Showing papers in "Transportation Research Record in 2012"

Impacts of cooperative adaptive cruise control on freeway traffic flow

Abstract: This study used microscopic simulation to estimate the effect on highway capacity of varying market penetrations of vehicles with adaptive cruise control (ACC) and cooperative adaptive cruise control (CACC). Because the simulation used the distribution of time gap settings that drivers from the general public used in a real field experiment, this study was the first on the effects of ACC and CACC on traffic to be based on real data on driver usage of these types of controls. The results showed that the use of ACC was unlikely to change lane capacity significantly. However, CACC was able to increase capacity greatly after its market penetration reached moderate to high percentages. The capacity increase could be accelerated by equipping non-ACC vehicles with vehicle awareness devices so that they could serve as the lead vehicles for CACC vehicles.

Better Understanding of Factors Influencing Likelihood of Using Shared Bicycle Systems and Frequency of Use

Abstract: Planning and transportation professionals are promoting a variety of sustainable travel alternatives, such as public transit usage, walking, and cycling, as affordable transportation options to counter the negative effects of widespread car use. In their traditional form, these alternative transport modes do not always offer the flexibility or convenience of the car; therefore, innovative solutions have been developed to allow active and public transport to compete better with the car. Shared bicycle systems have been adopted by a growing number of cities and regions throughout the world, yet little is known about the users of the systems and their motivations. A survey was conducted in Montreal, Quebec, Canada, in the summer of 2010 to determine the factors that encouraged individuals to use the system and the elements that influenced frequency of use. The factor found to have the greatest effect on the likelihood for use of a shared bicycle system was the proximity of home to docking stations. Ownership...

The Half-Mile Circle: Does It Best Represent Transit Station Catchments?

Abstract: The 0.5-mile distance has become accepted for gauging a transit station's catchment area in the United States and is the de facto standard for the planning of U.S. transit-oriented developments (TODs). Planners and researchers use transit catchment areas not only to make predictions about transit ridership and transit impacts (socioeconomic and on land use) but also to prescribe regulations (e.g., relaxing restrictive zoning or carving out TODs for financial plans). This radius is loosely based on the distance that people are willing to walk to transit, but the same reasoning has been used to justify other transit catchment areas. Station-level variables from 1,449 high-capacity American transit stations in 21 cities are used to determine whether a clear benchmark between distance and ridership provides a norm for station-area planning and prediction. Results indicate that, for the purposes of predicting station-level transit ridership, different catchment areas have little influence on a model's predicti...

Analysis of causes of major train derailment and their effect on accident rates

Abstract: Analysis of the causes of train accidents is critical for rational allocation of resources to reduce accident occurrence in the most cost-effective manner possible. Train derailment data from the FRA rail equipment accident database for the interval 2001 to 2010 were analyzed for each track type, with accounting for frequency of occurrence by cause and number of cars derailed. Statistical analyses were conducted to examine the effects of accident cause, type of track, and derailment speed. The analysis showed that broken rails or welds were the leading derailment cause on main, yard, and siding tracks. By contrast to accident causes on main tracks, bearing failures and broken wheels were not among the top accident causes on yard or siding tracks. Instead, human factor-related causes such as improper use of switches and violation of switching rules were more prevalent. In all speed ranges, broken rails or welds were the leading cause of derailments; however, the relative frequency of the next most common a...

Effects of Sample Preparation and Interpretation of Thermogravimetric Curves on Calcium Hydroxide in Hydrated Pastes and Mortars

Abstract: Calcium hydroxide [Ca(OH)2] is one of the major constituents of hydrated portland cement paste. Its content can be used to trace the progress of cement hydration or serve as an indicator of the extent of pozzolanic reaction. The thermogravimetric analysis (TGA) method is often used to determine the Ca(OH)2 content because it is a relatively easy and fast procedure. However, no universally accepted method exists for the preparation of TGA specimens and for the interpretation of the resulting TGA curves. This paper presents an investigation on the contents of Ca(OH)2 in samples subjected to different preparation techniques. The results showed that a certain amount of calcium carbonate (CaCO3) was produced as a result of carbonation during the sample preparation process. The degree of carbonation was dependent on the sample preparation, and carbonated Ca(OH)2 was considered to determine the accurate total Ca(OH)2 content. In addition, a modified interpretation of the TGA curve for Ca(OH)2 was suggested. In t...

Integrated Lane Change Model with Relaxation and Synchronization

Abstract: A proposed lane change model can be integrated with a car-following model to form a complete microscopic driver model. The model resembles traffic better at a macroscopic level, especially regarding the amount of traffic volume per lane, the traffic speeds in different lanes, and the onset of congestion. In a new approach, lane change incentives are combined for determining a lane change desire. Included incentives are to follow a route, to gain speed, and to keep right. Classification of lane changes is based on behavior that depends on the level of lane change desire. Integration with a car-following model is achieved by influencing car-following behavior for relaxation and synchronization, that is, following vehicles in adjacent lanes. Other improvements of the model are trade-offs between lane change incentives and the use of anticipation speed for the speed gain incentive. Although all these effects are captured, the lane change model has only seven parameters. Loop detector data were used to validat...

Inferring Road Maps from Global Positioning System Traces

Abstract: As a result of the availability of Global Positioning System (GPS) sensors in a variety of everyday devices, GPS trace data are becoming increasingly abundant. One potential use of this wealth of data is to infer and update the geometry and connectivity of road maps through the use of what are known as map generation or map inference algorithms. These algorithms offer a tremendous advantage when no existing road map data are present. Instead of the expense of a complete road survey, GPS trace data can be used to generate entirely new sections of the road map at a fraction of the cost. In cases of existing maps, road map inference may not only help to increase the accuracy of available road maps but may also help to detect new road construction and to make dynamic adaptions to road closures—useful features for in-car navigation with digital road maps. In past research, proposed algorithms had been evaluated qualitatively with little or no comparison with prior work. This lack of quantitative and comparativ...

Routing Strategies Based on Macroscopic Fundamental Diagram

Abstract: An excess number of vehicles in a traffic network will reduce traffic performance. This reduction can be avoided by traffic management. In particular, traffic can be routed such that the bottlenecks are not oversaturated. The macroscopic fundamental diagram provides the relation between the number of vehicles and the network performance. One can apply traffic control on this level, in order to overcome computational complexity of network-wide control using traditional control levels of links or vehicles. Main questions in the paper are: (1) how effective is traffic control using aggregate variables compared to using full information and (2) does the shape of the macroscopic fundamental diagram change under traffic control. A grid network with periodic boundary conditions is used as example, and is split up into several subnetworks. The following routing strategies are compared: (1) the shortest path in distance, (2) the path shortest in time (dynamic due to congestion), (3) an approximation of the path shortest in time, but calculated using only variables aggregated for over a subnetwork, (4) an approximation of the path shortest in time, but calculated using only subnetwork accumulation. For routing strategy 3 and 4 only information aggregated over the subnetwork is used. The results show improved traffic flow using detailed information. Effective control is also possible using aggregated information, but only with the right choice of a subnetwork macroscopic fundamental diagram. Furthermore, when optimizing with detailed information – an hence in a subnetwork – the macroscopic fundamental diagram changes.

Simplified Viscoelastic Continuum Damage Model as Platform for Asphalt Concrete Fatigue Analysis

Abstract: Cracking in asphalt concrete pavements is a major form of pavement distress in the United States. Because the cracking phenomenon is complex and cracking is often affected by both material and structural factors, field engineers have no quick and effective test and analysis protocols. A suite of fatigue analysis tools—as well as applications built around the simplified viscoelastic continuum damage (S-VECD) model—is presented. The S-VECD formulation is presented in a summarized form. Next, the characterization protocols, which are consistent with the capabilities of the asphalt mixture performance tester, are shown. Considerable attention is then given to S-VECD-based analysis tools for assessment of material- and pavement-level fatigue performance. Results show that the S-VECD model can be used to predict the number of cycles until fatigue failure for both constant stress and constant strain loading. The S-VECD model's sensitivity to mixture composition and external factors is shown through predictions o...

One-Way Carsharing: Solving the Relocation Problem

Abstract: Carsharing services allow users to benefit from the advantages of a private car without the costs of owning one. One-way systems provide users with a higher level of service than traditional carsharing systems in terms of flexibility because users do not need to return to the station of origin. Moreover, the added option to leave the vehicle at any free parking area, which is not necessarily a station, increases the flexibility offered by the one-way system. Introduction of such improvements to the carsharing system, however, leads to a vehicle relocation problem, which should be addressed carefully to avoid concentration of vehicles in certain areas. This paper reports on a study of this issue with the use of discrete event systems (DESs), which allowed an easy representation of the complex dynamics of the carsharing system. A user-based methodology was proposed on the basis of an optimal relocation policy in a rolling horizon framework. This methodology not only offers greater flexibility to users, it a...

Detection of Activities of Public Transport Users by Analyzing Smart Card Data

Abstract: During the past decade, a significant amount of research has been dedicated to the use of smart card data for various purposes. A method is presented for the detection and estimation of the location, time, duration, and purpose of activities undertaken by public transit users with the use of smart card databases and other available information about land use and user behavior. The method is applied to cases in Santiago, Chile, and Gatineau, Quebec, Canada, to identify activity purpose and time frame to characterize user behavior. The results obtained for each city are compared to discover differences in behavioral activity patterns due to sociological, cultural, and geopolitical differences.

Laboratory Performance Evaluation of Warm-Mix Asphalt Containing High Percentages of Reclaimed Asphalt Pavement

Abstract: This study evaluated the rutting resistance, moisture susceptibility, and fatigue resistance of warm-mix asphalt (WMA) mixtures containing high percentages of reclaimed asphalt pavement (RAP) through laboratory performance tests. The WMA mixtures were plant produced with a foaming technology commonly used in the United States. RAP content ranged from 0% up to 50%. Laboratory performance tests included the asphalt pavement analyzer rutting test, the Hamburg wheel-tracking test, the tensile strength ratio test, the Superpave® indirect tension test, and the beam fatigue test. For comparison purposes, hot-mix asphalt mixtures containing 0% and 30% RAP were also evaluated and compared with WMA. The laboratory test results indicated that WMA mixtures with high percentages of RAP exhibited higher resistance to rutting, better resistance to moisture damage, and better fatigue performance.

Porous Asphalt Pavement Temperature Effects for Urban Heat Island Analysis

Abstract: Increased nighttime temperatures caused by retained heat in urban areas is a phenomenon known as the urban heat island (UHI) effect. Urbanization requires an increase in pavement surface area, which contributes to UHI as a result of unfavorable heat retention properties. In recent years, alternative pavement designs have become more common in an attempt to mitigate the environmental impacts of urbanization. Specifically, porous pavements are gaining popularity in the paving industry because of their attractive storm water mitigation and friction properties. However, little information regarding the thermal behavior of these materials is available. This paper explores the extent to which porous asphalt pavement influences pavement temperatures and investigates the impact on UHI by considering the diurnal temperature cycle. A one-dimensional pavement temperature model developed at Arizona State University was used to model surface temperatures of porous asphalt, traditional dense-graded asphalt, and portlan...

Electric Bikes and Transportation Policy: Insights from Early Adopters

Abstract: Electric bikes (e-bikes) are increasingly common in China but are relatively rare in the United States. The findings from interviews with 28 e-bike owners in the Portland, Oregon, region provide insight into the potential market for and use of e-bikes in the United States. The interviews revealed several possible demographic markets for e-bikes that could expand the bicycling population: women, older adults, and people with physical limitations. Owners of e-bikes noted their ability to travel longer distances and over hills with relative ease and to arrive at a destination, such as work, less sweaty and less tired than a regular bicycle would allow. These features may overcome some of the common barriers to bicycling for all demographics. Most of the interviewed e-bike owners used their e-bikes to substitute for travel by either human-powered bicycles or traditional motor vehicles. Therefore, the e-bike can address concerns about health problems related to inactivity, pollution, and other public policy problems to which private vehicles contribute. Further research is needed to determine whether specific policies are needed to increase adoption of e-bikes. The potential for conflict between riders of e-bikes and of regular bikes because of speed differentials is a concern. Whether speed differentials will pose a significant problem will depend not only on the extent of adoption of e-bikes but the characteristics of the riders.

Rail Transit Travel Time Reliability and Estimation of Passenger Route Choice Behavior: Analysis Using Automatic Fare Collection Data

Abstract: Applications of automatic fare collection data were investigated, with a focus on analysis of travel time reliability and estimation of passenger route choice behavior. Beijing Metro was used as a case study. A rail journey was decomposed, and each component was studied with regard to the uncertainties involved. Methods were then designed and validated to infer platform elapsed time (PET) for through stations and platform elapsed time-transfer (PET-Trans) for transfer stations by using smart card transactional data, train schedules, and complementary manual surveys. With this information, the journey time distribution of any path can be established, and methods were proposed for inferring route choice proportions. After data preparation, the methods were applied to two typical origins and destinations from the Beijing Metro. Key values concerning travel time reliability, such as PET, PET-Trans, travelers left behind (unable to board), and path coefficients, were obtained and interpreted in detail. The out...

Traffic Safety for Electric Bike Riders in China: Attitudes, Risk Perception, and Aberrant Riding Behaviors

Abstract: The use of electric bikes (e-bikes) in China has grown tremendously in the past decade. Traffic safety for e-bike riders is an issue of growing public concern because the number of fatalities and injuries is increasing. A study was conducted to identify risk factors affecting involvement of e-bike riders in accidents and to establish the relationships between safety attitudes, risk perception, and aberrant riding behaviors. The data used for analysis were obtained from a self-reported questionnaire survey of a sample of 603 e-bike riders in two large cities in China. The results showed that both gender and automobile driving experience were significantly associated with at-fault accident involvement. Males were more likely to have at-fault accidents than were females, and riders with an automobile driver's license were less likely to have accidents than were those without a driver's license. Two types of aberrant riding behaviors, errors and aggressive behaviors, were found to be significant factors for predicting at-fault accident involvement. Analysis with a structural equation model indicated that safety attitudes and risk perception both significantly affected aberrant riding behaviors. E-bike riders with stronger positive attitudes toward safety and more worry and concern about their traffic risk tended to be less likely to have aberrant riding behaviors. Practical implications for improving road safety of e-bike riders are discussed.

Calibration of "Highway Safety Manual" Safety Performance Function: Development of New Models for Rural Two-Lane Two-Way Highways

Abstract: This paper documents the calibration of the "Highway Safety Manual" (HSM) safety performance function (SPF) for rural two-lane two-way roadway segments in Utah and the development of new SPFs through negative binomial regression. Crash data from 2005 to 2007 on 157 selected study segments in Utah provided a 3-year frequency of observed crashes to calibrate the HSM SPF and develop new models. The calibration factor for the HSM SPF for rural two-lane two-way roads in Utah is 1.16, indicating that the original HSM model underpredicts crashes in Utah. The HSM suggests that jurisdiction-specific SPFs may predict crashes with greater reliability than calibrated SPFs. The following variables were significant in each of the four models developed by this research: annual average daily traffic (AADT), segment length, speed limit, and the percentage of AADT composed of multiple-unit trucks. AADT and segment length are used in the HSM SPF; speed limit and the percentage of AADT composed of multiple-unit trucks were found to correlate significantly with observed crash frequencies. The fourth negative binomial model developed in the study would be the best SPF to predict crashes on rural highways in Utah. As encouraged by the HSM and contemporary research, the empirical Bayes method can be applied with each jurisdiction-specific SPF because the analysis provided an overdispersion parameter for each model.

Characterization of Fracture Properties of Asphalt Mixtures as Measured by Semicircular Bend Test and Indirect Tension Test

Abstract: The objective of this study was to investigate the intermediate temperature fracture resistance of various asphalt mixtures, as measured by the semicircular bending (SCB) and indirect tension (IDT) test methods, and to correlate these fracture properties to the cracking performance of Louisiana asphalt pavements. Effects of design and process-based factors such as mixture-producing technologies (e.g., hot mix versus warm mix), asphalt binder grades, aging of test specimens, and reclaimed asphalt pavement (RAP) content on the fracture properties were investigated. Results indicated that the SCB-measured critical strain energy release rate (Jc) values showed good correlation with the IDT-measured toughness index values, especially when laboratory-produced mixtures were compared. In addition, the asphalt binder grade and aging condition of specimens influenced the fracture properties of asphalt mixtures. Asphalt mixtures with polymer-modified asphalt binders exhibited greater fracture resistance than did tho...

Assessment of Interaction of Crash Occurrence, Mountainous Freeway Geometry, Real-Time Weather, and Traffic Data

Abstract: This study investigated the effect of the interaction between roadway geometric features and real-time weather and traffic data on the occurrence of crashes on a mountainous freeway. The Bayesian logistic regression technique was used to link a total of 301 crash occurrences on I-70 in Colorado with the space mean speed collected in real time from an automatic vehicle identification (AVI) system and real-time weather and roadway geometry data. The results suggested that the inclusion of roadway geometrics and real-time weather with data from an AVI system in the context of active traffic management systems was essential, in particular with roadway sections characterized by mountainous terrain and adverse weather. The modeling results showed that the geometric factors were significant in the dry and the snowy seasons and that the likelihood of a crash could double during the snowy season because of the interaction between the pavement condition and steep grades. The 6-min average speed at the crash segment...

Exploring Properties of Networkwide Flow-Density Relations in a Freeway Network

Abstract: The objective of this study is to investigate the properties of network-level traffic flow relationships in a freeway network with the use of commonly available loop detector data. The impact of the spatial and temporal distribution of congestion in a selected network on the shape and properties of the flow-density relation is investigated, with emphasis on the formation and characterization of hysteresis patterns. Accordingly, a path-dependent characterization of hysteresis patterns in freeway networks is introduced and illustrated conceptually as well as through empirical observations. Comparison of the spatial and temporal distribution of congestion throughout a selected subnetwork on different days suggests a relationship between the size of the hysteresis loop and the inhomogeneity of the traffic distribution. The maximum network average flow is not a constant value but varies across different days. In addition, for the same value of average network occupancy, the variation of occupancy is higher dur...

Can Results of car-following Model Calibration Based on Trajectory Data be Trusted?:

Abstract: Calibration of car-following models against trajectory data has been widely applied as the basis for studies ranging from model investigation and benchmarking to parameter correlation analysis. Other theoretical issues, such as inter- and intradriver heterogeneity or multianticipative driving behavior, are also addressed in such studies. However, very few of these studies attempted to analyze and quantify the uncertainty entailed in the calibration process and its impacts on the accuracy and reliability of results. A thorough understanding of the whole calibration problem (against trajectory data), as well as of the mutual effect of the specific problems raised in the field literature, does not yet exist. In this view, a general methodology to assess a calibration procedure was proposed and applied to the calibration of the Gipps' car-following model. Compact indicators were proposed to evaluate the capability of a calibration setting to find the known global solution regarding the accuracy and the robust...

Bayesian Updating Approach for Real-Time Safety Evaluation with Automatic Vehicle Identification Data

Abstract: Although numerous studies have attempted to use data from inductive loop and radar detectors in real-time crash prediction, safety analyses that have investigated the use of traffic data from an increasingly prevalent nonintrusive surveillance system have not included the tag readers on toll roads known as "automatic vehicle identification (AVI) systems" This paper (a) compares the prediction performance of a single generic model for all crashes and a specific model for rear-end crashes that used AVI data, (b) applies a Bayesian updating approach to generate full probability distributions for the coefficients, and (c) compares the estimation efficiency of the semiparametric Bayesian modeling with that of logistic regression with frequentist matched case control A comparison of AVI data collected before all crashes and rear-end crashes with matched noncrash data revealed that rear-end crashes could be identified with a 72% accuracy, whereas the generic all-crash model achieved an accuracy of only 69% whe

Assessment of Communitywide Bikeability with Bicycle Level of Service

Abstract: A novel method assessed the quality of bicycle travel throughout a community Most previous research on the quality of bicycle travel assessed bicycle suitability, that is, the perceived comfort and safety of a linear section of bikeway Assessment of bikeability (as defined by authors), however, considers comfort and safety of the entire bikeway network for access to important destinations, and there is ample research concerning the related concept of accessibility A proposed calculation for bikeability was developed on the basis of a common accessibility equation and was demonstrated through a case study of three capital investment scenarios The analysis used a geographic information system Engineers and planners can follow a similar procedure to the one used in the calculation development to prioritize improvement projects or to communicate the benefits of new projects

Path-Constrained Traffic Assignment

Abstract: This paper presents a mathematical programming model and solution method for the path-constrained traffic assignment problem, in which route choices simultaneously follow the Wardropian equilibrium principle and yield the distance constraint imposed on the path. This problem is motivated by the need for modeling distance-restrained electric vehicles in congested networks, but the resulting model and solution method can be applied to various conditions with similar path-based constraints. The equilibrium conditions of the problem reveal that any path cost in the network is the sum of corresponding link costs and a path-specific out-of-range penalty term. The suggested method, based on the classic Frank-Wolfe algorithm, incorporates an efficient constrained shortest-path algorithm as its subroutine. This algorithm fully exploits the underlying network structure of the problem and is relatively easy to implement. Numerical results from the examples of problems provided show how the equilibrium conditions are...

Microparticipation with Social Media for Community Engagement in Transportation Planning

Abstract: Transportation planning processes may be enhanced and plans improved by engaging the community through social media technologies. "Microparticipation" means the engagement of the public with social media methods for the purpose of maximizing the information going into a planning process while minimizing the plan's development time and the cost to the public. Twitter, Facebook, and other microparticipation media have been used for planning but have not been extensively evaluated for that purpose. This study examined more than 49,000 posts on Twitter and other social networking sites tracked by the Social Networking and Planning Project to determine public engagement in the Austin Strategic Mobility Plan. With the use of a mixed methods approach, relevant posts were examined to determine sentiment, extent of engagement, and impact on the decision-making process. The study found methods that could be used to analyze microparticipation. The report concluded that microparticipation could be effective in genera...

Measuring Nonmotorized Accessibility and Connectivity in a Robust Pedestrian Network

Abstract: This paper explores measures of pedestrian accessibility and network connectivity with a network that includes pedestrian facilities in addition to the street network. Studies that focus on walkability usually use available street networks that do not include pedestrian-only facilities. The effect of missing pedestrian connections where the street network is richer than the pedestrian network has been examined in some studies, but the case of suburban environments with robust pedestrian networks has mostly been ignored. In the current study, various measures of connectivity and accessibility were compared between the pedestrian network and the street network in different suburban settings and for accessibility to different land use activities, such as schools and retail centers. Documenting the degree to which the pedestrian network enhanced pedestrian accessibility over the street network alone was motivated by the desire to inform research and to inform policy. Nine neighborhoods in the city of Davis, C...

Effects of Oxidative Aging on Asphalt Mixture Properties

Abstract: Aging has long been recognized as a contributing factor to fatigue distress of asphalt concrete pavement. Several research studies have been undertaken to gain fundamental understanding of the aging phenomenon at the asphalt binder level. However, relatively little effort has been made to understand and to quantify the effects of aging on fundamental characteristics of asphalt mixtures. The effects of oxidative aging on the dynamic modulus and the fatigue performance of asphalt mixtures is examined. For this purpose, an asphalt mixture is aged in the laboratory at four aging levels. Mechanical tests for the four aged mixtures are performed to characterize the linear viscoelastic and damage properties. Such characterization is investigated to incorporate the aging effects into a more comprehensive analytical framework for predicting the performance of asphalt concrete pavements. Finally, this framework is used to evaluate the aging effects on an example asphalt concrete pavement. It is found that aging can...

Exit Choice Decisions during Pedestrian Evacuations of Buildings

Abstract: This paper assesses how exit choice behavior influences the total egress behavior of a crowd during building evacuation. A discrete choice model is proposed to represent pedestrian exit choice decisions during evacuation. The proposed model is based on responses to an Internet questionnaire conducted in the Netherlands and the United States. The results of the Internet questionnaire, consisting of 20 choice experiments by 100 respondents making trade-offs between distance, angular deviation, and group following behavior, are used to estimate a multinomial logit model. Accordingly, a new pedestrian simulation approach that uses a microscopic cellular automata model (EvacPed) is presented. Three levels of decision making are incorporated: global exit choice, regional adaptive route choice, and local operative behavior. Simulations estimate the difference in evacuation time between four exit choice strategies: least distance path, least travel time path, discrete choice incorporating hive knowledge, and disc...

Modeling Concepts for Mixed Traffic: Steps Toward a Microscopic Simulation Tool for Shared Space Zones

Abstract: A first step is presented toward a simulation tool for shared space zones, including all three prevailing individual modes of transport: cars, bicycles, and walking. Unlike on conventional roads, the behavior in shared spaces cannot be modeled by following a predefined path and strictly obeying traffic rules because the architectural design allows for many more degrees of freedom. Therefore, the research focused on two main aspects: finding a path for each individual and handling potential conflicts with other individuals. A simulation tool is needed because many urban planners see shared space as a modern design concept for busy urban roads. A growing number of cities are interested in experimenting with shared space zones but are uncertain about safety issues and the effectiveness of the design. Although mature simulation tools exist for conventional road designs, no such tool is available for shared space designs because of the added degrees of freedom in movement and more-complex social interactions. ...

Thirty Years of Gipps’ Car-Following Model: Applications, Developments, and New Features

Abstract: Researchers and practitioners commonly use car-following models for road traffic studies. Although dozens of models have been presented so far, the one proposed by Peter G. Gipps in 1981 is still one of the most extensively used. However, many features of the model are still not well known or neglected in common applications. In this context, the current study summarizes and analyzes the main findings available in the scientific literature for the Gipps' car-following model and introduces some of its novel features that may improve its capability to reproduce real trajectory data. In particular, the structure of the acceleration component of the model is analytically investigated for what concerns the meaning of some parameters that in common practice are usually kept to some empirically derived fixed values. Possible versions of Gipps' model are presented, and their performance to reproduce real vehicle trajectories is evaluated and compared. The results achieved show the necessity for these parameters t...