Rural Highway Design Consistency Evaluation Model

European Journal of Transport and Infrastructure Research, 2008

Crashes on two-lane rural highways are over-represented at horizontal curves, and speed inconsistency is a common contributing factor to these crashes. Road Consistency reflects the similarity or lack thereof of vehicle performance along an entire road segment. Consistency is measured by estimating the speed variation along successive geometric elements and evaluation of the speed deviation from the average speed. Because it has been shown in the past that speed variability has an impact on safety, it was hypothesized that design consistency is also related to safety. The purpose of this study is to examine the relationship between road design consistency and crash probability on two-lane rural highways. An enhanced consistency model is applied to examine this relationship in Israel and Germany. This consistency model is based on both the horizontal and vertical alignments and takes into account the impact of trucks and grades on road consistency. A statistically significant model that showed a reduction in average crash numbers per year with an increase in consistency is presented and discussed. It was found that the Israeli and German models have a similar trend. The enhanced-consistency model and the software may be used relatively easily to determine consistencies of different alternatives during the planning of new highways or the reconstruction of existing roads. Planners and decisionmakers could be advised of potential design deficiencies during the design process and consequently, modify a proposed design and thus improve safety levels and save lives.

Procedia - Social and Behavioral Sciences, 2014

One significant measure of the design quality of a road is consistency. In this study, consistency based on operating speed was calculated in two-lane rural highways of the province of Granada. Three consistency measures were calculated for 506 homogeneous road sections: the relative area, which represents the area bounded by the speed profile and average speed of a road segment, the standard deviation of the operating speed in each design element along the road segment and the consistency model defined by Polus and , based on the previous measures introduced. Some discrepancies have been found in the results obtained

1988

European design guidelines explicitly address horizontal design consistency for two-lane, rural roads in an attempt to promote smooth operating speed profiles and, in turn, safe operation. U.S. practice qualitatively advocates consistent alignment but provides little objective guidance to assure that consistency is achieved. This paper presents a procedure for measuring the consistency of horizontal design as defined by operating speed and accidents expected. Operating speeds and accident rates can be predicted for various lane widths based on degree of curve and posted recommended speeds, as derived from measurement of 261 sites in New York state. Guidelines for changes in operating speeds and acceptable accident rates for good, fair, and poor designs are suggested, and various nomographs are developed to evaluate roadway sections based on design parameters. In addition, an example application is provided to illustrate the case of fair design practices. It is concluded that such a ...

Arabian Journal for Science and Engineering, 2018

This study investigates the effect of geometric design consistency on road safety in the West Bank. Studies have shown that operating speed, vehicle stability, alignment indices, and driver's workload are the common consistency measures that might affect safety. A total of 118-km two-lane rural highways in the West Bank, Palestine, were studied based on limitations of available data. Comprehensive geometric and operating data for the selected highways obtained from field survey, maps, and official sources were used to investigate the effect of design consistency measures on road safety. Crashes for years 2008-2012, totaling 263, were used for model development using the generalized linear regression approach. Tested models were statistically significant at 95%, and adopted models showed acceptable levels of goodness of fit. The recommended model performed well across additional highway sections, additional years of data, validation of algorithm, and "%error" with a high linear correlation. The study adds to the evidence that several geometric design consistency measures contribute to roadway safety. The significant measures for the two-lane rural highways in the West Bank were segment length, traffic volume, difference between operating and design speeds, absolute difference in the 85th percentile speeds between successive design elements, and the ratio of individual curve radius to the average radius. The practical implication of this study, in addition to being able to predict crashes based on the recommended measures, highway designers should pay careful attention to inconsistent designs of two-lane rural highways to reduce their crash frequency.

American Journal of Traffic and Transportation Engineering, 2021

Different studies conducted, regarding the development of statistical models used to predict crash occurrences along two-lane rural highways, around the globe and particularly in Ethiopia, rely on geometric characteristics than explicitly considering measures of design consistencies. Recently, the issue of geometric design consistency in highway design is emerging as an important criterion. This study is therefore carried out to evaluate the design consistency on horizontal alignments using measures of design consistency and develop safety functions that exclusively include design consistency measures. Elements of all road sections considered in the study were rated as good, fair or poor design using design evaluation criteria. Poisson regression and Negative Binomial regression modeling approaches were used to assess the relationship between measures of design consistency and road safety. Using information criteria goodness-of-fit, Poisson regression model was found better fit to the data than NB regression models. Three different crash prediction models which explicitly incorporate design consistency measures were successfully developed. The models can be used to predict crashes of two-lane rural highway having similar characteristics with the road considered under this study. Finally, based on the results of this research, further detailed study on effect of highway design consistency on road safety and current design guides related to design speed selection to account for design consistency revision was recommended.

dica.unict.it

A methodological approach for the safety evaluation of two lane rural roads which use both analytical procedures referring to alignment design consistency models and the "Safety review" process is suggested. Alignment features and design consistency related to road safety conditions can be effectively evaluated using both Accident Prediction Models and "Safety Criteria" defining three different levels of judgment (good, fair, poor). The model of IHSDM was adapted to the Italian accident and road design characteristics. The Safety Criteria allow to evaluate three different levels of inconsistencies in the horizontal alignment. It is useful to integrate the results of the analyses carried out from the theoretical-experimental models with those deriving from the judgments collected on inspected sites (the Safety Reviews). The low cost of the procedure and his capability in addressing the safety problems not identified in the previous steps highlight the effectiveness of the Safety Inspection method as part of the safety evaluation process on existing roads. The methodological framework presented in the paper, consisting of safety inspections carried out as support of the analyses conducted through the theoretical-experimental models, will be applied in Italy as part of the "IASP" project financed by European Commission.

2020

SYNOPSIS One of the most frequent roadway characteristics that affect accidents is the horizontal curve. Accident rates increase in proportion to decreases in the radius of curves, in particular for radii of less than 250 m on twolane rural roads. Moreover, there are important differences in accident rates between similar curves, mainly due to the approaching speed. For this reason many countries have introduced in their standards certain rules, in different forms, to evaluate the design consistency that identifies unacceptable speed changes along the speed profile of the horizontal alignment. The Italian Road Design Standard also requires an evaluation of design consistency. In order to identify the speed differences between successive geometric features, a design speed profile has been prepared. However, the design speed does not always represent the real speed used by the driver on taking the curves, especially on sharp curves that are precisely the curves with the highest accide...

Procedia - Social and Behavioral Sciences, 2011

Keyword: Design speed, ergonomic design, horizontal alignment, operating speed, vertical alignment.

Procedia - Social and Behavioral Sciences, 2013

Safety on rural highways is of great concern as nearly two third of road fatalities are found to take place on such roads. High speed of vehicles is the characteristic of rural highways. Geometry is one of the factors that control the speed of vehicles and consequently, the crash occurrence. Alignment is one of the components of geometry and an abrupt change in the alignment is a leading cause for crashes in rural highways. Presence of a curve after a long tangent or a sharp curve after a flat curve is an example for inconsistency in the alignment. Such an alignment brings about unnecessary and unhealthy speed changes that may lead to crashes. Thus, a highway design can be evaluated based on consistency in geometry. Operating speed is the measure adopted for consistency evaluation in this study. The objectives of this study are to develop operating speed models for different classes of vehicles at salient locations of multiple horizontal curves and to develop criteria for evaluating the geometric design consistency. Data of 30 sites were made use for this purpose. Multiple linear regression technique was adopted for modelling. Models were developed for the tangent section and middle of curved sections. Length of preceding tangent is the variable influencing operating speed at tangent. Radius and length of curve significantly influence operating speed at middle of first curve and radius of first and second curve influences operating speed at middle of second curve. Operating speed Deviation from Design speed (ODD) and Speed Reduction (SR) are the consistency measures and Equivalent Property Damage Only (EPDO) crashes is the safety measure used in the study for developing criteria. The criteria developed can be used to evaluate the curve as a single element, and as successive elements (combinations of tangent/curve or curve/curve). Alignment can then be classified as Good, Fair or Poor using these criteria, and it helps a designer to make suitable modifications in the design of a multiple horizontal curve from safety point of view.

The number of accidents in Malaysia increases relatively from year to year, although there are many programmes organised by the authority to reduce them. There are several factors that lead to serious accident problems which are human behaviour, vehicle’s condition, weather condition, road surface and road alignments (vertical and horizontal curves). This research paper presents an empirical research and presents design consistency models to estimate the 85th percentile operating speed models for the horizontal and vertical alignments at two-lane rural highways. The speed data were carried out by using a laser gun metre detector to obtain the spot speed data in the selected location along the Lenggong to Sauk two-lane rural highway in Perak. Multiple linear regression analysis was conducted to develop the 85th percentile speed models by combining the operating speed data and geometric elements data from different selected horizontal and vertical alignments. Finally, the horizontal and vertical alignment models have successfully developed in the paper. The findings are hoped to provide a starting point towards the national design standard for the highway designer and planner to improving the consistency geometric design elements of the two-lane rural highways. Keywords: Design Consistency, Horizontal Alignment, Operating Speed Model, Vertical Alignment, Rural Highways