Comfort thresholds for horizontal curve design

2009 ◽  
Vol 36 (9) ◽  
pp. 1391-1402 ◽  
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.

Safety Benefits of Spiral Transitions on Horizontal Curves on Two-Lane Rural Roads

1998 ◽  
Vol 1635 (1) ◽  
pp. 10-17 ◽  
Author(s):  
Forrest M. Council
Keyword(s):  
Mountainous Terrain ◽  
Horizontal Curve ◽  
Inventory Data ◽  
Steering Angle ◽  
Rural Roads ◽  
Friction Forces ◽  
Horizontal Curves ◽  
Confounding Variables ◽  
Side Friction ◽  
Alternative Designs

A vehicle entering or departing a horizontal curve must safely undergo a change in steering angle and a resulting change in side friction forces. The safety-related effects of two alternative designs were evaluated for the “transition” sections of pavement where the curve and tangent meet— a spiral transition, where the tangent and curve are linked by an ever-tightening spiral curve, and a nonspiral transition where the tangent directly abuts the horizontal curve. Using crash and roadway inventory data from over 15,000 transition sections (curve ends) in the state of Washington, contingency table analyses and linear logistic modeling were conducted to explore differences in the probability of one or more crashes on the two types of transitions within each of three types of terrain—level, rolling, and mountainous. At level terrain sites, spiral presence is related to a decrease in crash probability on curve ends with degree of curve greater than approximately 3 degrees. For rolling terrain, a decrease was predicted for all sites on minor arterials and major collectors, and for principal arterial sites with average daily traffic greater than 3,700 vehicles per day. In contrast, in mountainous terrain, an increase in crash probability due to the spiral was predicted for all sites except those with both wider roadway widths and wider shoulders. The models for the mountainous terrain sites did not fit the data as well, indicating the presence of other unmeasured confounding variables.

Relationship between Predicted Speed Reduction on Horizontal Curves and Safety on Two-Lane Rural Roads in Spain

2014 ◽  
Vol 140 (3) ◽  
pp. 04013015 ◽  
Author(s):  
Juan de Oña ◽  
Laura Garach ◽  
Francisco Calvo ◽  
Teresa García-Muñoz
Keyword(s):  
Rural Roads ◽  
Speed Reduction ◽  
Horizontal Curves

Driver tolerance of lateral accelerations on horizontal curves

2010 ◽  
Vol 37 (3) ◽  
pp. 413-419 ◽  
Author(s):  
Eric D. Hildebrand ◽  
Jonathan Lewis
Keyword(s):  
Lateral Acceleration ◽  
Vehicle Speed ◽  
Design Standards ◽  
Driver Behaviour ◽  
Threshold Levels ◽  
Horizontal Curves ◽  
Unique Method ◽  
Short And Long Term ◽  
Digital Video Analysis

There are many roadways where existing horizontal curves fail to meet minimum geometric design standards for financial or geographic reasons. Advisory speeds, typically set with a ball-bank indicator, are posted on these curves to ensure that drivers are not subjected to uncomfortable levels of lateral accelerations as they negotiate the curve. The threshold levels of lateral acceleration as estimated by ball-bank indicators vary considerably between jurisdictions with many still basing their guidelines on studies dating back to the 1930s and 1940s. This study investigated present day ball-bank indicator tolerance levels by analyzing actual driver behaviour on 30 curves posted with advisory speeds in New Brunswick. A unique method of data collection involving digital video analysis enabled the development of vehicle speed profiles approaching and throughout the curves. The results indicated that drivers tolerate higher levels of discomfort as they navigate curves than currently assumed. This finding justifies raising the ball-bank indicator threshold levels used for posting advisory speeds. Inconsistencies between actual posted advisory speeds, policy guidelines, and jurisdictional implementation have also been identified. Recommendations address both short and long-term goals of updating ball-bank indicator thresholds used for signing to levels that better represent driver behaviour. Longer-term recommendations address the development of uniform signing standards across Canada so that driver expectation will not be violated between jurisdictions.

The Effects of Edgeline Presence on Performance in a Driving Simulator under Sober and Alcohol-Dosed Conditions

1983 ◽  
Vol 27 (4) ◽  
pp. 329-329
Author(s):  
Thomas A. Ranney ◽  
Valerie J. Gawron
Keyword(s):  
Visual Information ◽  
Driving Simulator ◽  
Lateral Acceleration ◽  
Task Demand ◽  
Rural Roads ◽  
Pavement Markings ◽  
Horizontal Curves ◽  
Varying Length ◽  
Alcohol Effects ◽  
And Performance

Accident studies have identified nighttime conditions on rural roads as particular problems for alcohol-impaired drivers. Uneventful driving is hypothesized to result in progressive degradation of tracking performance and a reduced capability to handle the demands of hazardous locations, such as curves. To address these problems, simulations of continuous roadway treatments (i.e., wide edge lines) and spot treatments for curves (i.e., post delineators, chevron alignment signs, patterned pavement markings, and flashing displays) were evaluated experimentally. Twelve subjects drove a simulator under two conditions of task demand and three levels of BAC (0.0, 0.07, 0.12%). The objectives of the study were to determine the effects of alcohol and task demand on driving performance and to determine if providing enhanced visual information concerning roadway alignment would improve the performance of subjects when sober and/or alcohol-dosed. Alcohol effects were measured in terms of overall scenario performance, which included the number of accidents and speed exceedances, and performance on the approach and negotiation of horizontal curves of varying length and curvature. Curve approach and negotiation behavior were also used to evaluate the effects of the roadway treatments. Specific measures included spot measures of speed and lateral placement taken at eight 100-foot intervals along the curve approach and lateral acceleration and position taken continuously over the fixed portion of the curves. The results presented pertain to the effects of the presence of standard and wide edgelines. The discussion relates current findings to those from a previously conducted study.

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

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.

scholarly journals KELIO TRASOS HORIZONTALIŲJŲ KREIVIŲ ĮTAKA TRANSPORTO SRAUTO GREIČIUI / INFLUENCE OF ROAD ALIGNMENT HORIZONTAL CURVE ON TRANSPORT FLOW OPERATING SPEED

2019 ◽  
Vol 11 (0) ◽  
pp. 1-7
Author(s):  
Mindaugas Šeporaitis ◽  
Viktoras Vorobjovas
Keyword(s):  
Road Network ◽  
Operating Speed ◽  
Horizontal Curve ◽  
The Road ◽  
Horizontal Curves ◽  
Legal Documents ◽  
Transport Flow ◽  
Design Speed ◽  
Side Friction ◽  
Curve Selection

Geometric parameters of road alignment are fundamental elements defining permissible speed and vice versa. Unlike permissible speed, determined operating speed in upgrade projects has a significant impact on the safe movement of transport on the roads. The article reviews the composition of the regional road network in Lithuania, the design speed, the permitted speed, the practical problems of applying the geometry parameters of the road alignment according to the legal documents valid in Lithuania, methods of horizontal curve selection in Lithuania and other countries are analysed in more detail. Comparative initial calculations of horizontal curves were performed using different side friction coefficients. Review summary of analysis conducted and statements are prepared for discussion.

Evaluation of design consistency on horizontal curves for two-lane state roads using bicycle-model and realistic parameters of driver behaviour

2021 ◽  
Author(s):  
◽  
Biljana Maljković
Keyword(s):  
Point Mass ◽  
Horizontal Curve ◽  
Vehicle Model ◽  
Mass Model ◽  
Driver Behaviour ◽  
Horizontal Alignment ◽  
Horizontal Curves ◽  
Road Design ◽  
Vehicle Path ◽  
Design Consistency

The loss of vehicle stability in horizontal curves is a clear indicator of horizontal alignment design inconsistency, which can easily be quantified by determining the margins of safety. The doctoral thesis presents an overview of current horizontal alignment design guidelines and most important research of the design consistency concept. The following significant shortcomings in current road design practice were noticed: selection of unrealistic relevant speeds, the assumption that drivers follow a path with a radius equal to curve radius and the application of too simple vehicle model, i.e. basic point mass model. To overcome the observed limitations, the new consistent design approach has been developed, with an emphasis on horizontal curves. The new approach is based on the margin of safety concept, improved in terms of using the bicycle vehicle model in combination with more realistic values of speed and vehicle path radii. The bicycle vehicle model considers longitudinal load transfer, on individual axles, due to grade and speed changes, i.e. factors affecting margins of safety that are completely ignored by the simple point mass model used so far. To collect the driver behaviour data, an experimental investigation was conducted on a segment of the two-lane state road DC1 (Croatia). Individual speeds and vehicle path radii achieved by representative sample of drivers were recorded with a highfrequency GPS device. Based on the analysis of recorded data, the implementation of naturalistic driver behaviour in the road design process is proposed through regression models for predicting operating speeds (for tangents and horizontal curves) and through the equation for calculating the critical path radius. The improvement of the safety margin concept has created the basis for designing horizontal curves with high level of safety, both for the values of available friction on modern pavements as well as for future measurements. Based on operating speed consistency criterion and improved safety criterion related to driving dynamic consistency, the graphs of applicable adjacent horizontal curve radii were developed. The results obtained showed that the values of minimum horizontal curve radii need to be increased and, finally, this analysis has provided a physical explanation of the most common causes of accidents in sharp horizontal curves.

Speed Reduction as a Surrogate for Accident Experience at Horizontal Curves on Rural Two-Lane Highways

2000 ◽  
Vol 1701 (1) ◽  
pp. 86-94 ◽  
Author(s):  
Ingrid B. Anderson ◽  
Raymond A. Krammes
Keyword(s):  
Linear Regression ◽  
Significant Relationship ◽  
Statistical Relationship ◽  
Speed Profile ◽  
Horizontal Curve ◽  
Accident Rate ◽  
Speed Reduction ◽  
Profile Model ◽  
Horizontal Curves ◽  
The Mean

A proposed speed profile model was used to estimate the reduction in 85th percentile speeds from the approach tangent to the midpoint of 1,126 horizontal curve sites on rural two-lane highways in three states. The sites were divided into eight speed-reduction intervals, the mean accident rate and mean speed reduction were computed for each category, and linear regression was performed to analyze the statistical relationship between mean accident rate and mean speed reduction. Similar analyses were performed with degree-of-curvature intervals to compare mean degree of curvature and mean speed reduction as predictors of accident experience. The results suggest that estimated speed reduction is a useful measure that helps explain how accident experience at horizontal curves on rural two-lane highways varies with degree of curvature. Horizontal curves that require speed reductions [generally, curves sharper than about 4°, a condition that corresponds with design speeds less than 100 km/h (60 mph) and estimated 85th percentile speeds less than drivers’ desired speeds on long tangents] have higher accident rates than curves that do not require speed reductions. When curve sites are grouped into speed-reduction intervals, there is a statistically significant relationship between the intervals’ mean accident rate and mean speed reduction. The mean accident rate increases approximately linearly with the mean speed reduction.

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

1996 ◽  
Vol 1523 (1) ◽  
pp. 34-45
Author(s):  
Ruediger Lamm ◽  
Basil Psarianos ◽  
George Soilemezoglou ◽  
George Kanellaidis
Keyword(s):  
Geometric Design ◽  
Driving Dynamic ◽  
Safety Criterion ◽  
Rural Roads ◽  
Safety Issues ◽  
Road Design ◽  
Friction Factors ◽  
The Status ◽  
Design Consistency ◽  
Side Friction

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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