing model to generate the coordinate timing scheme, and the micro traffic simulation is used to evaluate the traffic benefit. The result shows that (1) the optimal timing scheme can effectively reduce delays and queues and improve the intersection capacity; (2) the model calculation agrees well with the simulation result, which proves that the signal timing model is effective and accurate.

The Possibility for Implementing the Superstreet Unconventional Intersection Design in Jordan

This paper provides policy makers with an objective assessment on the possibility for implementing an unconventional arterial intersection design, the Superstreet, for improving safety and operational characteristics for an existing signalized intersection. The signalized intersection selected for analysis was Tabarbour, located in Amman, Jordan. Tabarbour intersection is considered one of the most significant signalized intersections in Amman. The intersection currently suffers from the following problems: long queues, delays and excessive emissions. SYNCHRO microscopic simulation software was used for signal optimization of the current conventional intersection. VISSIM microscopic simulation software was used to analyze and compare the Superstreet design to the conventional design. It was found that the proposed Superstreet reduced the average delay per vehicle by up to 87% and reduced the maximum queue length by almost 97%. This resulted in improving the level of service from F to C. Finally, five year future traffic demand analysis was performed; it was found that the Superstreet design didn’t perform as expected under heavy traffic volume.

Analysis of saturation flow rate at tandem intersections using field data

A tandem intersection is an unconventional intersection design that possesses the important property of increasing the traffic capacity using pre-signals and sorting areas. However, the operational efficiency of the lanes in the sorting areas may be affected by driver unfamiliarity and confusion. This study evaluates the effect of the tandem control on the saturation flow rate using field data. Statistical analyses were conducted to identify the difference in the saturation flow rate of the approach lanes when the tandem control was open and closed. A saturation flow rate adjustment model for tandem control was established in accordance with three factors: unequal distribution of traffic, red light violations at the pre-signal, and incomplete discharge of vehicles at the sorting area. The results indicate that the tandem control decreases the saturation flow rate of the approach lanes in the sorting area. Most of the observed reductions are caused by the first factor, i.e. the unequal distribution of traffic. The other two factors, red light violations and incomplete discharge, can be controlled by using appropriate traffic signs, markings, and signal timing design.

Signal Timing Optimization of an Isolated Intersection Considering the Allocation of Exit Lanes

Unconventional intersection designs have been used to increase the capacity of intersections that are over-saturated under conventional ones. However, existing unconventional designs typically require extra land space and their effectiveness often depends on drivers' familiarity with the uncommon operating rules. To overcome these challenges, we propose a new unconventional design, where movements that are mutually incompatible under the conventional design can be made compatible of each other by allocating exit lanes to them appropriately, thereby creating opportunities for capacity improvement. We develop a lane-based capacity optimization model that incorporates the allocation of exit lanes as decision variables. The model is formulated as a Binary Mixed Integer Linear Programming problem, which can be efficiently solved by standard branch-and-bound algorithms. Numerical experiments show that significant capacity improvement can be obtained under our design. Besides proposing a new unconventional design, we also contribute to the literature of lane-based signal optimization methods by providing a novel linear formulation for the latest, yet nonlinear, model described in Wong and Heydecker (2011). This improvement is methodologically beneficial as linear models are computationally much more convenient than nonlinear models.

Safety evaluation of intersections with dynamic use of exit-lanes for left-turn using field data

As a newly proposed unconventional intersection design, the exit-lanes for left-turn (EFL) intersection is found to be effective in increasing the intersection capacity with high level of application flexibility, especially under heavy left-turn traffic conditions. However, the operational safety of EFL is of most concern to the authority prior to its implementation. This paper evaluates the safety of the EFL intersections by studying the behavior of left-turn maneuvers using field data collected at 7 locations in China. A total of 22830 left-turn vehicles were captured, in which 9793 vehicles turned left using the mixed-usage area. Four potential safety problems, including the red-light violations, head-on collision risks, trapped vehicles, and rear-end crash risks, were discussed. Statistical analyses were carried out to compare the safety risk between the EFL intersection and the conventional one. Results indicate that the safety problems of EFL intersections mainly lie in higher percentages in red-light violations at the pre-signal (1.83% higher), wrong-way violation problems during the peak hours (the violation rate reaches up to 11.07%), and the lower travel speeds in the mixed-usage area (18.75% lower). Such risks can be counteracted, however, by providing more guiding information, installing cameras to investigate and punish violation maneuvers, and adjusting design parameter values for layout design and signal timing, respectively.

A continuous-flow-intersection-lite design and traffic control for oversaturated bottleneck intersections

Oversaturation has become a severe problem for urban intersections, especially the bottleneck intersections that cause queue spillover and network gridlock. Further improvement of oversaturated arterial traffic using traditional mitigation strategies, which aim to improve intersection capacity by merely adjusting signal control parameters, becomes challenging since exiting strategies may (or already) have reached their “theoretical” limits of optimum. Under such circumstance, several novel unconventional intersection designs, including the well-recognized continuous flow intersection (CFI) design, are originated to improve the capacity at bottleneck intersections. However, the requirement of installing extra sub-intersections in a CFI design would increase vehicular stops and, more critically, is unacceptable in tight urban areas with closed spaced intersections. To address these issues, this research proposes a simplified continuous flow intersection (called CFI-Lite) design that is ideal for arterials with short links. It benefits from the CFI concept to enable simultaneous move of left-turn and through traffic at bottleneck intersections, but does not need installation of sub-intersections. Instead, the upstream intersection is utilized to allocate left-turn traffic to the displaced left-turn lane. It is found that the CFI-Lite design performs superiorly to the conventional design and regular CFI design in terms of bottleneck capacity. Pareto capacity improvement for every traffic stream in an arterial system can be achieved under effortless conditions. Case study using data collected at Foothill Blvd in Los Angeles, CA, shows that the new design is beneficial in more than 90% of the 408 studied cycles. The testing also shows that the average improvements of green bandwidths for the synchronized phases are significant.

Signal design for displaced left-turn intersection using Monte Carlo method

Unconventional intersection designs have been receiving increased consideration at intersections that serve high traffic demands. Although operational performance of unconventional intersections has been evaluated in a number of studies, little research has been conducted regarding methodologies to obtain optimal signal timings for them. Several studies have reported that commercial signal timing packages have not been able to be utilized to develop optimal signal timings due to the unique design features of the unconventional intersections. In this paper a Monte Carlo simulation method to minimize intersection delay is described as well as a bandwidth maximization method for a Displaced Left-Turn (DLT) intersection, one of the most popular unconventional intersections. The proposed method is applied to a representative intersection design for two different traffic demand scenarios. It is seen that the two optimization approaches may result in different optimal solutions and the Monte Carlo simulation is able to provide near-optimum parameter selection ranges for the given traffic demands. Also, it is found that the Monte Carlo method is sufficiently flexible to provide intersection-tailored solutions with intersection specific design parameters.

Evaluation of Triangabout as Alternative for Intersection with Nonthrough Arterial Movement

At the majority of signalized intersections along an arterial, the mainline movement passes straight through the intersection. At four-leg intersections where the major arterial movement is not a through movement (i.e., an L-shaped corridor vertex), the intersection can sometimes experience more congestion than adjacent intersections along the corridor because the two minor approaches, which are adjacent conflicting movements, must be served in a split-phase fashion. A new, unconventional intersection design, referred to as a “triangabout,” is proposed to improve mobility and enhance safety for such intersections. The two approaches that are the mainline arterial form two legs of a triangle and a new diagonal section of roadway connecting those two legs is the hypotenuse. Flow within the triangabout is one-way counterclockwise, similar to a roundabout. The three intersections at the vertices of the triangle are signalized to provide a dedicated right-of-way. A case study is performed for the intersection of Van Voorhis Road and Chestnut Ridge Road in Morgantown, West Virginia, along the WV-705 corridor. Simulation results from VISSIM show that the triangabout design can reduce travel delay by 50% compared with the existing configuration. Also, the number of conflict points compared with a conventional intersection is reduced by 34%. There are a number of qualitative benefits of this design compared with conventional intersections at an L-shaped corridor vertex.

Analysis of unconventional arterial intersection designs (UAIDs): state-of-the-art methodologies and future research directions

The use of unconventional arterial intersection designs (UAIDs) has been advocated as a novel solution that can efficiently enhance the operational and safety performance of at-grade signalised intersections. Several studies suggest that UAIDs can lead to higher capacity, lower delays and fewer crashes. As well, these ‘non-traditional’ designs are cost-effective as only minor geometric modifications are usually required. In recent years, there has been considerable valuable research work undertaken to discuss methods for analysing the operational and safety performance of UAIDs. Nevertheless, these studies are sparse and no collective effort is currently available to identify the basic principles of the analysis of UAIDs and to determine gaps within the current methods. This article presents an in-depth literature review of existing methods of analysing the operational and the safety performance of unconventional intersection designs. These methods differ in principle issues, such as objective and scope, and in technical issues, such as experimental design, analysis tools and evaluation measures. Based on the reviewed methods, areas that need further research and improvements are identified.

Barriers to Implementation of Unconventional Intersection Designs

Numerous unconventional intersection and interchange designs (UIIDs) exist with documented benefits, but implementation is slow. There are public, professional, and political barriers. Numerous papers explain the benefits of one design or compare designs, but few identify common barriers. This research surveyed transportation professionals to identify the barriers inhibiting the implementation of promising UIIDs and to identify solutions. Engineers believe that the public’s main concerns are driver confusion and fear of the unknown. Survey results highlight education as important, and that public opinion generally improves once an UIID is constructed. Professionals and politicians want proof that a design will work and are reluctant to try nonstandard designs. An important political consideration is cost, but the life cycle cost can be competitive. We need guidelines to assist designers, increased focus on alternatives analysis, and inclusion of UIIDs in planning. This will make the designs more familiar to the public and decrease opposition.