Driving Dynamic Aspects and Related Safety Issues for Modern Geometric Design of Non-Built-Up Roads

Safety issues affecting modern highway geometric design of roads in non-built-up areas are discussed. The status of knowledge of Safety Criteria I and II (achieving operating speed consistency and design consistency) for two-lane rural roads is briefly reviewed. Considerations for design consistency are also extended to multiple-lane rural and suburban road design to evaluate good, fair, and poor design levels for these road categories. Utilization ratios (n) for maximum permissible side friction factors are developed for different road categories, topography levels, and maximum and minimum superelevation rates. Relevant minimum radii for curve design are established and compared with present AASHTO values insofar as possible. Safety Criterion III (achieving driving dynamic consistency) is further developed, through which reliable and quantitative ranges between the side friction assumed and the actual friction demand at curved sites could be established. AASHTO's design policy is evaluated on the basis of Criteria II and III. The evaluation showed, for lower design speeds (30, 40, and 50 mph), an unbalanced degree of curve and superelevation rate ranges, which lead to poor design practices from a safety viewpoint. By heeding the three safety criteria and the recommended side-friction utilization ratios, sound alignments can be established for the various design cases in future highway geometric design and redesign and for resurfacing, restoration, and rehabilitation strategies.

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Influence of Road Geometric Design Consistency on Familiar and Unfamiliar Drivers’ Performances: Crash-Based Analysis

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198119851446 ◽

2019 ◽

Vol 2673 (10) ◽

pp. 489-500 ◽

Cited By ~ 5

Author(s):

Paolo Intini ◽

Nicola Berloco ◽

Pasquale Colonna ◽

Sofie Ottersland Granås ◽

Eirin Olaussen Ryeng

Keyword(s):

Experimental Studies ◽

Related Factor ◽

Design Elements ◽

Safety Issues ◽

Vehicle Accidents ◽

Road Design ◽

Dangerous Behavior ◽

Run Off ◽

Single Vehicle ◽

Design Consistency

Drivers’ road familiarity is a safety-related factor. Familiar drivers may be prone to inattention and more dangerous behavior, whereas unfamiliar drivers may be affected by demanding and unexpected road environments. Previous research adequately described the role of familiarity in driving behavior and road safety performances. However, the relationships between drivers’ unfamiliarity and safety issues of road design elements are still largely unexplored and there is a lack of dedicated experimental studies. In this work, a database including run-off-road single-vehicle accidents at Norwegian rural two-lane road curves was investigated. Information about familiarity was derived from the distance from the residence of drivers involved in crashes. Road geometric variables were collected on the segment before the accident site, to provide indicators of design consistency of the previous road section. Thereafter, logistic regression was used to find relationships between predictor variables related to the geometric road design consistency and familiarity (the dependent variable). As a result of the analysis, familiarity was confirmed as a factor associated to possible dangerous behavior such as speeding in demanding road environments. However, crashes involving unfamiliar drivers are associated to unexpected curve parameters (radius and length) and the combination of horizontal and vertical curvature. Thus, as well as familiarity, drivers’ unfamiliarity may be considered as an accident factor. Moreover, some possibly useful consequences for road design are suggested for practitioners. They specifically concern provisions about radii of subsequent curves and coordination between radii of horizontal and vertical curves.

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Evaluation of design consistency on horizontal curves for two-lane state roads in terms of vehicle path radius and speed

The Baltic Journal of Road and Bridge Engineering ◽

10.3846/bjrbe.2016.15 ◽

2016 ◽

Vol 11 (2) ◽

pp. 127-135

Author(s):

Biljana Maljković ◽

Dražen Cvitanić

Keyword(s):

Horizontal Curves ◽

Percentage Difference ◽

Friction Factors ◽

The Difference ◽

Design Speed ◽

Vehicle Path ◽

Design Consistency ◽

Side Friction ◽

Curve Radius ◽

The Impact

Experimental investigation was conducted on a 24 km long segment of the two-lane state road to collect the driver behavior data. The research involved 20 drivers driving their own cars equipped with the GPS device. Considering the impact of path radius and speed on the side friction demand, the design consistency on horizontal curves was evaluated by determining the margins of safety. The analysis showed that the vehicle path radii were mainly smaller than curve radius, on average for 12%. Regression analysis indicated that the percentage difference between the curve radius and vehicle path radius is not affected by the speed, speed differential and geometric characteristics of the curve and surrounding elements. Two different margins of safety were analyzed. One is the difference between maximum permissible side friction (based on design speed) and side friction demand, while another is the difference between side friction supply (based on operating speed) and side friction demand. Generally, demands exceeded supply side friction factors on curves with radii smaller than 150 m, whereas “poor” conditions (in terms of Lamm’s consistency levels) were noted for curves under approximately 220 m. Both values are very close to the critical radius below which higher accident rates were observed according to several accident studies. Based on the results of the research, it is proposed to use a 12% smaller curve radius for the evaluation of margin of safety and that curves with radii smaller than 200 m should be avoided on two-lane state roads outside the built-up area.

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Operating speed models for two-lane rural roads in Pakistan

Canadian Journal of Civil Engineering ◽

10.1139/l07-126 ◽

2008 ◽

Vol 35 (5) ◽

pp. 443-453 ◽

Cited By ~ 12

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.

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Comfort thresholds for horizontal curve design

Canadian Journal of Civil Engineering ◽

10.1139/l09-075 ◽

2009 ◽

Vol 36 (9) ◽

pp. 1391-1402 ◽

Cited By ~ 4

Author(s):

Dalia Said ◽

Yasser Hassan ◽

A.O. Abd El Halim

Keyword(s):

Research Work ◽

Lateral Acceleration ◽

Horizontal Curve ◽

Driver Behaviour ◽

Rural Roads ◽

Speed Reduction ◽

Horizontal Curves ◽

Friction Factors ◽

Side Friction Factor ◽

Side Friction

A key to better geometric design of highways is designing horizontal curves conforming to driver behaviour. The values of side friction factors in the point mass formula, used for the design of the minimum radius of a horizontal curve, are based on the upper threshold of driver comfort. In the current guidelines, these driver comfort levels were established in research work carried out back in the 1930s. Recently, it was found that faster drivers tend to accept higher comfort thresholds to maintain their speed and minimize speed reduction between curve and tangent. An experiment was designed at Carleton University to collect newer data on driver behaviour including speed and lateral acceleration. The results confirmed the need to revise the values of side friction demand especially for sharp curves. In addition, a model was developed to determine the side friction factor to be used in design or in consistency evaluation of horizontal curves on rural roads and ramps.

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Sustainable design of rural roads with 2+1 road design: Levels of service and traffic flow performance

KSCE Journal of Civil Engineering ◽

10.1007/s12205-016-1696-1 ◽

2016 ◽

Vol 20 (3) ◽

pp. 1032-1039 ◽

Cited By ~ 1

Author(s):

Jaisung Choi ◽

Youngrok Kim ◽

Torsten Bergh ◽

Sangyoup Kim ◽

Sungkyu Kim

Keyword(s):

Traffic Flow ◽

Sustainable Design ◽

Rural Roads ◽

Road Design ◽

Levels Of Service

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Measurement and Prediction of the Effects of Nonuniform Surface Roughness on Turbulent Flow Friction Coefficients

Journal of Fluids Engineering ◽

10.1115/1.3243567 ◽

1988 ◽

Vol 110 (4) ◽

pp. 380-384 ◽

Cited By ~ 20

Author(s):

R. P. Taylor ◽

W. F. Scaggs ◽

H. W. Coleman

Keyword(s):

Turbulent Flows ◽

Rough Surfaces ◽

Reynolds Numbers ◽

Base Diameter ◽

Friction Coefficients ◽

Friction Factors ◽

Random Rough Surfaces ◽

The Status ◽

Uniform Array ◽

Prediction Approach

The status of prediction methods for friction coefficients in turbulent flows over nonuniform or random rough surfaces is reviewed. Experimental data for friction factors in fully developed pipe flows with Reynolds numbers between 10,000 and 600,000 are presented for two nonuniform rough surfaces. One surface was roughened with a mixture of cones and hemispheres which had the same height and base diameter and were arranged in a uniform array. The other surface was roughened with a mixture of two sizes of cones and two sizes of hemispheres. These data are compared with predictions made using the previously published discrete element prediction approach of Taylor, Coleman, and Hodge. The agreement between the data and the predictions is excellent.

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