Lane Capacity Research Articles

Evaluation of Freeway Lane Control for Incident Management

This paper presents and discusses the results and implications of an empirical study on the impact of the lane control signals (LCS) on resulting traffic patterns in the case of freeway lane closures. Effectiveness of LCS designs is evaluated through simulation experiments. A traffic simulation laboratory developed at the Massachusetts Institute of Technology, MITSIMLab, is used for simulating traffic and the operation of the LCS. The network used for the empirical study is a part of the Central Artery/Tunnel project in Boston. The use of LCS involves a trade-off between smooth lane changing and capacity underutilization. This paper explores this trade-off through two case studies. It is found that the effectiveness of the LCS design depends on lane configurations and directional volumes. Two measures of effectiveness are analyzed: (1) Total network travel time; and O-D specific travel time. The findings will help the evaluation of Intelligent Transportation Systems deployment projects from both economic (using total travel time) and equity (using O-D specific travel times) perspectives.

Lane Capacity for an Automated Highway with Mixed Vehicle Classes

This paper develops models to calculate an upper limit on per-lane throughput for an automated highway system with mixed vehicle classes and platooned operation. The models arc analytical and based on independent arrivals among the classes. The results indicate that a mixture of vehicle classes or categories can have u significant detrimental effect on vehicle capacity. With a single entrance lane, capacity drops by more than 40% when the traffic stream moves from 100% light vehicles to a 90%/10% split between light and heavy vehicles. The capacity drop is substantially less when different classes are allowed to queue in separate lanes, but still significant (a 20% drop). It also does not appear that sorting vehicles into destination groups at the point of entry is an effective strategy to enhance exit capacity. A separate model was developed to evaluate capacity losses at the point of exit, where exiting vehicles must be separated by a minimum distance that exceeds normal intra-platoon requirements. Our results show that capacity losses are moderate (10% or less) when less than 20% of vehicles exit at any particular off-ramp.

Bus Lane Capacity Revisited

Bus use of urban roadways and past bus-capacity experience are reviewed. Field studies and bus simulation analyses were used to validate, update, and extend existing bus stop and berth capacity procedures. A 60-percent coefficient of dwell time variation was used to obtain new estimates of likely failure, and the maximum achievable capacity was based on a 25-percent failure rate. Capacity adjustment factors for skip-stop operation and right turns are derived. Service planning implications are identified. Bus lane capacities depend on how frequently the stops are placed, how long the buses dwell at each stop, traffic conditions and control systems along the bus lane or route, and whether buses can pass and overtake each other. Keeping dwell times and dwell-time variations to a minimum, providing multiple berth stops, and establishing skip-stop patterns will increase the bus and passenger capacity of bus lanes.

Discrete event modeling and simulation for flow control in an automated highway system

This paper considers a lane routing problem in an Automated Highway System (AHS). Lane routing is important because the problem of managing the traffic flow on a multilane AHS plays a major role in an urban environment. On the other hand, because analytical approaches are impossible for various, almost unpredictable traffic situations, traffic simulations are indispensible for the design and the evaluation of various control strategies of the AHS. The discrete event modeling technique can be employed to describe both macroscopic and microscopic models according to the level of abstraction. The DEVS (Discrete Event System Specification) formalism has been employed for traffic modeling and simulation of the AHS. In this paper, we propose a lane routing algorithm for vehicles entering the highway to exit successfully at their destinations while balancing the lane capacity usage of the highway (even in the face of lane-blocking incident). After that, we present a methodology for the performance evaluation of the proposed algorithm using discrete event modeling and simulation. The simulation results show that the proposed algorithm gives good performance for traffic flow control in the AHS.

Saturation Flow and Capacity of Shared Lanes: Comparative Evaluation of Estimation Methods

The operation of shared lanes, especially in the case of permitted phasing control, is still considered a complicated task and one for which many procedures and methods have been introduced. Dealt with here is the complexity when left- or right-turn movements or both are made during the unsaturated part of the opposing traffic flow. Three main methods used for estimating the shared lane's saturation flow rate and capacity values—that used in the 1985 Highway Capacity Manual (HCM) and the Australian Road Research Board (ARRB) and the Canadian methods—were analyzed and evaluated. The methodology for the comparative evaluation was based on two main approaches. In the first approach, example 1 of Chapter 9 of the HCM was used as a case study in which left through and left through right shared lanes exist in permitted phase control. In this case several computer runs were performed using the programs SIDRA and SINTRAL to estimate saturation flow and capacity values of the shared lanes opposed by different traffic volumes of the conflicting movements. Results of this approach showed that the 1985 HCM and ARRB methods are fairly close in estimating saturation flow and capacity, whereas the Canadian method gave considerably different results. Analysis showed that the sensitivity of the Canadian method to estimate saturation flow rates of the shared lane in cases of different levels of opposing traffic was an average of 10 times higher than the average of the two other methods, which were very close in their estimation of levels of opposing traffic volumes. In the second approach, field measurements of saturation flow rate values of shared lanes at different locations and operational conditions were compared with the values estimated by the three methods under the same conditions. Results, based on field observations, revealed that the Canadian method estimates of saturation flow were always lower than the measured values. At low saturation flow values, HCM estimates were slightly higher than the observed values; however, at higher saturation flow rate values. HCM estimates closely matched the observed ones. The ARRB method estimates were quite close to the observed saturation flow values under all of the different conditions considered in the field observation task.

Saturation Flow and Capacity of Shared Lanes: Comparative Evaluation of Estimation Methods

The operation of shared lanes, especially in the case of permitted phasing control, is still considered a complicated task and one for which many procedures and methods have been introduced. Dealt with here is the complexity when left- or right-turn movements or both are made during the unsaturated part of the opposing traffic flow. Three main methods used for estimating the shared lane's saturation flow rate and capacity values-that used in the 1985 Highway Capacity Manual (HCM) and the Australian Road Research Board (ARRB) and the Canadian methods-were analyzed and evaluated. The methodology for the comparative evaluation was based on two main approaches. In the first approach, example 1 of Chapter 9 of the HCM was used as a case study in which left through and left through right shared lanes exist in permitted phase control. In this case several computer runs were performed using the programs SIDRA and SINTRAL to estimate saturation flow and capacity values of the shared lanes opposed by different traf...

Automating Urban Freeways: Financial Analysis for User Groups

The automation of urban freeways is intended to reduce travel time costs, reduce direct (distance) costs, improve the safety of travel, create smoother vehicle operation, increase freeway lane capacity, and improve the comfort of travelers. This study performs a financial analysis of the first four of these effects of automation on present urban travelers by estimating the financial costs of automating vehicles (net of the savings on fuel and insurance), and calculating the break-even values for the speed increases needed to offset these costs. The analysis shows that automation will benefit heavy trucks and buses. Automation will also be cost-effective for auto commuters if large, but plausible, freeway speed increases can be obtained. Automation in the future (when nonautomated freeway speeds will be lower) will be beneficial for more users, since the break-even speed increases will be lower than their present values. The results of this analysis are very sensitive to assumptions regarding the cost of the automation devices and the changes in annual insurance payments.

Estimation of Left‐Turn Traffic Parameters

The capacity of exclusive left‐turn lanes and the passenger car equivalent of left‐turn vehicles are two parameters commonly used for the planning, design, and operation of signalized intersections. Existing methods for estimating the two parameters, however, may not have adequately accounted for the effects of signal settings and the presence of multiple opposing lanes. This study examines whether such effects are significant enough to warrant modifications of existing models. It analyzes relationships of the left‐turn movement to signal settings and the presence of one and two opposing lanes on the basis of existing understanding and computer simulation. In estimating the leftturn lane capacity, the study reveals that the use of a single formula regardless of the number of opposing lanes could lead to significant errors. It also shows that signal settings and the number of opposing lanes should be treated explicitly in estimating the passenger car equivalent.

Operation of merge junctions in a dynamically entrained automated guideway transit system

Merge junctions and intersections are the principal capacity limiters and sources of delay in automated guideway transit (AGT) networks. The capacity and delay performance of the merge junctions must be thoroughly understood before an AGT network can be designed. This paper describes the modeling and simulation of a single merge junction, having two input lanes and one output lane, operating in a quasi-synchronous network. The simulation described here differs from previous merging models permitting slots to be of variable length to accommodate trains of different lengths, and allowing unlimited maneuvering of trains (if needed). It has the unique ability to represent the operation of a special, newly devised concatenating merge, which permits trains arriving on separate input lanes to combine themselves into a longer train at the merge. Details of merge operation are demonstrated by sample diagnostic plots, and statistical results (mean values and distribution percentiles) are used to identify performance trends, measured in terms of maneuver distances and slots slipped. Increasing train lengths are shown to require merges to operate at lower traffic intensities, somewhat attenuating the lane capacity advantages produced by long trains. The variable-length, variable-phase slots demonstrate significant performance improvements relative to more conventional fixed- length slots in the simulation results. The concatenating merge is shown to permit use of relatively short maneuver distances even at very high traffic levels. In addition, the effects on merge performance of changes in the incoming train-length distributions, the compressibility of the flow of trains, the merge priority discipline, longitudinal controller performance and the use of fixed-length slots are explained. The paper concludes with a discussion of how the merge performance results can be extended to draw conclusions about performance of AGT networks, including full two-way intersections with finite-length maneuver ramps. The trade-off between merge capacity and maneuver ramp length for different incoming train lengths is shown for the two types of merge control which have been modeled (concatenating and isocapacity).

Determining the effects of scheduling on automated automobile guideway utilization

This paper develops an analytic approach for measuring the effect of vehicle scheduling and of metering methods required to balance entrance rates among stations on lane capacity utilization of automated automobile guideways. The scheduling process at each entrance is represented by a probabilistic model which generates a system of nonlinear equations. The solution of this system yields the maximum steady state input rates at the entrances to the guideway system. The method developed is applicable to network configurations in which a small number of merges must be scheduled for each vehicle before it enters the guideway. It is demonstrated by application to a corridor guideway serving a major activity center during peak inbound demand, and also it is shown how the approach may be extended to more complex networks.

Safety Considerations for a High Density Automated Vehicle System

Simulation on the digital computer was used to evaluate systems safety for high-density traffic of automatically controlled vehicles. The response of vehicle-borne and wayside emergency control systems to sudden failure of a moving vehicle and failure to detect a stalled vehicle ahead was investigated. The number and severity of the resulting collisions were used as measures of the system’s ability to cope with accidents. The capacity and safety performance of the wayside control system was found to be distinctly superior to that of the vehicle-borne system. For a desired lane capacity, the most reasonable operating speed depends primarily on vehicle length. Finally, the results indicate that significant (systems') safety benefits are obtained if vehicles are able to maintain their speedy movement for a short time after a collision.