Crest Vertical Curve Research Articles

Leveraging LiDAR-Based Simulations to Quantify the Complexity of the Static Environment for Autonomous Vehicles in Rural Settings.

This paper uses virtual simulations to examine the interaction between autonomous vehicles (AVs) and their surrounding environment. A framework was developed to estimate the environment's complexity by calculating the real-time data processing requirements for AVs to navigate effectively. The VISTA simulator was used to synthesize viewpoints to replicate the captured environment accurately. With an emphasis on static physical features, roadways were dissected into relevant road features (RRFs) and full environment (FE) to study the impact of roadside features on the scene complexity and demonstrate the gravity of wildlife-vehicle collisions (WVCs) on AVs. The results indicate that roadside features substantially increase environmental complexity by up to 400%. Increasing a single lane to the road was observed to increase the processing requirements by 12.3-16.5%. Crest vertical curves decrease data rates due to occlusion challenges, with a reported average of 4.2% data loss, while sag curves can increase the complexity by 7%. In horizontal curves, roadside occlusion contributed to severe loss in road information, leading to a decrease in data rate requirements by as much as 19%. As for weather conditions, heavy rain increased the AV's processing demands by a staggering 240% when compared to normal weather conditions. AV developers and government agencies can exploit the findings of this study to better tailor AV designs and meet the necessary infrastructure requirements.

PERANCANGAN GEOMETRIK JALAN ANTAR KOTA MENGGUNAKAN AUTOCAD CIVIL 3D STUDENT VERSION (STUDI KASUS JALAN MANDEH PROVINSI SUMATERA BARAT)

The roadway geometric designing must consider as optimal as possible time spent in designing and building a road. This study aims to determine the results of road geometric design using manual calculation methods and calculations by using AutoCAD Civil 3D Student Version 2016 with a case study of St. Mandeh STA 30 + 000 - STA 37 + 000. The design scope consists of horizontal alignment design, superelevation, and vertical alignment. The method used by reference standard of AASHTO 2011, and for criteria design used by Bina Marga 1997 standard. The results of the horizontal alignment design, obtained 6 SCS curves, 3 FC curves, and 5 SS curves. The manual calculation results are the same as the results of AutoCAD Civil 3D calculations for FC curves and SCS curves. For the SS curve, the result difference is <0.2 m. AutoCAD Civil 3D only calculates the superelevation of FC curve and SCS curve, then the calculation of SS curve have done by manual design. In the vertical alignment design there were 4 crest vertical curves and 3 sag vertical curves with a slope of 0.02% - 5.23% approprite the maximum slope requirement of 11%. The length of crest and sag vertical curve Lv approprite the K value requirement for stopping visibility and preceding visibility

Analysis of Relationship between Road Geometry and Automated Driving Safety for Automated Vehicle-Based Mobility Service

Various mobility services have been proposed based on the integration of automated vehicle (AV) and road infrastructure. Service providers need to identify a set of road sections for ensuring the driving safety of an AV-based mobility service. The main objective of this research is to analyze the safety performance of AVs on the road geometrical features present during this type of mobility service. To achieve the research goal, a mobility service is classified by a combination of six road types, including expressway, bus rapid transit (BRT) lane, principal arterial road, minor arterial road, collector road, and local road. With any given road type, a field test dataset is collected and analyzed to assess the safety performance of the AV-based mobility service with respect to road geometry. Furthermore, the safety performances of each road section are explored by using a historical dataset for human-driven vehicle-involved accident cases. The result reveals that most of the dangerous occurrences in both AV and human-driven vehicles show similar patterns. However, contrasting results are also observed in crest vertical curve sections, where the AV shows a lower risk of dangerous events than that of a human-driven vehicle. The findings can be used as primary data for optimizing the physical and digital infrastructure needed to implement efficient and safe AV-based mobility services in the future.

Influences of Crest Vertical Curve Curvature on Exhaust Emissions of Heavy-Duty Diesel Trucks at Grade Change Point Section in Highway

The vertical curve is a major factor affecting vehicle exhaust (CO2, CO, NOx, PM2.5) emissions. This article takes a heavy-duty diesel truck as a typical vehicle, combining instantaneous speed, acceleration and the vehicle-specific power VSP to divide the operating mode, and the exhaust emission of a heavy-duty diesel truck is then calculated by using MOVES. Finally, the environmental modification factors (EMFs) are used to evaluate the influence of curvature change on the exhaust emissions. The results show that CO2 and PM2.5 emissions of heavy-duty diesel trucks are increasing with the curvature of the crest vertical curve changing; with the increase and decrease of curvature K of the crest vertical curve by 50%, CO and NOx emissions showed an increasing trend. Among the four main emissions, CO2 emission amount is the largest, followed by NOx, CO and PM2.5. The emission rates of CO2 and PM2.5 increase with the increase of curvature of the crest vertical curve, and the minimum values of CO2 and PM2.5 emission rates are 46.7 g/s and 0.022 g/s, respectively. The emission rates of CO and NOx increase with the increase of curvature. The minimum point of emission rates of CO and NOx are 0.042 g/s and 0.259 g/s, respectively.

Feasibility study of highway alignment design controls for autonomous vehicles

In recent years, the development and testing of autonomous driving technology have become widespread around the world. However, due to differences in perception abilities between autonomous vehicles and human drivers, the current geometric design controls for highway alignments, designed for the human driver, may not be applicable to the autonomous vehicle (AV). Few studies, however, have systematically investigated the design controls for autonomous vehicles, though we face full driving automation in the next few decades. Because the range of modern AV sensors reaches 250 m, with expected further improvements in the near future, there is a need to determine how the sensors’ perception field and perception-reaction time may affect the current road design standards developed for human drivers. This study therefore tested the feasibility of the current design controls for fully-autonomous vehicles by separately computing controls for vertical alignments and combined horizontal and vertical alignments, considering the AV’s perception abilities of perception-reaction time (PRT), sensor height, and upward angle from the horizontal. The required stopping sight distance (SSD) and minimum length of sag and crest vertical curves were derived and compared with those for human drivers. Computations for combined alignments were based on Green Book coordination guidelines: as the minimum length of horizontal curve can be used for alignments adhering to guidelines, preview sight distance (PVSD) was computed for alignments that do not. Results showed that 1) AV-based design controls on vertical curves were more tolerant than those based on human drivers; and 2) the dominating criterion of sag vertical curve design control was comfort for autonomous vehicles, versus required SSD for human drivers.

A system to determine advisory speed limits for horizontal curves based on mental workload and available sight distance

This study proposes a framework that accounts for mental workload and available sight distances to estimate advisory speed limits on horizontal curves. To achieve this goal, automated scripts were used to extract data on horizontal curve elements (i.e., the degree of curvature and the deflection angle), to detect crest vertical curves, and to compute the available sight distance from remote sensing data collected on highways in Alberta, Canada. Mental workload ratings were then assigned to each horizontal curve to calculate the perception–reaction time needed by drivers to maintain control of their vehicles while negotiating these curves. Finally, a curve advisory speed was calculated based on the available sight distance and the mental workload perception–reaction time needed to ensure a safe driving environment. This study presents a unique approach that incorporates human factors, including the responses of drivers based on their perception of the driving environment, in the development of speed advisory systems.

Grade impact investigation during stopping sight distance determination on 3D road environment

In the present research, Stopping Sight Distance (SSD) adequacy is assessed through a three-dimensional approach, which associates road visibility in terms of grade effect. SSD adequacy is controlled through the difference between the available and the required SSD. The research is focused on a right turned, two lane rural road, associated with a crest vertical curve for a given speed value. The road design is in accordance with the Greek Road Design Guidelines (OMOE-X, 2001) by utilizing the control design parameters for a design speed of 80 km/h and a wide range of grade values, where the vertex point of the crest vertical curve is positioned at fixed points along the road axis. The investigation is based on a vehicle speed exceeding the design speed by 20 km/h. In total 1874 cases of compound alignments were examined and the results revealed that the available sight distance is decreasing while grade increases. The vehicle speed on the tangent sections was proved unacceptable in terms of providing SSD adequacy. However, it was found that SSD adequacy is granted when the vertical vertex falls inside the circular arc of the curve’s horizontal alignment, while the optimum area is defined shortly before the horizontal vertex point.

Two-Lane Highways Crest Curve Design. The Case Study of Italian Guidelines

The main purpose of the research is to evaluate the crest vertical curves radii Rv, not considering a conventional value of the opposing vehicle height h2, but the average vehicle heights h2(m) and the value of the 15th percentile of the height distribution h2(15) of the passenger car population. The study only considered car models with more than 20,000 registered vehicles in Italy. One hundred and fifteen car models belonging to different brands were taken into consideration, for a total of over 9 million vehicles. For the statistical sample analyzed, the following vehicle heights were estimated: h2(m) = 1.48 m and h2(15) = 1.39 m. The deviations between the crest radii calculated with the Italian standard (h2 = 1.10 m), and those obtained for h2(m) = 1.48 m and h2(15) = 1.39 m are up to 12%. The differences ΔHv between the values of the visible vehicle body height Hv = Hv(t) calculated using, respectively, h2(15) = 1.39 m and h2(m) = 1.48 m are modest. The value h2(m) = 1.48 m could be adopted in order to reduce the highways construction costs. In fact, the research shows that the value h2 = 1.10 m is too conservative and leads to oversizing of the crest vertical curves. Therefore, it would be necessary to make an appropriate choice of h2 value in order to take into account the current heights of passenger cars.

Evaluation of horizontal curve radius in overlap with longitudinal slope and vertical curve

ABSTRACT The equations used to calculate horizontal curve radius are presented in geometric design regulations based on the following assumption: the curve is on the flat ground without overlap with longitudinal slope or any vertical curve. The aim of this study is to evaluate the effect of overlapping longitudinal slope and vertical curves on the horizontal curve radius. For this purpose, three different cases are investigated: horizontal curve in a flat road, horizontal curve in a sloping road, and horizontal curve in the presence of a vertical curve. For the above-mentioned cases, different forces are exerted on the vehicle. The direction of their effect is modeled using the point-mass method, and the equations for determining minimum horizontal curve radius are extracted. The results demonstrate that the equations for the overlap of a horizontal curve with a crest vertical curve indicate a need for increasing the horizontal curve radius in some cases.

Crest Vertical Curvature Safety Assessment through Variable Grade Stopping Sight Distance Control

Stopping Sight Distance (SSD) is a vital design element, which directly affects the control values of critical road design parameters. Although grade marginally affects SSD values, most design guidelines disregard the grade impact during vehicle braking on variable grades. The paper investigates possible deficiency of this approach, regarding cases where the length of the vertical curve exceeds the control SSD values. The authors addressed the SSD calculation on variable grades during the braking process through a recently developed process that relates the point mass model and the laws of mechanics. The paper investigates the adequacy of the American AASHTO (2018), the Greek OMOE-X (2001) and the Italian DM, n.6792 (2001) design guidelines, during the determination of crest vertical curvature rates, from the variable grade SSD calculation point of view for rural arterials and freeways. The assessment was performed for high design speed values of 80km/h, 100km/h and 120km/h respectively, where for each case amended crest vertical curvature rates are delivered as a function of the crest vertical curve’s exit grade value, aiming to grant SSD adequacy throughout the braking process. The analysis, excluding the Greek OMOE-X design guidelines where costly overdesigned control crest vertical curvature rates are adopted, for AASHTO (2018) and DM, n.6792 (2001), revealed a SSD inadequacy on the downgrade area with exit grade values grades below -2% approximately.

Effect of driving style on operating speed in crest vertical curves of two-lane highways

Models that predict the operating speed (OS) in terms of highway geometry assume that drivers are homogenous individuals. However, road users build the way they drive based on their behaviour and skills, thereby configuring a so-called driving style. The state-of-the-art literature defines at least eight driving styles that affect the OS of drivers, but OS–geometry models do not consider this aspect. The purpose of this work was to study the effect of driving styles on OS in crest vertical curves (CVCs) of two-way highways. To this end, 16 drivers were selected and classified according to their driving style, based on the multidimensional driving style inventory. Subsequently, the circulation speed of each driver was tested on 40 CVCs through a 10 Hz Global Positioning System logger installed in each vehicle. New OS–vertical geometry models were developed and classified according to driving style. It was concluded that models that do not consider driving styles conceal the sensitivity of the OS to the vertical geometry of highways. Additionally, among the different driving styles there is an OS difference of up to 8 km/h. Therefore, including the driving style variable in OS models of two-way roadways is a relevant factor.

An Initial Investigation of the Effects of a Fully Automated Vehicle Fleet on Geometric Design

This paper investigates the potential changes in the geometric design elements in response to a fully autonomous vehicle fleet. When autonomous vehicles completely replace conventional vehicles, the human driver will no longer be a concern. Currently, and for safety reasons, the human driver plays an inherent role in designing highway elements, which depend on the driver’s perception-reaction time, driver’s eye height, and other driver related parameters. This study focuses on the geometric design elements that will directly be affected by the replacement of the human driver with fully autonomous vehicles. Stopping sight distance, decision sight distance, and length of sag and crest vertical curves are geometric design elements directly affected by the projected change. Revised values for these design elements are presented and their effects are quantified using a real-life scenario. An existing roadway designed using current AASHTO standards has been redesigned with the revised values. Compared with the existing design, the proposed design shows significant economic and environmental improvements, given the elimination of the human driver.

Evaluating new treatments for improving driver performance on combined horizontal and crest vertical curves on two-lane rural roads: A driving simulator study

Combined horizontal and crest vertical curves are among the most hazardous road segments because of drivers’ difficulties in perceiving early road geometry. This study evaluates new treatments to improve the safety of horizontal and crest vertical curves and compares their efficiency for driver performance based on design consistency criteria under free flow traffic and on-coming traffic. A combination of chevron signs with three promising treatments included herringbones, sealed shoulder and a yellow blinking signal was applied to hazardous curve sections in a driving simulator. Performance measures consisted of mean of speed and lateral position. The results indicated that combining chevrons and a warning blinking signal is the most appropriate treatment for horizontal and crest vertical curves, as this resulted in lower speed and lateral position. In addition, speed and lateral position variations along the curves were lower compared to other treatments specially, with an on-coming vehicle. Sealed shoulder makes drivers drive faster while entering a curve and brake suddenly while changing direction. Using herring bones is found to reduce speed and speed differential along the curve but not lateral position which was even higher in treated curves particularly, in presence of an on-coming vehicle.

The Effect of New Treatments and On-Coming Traffic on Driver Performance on Combined Horizontal and Crest Vertical Curves of Two-Lane Rural Roads: A Driving Simulator Study

Undoubtedly, driver performance is one of the most important contributing factors to road safety. A great portion of crashes occurs because of drivers’ misperception of road characteristics, particularly on mountainous two-lane rural roads which consist of many curves. Among the most hazardous road segments are combined horizontal and crest vertical curves which have complicated geometric features and insufficient sight distance. This study aims at investigating driver performance on combined horizontal and crest vertical curves under free flow traffic and head-on traffic conditions. In addition, three new treatments are applied to the same curves in order to compare driver performance with/without treatments and under free flow traffic and head-on traffic. The three treatments include a combination of chevron signs with the herringbones, sealed shoulder and a yellow blinking signal which is a new treatment for warning of on-coming vehicles. Fifteen kilometers of “Karaj–Chalus” two-lane rural road in Iran was replicated in a driving simulator, and the treatments and on-coming traffic were applied to some combined curves of it. Driver performance measures consisting of mean of acceleration and steering wheel angle were obtained from the simulator, and statistical tests were performed. Results indicated that combining chevrons and a warning signal resulted in lower acceleration and steering wheel angle while sealed shoulder reduced neither acceleration nor steering wheel angle. Using herring bones was found to increase only steering wheel angle. Therefore, warning signal application is suggested as the most appropriate treatment for horizontal and crest vertical curves to be applied before combined crest curves.

Three-Dimensional Virtual Highway Model for Sight-Distance Evaluation of Highway Underpasses

When it comes to the safe design and operation of highways, sight distance is of utmost importance. The estimation of sight distance must be performed taking the three-dimensional (3D) nature of roadways and related features into account. Horizontal curves and crest vertical curves were the common sight restrictions considered in highway design. However, overhanging features may also affect sight distance. This paper presents a 3D virtual model for evaluating sight distance on sites where overpass structures restrict sight distance and for detecting sight-distance-related issues. The procedure and inputs for the computation of sight distance are described as are the results, which were validated and applied to a case study of an in-service highway underpass. Stopping sight distance and passing sight distance were evaluated for a section of highway with specific sight-distance characteristics of overpasses. The effect of the observer and target heights on sight distance for underpasses proved the opposite of those on horizontal curves and crests. Near an overpass, the heights should be switched from those used on curves and crests to evaluate stopping and passing sight distance according to operational and safety criteria. Finally, the currently existing passing zones were evaluated by means of the results obtained, revealing possible deficiencies in the establishment of passing zones.

Investigating the effectiveness of perceptual treatments on a crest vertical curve: A driving simulator study

Rural roads are characterized by a high percentage of run-off-the-road accidents and head-on collisions, mainly caused by inappropriate speeds and failure to maintain a proper lateral position along the roadway alignment. Among several road safety treatments, low-cost perceptual measures are considered an effective tool, as they generally increase the risk perceived by drivers, or even alter the drivers’ speed perception, and consequently tempting them to decrease their speeds. Their effectiveness has been widely recognized in a number of studies, especially with respect to road intersections and curves.The overall aim of this study is to investigate the effects of different perceptual treatments on driving speed, along a crest vertical curve of an existing two-lane rural road, in order to identify the most effective measure to reduce speed and define its subsequent implementation in the field. Three perceptual treatments were tested using a driving simulator: white peripheral transverse bars, red peripheral transverse bars and optical speed bars, with each one being painted along the approaching tangent to the crest vertical curve. The effects of these speed-reducing measures were investigated using a sample of forty-four participants, by comparing the driving speeds with those recorded under a baseline condition (without a treatment); these were also used to validate the driving simulator’s speed measurements with those found in the field. Moreover, subjective measures were collected, consisting of the driver’s static evaluation of the desired speed, risk perception and markings comprehension, based on screen shot pictures that represented the simulated configurations of the treatments.The findings demonstrated an overall effectiveness of the perceptual treatments, although only the red peripheral transverse bars were found to significantly reduce the driving speeds (−6 km/h). The analysis of the questionnaire yielded interesting information and demonstrated the importance of performing driving simulation tests for evaluating the effectiveness of perceptual treatments.Finally, the results confirmed the enormous potential of using driving simulators to pinpoint a number of speed-reducing measures, and consequently select the most effective one that reduces cost and promotes safety before its actual implementation in the field.

Stopping sight distance adequacy assessment on freeways: the case of left horizontal curves over crest vertical curves

ABSTRACT This paper investigates potential Stopping Sight Distance (SSD) violation on divided highways at left horizontal curves overlapped with crest vertical curves. The authors previously developed a SSD control methodology that relates the 3D configuration to the dynamics of a vehicle moving along the roadway. This methodology is applied for the assessment of critical design parameters related to both demanded and available SSD values. Initially, utilizing control geometric and driver – obstacle values adopted by AASHTO 2011 design policy, SSD inadequacy areas were revealed. Subsequently, on the basis of an explanatory modeling approach for a number of geometry parameters, evaluation of SSD sufficiency was carried out in terms of the probability of SSD inadequacy and the prediction of the object height in order to grant SSD adequacy (amended object height). These models may be useful to researchers and practitioners aiming to evaluate the interaction of the utilized design parameters in terms of SSD inadequacy.

Vertical curve design insights of road tunnels versus highways

ABSTRACTThe design of road tunnels is an essential infrastructure component in the highway system. The study implements reasonable criteria for obtaining vertical curve length based on sight distance requirements of road tunnels versus open roadways. The infrastructure impact of sight distance tunnel characteristics on the design of crest and sag vertical curve radii is based on safety and driving comfort criteria. Both results of crest and sag vertical curves show significant reductions of vertical radii in road tunnels compared to open roadways, that is, percentage reduction range of 35% to 71% depending on the design speed, curve type, and tunnel pavement characteristics. The driving comfort criterion generally overrides in the lower range of design speeds whereas the safety criterion overrides in the upper range of design speeds: 100– to 120 km/h for moist and dry tunnel sag vertical curve, 90 to 120 km/h for dry tunnel crest vertical curve, and 80 to 120 km/h for moist tunnel crest vertical curve.This impact of a reduced vertical curve length triggers the possibility of shorter tunnel construction length, lower tunnel construction cost and maintenance cost including components of complementary systems, and flexibility in tunnel construction due to geotechnical, groundwater, and other infrastructure constraints. Still, the selected tunnel alignment, even if it is shorter than other alternatives, requires field tests such as geological investigation, vibrations and building inspection, and hydrologic balance.

Three-dimensional stopping sight distance control on passing lanes of divided highways

Stopping Sight Distance control of passing lanes of divided highways represents currently a discussion point among researchers. A 3-D approach to address the issue is accepted as the overall solution to the problem by both researchers and contemporary design policies. This paper aims to contribute to the problem by presenting a sound and practical design solution to it with an analytic and a design values based format. The solution approach consists of both a realistic description of the 3-D highway configuration and a 3-D vehicle kinematics calculation of the stopping maneuver along the vehicle’s actual path. A SSD control method, previously developed by the authors’, that relates concurrently the 3D configuration of a roadway to the kinematics of a vehicle moving along the actual roadway path, is applied, as a tool for the assessment of critical design parameters directly related to SSD adequacy. A rather comfortable alignment case consisting of a left curved divided highway overlapped with crest vertical curve parameters for numerous horizontal—vertical arrangements is examined, where an extensive area of SSD inadequacy during emergency braking procedure is reported. The authors propose that the optimal solution to achieve SSD adequacy on left curved divided highways is to increase object height. This would preserve design consistency as well as driver expectations, by avoiding the need for lateral widening or site-specific speed limits. More specifically the object height is suggested to be equivalent to the driver’s height of 1.08 m (AASHTO 2011). This would require additional stop lights on those vehicles whose stop lights are currently below this level. Although such a requirement regarding the current vehicle fleet is not feasible, vehicle industries as well as road design guidelines should address this issue in the near future.

Finding and characterizing hidden dips in roads

Sometimes when connecting a crest vertical curve, followed by a sag and another crest, a road disappears from the view of a driver to reappear later. Then, there is a loss of path or a hidden dip in a road. It is essential to avoid losses when they hide dangerous points, such as intersections or unexpected changes in direction. In addition, this loss disrupts drivers and its effect depends on quantitative relationships between the variables involved in the problem. This paper presents a quantitative procedure for studying hidden dips in roads. The method is based on calculating the sections visible and hidden by a driver using a Geographic Information System. An application to a Spanish road is presented. Procedure results were compared with in situ carried out studies and with a video of the highway recorded using a Global Positioning System equipped video camera embarked in a vehicle. The main quantitative issues related to hidden dips are discussed.