Formulation and Validation of Operating Speed-Based Design Consistency Models by Bootstrapping

1997 ◽  
Vol 1579 (1) ◽  
pp. 97-103 ◽  
Author(s):  
John McFadden ◽  
Lily Elefteriadou
Keyword(s):  
Additional Data ◽  
Original Data ◽  
Statistical Technique ◽  
Geometric Design ◽  
Operating Speed ◽  
Horizontal Alignment ◽  
Alternative Means ◽  
Design Speed ◽  
Design Consistency ◽  
Consistency Models

Current U.S. policy for designing rural two-lane highways is based on design speed to ensure consistency among consecutive highway segments. The design speed concept, however, does not ensure that a consistent alignment will be achieved. A recent FHWA-sponsored project (Horizontal Alignment Design Consistency for Rural Two-Lane Highways) led to three operating speed-based geometric design consistency models, which have not yet been validated. Traditionally, the validation of such models involves the collection of additional data. The statistical technique known as “bootstrapping” was used to formulate and validate the operating speed-based geometric design consistency models by using the existing FHWA database. Bootstrapping involves random sampling with replacement from the existing database, which becomes the population. One-half of the original data collected are used in formulating the models. The remaining half of the data are subsequently used for validation. The models resulting from bootstrapping were statistically equivalent to the models developed in the FHWA study. In addition, the model validation indicated that the bootstrapping technique used to validate the operating speed models is a viable alternative means of validation. It was concluded that bootstrapping is a very useful tool that can be exploited in many related areas in the transportation field, especially because of the large amounts of data typically required in developing and validating empirical models.

Summary of Design Speed, Operating Speed, and Design Consistency Issues

2000 ◽  
Vol 1701 (1) ◽  
pp. 116-120 ◽  
Author(s):  
Douglas W. Harwood ◽  
Timothy R. Neuman ◽  
Joel P. Leisch
Keyword(s):  
Design Process ◽  
Operating Speed ◽  
Current Design ◽  
Design Speed ◽  
Design Consistency ◽  
The Many ◽  
Relationship Of ◽  
Formal Design ◽  
Conference Session

Six papers in this Record were presented at a conference session during the January 1994 TRB annual meeting. They address various aspects of the relationships among design speed, operating speed, and design consistency. All six papers are examined to show the interrelationships of design speed, operating speed, and design consistency; what changes are needed in the current design process and current design policies; how the concept of design consistency can produce better designs; and what research is needed to develop these concepts further. The improvements involve three key principles. First, design speeds must not be arbitrary but must be selected realistically based on projected operating speeds. Second, if lower design speed is used, all aspects of the roadway and its environment must be consistent with the lower speed. Third, large differences in operating speed between successive roadway elements represent design inconsistencies that can lead to safety problems. These principles can be used to develop a design process that leads to safer, more efficient, and more consistent designs. The TRB Committees on Operational Effects of Geometrics (A3A08) and on Geometric Design (A2A02) jointly sponsored the January 1994 conference session to call attention to the many unresolved issues about the roles of design speed, operating speed, and design consistency in creating highway designs that operate efficiently and safely and meet the needs of drivers. Originally, two alternative topics were considered: relationship of design speed and operating speed and the role of formal design consistency criteria in creating good highway designs. These topics were so interrelated that it was difficult to address one without the other. A key insight from the papers was that in a consistent design the design speed selected for use in determining the geometrics of the facility is similar to the operating speed of the completed facility. To call attention to the central role of several speed-related parameters in creating consistent designs, the session was titled “Speed.” Key points of the papers are summarized, generalizing the principles and philosophy for creating consistent designs, and suggesting directions for research to develop the ideas into practical design policies that highway engineers can apply.

scholarly journals Geometric Design, Speed, and Safety

2012 ◽  
Vol 2309 (1) ◽  
pp. 39-47 ◽  
Author(s):  
Richard J. Porter ◽  
Eric T. Donnell ◽  
John M. Mason
Keyword(s):  
Geometric Design ◽  
Operating Speed ◽  
Highway Safety Manual ◽  
Road Geometry ◽  
Speed Management ◽  
Design Speed ◽  
Synthesis Report ◽  
Definition Of ◽  
Roadway Design ◽  
Selection Of

A performance-based approach to the interaction of geometric design, speed, and safety is considered given the availability of two key documents: the Highway Safety Manual and Modeling Operating Speed: Synthesis Report. A historical look at the concept of design speed shows that although the definition of design speed has changed on more than one occasion, the same basic philosophy that related design speed to a safe speed is still reflected in current policy in supplemental guidance related to the selection of design speed. A conservative approach to establishing design criteria, used to address the range of driver, vehicle, and roadway conditions and capabilities that a designer must consider, is demonstrated. Operating speeds are shown to be higher than design speeds for design speeds of approximately 55 mph or less. This outcome may be considered undesirable, but that categorization seems to be based more on subjective judgments of what is desirable than on actual safety findings. Finally, the idea of speed management through the use of roadway geometrics (i.e., geometric designs that influence driver selection of operating speed)—one component of self-enforcing, self-explaining roadway design—is explored. Findings uncover possible challenges to implementing this idea. Five related questions are addressed: (a) What is known about the relationships between road geometry and operating speeds? (b) To what degree does road geometry influence operating speeds? (c) How are safety and security influenced by road geometry? (d) What are the potential impacts on large vehicles? and (e) What is the nature of the speed–safety trade-off?

scholarly journals New geometric design consistency model based on operating speed profiles for road safety evaluation

2013 ◽  
Vol 61 ◽  
pp. 33-42 ◽  
Author(s):  
Francisco J. Camacho-Torregrosa ◽  
Ana M. Pérez-Zuriaga ◽  
J. Manuel Campoy-Ungría ◽  
Alfredo García-García
Keyword(s):  
Road Safety ◽  
Safety Evaluation ◽  
Geometric Design ◽  
Operating Speed ◽  
Model Based ◽  
Consistency Model ◽  
Design Consistency

scholarly journals Evaluation of driver visual demand at different design speeds on complex two-dimensional rural highway alignments

2021 ◽  
Author(s):  
Ahmad Muneeb
Keyword(s):  
Human Life ◽  
Geometric Design ◽  
Two Dimensional ◽  
Design Features ◽  
Highway Design ◽  
Complex Curves ◽  
Design Characteristics ◽  
Design Speed ◽  
Design Consistency ◽  
Demand Profile

Road crashes are a major cause of loss of human life, property and money throughout the world. One of the reasons behind these crashes is the interaction between drivers and road alignments. The need to understand the factors that affect drivers has become obvious and is now being addressed by researchers. Moreover, driver workload is gaining attention as a measure of highway-design consistency as it directly reveals design features to the driver. This research focuses on evaluating driver visual demand at different design speeds along with other geometric design features for two-dimensional rural horizontal roadway alignments. Twelve such alignments having simple and complex curves were designed following the standards of the American Association of Highway and Transportation Officials (AASHTO) and the Transportation Association of Canada (TAC). The driver simulator at Ryerson University, Toronto, recently modified after the integration of a car, was used for the simulation of roadway alignments. Scenario Definition Language (SDL) was used to develop Event files for simulation and to save the required data. Twelve drivers drove the simulated alignments. The output data relating to driver visual demand were processed using MS Notepad and MS Excel. The visual demand calculations for full-element length (VDF), half-element length (VDH) and the first 30 m of element length (VD30) for curve and tangent sections of alignments were done using MS Excel. Statistical Analysis Software (SAS) was used to anlayze and develop models for VDF, VDH and VD30 for curve and tangent sections, first considering design speed only as explanatory variable and then considering design speed along with other geometric design characteristics as explanatory variables. It has been observed that visual demand increases with the increase in design speed. Besides, the combined effect of design speed an other geometric design characteristics (e.g., the type of preceding element, the turning direction of a curve) has significant effect on visual demand. It was also found that visual demand followed a Log Normalized distribution which was also observed by previous research. The developed models were used to establish the visual demand profile for highway design consistency evaluation. The comparison of visual demand profile and operating speed profile has shown that the visual demand can be an acceptable measure for evaluating the highway design consistency.

scholarly journals Geometric design of single-lane roundabouts for optimum consistency and operation

2021 ◽  
Author(s):  
Atif Mehmood
Keyword(s):  
Optimum Design ◽  
Optimization Model ◽  
Operational Performance ◽  
Design Parameters ◽  
Operating Speed ◽  
Site Conditions ◽  
Design Speed ◽  
Vehicle Path ◽  
Design Consistency ◽  
Geometric Layout

The objectives while designing roundabout is design consistency and operational performance. Design consistency affects roundabout safety while operational performance affects its level of service. Along with design consistency, roundabout will be more safe if its geometry forces traffic to enter and circulate at less than specified design speed. Vehicle path radii control speeds at each vehicle path. Vehicle path radii are traditionally obtained from drawing freehand each vehicle paths on proposed roundabout geometry. Existing design approaches for roundabouts use a trial-and-error procedure to choose the design parameters in order to satisfy design standards. With this approach it is quite complicated to satisfy design guidelines and site conditions at the same time. A minor change in geometry can result in significant changes in safety and operational performance. Therefore, many iterations of geometric layout would be required to evaluate safety and operational analysis at given traffic conditions. Designer needs to revise and refine the initial geometric layout to enhance safety and its operational performance. In this thesis, an optimization model is developed that predicts optimum design parameters with multiple objectives: maximum design consistency and minimum average intersection delay. At optimum design parameters, this model also provides vehicle path radii for each path. These vehicle path radii were used to predict operating speed along each path using an existing operating speed prediction model. The optimization model takes site conditions as input and satisfies the two objectives for given traffic and geometric conditions. This is a new approach of optimum design of single-lane roundabouts with four legs intersecting at right angle. The model not only satisfies the two objectives, but also limits the operating speed along each path (left, through, and right), below the specified design speed of roundabout.

Operating speed models for two-lane rural roads in Pakistan

2008 ◽  
Vol 35 (5) ◽  
pp. 443-453 ◽  
Author(s):  
Rizwan A. Memon ◽  
G. B. Khaskheli ◽  
A. Sami Qureshi
Keyword(s):  
Global Positioning System ◽  
Prediction Models ◽  
Geometric Design ◽  
Operating Speed ◽  
Rural Roads ◽  
Horizontal Curves ◽  
Measuring Devices ◽  
Global Positioning ◽  
Speed Prediction ◽  
Design Consistency

One of the suitable techniques used to improve safety on roads is to check the consistency of geometric design. The concept of design consistency has emerged worldwide, but no research has been found to date on design consistency in Pakistan. The most common parameter for the evaluation of design consistency is operating speed. Several models have been developed to predict operating speed on two-lane rural roads. However, these models were based on spot speed data collected through traditional speed measuring devices. This study uses continuous speed profile data collected using a vehicle equipped with a VBox (a global positioning system based device). Eleven test sections were selected in two provinces of Pakistan (i.e., Sindh and Balochistan). Driver behavior is also studied in the present research. Models were developed for prediction of operating speed on horizontal curves and on tangents. Validation of the developed models shows compatibility with the experimental data; hence, the developed speed prediction models can be used to evaluate the geometric design consistency of two-lane rural roads in Pakistan.

scholarly journals OPERATING SPEED PREDICTION MODEL AS A TOOL FOR CONSISTENCY BASED GEOMETRIC DESIGN OF FOUR-LANE DIVIDED HIGHWAYS

Transport ◽  
2019 ◽  
Vol 34 (4) ◽  
pp. 425-436 ◽  
Author(s):  
Gourab Sil ◽  
Avijit Maji ◽  
Suresh Nama ◽  
Akhilesh Kumar Maurya
Keyword(s):  
Prediction Model ◽  
Lateral Position ◽  
Geometric Design ◽  
Operating Speed ◽  
Vehicle Speed ◽  
Horizontal Curve ◽  
Passenger Cars ◽  
Horizontal Curves ◽  
Speed Prediction ◽  
Design Consistency

Researchers have studied two-lane rural highways to predict the operating speed on horizontal curves and correlated it with safety. However, the driving characteristics of four-lane-divided highways are different. Weak lane discipline is observed in these facilities, which influences vehicle speed in adjacent lane or space. So, irrespective of its lane or lateral position, vehicles in four-lane divided highways are considered free flowing only when it maintains the minimum threshold headway from any lead vehicle. Examination of two conditions is proposed to ensure the free flow. Vehicles meeting both conditions, when tracked from the preceding tangent section till the centre of the horizontal curve, are considered as free flowing. The speed data of such free flowing passenger cars at the centre of eighteen horizontal curves on four-lane divided highways is analysed to develop a linear operating speed prediction model. The developed model depends on curve radius and preceding tangent length. The operating speed of passenger car in four-lane divided highways is influenced by horizontal curve of radius 360 m or less. Further, longer tangent would yield higher operating speed at the centre of the curve. Finally, two nomograms are suggested for conventional design, consistency based design and geometric design consistency evaluation of four-lane divided horizontal curves.

Geometric design of single-lane roundabouts for optimum consistency and operation

2021 ◽  
Author(s):  
Atif Mehmood
Keyword(s):  
Optimum Design ◽  
Optimization Model ◽  
Operational Performance ◽  
Design Parameters ◽  
Operating Speed ◽  
Site Conditions ◽  
Design Speed ◽  
Vehicle Path ◽  
Design Consistency ◽  
Geometric Layout

The objectives while designing roundabout is design consistency and operational performance. Design consistency affects roundabout safety while operational performance affects its level of service. Along with design consistency, roundabout will be more safe if its geometry forces traffic to enter and circulate at less than specified design speed. Vehicle path radii control speeds at each vehicle path. Vehicle path radii are traditionally obtained from drawing freehand each vehicle paths on proposed roundabout geometry. Existing design approaches for roundabouts use a trial-and-error procedure to choose the design parameters in order to satisfy design standards. With this approach it is quite complicated to satisfy design guidelines and site conditions at the same time. A minor change in geometry can result in significant changes in safety and operational performance. Therefore, many iterations of geometric layout would be required to evaluate safety and operational analysis at given traffic conditions. Designer needs to revise and refine the initial geometric layout to enhance safety and its operational performance. In this thesis, an optimization model is developed that predicts optimum design parameters with multiple objectives: maximum design consistency and minimum average intersection delay. At optimum design parameters, this model also provides vehicle path radii for each path. These vehicle path radii were used to predict operating speed along each path using an existing operating speed prediction model. The optimization model takes site conditions as input and satisfies the two objectives for given traffic and geometric conditions. This is a new approach of optimum design of single-lane roundabouts with four legs intersecting at right angle. The model not only satisfies the two objectives, but also limits the operating speed along each path (left, through, and right), below the specified design speed of roundabout.

Time-Based Calibration of the Inertial Operating Speed to Enhance the Assessment of the Geometric Design Consistency

2018 ◽  
Vol 2672 (38) ◽  
pp. 223-232 ◽  
Author(s):  
David Llopis-Castelló ◽  
Francesco Bella ◽  
Francisco Javier Camacho-Torregrosa ◽  
Alfredo García
Keyword(s):  
Human Factors ◽  
Short Term Memory ◽  
Weighted Average ◽  
Geometric Design ◽  
Accurate Estimation ◽  
Operating Speed ◽  
Speed Profile ◽  
Consistency Model ◽  
Global Consistency ◽  
Design Consistency

Road crashes are mainly caused by three concurrent factors: infrastructure, vehicle, and human factors. The interaction between the infrastructure and human factors leads to the concept of geometric design consistency. Recently, a global consistency model was developed based on the difference between the inertial operating speed profile and the operating speed profile. The first was defined as the weighted average operating speed of the previous road section based on distance, and represents drivers’ expectancies, whereas the second represents road behavior. However, drivers’ expectancies are related to short-term memory which declines gradually and depends on time. Thus, a time-based inertial operating speed would allow a more accurate estimation of the phenomenon. This research analyzes different periods of time and weighting distributions to identify how drivers’ expectancies should be estimated. A set of 71 homogeneous road segments located in Italy were considered in the study. As a result, 25 seconds and a convex parabolic distribution should be used to calculate the inertial operating speed profile. This new way of estimating drivers’ expectancies showed better results than those obtained based on distance. Finally, the proposed consistency model was compared with the previous models and was found to be able to assess more accurately the geometric design consistency. Therefore, the proposed consistency model is a useful tool for engineers to estimate the number of crashes so that they can incorporate road safety considerations into the geometric design of either new two-lane rural roads, or improving the existing ones.

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