General Purpose Lanes Research Articles

An optimal algorithm for automated truck freight transportation via lane reservation strategy

This paper investigates an automated truck transportation problem via lane reservation strategy. The focus of the problem is to design lane reservation based paths for time-efficient transportation. The lane reservation strategy requires to select some existing general-purpose lanes from a transportation network and convert them to automated truck lanes in order to ensure the time-guaranteed transportation. However, such conversion may cause traffic impact such as increase of travel time on adjacent lanes due to the disallowing use of the automated truck lanes by the general-purpose vehicles. Thus, the problem aims at optimally designing the time-efficient truck paths while minimizing the impact on the overall network performance. The considered problem is formulated as an integer linear program and is demonstrated NP-hard. To solve it, an optimal algorithm based on the cut-and-solve method is proposed. Numerical computational results of randomly generated instances show the efficiency of the proposed algorithm compared with a referenced software package CPLEX 12.1.

Cross-Section Designs for the Safety Performance of Buffer-Separated High-Occupancy Vehicle Lanes

This study proposes a methodology to determine the optimal cross-sectional design of a high-occupancy vehicle (HOV) facility for safety performance by evaluating the effects of each relevant design element on safety and tradeoffs among multiple design variables. This aspect of geometric design is critical because it is often difficult to acquire sufficient right-of-way for retrofitting HOV lanes to existing freeway systems with recommended cross-sectional design. Detailed collision data of concurrent-flow buffer-separated HOV lanes, along with their geometric features and traffic flow data, were analyzed to establish collision predictive models by injury types for HOV and the adjacent general-purpose lanes. These models were used to determine the set of cross-sectional design elements that minimizes the expected collision occurrences. As a case study, a real freeway corridor where a conversion from contiguous to buffer-separated types was recently completed was selected to demonstrate the applicability of the proposed method. The evaluation through this case study shows that the proposed methodology is useful in determining the cross-sectional design of HOV facilities for safety based on selective use of available geometric space.

Incident-Induced Diversion Behavior: Existence, Magnitude, and Contributing Factors

AbstractThe need to understand the effects of diverting traffic is emphasized by growing congestion and delays. This paper examines incident-induced diversion behavior by using loop-detector data and incident records on a freeway in Virginia. This work diverges from previous studies by (1) addressing both existence of diversion and its magnitude, (2) relying on field data rather than surveys, and (3) statistically relating diversion behavior and magnitude to quantifiable incident characteristics and traffic conditions. A dynamic programming-based procedure is used to identify diversions by isolating transient level shifts, and the diversions are associated with incident and traffic characteristics and variable message sign (VMS) displays through a binary logit model. The magnitude of the diversion is statistically related to traffic conditions via a linear regression model. The models indicate that the probability of triggering a diversion increases when an incident lasts longer, more general-purpose lane...

Quantifying Cross-Weave Impact on Capacity Reduction for Freeway Facilities with Managed Lanes

With the increasing concerns about environmental effects and the sustainability of roadway capacity expansion, transportation agencies are seeking alternative solutions to mitigate congestion. Managed lanes (MLs) promote person throughput on freeways and manage congestion through improving efficiency. The ML concept therefore has been gaining popularity in past decades. However, the lack of guidance on evaluating the performance of the ML facility poses challenges for agencies wanting to design and implement the strategy effectively. Many MLs are designed to be left-lane concurrent; vehicles entering the freeway from general purpose (GP) lane on-ramps need to cross weave over multiple GP lanes to access the ML. These weaving vehicles will have a negative effect on the operating performance of the parallel GP lanes. This paper investigates this cross-weaving effect as a function of different roadway geometric configurations as well as traffic conditions. A microscopic simulation model was built and calibrated on the basis of video data collected along I-635 in Dallas, Texas. Multiple scenarios were tested to explore the effect of the following parameters: number of GP lanes, cross-weave demand, and cross-weaving length. A set of capacity adjustment factors was determined to account for this effect as a function of those parameters. Results showed that the capacity-reducing effect was higher with a reduction in cross-weaving length, an increase in the number of GP lanes, or a rise in cross-weave demand volumes. The results are important in evaluating the operational performance of freeway segments in the presence of concurrent GP lanes and MLs in a Highway Capacity Manual context.

Modeling Traffic Flow Dynamics on Managed Lane Facility

With the increasing attention paid to environmental effects and sustainable infrastructure, transportation agencies are now seeking more cost-effective and environmentally friendly countermeasures against traffic congestion than the traditional roadway expansion. Managed lane (ML) systems, as an innovative strategy for managing the roadway conditions in real time, have been gaining increasing popularity in the recent decade. However, the unique characteristics of ML facilities, such as the frictional effects between general purpose lanes (GPLs) and their adjacent ML, are not well studied and modeled. This paper investigates the interaction between GPLs and MLs, as buffer-separated ML facilities are readily affected by congestion in the adjacent GPLs. The frictional effect is quantified through development of speed–flow curves for the ML facility. A traffic flow model is developed on the basis of the cell transmission model incorporating this frictional effect to model the traffic evolution on the ML facility. This model is capable of replicating the traffic flow pattern, including congestion onset, propagation, and dissipation at a macroscopic level. The model also captures the effect of GPL congestion on the ML. This model can serve as the underlying ML traffic flow model in future research for evaluating the effectiveness of different tolling strategies.

Operational Performance and Speed–Flow Relationships for Basic Managed Lane Segments

Managed lane facilities, including high-occupancy vehicle (HOV) lanes, high-occupancy toll lanes, and express lanes, have become attractive tools for managing today's transportation system. Although managed lanes, specifically, HOV lanes, have existed for several decades, there has been little documentation of their traffic flow behaviors. Because these facilities tend to take on a variety of configurations, including different numbers of managed lanes and separation types from abutting general purpose lanes, transportation engineers should understand the traffic flow differences among facility types. An understanding of the interaction between managed lanes and parallel general purpose lanes is also needed for assessing the performance of managed lanes. A study was done to investigate the performance and traffic flow behavior of managed lane facilities at sites across the country. Traffic flow behavior for five facility types, based on separation type and number of lanes, was analyzed. Factors such as frictional impact on the managed lane—caused by poor performance of the general purpose lanes and slow vehicle effects on managed lane facilities where passing is prohibited—were considered in development of a set of speed–flow curves for each of the five basic facility types. These speed–flow relationships are expressed similarly to basic freeway segments in the Highway Capacity Manual and can be readily incorporated into the manual for predicting the performance of combined general purpose and managed lane facilities.

Deterministic Approach to Managed Lane Analysis on Freeways in Context of Highway Capacity Manual

The building of managed lanes parallel to general purpose lanes is an increasingly common approach to optimizing freeway capacity. Managed lanes allow agencies to classify customers and assign a portion of the freeway capacity to them. With no methodology in the Highway Capacity Manual (HCM) for analyzing these facilities, analysts rely on more time-consuming simulation analyses. A methodology is presented for estimating the performance of a parallel system of general purpose and managed lane facilities in an HCM context based on NCHRP Project 3–96. The methodology defines new managed lane segment types to use in an HCM analytical framework and is associated with a new set of speed–flow curves. It is sensitive to the number of lanes and the type of separation between managed lanes and general purpose lanes. The method introduces the concept of parallel lane groups of general purpose and managed lanes and thus can account for speed reduction in managed lanes caused by congestion in adjacent general purpose lanes. The method was implemented in a computational engine, FREEVAL-ML, which was built on the freeway facilities method in HCM 2010 but which was updated to incorporate inputs and outputs of the managed lane components. The geometry of two existing managed lane facilities in Washington State is used to illustrate the method, demonstrating the applicability of the analytical framework to real-world facilities.

Time-Variant Travel Time Distributions and Reliability Metrics and Their Utility in Reliability Assessments

Several metrics of reliability have been recommended for use. These metrics may need to be calculated at relatively fine levels of aggregation of travel time data when used for advanced management strategies and transportation system modeling and analysis. This study investigates the variation of travel time distributions by time of day at fine temporal aggregation levels, the sensitivity of various reliability metrics to these variations, the effect of the aggregation level choices on the calculated metrics, and the amount of data required to estimate stable values of the reliability metrics. The investigation is made for a facility that has general purpose lanes and high-occupancy-toll lanes. The results show that the parameters of travel time distributions vary during the peak period, reflecting the effects of traffic congestion, traffic flow dynamics, and how much nonrecurrent factors, such as incidents, contribute to the unreliability of travel time on the investigated facility. Trends of variations are observed when reliability metrics are used to assess reliability as the congestion level changes during the peak period. The results also show that examining combinations of time-variant static distribution parameters and reliability metrics of the general purpose and high-occupancy-toll lanes can provide valuable information that cannot be obtained when the analysis is performed at higher aggregation levels. The study results suggest using at least one year of data to obtain stable values of reliability metrics.

Low-Cost Median Barrier Gate

Median barriers are commonly used to separate opposing lanes of traffic on divided highways and to separate managed lanes from general purpose lanes. Concrete median barriers (CMBs) are often preferred on urban freeways with narrow medians because of their minimal deflection and low maintenance. However, long, continuous runs of CMBs limit access of emergency and maintenance vehicles to the other side of a roadway or a managed lane. Implementation of crashworthy median barrier gates at these locations can maintain the desired level of median protection for motorists while offering improved cross-median access for emergency and maintenance vehicles. A new median barrier gate was developed and crash tested. The gate spans a 30-ft opening in a CMB and consists of two vertically stacked 12- x 12- x ¼-in. steel tubes connected to steel end brackets with 2¼-in. diameter steel pins. The gate is economical to fabricate and install. It can be manually operated by a single person and is designed to accommodate reversible traffic flow on both sides of the median and be operable in both directions on each end. The median barrier gate satisfies the criteria for impact performance of Test Level 3 of the Manual for Assessing Safety Hardware and is considered suitable for implementation on divided highways at locations where cross-median access is desired.

Traffic Characteristics of High-Occupancy Vehicle Facilities

Traffic characteristics intrinsic to contiguous and buffer-separated high-occupancy vehicle (HOV) facilities were explored by examining flow–density–speed relations and an intervening effect from the adjacent general purpose (GP) lane. Detector data were collected from multiple locations and systematically filtered to form well-defined relations between flow, density, and speed that characterize the traffic stream in the HOV lane. Analysis outcomes of the collected data indicated patterns of flow–density–speed relations for contiguous and buffer-separated HOV lanes. The data from the contiguous HOV lanes exhibited relationships as a function of the adjacent GP lane speed, whereas those in the buffer-separated HOV lanes were rather independent of the adjacent GP lane speed. Implications were drawn for capacity and speed of HOV lanes and documented in this paper. These findings were confirmed by comparative analysis of pre- and postconversion HOV configurations, from buffer-separated to contiguous, in a real freeway site.

Ramp Meters Evaluation: Using ITS Archived Data

In December 2009, ramp meters along US 95 in Las Vegas between Rancho Drive and Craig Road were activated. A study was performed to quantify the benefits of ramp meters on the freeway mainline by using archived ITS data. Traditional performance measures such as average travel speed, speed standard deviation, interquartile speed range, travel time index, and buffer index were employed to conduct the evaluation. In addition, two new performance measures—delay volume (DV) and average vehicle delay (AVD)—developed by the Freeway and Arterial System of Transportation (FAST) Division of the Regional Transportation Commission of Southern Nevada were used to enhance the evaluation. Specifically, DV quantifies the congestion with temporal, spatial, and congestion intensity values, and AVD measures the average delay per vehicle with traffic volume as a weighting factor. Comparing both the freeway and ramp performance with and without ramp meters clearly demonstrates that ramp meters are very effective in mitigating the recurring heavy congestion for southbound US 95 during weekday peak periods. The improvement is comparatively little on the more lightly congested northbound section of US 95. The evaluation results also demonstrate that the DV and AVD metrics are useful in evaluating operational strategies such as ramp metering. Finally, informative results are achieved regarding the influence of ramp meters on the bottleneck, and the comparative effects metering has on the general purpose and high occupancy vehicle lanes.

Impact of Bus-Only Lane Location on the Development and Performance of the Logic Rule-Based Bus Rapid Transit Signal Priority

Curb bus-only lanes and median bus-only lanes are two commonly used types of the on-street running ways of bus rapid transit (BRT) systems. Transit signal priority (TSP) has proven viable in improving transit schedule adherence and in expediting transit service and is recognized as a key element of BRT systems. From a TSP designer’s point of view, it provides a systematic analysis of the impact of bus-only lanes location on the development and performance of the logic rule-based bus rapid transit signal priority (BRTSP). As an emerging active TSP for use at isolated signalized intersections, BRTSP is centered on five categories of logic rules and can fully accommodate the variety of phase scheme. Green extension, early green, and phase insertion can be provided to prioritized vehicles within specific priority windows. The signal operations on bus-only lanes and general-purpose lanes are influenced by prioritized vehicle arrivals and departures and general traffic demands that are detected. Compared with c...

Pareto-improving congestion pricing on multimodal transportation networks

This paper determines a Pareto-improving pricing scheme for alleviating congestion in a multimodal transportation network that includes, e.g., transit services, high-occupancy/toll and general-purpose lanes. In this setting, a pricing scheme refers to a strategy for tolling roads and highways as well as adjusting fares on various transit lines. In addition, such a scheme is Pareto-improving if it maximizes the social benefit without increasing travel-related expense of stakeholders that include individual road users, transit passengers, transit operators, transportation authorities, etc. The user equilibrium and system optimum problem in the multimodal transportation network are discussed along with a model for determining Pareto-improving tolls. The latter is formulated as a mathematical program with complementarity constraints. Two numerical examples are presented to illustrate results from various models.

Value of Reliability: High Occupancy Toll Lanes, General Purpose Lanes, and Arterials

In the Minneapolis-St. Paul region (Twin Cities), the Minnesota Department of Transportation (Mn- DOT) converted the Interstate 394 High Occupancy Vehicle (HOV) lanes to High Occupancy Toll (HOT) lanes (or MnPASS Express Lanes). These lanes allow single occupancy vehicles (SOV) to access the HOV lanes by paying a fee. This fee is adjusted according to a dynamic pricing system that varies with the current demand. This paper estimates the value placed by the travelers on the HOT lanes because of improvements in travel time reliability. This value depends on how the travelers regard a route with predictable travel times (or small travel time variability) in comparison to another with unpredictable travel times (or high travel time variability). For this purpose, commuters are recruited and equipped with Global Positioning System (GPS) devices and instructed to commute for two weeks on each of three plausible alternatives between their home in the western suburbs of Minneapolis eastbound to work in downtown or the University of Minnesota: I-394 HOT lanes, I-394 General Purpose lanes (untolled), and signalized arterials close to the I-394 corridor. They are then given the opportunity to travel on their preferred route after experiencing each alternative. This revealed preference data is then analyzed using mixed logit route choice models. Three measures of reliability are explored and incorporated in the estimation of the models: standard deviation (a classical measure in the research literature); shortened right range (typically found in departure time choice models); and interquartile range (75th - 25th percentile). Each of these measures represents distinct ways about how travelers deal with different sections of reliability. In all the models, it was found that reliability was valued highly (and statistically significantly), but differently according to how it was defined. The estimated value of reliability in each of the models indicates that commuters are willing to pay a fee for a reliable route depending on how they value their reliability savings.

Analysis of Operational Interactions between Freeway Managed Lanes and Parallel, General Purpose Lanes

Roadway agencies face growing challenges to expand freeway capacity. Under the constraints of rising construction costs, right-of-way limitations, and environmental regulations, transportation agencies are seeking solutions for efficiently managing the demand on existing freeway facilities and for providing options for travelers. The concept of managed lanes (MLs) is an increasingly popular countermeasure that aims to make the most efficient use of freeway facilities by restricting access to one or more lanes to certain vehicle classes on a facility that is parallel to existing general purpose (GP) lanes. With different strategies for separating ML and GP lanes, this study examines the interaction between GP lanes and ML operations. It scrutinizes this interaction as a function of different separation types, the number of MLs, and operational ML strategies, including high-occupancy toll (HOT) and high-occupancy vehicle (HOV) lanes. Four freeway sites were selected to explore the effect of this interaction. The research shows that, for HOT facilities, separation type has the most significant impact on explaining the intensity of the frictional effect, as paint-separated ML facilities are readily affected by congestion in adjacent GP lanes. For HOV facilities, the frictional effect was observed by adopting a stochastic approach to capacity estimation to estimate the capacity distribution function for both GP and HOV lanes. It was determined that GP lanes had a stochastic dominance over HOV lanes under any breakdown probability. The results make the case that ML operations should not be evaluated independently of adjacent GP lanes, and these results have implications for both proposed analytical approaches and simulation-based analyses.

Development of Managed-Lane Access Guidelines Based on Gap Acceptance Theory

One strategy for improving freeway performance is implementation of managed lanes (MLs). Vehicles access an ML located in the freeway median by weaving across the general purpose lanes (GPLs) and entering the ML from the leftmost lane of the GPLs. Such intense lane-changing maneuvers cause traffic turbulence, which induces special operational problems with capacity, level of service, and safety. The principal objective of this research is to develop design guidelines for the ML access (or exit) spacing between the entrance (or exit) ramp and the ML access opening and for the ML access opening length. This research develops analytical weaving models based on gap acceptance theory; the models estimate the probability of successful weaves in these weaving distances. The research also develops design guidelines for these distances on the basis of the analytical weaving models.

Rethinking the Politics of Freeway Congestion Pricing

A growing community of transport economists and urban planners has concluded that the best solution to U.S. freeway congestion would be to implement congestion pricing on all such freeways. At the same time, many political scientists and other political observers consider doing so to be politically impossible, primarily because of strong opposition from taxpayers, voters, and highway user groups. Federal efforts (dating to the 1970s) to induce one or more urban areas to price its freeways have been unsuccessful; this lack of success reinforces the political scientists' skepticism. This paper suggests that even if the political difficulties could be overcome, the conventional model of freeway congestion pricing (charging all users the same variable price) may not be optimal: this model could well create more losers than winners. In analyzing this conundrum, the author looks more closely at two assumptions implicit in the standard congestion pricing model: uniformly applied (variable) pricing and all general purpose lanes. Revisiting both assumptions leads to a proposal for multitier pricing on differentiated lanes, which the author suggests could be more politically feasible and productive of larger economic benefits. This approach also lends itself to being implemented in an evolutionary manner, in which each step is justified on its own merits, without regard of the possible longer-term end.

Quantifying the Attractiveness of High-Occupancy Toll Lanes with Traffic Sensor Data under Various Traffic Conditions

Different states have used different tolling strategies for their high-occupancy-toll (HOT) lane facilities, and the performance of an HOT lane system has tied directly to the tolling strategy. However, comparing tolling strategies has been a difficult problem because of the lack of field data as well as missing pieces of information critical to the analysis of HOT lane operations. For example, how single-occupancy vehicles (SOVs) choose the type of lane to use under the effect of tolling and the flow friction between HOT and general purpose lanes remains unclear. This research attempts to analyze the heterogeneity among the SOV users of HOT lanes and to quantify the attractiveness of HOT lanes for SOV drivers. The study uses field data collected by point traffic sensors and transponder toll tags on Washington State Route 167 (SR-167). SOVs are categorized as infrequent users and frequent users, according to the frequency with which their transponder identification tags appear in the database. Their value of time distributions are studied separately at the microscopic level. A logit-like model is further developed to quantify the relationship between SOV demand and HOT lane use under different traffic phases. The analysis results show that travel patterns on HOT and general purpose lanes can be better interpreted and modeled for performance enhancement with motorists' willingness to pay HOT lane tolls considered.

Exploiting the Capacity of Managed Lanes in Diverting Traffic around an Incident

This paper studies the potential benefits of traffic diversion in incident management for freeway operations of concurrent flow lane facilities. Techniques that exploit the capabilities of the component object module interface of the microscopic simulation tool, VISSIM, were devised for modeling freeway incidents and the implementation of diversion strategies. The potential for mobility improvement in general purpose lanes as a consequence of diverting traffic around an incident using existing managed lanes and the resulting degradation in managed lane performance are considered in a case study. Results from experiments employing the developed simulation tool show that the benefit to general traffic from implementation of a diversion strategy depends on the following factors: the location of the incident scene relative to the starting point of the diversion opening, the total length of access to the managed lane under the diversion strategy, incident duration, and number of lanes blocked (i.e., incident severity). When diversion implementation lags, travel time reductions achieved through diversion are diminished.

Preliminary Evaluation of Operational Performance of Different Types of High-Occupancy Vehicle Facilities in California Continuous Access versus Limited Access

High-occupancy vehicle (HOV) facilities have been regarded as an effective and environmentally friendly approach to improving the mobility and productivity of freeway systems in metropolitan areas. With 6 months of traffic data from more than 700 vehicle detector stations, the authors conducted a comparative study of the operational performance of continuous-access and limited-access HOV facilities at the route level in California. The evaluation results of both HOV lanes and adjacent general purpose (AGP) lanes include several operating characteristics of these lanes: (a) the ingress–egress areas in limited-access HOV facilities may affect the formation of bottlenecks along HOV lanes; (b) the speed on HOV lanes and the speed differential between the HOV and AGP lanes are statistically greater in continuous-access facilities than in limited-access facilities; and (c) the characteristics of speed–flow distribution of HOV lanes exhibit observable differences between the two types of HOV facilities, but those of AGP lanes are similar regardless of the access type. Furthermore, statistical analyses show that some performance measures at the route level, including the space mean speed and vehicle-miles-traveled share of the HOV lanes, are significantly different for HOV facilities with different access types.