Adjacent General Purpose Lanes Research Articles

Quantifying the Mobility Benefits of Express Lanes using Real-Time Traffic Data

Traffic congestion is one of the major problems facing transportation agencies, especially in urban areas. Agencies are exploring ways to use the existing transportation infrastructure efficiently by deploying appropriate traffic management strategies. One of these strategies is the use of express lanes, which are expected to effectively mitigate congestion and increase the reliability of highway facilities. Express lanes are managed toll lanes, separated from general-purpose lanes within a freeway facility. The goal of this study was to quantify the mobility benefits of express lanes by comparing the performance of express lanes with that of their adjacent general-purpose lanes, and by assessing the performance of the general-purpose lanes when the express lanes were open versus when the express lanes were closed. The Buffer Index (BI), a travel time reliability measure, was selected as the performance measure. The analysis was based on 95Express, express lanes along I-95 in Miami, Florida. Overall, the results indicated that BIs for the express lanes were significantly lower than the BIs for the general-purpose lanes, and the BIs for the general-purpose lanes were significantly lower when the express lanes were open compared with the periods when the express lanes were closed. The study results showed mobility improvements on both the express lanes and the general-purpose lanes, although the extent of the improvements varied by direction (i.e., northbound and southbound) and time of day (i.e., a.m. peak, p.m. peak, daytime off-peak, and nighttime off-peak). Transportation agencies may use these findings to quantify and evaluate the mobility benefits of the express lanes and the general-purpose lanes on express lane facilities.

Psychological items: a useful addition in modeling travel behavior on managed lanes

Managed lanes (MLs) are a tool to more efficiently operate segments of a freeway. As ML prevalence increases in the United States of America, it is important to understand travel behavior in a ML setting (i.e., lane choices and carpooling decisions). Socio-demographic and trip data, along with travel time and toll, have been commonly used in this endeavor. However, there are some travelers who pay to use the ML despite there being little to no improvement in travel time over the adjacent general purpose lanes. This gives rise to the possibility that psychological traits and characteristics are a greater influence on ML use than even travel time savings for some travelers. This research examined this issue through a set of largely transportation-framed psychological items. After an initial creation and refining process, 25 psychological items were included in a survey advertised in five cities with MLs. In addition to psychological items, trip and demographic questions, and three SP questions were included in the online survey. Mixed logit models were estimated based on survey responses obtained from three study areas. Models that included psychological items performed better (in terms of adjusted rho squared value and percent correctly predicted values) than models with only trip and demographic variables. Likewise, models including psychological items plus trip and demographic data performed best. This information may be useful for traffic and revenue estimating firms interested in potentially including psychological items in future ML surveys intended to facilitate better estimation of ML use.

Tracking the Impact of a Toll Increase on Managed Lane Travel Behavior

Tolled managed lanes (ML) are an innovative way to increase capacity and regulate demand on roadways. They are still relatively new and a lot remains unknown about how travelers choose to use MLs or not. This paper uses disaggregate real-world travel data of travelers who choose between paying a toll to use ML or travel toll free on the adjacent general purpose lanes (GPL). The travel behavior before and after a toll increase is evaluated. The change in toll rates did not affect the overall ML use as anticipated. Overall, ML use increased after the toll increase. In addition, frequent ML users (more than 10 ML trips in a month) and infrequent ML users (1–3 ML trips in a month) behaved differently following the increase in the toll.

The Influence of General Purpose Lane Traffic on Managed Lane Speeds: An Operational Study in Houston, Texas

Freeway networks are a critical component of the transportation systems at large metropolitan areas. The use of managed lanes (MLs) is a very important tool in accommodating directional demand, often heavily asymmetrical at peak hours. Current literature establishes that operational performance of MLs may impact, and be impacted by, operations of adjacent general purpose lanes (GPs), despite some degree of physical separation. Such operational co-dependence may especially exist between the GP lane adjacent to the separation buffer and the ML lane. This paper examines how the operations of these lanes relate to each other. Operational data were collected from 2 freeway sites in Houston TX (U.S.A.) for analysis. Both sites feature a buffer separating a single ML from the GP lanes at each site. One of those sites features vertical pylons in its buffer while the other site does not. This dataset spans several months of year 2014, from January to December. Results highlight the influence of the left-most GP lane on the ML operational speed, as well as the apparent degree of mitigation to that influence that the presence of pylons provides.

Operational Effects of Design of Access Points on Katy Freeway Managed Lanes in Houston, Texas

The construction of the managed lane facility on the Katy Freeway in Houston, Texas, provided a unique opportunity to meet the needs of motorists by providing a completely new set of access points to and from the managed lane facility as compared with many similar facilities that were predominantly retrofit installations. The access points on the Katy Freeway managed lanes were intended to provide timely, useful access between the managed lanes and the I-10 general purpose lanes at locations that facilitated effective access to origins and destinations beyond the freeway. Researchers investigated operational characteristics of selected access points to assess how they were being used by motorists. Provided here are an overview of the access points on the Katy Freeway managed lanes, a discussion of the field data collected and how they were reduced and analyzed, and the research team's conclusions concerning how the access points performed on the basis of the analysis. The study analyzed the number of ingress and egress maneuvers at selected access points and compared them with traffic volumes in the managed lanes and adjacent general purpose lanes, with a focus on the amount of time drivers took to make their maneuvers and where the maneuvers occurred within the access points.

Express Lanes Performance Evaluation

Transportation authorities around the United States are challenged to develop highway projects that deliver the best operational performance for the public investment. Congestion pricing has been promoted as an efficient operational performance strategy that helps to add roadway capacity when it is needed most, during peak periods of the day. The Minnesota Department of Transportation has implemented its second high-occupancy toll lane in the I-35W MnPASS express lane. This paper examines the performance of the southern 7 mi of the MnPASS lane and considers a number of performance indexes as reported through the project evaluation process. Since the opening of the MnPASS express lanes on the I-35W corridor, average speeds on those lanes during the a.m. peak period have increased by 3 to 4 mph. Average speed in the adjacent general purpose lanes appears to have declined by about 1 to 2 mph in the evaluation period. Vehicle throughput on the MnPASS lanes has increased by 77% and person throughput has increased by 39% over the base year of 2008. Through dynamic pricing, MnPASS lanes are able to ensure free-flow speeds more than 95% of the time. Customers are generally pleased with MnPASS operations and performance, citing value for their money in the form of time savings, less traffic, faster travel, and reduced stress. The I-35W MnPASS express lanes ensure greater speed and reliability for transit service and systems, encourage greater transit use through higher performance, and provide a congestion-free lane for those who choose to pay and those who carpool or ride transit.

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.

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.

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.

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.

Investigating the Impact of Tolls on High-Occupancy-Vehicle Lanes Using Managed Lanes

For nearly 40 years, high-occupancy-vehicle (HOV) lanes have been used to combat congestion. These lanes allow only vehicles with multiple occupants and generally offer a free-flow trip, unlike adjacent general purpose lanes. In theory, this encourages additional carpooling, reduces overall vehicle miles of travel, and improves the commute trip. However, as a result of the underutilization of some of these lanes, some HOV lanes are migrating to high-occupancy-toll (HOT) lanes, where HOVs may travel free of charge but lower-occupancy vehicles can pay a toll to use the lane. This research investigated the impacts of offering preferential treatment for HOVs on these lanes. To determine the impact of different HOT lane operating strategies on their travel behavior, freeway travelers in the Houston and Dallas metropolitan areas of Texas were surveyed. A nested logit model was developed to estimate the mode choice for travelers. This model was used to predict the impact of converting an HOV lane to a HOT lane on which all travelers pay a toll. It was found that the overall percentage of HOV2 and HOV3+ vehicles in the traffic stream decreased by only a small amount when a toll was required for them to use the HOV lane. However, that decrease did represent a significant portion of those modes (more than 9%) and resulted in more than a 10% increase in HOT lane revenue. Therefore, elimination of preferential treatment for these vehicle types has significant implications and becomes a difficult policy decision—not just a straightforward choice.

So You Want to Make a High-Occupancy Toll Lane?: Project Manager's Guide for Conversion from High-Occupancy Vehicle Lane to High-Occupancy Toll Lane

Although high-occupancy toll (HOT) lanes have been studied or have existed for more than 10 years, the continuing developmental nature of these concepts means that there is little guidance for project managers on how to manage the process of converting a high-occupancy vehicle (HOV) lane to a HOT lane. Many guidelines have been published about the technical elements of HOT lane development and operations. A project manager of an HOV to HOT lane conversion process would face issues that differ from those of the typical highway construction project, and managing these issues can be difficult and arduous. The intent of this paper is to address issues from the perspective of the implementing agency's project manager. Eight specific issues to be addressed within the conceptual development of the HOT lane conversion process are identified here: (a) presence of significant and predictable excess capacity in the HOV lanes, (b) presence of significant and recurring congestion in the adjacent general purpose lanes,...

So you want to Make a High-Occupancy Toll Lane?

Although high-occupancy toll (HOT) lanes have been studied or have existed for more than 10 years, the continuing developmental nature of these concepts means that there is little guidance for project managers on how to manage the process of converting a high-occupancy vehicle (HOV) lane to a HOT lane. Many guidelines have been published about the technical elements of HOT lane development and operations. A project manager of an HOV to HOT lane conversion process would face issues that differ from those of the typical highway construction project, and managing these issues can be difficult and arduous. The intent of this paper is to address issues from the perspective of the implementing agency's project manager. Eight specific issues to be addressed within the conceptual development of the HOT lane conversion process are identified here: (a) presence of significant and predictable excess capacity in the HOV lanes, (b) presence of significant and recurring congestion in the adjacent general purpose lanes, (c) nature of traffic separation on the HOV lanes, (d) primary means of funding for the HOV lanes, (e) identification of the HOT lane program's primary objective, (f) determination of the appropriate implementing agency, (g) avoidance of overwhelming public opposition, and (h) ability to build political support for the process. This paper has summarized the first of what the authors see as four steps to the successful conversion of an HOV lane to a HOT lane: conceptual development. Planned subsequent papers will address the remaining three steps: program design, implementation, and ongoing operations.

High occupancy vehicle lanes: Not always more effective than general purpose lanes

The success of a high occupancy vehicle lane in motivating people to shift to carpools and buses depends on maintaining a travel time differential between it and the adjacent general purpose lanes. This differential, in turn, depends on the level of continuing delay on the general purpose lanes. Therefore, it is clear that a high occupancy vehicle lane that will motivate people to shift to high occupancy vehicles will not eliminate congestion. Consequently, it is not clear that constructing a high occupancy vehicle lane will necessarily reduce delay more than construction of a general purpose lane. The objective of this research is to determine the circumstances in which this would be the case. The hypothesis is that such circumstances would be quite limited, and this proves to be the case. The intended benefits of high occupancy lanes are defined as reduced person-delay and reduced emissions. A model is developed to calculate these benefits for four alternatives: add a high occupancy vehicle lane, add a general purpose lane, convert an existing lane to a high occupancy vehicle lane, and do nothing. The model takes into account the initial conditions, the dynamic nature of the travel time differential between the high occupancy vehicle lane and other lanes, and the uncertainty regarding the extent to which people will shift modes. It combines queueing theory and mode choice theory and provides a robust method for comparing alternatives using a small amount of easily observed data. Application of the model in typical situations shows that with initial delays on the order of 15 min or more, adding a high occupancy vehicle lane would provide substantial reductions in delay and some reduction in emissions. However, in a wide range of such situations, adding a general purpose lane would be even more effective. Only if the initial delay is long and the initial proportion of high occupancy vehicles falls in a rather narrow range, would an added high occupancy vehicle lane be more effective. The proportion of high occupancy vehicles must be such that it allows good utilization of the high occupancy vehicle lane while maintaining a sufficient travel time differential to motivate a shift to buses or carpools. Adding a high occupancy vehicle lane to a three lane freeway will be more effective than adding a general purpose lane only if the initial maximum delay is on the order of 35 min or more and the proportion of high occupancy vehicles is on the order of 20%. Federal policies encourage construction of high occupancy vehicle lanes and restrict funding for general purpose lanes in areas that have not attained air quality standards. The findings of this research suggest a need to reconsider these policies.