VISSIM Calibration for Urban Freeways

In urban areas, interchange spacing and the adequacy of design for weaving, merge, and diverge areas can significantly influence available capacity. Traffic microsimulation tools allow detailed analyses of these critical areas in complex locations that often yield results that differ from the generalized approach of the Highway Capacity Manual. In order to obtain valid results, various inputs should be calibrated to local conditions. This project investigated basic calibration factors for the simulation of traffic conditions within an urban freeway merge/diverge environment. By collecting and analyzing urban freeway traffic data from multiple sources, specific Iowa-based calibration factors for use in VISSIM were developed. In particular, a repeatable methodology for collecting standstill distance and headway/time gap data on urban freeways was applied to locations throughout the state of Iowa. This collection process relies on the manual processing of video for standstill distances and individual vehicle data from radar detectors to measure the headways/time gaps. By comparing the data collected from different locations, it was found that standstill distances vary by location and lead-follow vehicle types. Headways and time gaps were found to be consistent within the same driver population and across different driver populations when the conditions were similar. Both standstill distance and headway/time gap were found to follow fairly dispersed and skewed distributions. Therefore, it is recommended that microsimulation models be modified to include the option for standstill distance and headway/time gap to follow distributions as well as be set separately for different vehicle classes. In addition, for the driving behavior parameters that cannot be easily collected, a sensitivity analysis was conducted to examine the impact of these parameters on the capacity of the facility. The sensitivity analysis results can be used as a reference to manually adjust parameters to match the simulation results to the observed traffic conditions. A well-calibrated microsimulation model can enable a higher level of fidelity in modeling traffic behavior and serve to improve decision making in balancing need with investment

Investigation Of Free-Flow Speed At Basic Segment Expressways For Level Terrain In Malaysia

Free-flow speed (FFS) is an important parameter in the speed-flow relationship, analyses of capacity and level of service (LOS) for basic segment expressways. Relevant authorities in Malaysia have been referring to the ArahanTeknik (Jalan) 8/86 to estimate LOS for basic segment expressways based on v/c ratio. However, due to the technological advancement and the surge of vehicle numbers on roads, the values obtained in the study may not show the actual resemblance of current Malaysian traffic conditions in Malaysia. There are several FFS models presented in major references and previous studies throughout the world. However, the suitability of these models for Malaysian traffic conditions is limited to some extent. Therefore, this study was conducted to understand in more detail about FFS at basic segment expressways and to develop FFS model based on current local standards. Six FFS models are developed based on regression analysis. However, one final model is selected as the best FFS model through the performance indicators. In this study, FFS of vehicles without motorcycles using headway (≥ 8 s) is selected as the best FFS model. Sensitivity analysis had also been performed in order to measure the sensitivity of each parameter for the developed FFS model. Thus, the outcome of this study is valuable for local traffic engineers and highway authorities in Malaysia for better understanding of the FFS and to estimate LOS at basic segment expressways

Development and validation of a driving simulator for traffic control using field data

This paper presents the development and validation of a driving simulator for ramp traffic control on expressways using a traffic simulator and control (TSC). The TSC consists of two main components: car-following model (CFM), and traffic controller (TC). The CFM simulates the car-following behavior and delivers aggregated traffic parameters to the TC to derive control actions. The CFM and TC are harmonized and integrated in a close-loop control manner, where the effects of the control by the TC are fed-back as inputs for the CFM in real-time applications. Although the following behavior of individual vehicles is simulated, the aggregated outputs such as average speed and flow rate from the model are the parameters of interest. For simplicity in the model development and validation and to capture lane-changing effects, the traffic in the multi-lane expressway where the data were obtained was equivalently represented as a single-lane system. The validation of the CFM was performed at macroscopic level where aggregated outputs from the model were compared to observed data in a segment of the Pan Island Expressway of Singapore under various traffic conditions. The result shows that the simulated speed is not significantly different from the actual speed at 5% significance level, and the aggregated flow rate discrepancies fall in a small range, from 2.21% to 3.15%. This shows that the TSC model is a reliable model for traffic simulation and control applications

Incorporating the standstill distance and time headway distributions into freeway car-following models and an application to estimating freeway travel time reliability

Standstill distances and following time headways are two important microsimulation model parameters associated with driver aggression. This paper investigates the distributions of standstill distances and time headways and incorporates these distributions into car-following models to estimate travel time reliability. By incorporating standstill distance and following headway into car-following models as stochastic parameters, a speed-density region can be generated, based on which various travel-time-reliability measures can be calculated. Key findings of this study are as follows: (1) Both standstill distances and time headways follow fairly dispersed distributions. Therefore, it is suggested that microsimulation models should include the option of allowing standstill distances and time headways to follow distributions as well as to be specified separately for different vehicle classes. (2) By incorporating stochastic standstill distance and time headway parameters in car-following models, travel-time-reliability measures can be estimated more precisely and faster compared with using VISSIM

Statistical and simulation methods for evaluating stationary and mobile work zone impacts

In 2014, nearly 10% of overall congestion on freeways was due to the presence of work zones (WZs), equivalent to 310 million gallons of fuel loss (FHWA, 2017a). In terms of safety, in the US, every 5.4 minutes, a WZ related crash occurred in 2015 (96,626 crashes annually) (FHWA, 2017b). Maintenance work involves both Stationary Work Zones (SWZs) and Mobile Work Zones (MWZs). There are many analytical and simulation-based tools available for analyzing the traffic impacts of SWZs. However, the existing traffic analysis tools are not designed to appropriately model MWZs traffic impacts. This study seeks to address this gap in existing knowledge through the use of data from MWZs to develop and calibrate traffic impact analysis tools. This objective is accomplished through data fusion from multiple sources of MWZ, probe vehicle and traffic detector data. The simulation tool VISSIM is calibrated for MWZs using information extracted from videos of MWZ operations. This is the first study that calibrated the simulation based on real driving behavior behind a MWZ. The three recommended calibration parameters are safety reduction factor of 0.7, minimum look ahead distance of 500 feet and the use of smooth closeup option. These calibration values can be used to compare MWZ scenarios. Also, the data collection framework and calibration methodology designed in this study could be used in future research. The operational analysis concluded that a moving work activity lasting one hour or more are suggested to be done when traffic volumes are under 1400 veh/hr/ln, and preferably under 1000 veh/hr/ln, due to the drastic increase in the number of conflicts. In addition, three data driven models were developed to predict traffic speed inside a MWZ: a linear regression model and two models that used Multi-Gene Genetic Programming (MGGP). The second objective is to develop models and tools for safety assessment of stationary work zones. In the WZ safety literature, few studies have quantified the safety impact of SWZ and almost no quantitative study assessing MWZ safety impact. Using Missouri data, this study introduces 20 new crash prediction models for SWZs on freeways, expressways, rural two lane highways, urban multi-lane highways, arterials, ramps, signalized intersections, and unsignalized intersections. All the models except freeway SWZs are proposed for the first time in the literature. The mentioned SWZ models are implemented in a user-friendly spreadsheet tool which automatically selects the most appropriate model based on user input. The tool predicts crashes by severity, and computes the crash costs. For MWZs, there is no crash data available to develop crash prediction models. Thus, this dissertation analyzed conflict measures as a surrogate for safety impacts of MWZs. Conflict measures were generated from the trajectories of traffic simulation model. The safety trade-off plots between conflicts and combination of MWZ's duration and traffic volume were introduced. A transportation agency can use these plots to determine, for example, if they should conduct a MWZ for a short duration when the volume is high or for a longer duration when the volume is lower.Includes bibliographical reference

An investigation of freeway standstill distance, headway, and time gap data in heterogeneous traffic in Iowa

Microsimulation models have been growing in popularity in traffic engineering in recent years, and are often used as an important tool in the decision making process on large roadway design projects. In order to get valid results, it is necessary to calibrate such microsimulation models to local conditions. This is frequently achieved through a trial and error process of adjusting model parameters to get simulation results to match real world calibration data. Rarely is data collected on the model parameters themselves to provide a physical basis for the selection of their value. Two of the most important microsimulation model parameters for freeway models are standstill distance (the distance between stopped vehicles) and preferred time headway or time gap (the time between successive vehicles). Many simulation models treat these values as constants for all drivers and do not allow them to be set separately for different vehicle classes. This study presents a repeatable methodology for collecting standstill distance and headway/time gap values on freeways (mostly urban, with one rural location). It applies that methodology to locations throughout the state of Iowa. It continues by analyzing that data and comparing it for different locations and conditions. It finds that standstill distances vary by location and vehicle pair type. Headways/time gaps are found to be consistent within the same driver population and across different driver populations when the conditions are similar. An initial comparison between headways/time gaps at three urban areas to one rural location indicates a potential difference in driver behavior between those two conditions. Both standstill distance and headway/time gap are found to follow fairly disperse and skewed distributions. As a result of these findings, it is recommended that microsimulation models are modified to include the option for standstill distance and headway/time gap to follow distributions as well as be set separately for different vehicle classes. Additionally, the standstill distances and headway/time gaps found in this study may be used as a starting point for future microsimulation calibration efforts on urban freeways in Iowa

Intersection Safety

The objectives of this project included a study to determine the safety effects of intersection type (unsignalized, signalized, and interchange) on Nebraska expressway intersections, quantification of the safety effects of a Collision Countermeasure System (CCS), and update of the Nebraska Department of Roads (NDOR) expressway intersection guidelines. The CCS is an Intelligent Transportation Systems (ITS) traffic control device to warn drivers of conflicting cross-traffic at rural, non-signalized intersections. The goal was that if found effective, the CCS will become part of the intersection designer’s options for expressway intersection design (other options being an interchange, traffic signals, and traffic control signs). Analysis results indicated that exposure (measured as total entering traffic) is an important factor affecting expressway intersection safety – expected number of accidents on an intersection approach increase with increasing exposure. While the analysis did not reveal any differences in safety of unsignalized and signalized intersections, the presence of horizontal curves on intersection approaches was found to increase accidents while vertical curves placed through intersections were also found increase accidents on intersection approaches. Expressway approaches with offset left turn lanes were found safer when compared to conventional left turn lanes and expressway approaches with no exclusive left-turn lanes. The above information is recommended for addition to the existing NDOR expressway intersection guidelines to make Nebraska expressway intersections safer. This report also provides directions for future expressway safety investigative research efforts

Intersection Safety

The objectives of this project included a study to determine the safety effects of intersection type (unsignalized, signalized, and interchange) on Nebraska expressway intersections, quantification of the safety effects of a Collision Countermeasure System (CCS), and update of the Nebraska Department of Roads (NDOR) expressway intersection guidelines. The CCS is an Intelligent Transportation Systems (ITS) traffic control device to warn drivers of conflicting cross-traffic at rural, non-signalized intersections. The goal was that if found effective, the CCS will become part of the intersection designer’s options for expressway intersection design (other options being an interchange, traffic signals, and traffic control signs). Analysis results indicated that exposure (measured as total entering traffic) is an important factor affecting expressway intersection safety – expected number of accidents on an intersection approach increase with increasing exposure. While the analysis did not reveal any differences in safety of unsignalized and signalized intersections, the presence of horizontal curves on intersection approaches was found to increase accidents while vertical curves placed through intersections were also found increase accidents on intersection approaches. Expressway approaches with offset left turn lanes were found safer when compared to conventional left turn lanes and expressway approaches with no exclusive left-turn lanes. The above information is recommended for addition to the existing NDOR expressway intersection guidelines to make Nebraska expressway intersections safer. This report also provides directions for future expressway safety investigative research efforts

Evaluation of the Monroe Expressway Wrong Way Vehicle Detection Program

NCDOT RP 2019-25In North Carolina, wrong way driving (WWD) crashes are one of the most severe traffic crashes that often result in a fatality or serious injury since they involve head-on or opposite direction sideswipe crashes at high speeds. To minimize the occurrence of WWD crashes, the North Carolina Turnpike Authority (NCTA), which is a unit of the North Carolina Department of Transportation (NCDOT), deployed a wrong way vehicle detection system along the Monroe Expressway in 2018. The system can automatically detect wrong way vehicles at mainline stations and inform traffic management center operators. This project evaluated the effectiveness of wrong-way traffic control devices installed at the ramp and mainline locations along the Monroe Expressway. A comprehensive literature search was conducted to summarize the state-of-the-practice of WWD crash modeling, detection, and prevention. Real-world traffic data including traffic volume, traffic control devices present, geometry and configuration of interchanges were employed for identifying the relationship between the frequencies of wrong way incidents and facility characteristics. During the study period of approximately 1.5 years of data collection, there were 13 actual WWD events, of which five wrong way movements originated from the roundabout parclo interchanges on the Monroe Expressway. In addition, this project collected statewide data on partial cloverleaf interchanges to assess the risk for wrong way movements. It was found that the partial cloverleaf interchange configuration was associated with the highest number of WWD activities, and factors that affect the risk of WWD mainly include: entrance and exit ramp traffic volume and control type, divided or undivided exit ramp, median cut turn access, left-turn perpendicular turning distance, skew angle, and distance between ramp terminals

A Master Highway Transportation Plan for Tampa Metropolitan Area, Hillsborough County, Florida

Fully recognizing the need for a comprehensive study of an integrated expressway and arterial highway system for the Tampa Metropolitan area, the State Road Department of Florida, jointly with the County of Hillsborough and the City of Tampa, engaged Wilbur Smith and Associates to develop a Master Highway Transportation Plan for the Tampa Area. The geographic limits of the study area are defined as the city limits of Tampa on the north, Tampa Bay on the west, Hillsborough Bay on the south, and U. S. Route 301 on the east. The development of basic planning data and necessary field studies were initiated in November of 1956. The report, as contained herein, is an objective, factual study of traffic needs, roadway facilities and terminal parking necessary to meet these needs. The arterial street system necessary to supplement and complement the interstate highways traversing the area is recommended, together with detailed functional plans for the proposed expressway system. All traffic needs were evaluated in terms of projected 1975 traffic requirements