Merging Maneuvers Research Articles

Modeling Driver Behavior and Safety on Freeway Merging Areas

Access to freeways is provided through interchanges to maintain the design concept of uninterrupted traffic flow. Therefore, provision of an appropriate entrance ramp and acceleration lane geometry that allows the entering vehicle to accelerate to a speed closer to the through lane speed is important for comfortable and safe merging maneuvers. In this paper, speed and traffic data were collected from 23 merging sites on Highway 417 located within the City of Ottawa, Canada, to study the traffic behavior at freeway merge areas. Analysis of traffic behavior showed that merging speed depends on both ramp and speed-change lane (SCL) geometrics. Lower merging speed was shown to be associated with higher collisions on the acceleration lanes. Right lane traffic volume and merging speed of entering vehicles were shown to significantly affect right lane speed along the acceleration lane. In addition, several statistically significant models were developed for the prediction of 85th percentile passenger car right lane speed, merging speed, merging distance, and acceleration on the SCL. A safety performance model was also developed to relate the total number of collisions on the acceleration SCL to the features of the merge area including the merging speed.

Evaluation of Effects of Ramp Metering on Merging Operations

Merging on motorways represents one of the most difficult and dynamic maneuvers of all driving subtasks. Merging operations at uncontrolled ramp junctions have been extensively investigated. With the rapid implementation of ramp metering techniques, many junctions are now operated under ramp metering control. Little research has been done to investigate the possible effects of ramp metering on the merging operation. The research described in this paper focuses on the comparisons of merging operations under both metered and unmetered scenarios. Time series data of the merging process were collected with the Transportation Research Group instrumented vehicle and video cameras at a tapered motorway merge site. The data included accurate vehicle speed measured by laser speedometer, leading and following headway measured by radar, and driver's eye movement derived from an in-car camera. Following a comprehensive analysis of the data, it was found that merging operations under ramp control could be significantly different from free merging. Merging maneuvers may become more difficult as a result of ramp control. The equity implications of such effects are discussed. It is believed that the understanding gained from this research will be useful for the design and operation of ramp metering.

Automated Vehicle Merging Maneuver Implementation for AHS

Summary This paper presents a real-time implementation of a general merging algorithm for automated highway systems. A merging control problem is proposed first. A real-time algorithm is then presented, which is used to calculate a smooth reference speed trajectory for the merging vehicle based on the speed of the main lane vehicle. This algorithm can also be applied even when the main lane vehicles change speed. To make the algorithm adapt to different road layouts and to increase safety, a concept of virtual platooning is proposed. It effectively shifts the time of platoon formation forward prior to the start of real merging. Aspects closely related to real-time implementation are discussed, such as the controller adopted, the use of magnetometer based distance measurement and information passing by communication from main lane vehicles. Test results are presented and briefly analyzed.

Longitudinal control algorithm for automated vehicle merging

This paper considers longitudinal control of automated vehicle merging in a mathematical approach for automated highway systems. Merging manoeuvre is defined as one vehicle in the merging lane to be inserted in the middle between two vehicles in the main lane at fixed merging point which is the intersection of those two lanes. The main lane vehicles can change speed. To achieve this, the merging vehicle must properly adjust its speed and acceleration such that it reaches the merging point at the right time with the same speed and acceleration as the main lane vehicles. This problem is a little similar to but different from the well-known missile interception problem. The longitudinal control problem is proposed for different road layouts, based on which a unified mathematical model is established. Then a new concept, virtual platooning, is introduced, which effectively avoids a two-point boundary value problem . Based on this concept, an analytic solution with mathematical proof is provided. It is also discretized as a recursive algorithm for real-time use. A dynamic real-time simulation is published at PATH website. This algorithm has been successfully implemented with automated cars.

Driver Misperception of Maneuver Opportunities and Requirements

Misperceptions of the time available or time required for various driving maneuvers under a range of conditions were studied. In the laboratory experiment, research participants viewed video scenes of a wide variety of situations and made judgments about when some event would occur (e.g., approaching vehicle reaches them) or when some maneuver would be completed (e.g., own vehicle clears roadway when making a crossing maneuver). Participants' judgments were compared with objectively determined values. A parallel on-road experiment, using similar procedures and a subset of the laboratory situations, was used to validate and benchmark the laboratory findings. The study found a general tendency for people to underestimate the time required for a maneuver. This misjudgment is safety-critical, because it may lead to decisions to accept maneuver opportunities that actually afford a smaller margin of error than the driver perceives. Such misestimates were particularly common for judgments of the time to achieve the prevailing traffic speed during turning or merging maneuvers, and for the time until one's vehicle reaches an intersection ahead. For judgments of the time available for a maneuver, people more frequently felt they had less time than they actually did, so would be less likely to attempt a maneuver. However, even for time available judgments, there were meaningful numbers of safety-critical errors. Some situations emerged as particularly meriting consideration for safety countermeasures. These included: (1) approach to signalized intersections; (2) turns onto higher-speed roadways; (3) freeway merges; (4) passing; and (5) headway maintenance. A number of promising countermeasure ideas addressing these issues were developed and recommended for formal evaluation.

Safety Models for Rural Freeway Work Zones

Construction and maintenance work zones have traditionally been hazardous locations within the highway environment. Studies show that the accident rates during road construction are generally higher than during periods of regular traffic operations. The increase in the number of crashes may be attributed to ( a) general disruption to the flowing traffic due to sudden discontinuities caused by closed lanes, ( b) improper lane merging maneuvers, ( c) the presence of heavy construction equipment within the work area, ( d) inappropriate use of traffic control devices, and ( e) poor traffic management. Research was conducted to develop regression models predicting the expected number of crashes at work zones on rural, two-lane freeway segments. Crashes on approaches to work zones and those inside the work zones were analyzed separately. For developing these models, an extensive database was obtained, including freeway data, crash data, and work zone characteristics. Negative binomial models were developed with average daily traffic, the length of the work zones, and the duration of the work projects as exposure-to-risk variables. The cost of the various work projects was found to be a good substitute for some of the exposure-to-risk variables. The investigated variables included the number of on and off ramps, both on approaches and inside the work zones; the type of work; and the intensity of the road work involved. The models may be used to evaluate beforehand the expected number of crashes on the work zone, given the work zone characteristics.

A microscopic simulation model for merging control on a dedicated-lane automated highway system

The automated highway systems (AHS) are not designed as stand-alone transportation facilities. Drivers will by necessity drive from their origins to the AHS entrance, and from the AHS exit to their final destinations. Therefore, the AHS will affect other transportation facilities, and should be integrated with all other facilities in the transportation system. Interfaces create much of the congestion for today’s transportation systems. Likewise, AHS interfaces may cause a similar problem, due to either AHS interactions with conventional systems or internal limitations from AHS merging capabilities. If these problems exist, either the AHS or the conventional road network cannot function properly. Consequently, the system as a whole may break down and the AHS could potentially become a detriment to the overall transportation system. Clearly, not enough is known about the automated merging process to determine what conditions would lead to congestion at interface points. The current macroscopic analysis techniques assume parameters that are not applicable to an AHS, and no detailed AHS merging models have been developed and validated. This paper addresses the interface problem between an AHS, and conventional roadway. Specifically, it presents a microscopic simulation model for one scenario of the automated merging maneuver. The results of the model show that for low flows and conventional highway speeds, an one-lane AHS merging section with a dedicated automated entrance ramp has many similar characteristics as a two-lane conventional freeway with or without fixed-time ramp metering. However, when the conventional freeway starts to “break down” near its capacity, the AHS continues to perform with little delay. The model also validates that the minimum ramp length requirements are a function of the merging vehicle’s speed, the mainline vehicles’ speed, and the acceleration and deceleration rates of the merging vehicle.

Microscopic Simulation Analysis for Automated Highway System Merging Process

The automated highway system (AHS) concept with dedicated lanes is not designed as a stand-alone transportation facility. Drivers will by necessity need to drive from their origins to the AHS entrance and from the AHS exit to their final destinations. Therefore, the AHS will affect other transportation facilities and will need to be integrated with all other facilities in the transportation system. Interfaces create much of the congestion for today’s transportation systems. AHS interfaces may cause similar problems, as a result of either AHS interactions with conventional systems or internal limitations from AHS merging capabilities. If these problems exist, either the AHS or the conventional road network cannot function properly. Then the system as a whole will break down, and the AHS could prove a detriment to the overall transportation system. Clearly not enough is known about the automated merging process to determine what conditions would lead to congestion at interface points. Current macroscopic techniques assume parameters that are not applicable to an AHS, and no detailed AHS merging models have been developed and validated. The AHS to conventional roadway interface problem is addressed by presenting a microscopic simulation model for one scenario of the automated merging maneuver. Some numerical results are presented for this merging scenario.

Modeling vehicle acceleration deceleration behavior during merge maneuvers

Freeway merge maneuvers are complex and may involve a lane change, continuous acceleration, possible deceleration, and finally a gap acceptance. This paper presents a methodology to model ramp vehicle acceleration-deceleration behavior at freeway entrance ramps. Primary data capturing a wide range of information were collected using video tape methods and manually reduced through image processing techniques. Ramp vehicle merging position in conjunction with freeway and ramp flow levels was analyzed for both parallel and taper type entrance ramps. Where vehicle trajectory data were available, merging positions with respect to ramp vehicle speed as well as relative speed and time gap between a ramp vehicle and freeway vehicles were examined. Results show that the merge position has a statistically insignificant effect upon individual traffic parameters. Methodology presented in this paper used the stimulus-response equation as a fundamental rule to model ramp vehicle acceleration=deceleration behavior. The timebase car-following model was modified to a nonlinear distance-base stimulus-response equation to capture the characteristics of the collected traffic data. Calibration of the proposed nonlinear model from a pilot study demonstrated satisfactory results and indicated that a time lag before ramp drivers respond to stimuli does exist. Effects of surrounding freeway vehicles on ramp vehicle acceleration-deceleration behavior were found to be significant. (A)

Modeling vehicle acceleration deceleration behavior during merge maneuvers

Modeling vehicle acceleration deceleration behavior during merge maneuvers

Safety Oriented Maneuvers for IVHS

SUMMARY The IVHS architecture of the California PATH program organizes traffic into platoons of closely spaced vehicles. Platoons are formed and broken up by two longitudinal control maneuvers, the merge and the split. A third longitudinal maneuver, decelerate to change lane, allows a platoon switching from one lane to another to enter its new lane at a safe spacing and speed. The maneuvers, particularly the merge, can be potentially hazardous. In a merge, the cars in the trail platoon are moving faster than those in the lead platoon, while the gap separating the two platoons is smaller than usual. A sudden deceleration by the lead platoon could cause a high-speed collision. If the relative velocities of the merging platoons can be constrained so that they are guaranteed never to collide at a high relative velocity, the merge can be considered safe. A maximum safe velocity for the trail platoon can be found for any given spacing and lead-platoon velocity. This paper presents a merge maneuver in which the ...

Comments on flow characteristics on acceleration lanes

This paper deals with driver behavior while travelling on and merging from acceleration lanes. Two possible groups of drivers were identified: drivers who always perform the merging maneuver during the second part of the acceleration lane, regardless of whether an appropriate gap or lag was available to them previously. Three components of the aggregated delay for the merging process were suggested and evaluated. A method of estimating the random delay and travel time on acceleration lane was proposed and evaluated against an aggregated empirical data obtained on three freeway acceleration lanes. An evaluation of the contribution of the ramp volume to the traffic delay was also performed and discussed and a graph which may be of practical use for road and traffic engineers in assessing the expected influence of various ramp and freeway volume combinations is presented.

Driver Gap Acceptance Phenomena

Results from a field study of gap acceptance characteristics of drivers executed merging maneuvers from stopped positions on side roads to main roads are presented. Gap acceptance parametrs are first estimated from the field data in an aggregated form and then for individual traffic flows observed on the main roads. It is found that flow on the main roads substantially influences the gap acceptance characteristics of drivers on the side roads. The practical implications of this influence on the accurate computations of average delays and intersection capacity, normally based on gap acceptance parameters, are also investigated. It is found that when these values are derived from gap acceptance parameters estimated from the aggregated data; they differ by as much as 20% from those derived from gap acceptance parameters estimated from the disaggregated data.

Driver Behaviour at Unlit Non-urban T-Junctions in Daylight and Darkness

Observations on driver gap acceptance at rural T-junctions without road lighting in daylight and darkness are reported. It is found that drivers crossing the near side main road stream and merging with the far side stream are more cautious in darkness when the far side gap is large. There are no significant differences between behaviour in daylight and darkness in the simple crossing and merging manoeuvres. This contrasts with earlier observations of merging at T-junctions with road lighting.

A merging control system for the urban freeway

A computer-directed traffic-control system is described which is being designed under the sponsorship of the Bureau of Public Roads. The system is intended to increase the efficiency and safety of the merging maneuver by detecting and tracking gaps in the merging lane of the freeway and by dynamically controlling ramp vehicles into these gaps. This system is also concerned with optimizing throughput in the freeway corridor by distributing traffic demand between the freeway facility and supporting network of arterial streets. The description of this system is supported by a treatment of the parametric relationships governing traffic control on freeway, and reference to the historical development of merging control systems.

Forced Merging in Traffic

A vehicle waiting at an intersection with a major road makes a merging maneuver into the mainstream traffic, thus possibly requiring oncoming traffic to slow down. This paper examines the resulting disturbance that this forced entry may create in the main stream, assumed to be a renewal process. After showing that the disturbance propagation is formally equivalent to the busy period of a related queuing model, explicit results on the length of disturbance period and the number of vehicles affected are obtained for the case of Poisson traffic. It is shown that there is some minimal main-stream headway which should be forced in order to maximize the rate at which entries can be made from the secondary road. Finally, two measures of accident potential for the merging maneuver are discussed.