bluuebunny/crossref_metadata_2025 huggingface dataset:
On Modeling Departure-Time Choice for Home-Based Social/Recreational and Shopping Trips
Authors: Steed Jennifer L. , Bhat Chandra R.
Published: April 2007

The existing literature on departure-time choice has primarily focused on work trips. Departure-time choice for nonwork trips, which constitute an increasingly large proportion of urban trips, is examined. Discrete choice models are estimated for home-based social/recreational and home-based shopping trips using the 1996 activity survey data collected in the Dallas—Fort Worth metropolitan area. The effects of individual and household sociodemographics, employment attributes, and trip characteristics on departure-time choice are presented and discussed. The results indicate that departure-time choice for social/recreational trips and shopping trips is determined for the most part by individual or household sociodemographics and employment characteristics, and to a lesser extent by trip level-of-service characteristics. This suggests that departure times for social/recreational and shopping trips are not as flexible as one might expect and are confined to certain times of day because of overall scheduling constraints. Future methodological and empirical extensions of the current research are identified.
Hazardous Materials Transportation on U.S. Railroads: Application of Risk Analysis Methods to Decision Making in Development of Regulations
Authors: Raj Phani K. , Pritchard Edward W.
Published: April 2007

The Office of Safety of the Federal Railroad Administration (FRA) is responsible for ensuring public and personnel safety in U.S. railroad operations. This office ensures the safe rail transportation of hazardous materials by conducting inspections of railroad operations and equipment, including tank cars, and developing safety-related regulations. In the past few years, the Office of Safety has been using risk analysis as a tool in making rational regulatory decisions on hazardous materials transportation in tank cars. A risk analysis protocol developed by FRA is described to evaluate the risks to the U.S. population arising from the transportation of different types of chemicals in tank cars on the U.S. railroad system. Following several recommendations of the National Transportation Safety Board requiring the shipment of several hazardous chemicals in highly protected, pressure-rated tank cars rather than in the minimum packaging authorized by the Code of Federal Regulations, a risk-based evaluation was made on the effect of implementing these recommendations on the overall risk reduction. The risk results were presented in the parameters of Military Standard 882-B. Policy decisions were made based on the results.
Reducing Hazardous Materials Releases from Railroad Tank Car Safety Vents
Authors: Barkan Christopher P. L. , Treichel Todd T. , Widell Gary W.
Published: April 2007

The leading cause of hazardous materials releases in railroad transportation over the 5 years prior to this research was burst frangible disks on tank cars. These burst disks occur as a result of pressure surges in the tank car safety vent during transportation. More than a dozen different surge pressure reduction devices (SPRDs) have been developed to protect the frangible disk from these surges. A statistical analysis of tank cars in service indicated that cars equipped with SPRDs experienced a lower rate of leakage due to burst frangible disks than similar cars without SPRDs. This analysis, however, did not provide sufficient resolution to determine the relative effectiveness of the different SPRD designs. A series of controlled experiments was conducted to determine the surge reduction effectiveness and the flow performance of different SPRDs. These tests showed that there were significant differences in the performance of the various surge pressure reduction devices in both surge reduction and flow rate. The results of these tests will help tank car builders, owners, and operators improve the safety performance of tank cars by installing SPRDs that will reduce non-accident-caused releases of hazardous materials and still function adequately to relieve pressure when necessary. The results also will provide a basis for setting SPRD performance and testing requirements and identify promising design elements for new SPRDs.
Relationship of Freight Facilities in Central Business District Office Buildings to Truck Traffic
Authors: Morris Anne G. , Kornhauser Alain L.
Published: April 2007

Intracity goods movement is profoundly affected by the facilities and services available for pickups and deliveries in commercial office buildings (COBs). Inadequate freight-handling facilities in New York City’s central business district (CBD) were identified as major barriers to freight mobility by shippers and carriers in industry-sector focus groups and in freight mobility interviews. Property managers of COBs completed 28 surveys that provided data about building characteristics, the number and size of freight elevators, a description of the dock area, and delivery windows. Results indicated that inadequate docks or receiving areas and insufficient freight elevators did not support the increasing number of freight deliveries, resulting in a significant amount of off-loading on the streets. Most property managers surveyed believed that enlarging docks would increase dock functionality. A time-and-motion study of vehicular deliveries to loading docks was carried out at two COBs located in the CBD. It documented time of delivery, dwell time in the dock, dwell time on the street, size and type of vehicle, and so forth, for a 10-week period in the summer of 1997. Most deliveries occurred in the mornings; dwell times averaged 33 min in the dock and on the street. A majority of straight trucks were under 7.31 m (24 ft) in length.
Value Pricing and Freight Traffic: Issues and Industry Constraints in Shifting from Peak to Off-Peak Movements
Authors: Vilain Pierre , Wolfrom Paul
Published: April 2007

The Port Authority of New York and New Jersey (PANYNJ), in association with Louis Berger & Associates, Inc., completed a study to determine the potential for reducing peak-period commercial traffic at the interstate crossings between New Jersey and New York City. One of the policy options examined, and the focus here, was the feasibility of encouraging a reduction in peak-period congestion through the use of congestion- or value-pricing incentives. (PANYNJ recognizes the need for a coordinated approach to reducing congestion involving as many of the regional transportation authorities as possible. Also, it is clear that congestion reduction strategies must focus on all vehicles and not simply commercial traffic. The purpose of this research was to better understand the constraints facing that segment of the market. It was not intended to suggest pricing policies focusing exclusively on commercial traffic.) Summarized are some of the findings of a large number of interviews carried out with trucking firms, in particular key personnel of the firms in positions of responsibility or authority with respect to scheduling of deliveries. The interviews, each fairly detailed and in-depth, elicited significant and valuable information to help understand what could be the response of commercial traffic to value-pricing initiatives. Another part of the analysis also is discussed, involving calculating the total value of tolls at the interstate crossings as a proportion of the generalized cost of travel (GCT) facing trucks. The analysis was carried out to assess how much the GCT would be affected by value-pricing incentives.
Implementation of Wider Lane Lines to Improve Sight Distance from Opposing Left-Turn Lanes
Authors: Byrd Patrick S. , McCoy Patrick T. , Pesti Geza , Singh Virendra A.
Published: April 2007

Vehicles turning left at intersections from opposing left-turn lanes often restrict each other’s sight distance. Previous research has developed guidelines for offsetting opposing left-turn lanes to provide adequate sight distances. Implementation of these guidelines at existing intersections typically involves reconstructing the left-turn lanes. However, the results of the before-and-after studies presented demonstrate that increasing the width of the lane lines between left-turn lanes and the adjacent through lanes also can be used as a means of improving the sight distance between opposing left-turn lanes. Regression analysis was used to determine a relationship between lane-line width and available sight distance that can be used to design lane-line widths that provide the required sight distance for opposing left-turn vehicles.
Setting Speed Limits on Kansas Two-Lane Highways: Neuronet Approach
Authors: Najjar Yacoub M. , Stokes Robert W. , Russell Eugene R.
Published: April 2007

Recent federal legislation allowing states to set their own speed limits on highways, as well as increases in the number of requests from citizens and neighborhood groups to implement actions to reduce “excessive” speeding on their streets and highways, has created considerable debate about and scrutiny of the appropriate speed limits that should be posted on state highways. Various speed studies have indicated that sensible and cautious drivers will most likely drive at the speed dictated by roadway and traffic conditions rather than relying on a posted speed limit. To incorporate roadway characteristics and traffic volumes into the selection of the most appropriate (i.e., comfortable, safe, and efficient) speed limit, actual engineering field speed studies are carried out. Generally, the 85th percentile speed at which the drivers surveyed are driving is selected as a primary factor in determining the posted speed limit. Carrying out such field studies for all highway sections is a costly and time-consuming process. Therefore, characterizing the relationship between the 85th percentile speed and the roadway characteristics will assist in selecting the most appropriate posted speed limit on highway sections where field surveying is difficult due to resource limitations. A back-propagation neural network is used to extract the relationship between roadway characteristics and 85th percentile speed. The developed neural-network-based speed model was found to perform satisfactorily for characterization of speed on Kansas two-lane, uninterrupted-flow rural highways and for quantifying the influence of prevailing roadway characteristics on the anticipated 85th percentile speed.
Computer-Based Modeling to Determine the Visibility and Minimum Retroreflectivity of Pavement Markings
Authors: Schnell Thomas , Zwahlen Helmut T.
Published: April 2007

The Federal Highway Administration was mandated by the U.S. Congress to establish in-service levels of minimum pavement-marking retroreflectivity and commissioned research to determine the minimum in-service level from a driver’s point of view. Computer Aided Road Marking Visibility Evaluator (CARVE) was developed and refined to systematically investigate drivers’ visual needs in terms of nighttime pavement-marking visibility and to allow the formulation of minimum retroreflectivity recommendations. The components within CARVE and the methods, algorithms, and equations that are used to determine the visibility distance of a given pavement-marking treatment are presented and discussed. CARVE systematically manipulates the pavement-marking efficiency (ηPM) up and down using a bisecting-search algorithm until the desired minimum required preview distance for selected conditions is achieved. Future expansions of CARVE, or the development of models that supersede it, may require additional research to investigate the wet-weather visibility of pavement markings, the effects of combined treatments consisting of pavement markings and raised reflective markers, and the visibility in inclement weather such as fog and blowing snow.
Prioritizing Traffic-Calming Projects Using the Analytic Hierarchy Process
Authors: Guegan Dawn P. , Martin Peter T. , Cottrell Wayne D.
Published: April 2007

The analytic hierarchy process (AHP), a multiple-criteria decision-making tool, is used to prioritize traffic-calming projects. AHP is proposed as an alternative to existing point scoring systems. Prioritization methods used in traffic-calming programs in Portland, Oregon, and Canberra, Australia, are applied; the results are compared to those of AHP. The three methods apparently produce similar rankings when applied to local streets that have speeding problems. AHP produces rankings different from those of the other two methods, however, when complex issues and qualitative factors must be taken into account. AHP may be more suitable in cases in which some factors cannot be quantified. In the examples studied, these factors included traffic diversion, the importance of the street, the impacts of existing traffic-control devices and measures adjacent to elementary schools, terrain, and neighborhood residents’ opinions. None of these factors could readily be assigned a value in a point scoring system. Some of the concerns in applying AHP are the tediousness of making pairwise comparisons between alternatives, the consistency of the comparisons, and the defensibility of the scores. The decision maker should examine the scores to ensure that they are sensible and should be adequately aware of the issues so as to defend the scores. If there are n alternatives, then n( n - 1)/2 pairwise comparisons are needed. Clearly, for expedient application of AHP, the alternatives must be limited to a reasonable number.
Automated-Horn Warning System for Highway-Railroad Grade Crossings: Evaluation at Three Crossings in Ames, Iowa
Authors: Gent Steve J. , Logan Scott , Evans David
Published: April 2007

Traditionally, locomotive engineers begin sounding the train horn approximately one-quarter mile from the crossing to warn motorists and pedestrians approaching the intersection. To be heard over this distance, the train horn must be very loud. This combination of loud horns and the length along the tracks that the horn is sounded creates a large area adversely impacted by the horn noise. In urban areas, this area likely includes many nearby residents. The automated-horn system provides a similar audible warning to motorists and pedestrians by using two stationary horns mounted at the crossing. Each horn directs its sound toward the approaching roadway. The horn system is activated using the same track–signal circuitry as the gate arms and bells located at the crossing. Once the horn is activated, a strobe light begins flashing to inform the locomotive engineer that the horn is working. Horn volume data collected near the crossings clearly demonstrate the significant reduction of land area negatively impacted by using the automated horns. Residents overwhelmingly accepted the automated-horn systems and noted a significant improvement in their quality of life. Motorists preferred the automated-horn systems, and locomotive engineers rated these crossings slightly safer compared with the same crossings in the before (train horn) condition.
Assessment of Falling Weight Deflectometer Data for Stabilized Flexible Pavements
Authors: Appea Alexander K. , Al-Qadi Imad L.
Published: April 2007

Backcalculation of pavement moduli through the utilization of the falling weight deflectometer (FWD) is used for pavement monitoring and evaluation. The performance and structural condition of nine flexible pavement test sections built in Bedford County, Virginia, have been monitored over the past 5 years using FWD. The nine sections include three groups with aggregate base layer thicknesses of 100, 150, and 200 mm, respectively. Sections 1, 4, and 7 are control, whereas Sections 2, 5, 8 and 3, 6, 9 are stabilized with geotextiles and geogrids, respectively. The FWD testing used five double-load drops ranging from 26.5 to 58.9 kN. The deflection basins obtained from the testing have been analyzed using the ELMOD backcalculation program to find the pavement structural capacity and to detect changes in the aggregate resilient modulus. The analysis shows a reduction in the backcalculated resilient modulus of the 100-mmthick base layer. The reduction was 33 percent over 5 years for the nonstabilized section compared with the geosynthetically stabilized section. The reduction in base layer resilient modulus may have resulted from subgrade fine migration into this layer as confirmed by excavation. The study confirms the effectiveness of using woven geotextile as a separator in a pavement system built over weak subgrade. This supports the continuous rutting measurements and ground truth excavation conducted in late 1997.
Field Evaluation of Geocell Use in Flexible Pavements
Authors: Al-Qadi Imad L. , Hughes John J.
Published: April 2007

Wheel rutting in excess of 100 mm occurred within 7 days after reconstruction of a section of Route 30 in Delaware County, Pennsylvania, an urban roadway with high average daily traffic. The road was reconstructed on a weak subgrade, and soil tests produced California bearing ratio values between 1.5 and 6.5 percent. A geocell confinement system was used to stabilize the subgrade and solve this problem. The geocell used was constructed of high-density polyethylene. Each geocell panel was fabricated using 60 strips 3.3 m long and 100 mm thick. The panels were 2.4 m × 6.1 m when expanded and created a honeycomb-patterned cellular confinement system. The geocell system was used in combination with other geosynthetics (geogrid or geotextiles, or both). The findings indicated that the geocell system used in this project performed very favorably. The roadway has not shown any pavement distress (alligator cracking, rutting, etc.) during the 3-year evaluation period. To date, falling weight deflectometer data, initially collected after construction, have since been collected annually for 2 years. Analysis suggests that the geocell, in combination with a geosynthetic layer, provides a significant improvement to the pavement structure capacity when built over a weak subgrade. The resilient modulus of the 150-mm-thick aggregate layer was improved almost twofold. There is a good possibility that this increase was caused by the aggregate confinement resulting from the geocell and the separation provided by another geosynthetic layer.
Three-Dimensional Modeling of Spatial Soil Properties via Artificial Neural Networks
Authors: Itani Omar M. , Najjar Yacoub M.
Published: April 2007

Geotechnical engineers recognize the variability of the geological materials they work with, including uncertainties associated with subsurface characterization tasks. These uncertainties include data scattering, such as real spatial variation in soil properties, or random testing errors. Systematic errors, as can occur in bias measurement procedures, are also common. In almost all construction projects, penetration tests play a major role in subsoil characterization. Interpretation of test results is mostly empirical, and it is therefore prudent to find a suitable computational method to minimize the error in predicting values at points away from actual test locations. In this research, the capabilities of artificial neural networks (ANNs) are assessed as a computational method for predicting standard penetration test (SPT) results at any point ( x, y, z) in a field where a set of SPTs is performed. SPT and moisture content data for five bore holes are used to train and test the developed three-dimensional network models. To graphically visualize the underlying soil strata, select contour maps of blows and moisture content values at various locations are presented. The results obtained indicate the viability and flexibility of ANN methodology as an efficient tool for site characterization tasks.
Effectiveness Analysis of Subsurface Drainage Features Based on Design Adequacy
Authors: Wyatt Timothy Robert , Macari Emir Jose
Published: April 2007

To prevent the deleterious effects of undrained moisture in pavement structures, it has become common to incorporate subsurface drainage features such as permeable bases and edgedrains into pavement design. A theoretical design methodology has been developed to ensure that the level of subsurface drainage is adequate for the specific pavement structure. However, recent research has called into question the effectiveness of subsurface drainage for certain types of pavement structures. Correlating the presence of moisture-related pavement distress with drainage features has revealed that drainage features do not significantly reduce faulting of doweled jointed concrete pavements, and that edgedrains may negatively impact hot-mix asphalt pavements. However, the study in which this correlation was accomplished did not attempt to assess the adequacy of the provided drainage features using the theoretical design methodology. This research presents an alternative method of effectiveness assessment based on design adequacy. The theoretical drainage capacity of a design feature, such as a pavement base or edgedrain system, is computed using the design methodology and compared with the expected inflow to that feature. The adequacy of the design is expressed as the proportion of the computed capacity to the expected service requirement. The method is applied to cases in the Long-Term Pavement Performance database. Examples are provided in which adherence to the design methodology would have indicated that the drainage features were inadequate; however, the more simplistic observational approach would reflect poorly on the effectiveness of the provided drainage features.
Tube Suction Test for Evaluating Aggregate Base Materials in Frost- and Moisture-Susceptible Environments
Authors: Syed Imran , Scullion Tom , Randolph Robert B.
Published: April 2007

A simple tube suction test has been developed by the Finnish National Road Administration for evaluating unstabilized granular base material. The test consists of monitoring the capillary rise of moisture within a 150-mm-diameter by 200-mm-high cylinder of compacted aggregate. A probe is used to measure the dielectric constant at the surface of the sample. The dielectric constant is a measure of the free, or unbound, water within the aggregate sample. It is this unbound water that is thought to be directly related to the strength of the material and its ability to withstand repeated freeze-thaw cycling. Measurements of dielectric constants are made over a period of 10 days. The poorest performing materials are those that rapidly reach saturation and exhibit high surface dielectric values. A study was conducted on four marginal aggregates from Alaska, Nevada, New Mexico, and Texas. These aggregates have been reported to be poor performers in their environments. Each aggregate failed the tube suction test. A mineralogical evaluation was performed to identify the mineral composition of each aggregate and to explain their high affinity for moisture. Subsequently the aggregates were treated with a concentrated liquid stabilizer. Upon treatment the aggregates showed improved performance in the tube suction test. The Alaska, Nevada, and New Mexico aggregates were then used in construction projects. Initial performance reports have been promising. The tube suction test described in this research has the potential to identify moisture-susceptible aggregates and to serve as a guide in selecting the optimal stabilizer type and amount.
Using a Multisegment Time Domain Reflectometry Probe to Determine Frost Depth in Pavement Systems
Authors: Roberson Ruth L. , Siekmeier John
Published: April 2007

Determining frost depth below the pavement is important for timely implementation of winter and spring load limits. Unfortunately, existing instruments such as resistivity probes, frost tubes, and moisture blocks are limited in terms of both data acquisition (automated and continuous measurements) and data interpretation. Consequently, a delay between data collection, interpretation, and dissemination of information occurs. A laboratory study was conducted by the Minnesota Department of Transportation to investigate the use of the Moisture Point probe as an instrument for locating the depth to the freezing front. The Moisture Point probe combines time domain reflectometry with remote diodeswitching to provide a profile of aggregate base and subgrade dielectric properties. From this, the frost depth can be estimated. The Moisture Point probe works well in locating the frost depth, and it improves the ability to successfully implement spring and winter load limits. This method also provides the opportunity to validate air temperature–based models that are currently used to set spring and winter load limits.
New Model for Evaluation of Traffic Operations at Electronic Toll Collection Plazas
Authors: Al-Deek Haitham M. , Mohamed Ayman A. , Radwan Essam A.
Published: April 2007

Traffic simulation models are used to enhance planning, design, operation, and management of transportation facilities. A discrete-event stochastic object-oriented microscopic simulation model is presented that was specifically developed to evaluate the operational performance of toll plazas. Traffic behavior is represented using a set of mathematical and logic algorithms that control the conflicts among vehicles within the toll plaza area. Modified versions of car-following and lane-changing algorithms and a new toll-lane selection algorithm are integrated into this new model to simulate traffic operation at toll plazas. The model output includes measures of effectiveness (MOEs) that can be used to evaluate the performance of existing and future individual toll lanes and the entire toll plaza system. Real-world data collected at the busiest toll plaza in the Orlando–Orange County Expressway Authority system were used to validate the developed model. Statistical tests indicate that there is no significant difference at the 95 percent confidence level between MOEs obtained from the model and those collected in the real world. Sensitivity analysis of market penetration of the electronic toll collection (ETC) system indicates that an increase in ETC subscription rate improves the efficiency of toll plaza operation. The benefits of ETC depend on the specific plaza configuration. One of the most interesting results of this study is that for all plaza configurations simulated with manual payment lanes operating over capacity, total plaza delay can be reduced by half if only 10 percent of the users switch from manual payment lanes to ETC lanes.
Quasi-Variational Inequality Approach to Multi-User-Class Dynamic Traffic Assignment
Authors: Bliemer Michiel C. J.
Published: April 2007

The extension of a single-user-class macroscopic dynamic traffic assignment model to include multiple user classes is considered. The distinction between user classes is based on vehicle characteristics. Cars and trucks are two typical classes. To deal with various asymmetries that may occur, such as intra-user-class interaction and spatial and temporal asymmetries, the model is specified as a quasi-variational inequality problem. A nested modified projection method is successfully adopted to solve the assignment problem. The solution of the problem depends heavily on the choice of some very important input: the multiclass link travel time functions. Under mild restrictions there exists a solution, which need not be unique. A case study illustrates the model.
Analytical Expressions of Incident-Induced Flow Dynamics Perturbations: Using Macroscopic Theory and Extension of Lighthill-Whitham Theory
Authors: Mongeot Hélène , Lesort Jean-Baptiste
Published: April 2007

The impact of immobile traffic incidents on traffic flow dynamics is modeled using first-order macroscopic flow theory, in which an incident is characterized by dual severity, possibly extensive length, and duration. Incident-induced flow perturbation variations through space and time are then developed as are associated analytical expressions of shock waves, perturbation clearing time, and maximum queue length.
Evaluation of CORSIM Car-Following Model by Using Global Positioning System Field Data
Authors: Chundury Sastry , Wolshon Brian
Published: April 2007

It has been recognized that CORSIM (and its constituent program, NETSIM) is one of the most widely used and effective computer programs for the simulation of traffic behavior on urban transportation networks. Its popularity is due in large part to the high level of detail incorporated into its modeling routines. However, the car-following models, used for the simulation of driver behavior in the program, have not been formally calibrated or validated. Since the model has performed well in a wide range of applications for so many years, it has always been assumed to have an implied validity. This study evaluated the NETSIM car-following models by comparing their results with field data. Car-following field data were collected using a new data collection system that incorporates new Global Positioning System and geographic information system technologies to improve the accuracy, ease, speed, and cost-effectiveness of car-following data collection activities. First, vehicle position and speed characteristics were collected under field conditions. Then simulated speeds and distances were based on identical lead vehicle actions using NETSIM car-following equations. Comparisons of simulated and field data were completed using both graphical and statistical methods. Although some differences were evident in the graphical comparisons, the graphs overall indicated a reasonable match between the field and simulated vehicle movements. Three statistical tests, including a goodness-of-fit test, appear to support these subjective conclusions. However, it was also found that definitive statistical conclusions were difficult to draw since no single test was able to compare the sets of speed and distance information on a truly impartial basis.
Simulation Laboratory for Evaluating Dynamic Traffic Management Systems
Authors: Yang Qi , Koutsopoulos Haris N. , Ben-Akiva Moshe E.
Published: April 2007

Advanced traffic management systems (ATMS) and advanced traveler information systems (ATIS) are promising technologies for achieving efficiency in the operation of transportation systems. A simulation-based laboratory environment, MITSIMLab, is presented that is designed for testing and evaluation of dynamic traffic management systems. The core of MITSIMLab is a microscopic traffic simulator (MITSIM) and a traffic management simulator (TMS). MITSIM represents traffic flows in the network, and the TMS represents the traffic management system under evaluation. An important feature of MITSIMLab is its ability to model ATMS or ATIS that generate traffic controls and route guidance based on predicted traffic conditions. A graphical user interface allows visualization of the simulation, including animation of vehicle movements. An ATIS case study with a realistic network is also presented to demonstrate the functionality of MITSIMLab.
Effects of Relaxation and Anticipation on Riemann Solutions of Payne-Whitham Model
Authors: Zhang H. M. , Kim T.
Published: April 2007

The solutions of Riemann problems of a particular higher-order model—the Payne-Whitham (PW) model—are studied using Roe’s flux splitting scheme as presented by Leo and Pretty. Despite numerous works on higher-order models, little is known about Riemann solutions of these models and how relaxation and anticipation affect these solutions. Riemann solutions of the PW model are computed and compared with those of the Lighthill-Whitham-Richards (LWR) model having the same initial (density) data. It was found that faster relaxation forces the PW model to behave much like the LWR model, that strong anticipation has a stabilizing effect on traffic, and that shock waves travel at different speeds in the PW model than they do in the LWR model. These findings provide a basic checklist for experimental validation of PW-like higher models.
Validation Results for Four Models of Oversaturated Freeway Facilities
Authors: Hall Fred L. , Bloomberg Loren , Rouphail Nagui M. , Eads Brian , May Adolf D.
Published: April 2007

Some researchers have noted that the current procedures in the Highway Capacity Manual (HCM) may not be appropriate for analyzing complex or oversaturated freeway facilities. The results of a comparison of an HCM-based procedure with field data from six such freeway sites are reported. Because simulation has often been suggested as an alternative to the HCM for oversaturated freeway facilities, three simulation models (CORSIM, FREQ, and INTEGRATION) were also used to analyze these same six sites. The results suggest that the HCM-based procedures do as well as the three simulation models in reproducing the average speeds across the freeway facilities.
Variations in Capacity at Signalized Intersections with Different Area Types
Authors: Le Xuewen , Lu Jian , Mierzejewski Edward A. , Zhou Yanhu
Published: April 2007

The capacity analysis procedure for signalized intersections included in the Highway Capacity Manual (HCM) needs to consider the area type of a given intersection. The area-type adjustment factor used in the procedure is based on conclusions from a limited number of studies. In addition, the procedure for using an area-type adjustment factor is not well defined in the HCM. A study undertaken in central Florida to study the effects of four different area types on the capacity of signalized intersections is summarized. These four area types include recreational, business, residential, and shopping. Study results indicated that differences in saturation headways among different area types were significant. The saturation headways observed in recreational areas were significantly higher than those in other areas for both left-turn and through movements. The through-movement saturation headways obtained in residential, shopping, and business areas were not significantly different. This study resulted in a new area-type adjustment factor of 0.92 for recreational areas, whereas the factor is 1.00 for other areas. Results in this study also indicated that the differences in start-up lost time among different area types were not significantly different. In addition, according to the results of the analysis, 75 percent of the yellow interval in undersaturated conditions and 35 percent of the yellow interval in oversaturated conditions were found to be unused and considered clearance lost time.
Determination of Capacity at All-Way Stop-Controlled Intersections
Authors: Wu Ning
Published: April 2007

A new theoretical approach for the determination of capacity at all-way stop-controlled (AWSC) intersections is presented. This approach is based on the addition-conflict-flow method developed from graph theory. The new approach takes all the traffic streams into account, in contrast to existing procedures, which handle only the approaches. It allows a systematic and realistic analysis of the traffic process at AWSC intersections. The new approach can deal with most common lane configurations in the real world. A simple and more practical procedure is recommended. In practice, this simplified procedure can be used for single-lane approaches as well as approaches with separate left-turn traffic lanes. This procedure is verified and calibrated with measured data. For the calculation of capacity at AWSC intersections, general parameters, which are found by calibration, are proposed. The new procedure produces results more precise than the existing ones compared with the measured data. As a result, the maximum total capacities of AWSC intersections with single-lane approaches are found to be between 1,500 and 1,900 passenger cars per hour. The total maximum capacities of AWSC intersections with single-lane approaches and separate left-turn lanes are between 1,800 and 1,950 passenger cars per hour. Furthermore, the procedure shows that additional (left-turn) lanes significantly affect capacity increases only for asymmetric street-flow splits. The present procedure can easily be extended to AWSC intersections with multilane approaches.
Analyzing Arterial Streets in Near-Capacity or Overflow Conditions
Authors: Tarko Andrzej P.
Published: April 2007

Filtering and metering of traffic at highway bottlenecks influence delay and travel speeds along congested arterial streets. The current Highway Capacity Manual (HCM) method of analyzing urban arterial streets uses the filtering and metering adjustment factor I but does not give recommendations on how to adjust traffic volumes. An improved method of analyzing signalized arterial streets affected by bottlenecks is proposed. A set of equations has been derived to calculate the coefficient I and to adjust the traffic volumes. Conditions in which measured or predicted volumes should be adjusted and conditions in which they do not have to be adjusted are specified. The proposed method incorporates the effect of turning volumes, a feature not present in the current HCM method. A sensitivity analysis of travel speeds along an example signalized arterial street illustrates the filtering and metering effects and compares the results produced by the existing and proposed methods. The differences in the results are considerable. In addition, the significant effect of turning volumes has been confirmed. The proposed method tends to produce travel speeds higher than the values obtained with the current method, which concurs with comments from the users of the HCM that the current method underestimates travel speeds. The filtering equation has been derived with the assumptions of fixed capacity and no vehicle dispersion. Under the conditions violating these assumptions, the filtering equation may underestimate I. Further, the proposed method does not incorporate the effect of long queues blocking upstream lane groups. The negative effect on travel speed estimates along the entire arterial should be limited or negligible.
Cost-Effectiveness of High-Occupancy Vehicle Lanes in Texas
Authors: Daniels Ginger , Stockton William R.
Published: April 2007

One method of evaluating the cost-effectiveness of high-occupancy vehicle (HOV) lanes is examined. By use of MicroBENCOST, a planning-level economic analysis tool, and more than a decade of HOV lane documentation in Texas, benefit-cost ratios for all HOV lanes in the state are developed. Estimates of benefits using actual cost data are compared with benefits calculated using the Highway Capacity Manual techniques incorporated into the program. Each HOV lane is assessed as both a stand-alone project and an alternative to two additional general-purpose freeway lanes. The results show that the potential benefit of either alternative varies significantly by corridor. One key variable is manipulated in order that the impact of the HOV lane under increasing total daily traffic in the corridor can be determined. The findings show that the role and effectiveness of the HOV lane vary significantly by type of lane (reversible, contraflow, concurrent) as total corridor traffic increases. These findings may be useful in examination of corridors where HOV lanes are being considered.
Are High-Occupancy Vehicle Lanes Effective? Overview of High-Occupancy Vehicle Facilities Across North America
Authors: Wellander Chris , Leotta Kathy
Published: April 2007

An overview of the performance of a sample of freeway high-occupancy vehicle (HOV) lanes across North America is presented, to describe how they are performing with respect to their true intent and to identify issues for the long-term viability of HOV lanes. Measures of effectiveness evaluated include person-throughput, HOV lane utilization, and travel time savings. The analysis, which was based on a limited amount of data, showed that of the HOV lane facilities reviewed, the vast majority appear to be operating effectively with respect to the measures assessed. In addition, despite recent media criticism and political questioning of HOV lanes, recent surveys from several parts of the country indicate strong public support for the facilities. A number of critical issues for long-term viability of HOV lanes were identified. In the planning stages, it is critical that any HOV facility recommended will meet the minimum standards for utilization and person-throughput, because ineffective or poorly implemented HOV lanes have been known to turn public and political opinion against HOV lanes in general and may serve to discredit other potentially effective HOV facilities. Also recommended is identification of contingency strategies, which, in cases of marginal or under-utilized facilities, could be implemented to make the facility more effectively utilized in the near term and to preserve the HOV option for the long term. Rather than redesignation of a facility for general-purpose (GP) use, alternative ways to manage the facility should be considered, since redesignation of a lane for HOV use is difficult, if not impossible in most areas, once that lane has been turned over to GP traffic.
Reducing Numbers of Vehicle Trips and Vehicle Miles of Travel Through Customized Travel Options
Authors: Cleland Francis
Published: April 2007

A new application was implemented to help reduce total vehicle trips and vehicle miles of travel (VMT) by means of encouraging use of trip chaining and substitution for all types of trips. Travel diaries were provided to employees of a local YMCA for measurement of travel behavior before and after provision of customized travel suggestions. An analysis of covariance was conducted on the average contributed VMT and contributed vehicle trips, with the use of the second period results as the dependent variable. The provision of suggestions had a statistically significant effect on vehicle miles and trips contributed. Overall, it was shown that the provision of travel information would reduce VMT. Further research should be conducted in order to indicate the extent to which such information must be customized. Further research should also be conducted on the durability and sustainability of the impacts of the information.
Effective Transportation Demand Management: Combining Parking Pricing, Transit Incentives, and Transportation Management in a Commercial District of Portland, Oregon
Authors: Bianco Martha J.
Published: April 2007

The Lloyd District is a high-density commercial and residential district located a short distance from downtown Portland, Oregon. To address parking and congestion problems, the city of Portland implemented a Lloyd District Partnership Plan in September 1997. This plan consists of a number of elements aimed at curbing single-occupancy vehicle use for the commute to and from the district. This plan included parking pricing in the form of meters (whereas on-street parking had been free), discounted transit passes, and other transportation demand management strategies. The effects of these strategies on travel and parking behavior were assessed, with an emphasis on the relationship between parking pricing and mode choice. A random sample of 1,000 employees in the Lloyd District was surveyed about their travel and parking behavior before and after the installation of the new meters. Research found that, during the 1 year that had elapsed between the implementation of the Lloyd District transportation management programs and the survey information collected, the drive-alone mode for the trip to work by employees in the Lloyd District had decreased by 7 percent. For the district as a whole, the drive-alone commute share is now about 56 percent. The program strategies that have emerged as the most significant in effecting this decrease are the installation of the meters and the discounted transit pass program.
Market-Based Approach to Customized Trip-Reduction Program Design
Authors: Cleland Francis , Winters Philip
Published: April 2007

Frequently a conflict is observed between the desires of central authorities to implement regionwide commuter service plans (e.g., statewide plans) and the desire of local authorities to customize those plans. The hypothesis that commuters in different cities would have no significant differences in their responses to alternate commute incentives was tested, for the purpose of supporting the notion that a statewide plan is an acceptable and efficient method of designing such incentive plans. Literature on various commute choice modeling techniques was reviewed, as well as literature on the comparison of the effectiveness of various incentives in increasing use of alternative commute modes. From this review, a multivariate regression modeling process was adopted and four incentives were chosen, to be tested by means of a phone-mail survey approach in three different cities in Florida. Models were built and tested for the entire data set, and interaction terms for the impact of cities were tested for significance. Two of the incentives met the 95 percent criterion for falsifying the hypothesis that incentive levels for the three cities were the same. The alternative null hypothesis that all of the cities would have different responses could not be disproved. The conclusion of the research is that the burden of proof rests with those who would state that all of the cities would respond the same way. The data available from the study do not support that conclusion.
Coarse Superpave Mixture Sensitivity
Authors: Epps Amy L. , Hand Adam J.
Published: April 2007

Asphalt-aggregate mixture sensitivity has long been recognized for its potential negative impact on performance if variables including the asphalt content (AC) and the percent that passes the 0.075-mm sieve (p0.075) are not carefully controlled during construction. Typical production standard deviations for AC and p0.075 are 0.3 and 0.9 percent, respectively. This mixture sensitivity analysis shows that variations of this magnitude can result in significant changes in coarse Superpave mixture volumetrics. Three coarse mixtures designed for the WesTrack project were examined, including the original coarse mixture and the replacement mixture. The coarse mixture was most sensitive to both AC and p0.075, contradicting the relatively worse performance of the replacement mixture. The replacement mixture was relatively insensitive to p0.075, and the third mixture was extremely sensitive to reductions in p0.075. Results also suggest that mixture sensitivity may affect optimum AC by up to 1.0 percent. When measured sensitivities were compared with those predicted from models calibrated in the field, the potential for extreme sensitivity was demonstrated by errors in predicted changes in air voids that ranged from 0 to 98 percent because of small changes in AC or p0.075. These findings are disturbing when one considers the current industry trend toward the use of coarse Superpave mixtures. The conclusions drawn warrant a recommendation that mixture sensitivity analyses are needed in the Superpave volumetric mix design process. A mixture sensitivity analysis that is useful for identification of sensitive mixtures and that serves as an excellent field quality management tool is presented.
Evaluation of Notched-Wedge Longitudinal Joint Construction
Authors: Buchanan M. Shane
Published: April 2007

The proper construction of longitudinal joints is critical to the overall performance of a hot-mix asphalt (HMA) pavement. Many times the in-place density at and across the longitudinal joint is substantially lower than the density of the remainder of the HMA surface. This low in-place density increases the potential for cracking and raveling to develop along the joint. Research has shown that the use of the notched-wedge joint has the potential to increase the density at the longitudinal joint, which should result in a longer-lasting pavement. The notched-wedge joint construction technique was compared with conventional longitudinal joint construction techniques on projects in five states (Colorado, Indiana, Alabama, Wisconsin, and Maryland). The evaluation consisted of comparing the in-place densities obtained through pavement cores at five locations across the longitudinal joint of the pavement: at the centerline and at 150 mm (6 in.) and 450 mm (18 in.) on either side of the centerline. The results of the study indicate that the notched-wedge joint can be successfully used to increase the in-place density at the longitudinal joint. Some decrease in the in-place density was observed at the 150-mm (6-in.) location in the second lane (hot side) when the notched-wedge joint was used.