Four-lane Divided Highways Research Articles

Multilevel Discrete Outcome Modeling for Crash Severity: A Novel Approach for Crash Severity Models

Combining a total crash count model and a crash severity probability model simultaneously to predict crashes by severity is challenging because crash count models are implemented at an aggregate scale, that is, by sites (segments or intersections), while crash severity probability models are at a disaggregate scale, that is, by crashes or persons (drivers or occupants). This study develops a multilevel discrete outcome modeling framework to estimate crash counts by severity for California, U.S., rural four-lane divided highways by estimating and combining three models: a univariate count model for total crashes at the site level predicts total crash counts; an ordered logit discrete outcome crash severity prediction model at the crash-level predicts proportion of crashes by severity; and a proportional regression connection model that predicts proportion of groups of drivers and vehicles to connect the other two models. The combination of all three models provides crash counts by severity at the site level considering both aggregate and disaggregate factors. The prediction from the multilevel discrete outcome model is compared with predictions made by traditional univariate count models by severity for accuracy and transferability using estimation and validation data. Based on the estimation data, the multilevel discrete outcome model predicts injury and fatal crashes more accurately than the univariate count model. For validation data, the multilevel model has slightly better prediction accuracy for minor and possible injuries. Finally, the calibration factor indicates the multilevel discrete outcome model is more transferable than the univariate count model.

Surrogate safety evaluation of curve sections on an interurban highway under heterogeneous traffic conditions in India

<p class="H1">Road traffic safety is a global concern. Conventionally, road safety evaluation is carried out by analyzing historical crash data, which is a reactive approach to safety analysis. The safety analyst has to wait for sufficient time to accumulate crash data before taking up any safety analysis as a sample of substantial crashes is required for analysis. But in safety analysis with a proactive approach no crash data is required, which is replaced with surrogate “conflicts”, which can be obtained from the new techniques of traffic conflict technique and surrogate safety parameters. Other approaches can be applied in traffic safety evaluation in anticipation of the crash occurrence. The advent of traffic conflict techniques, i.e., use of traffic conflicts in place of crashes and microsimulation methods like modeling of the traffic flow and pattern in traffic streams on a road network, started to apply as a method of analyzing microscopic simulation models and traffic conflict techniques to determine the safety issues in traffic systems and correlate them to the probable incidences of collisions. In this regard, surrogate safety parameters have been used to determine the level of safety on the typical curve sections of an interurban highway namely, Faridabad-Gurgaon four-lane divided highway in Haryana, India. This is accomplished by the use of vehicle trajectory data extracted through microscopic simulation in Verkher in Staedten Simulation (VISSIM) and analysis in Surrogate Safety Assessment Model (SSAM) for the above-referred corridor. Further, efforts have been made to present the intensity of traffic conflicts happening at the curved sections. The surrogate safety measures time to collision (TTC), deceleration rate (DR), and change in velocity (<em>ΔV</em>), as well as conflicting vehicle speed (Max <em>S</em>), are obtained by analysis from the SSAM model for all the curve sections and are validated using the reported crash data on the curve sections of the candidate corridor for 3 years. With the help of statistical elaboration, the critical threshold for TTC with the heterogeneous traffic movement is found 1.6 s, meaning any conflict occurring less than this time would invariably lead to a fatal crash. Similarly, the critical deceleration rate is observed as 0.569 m/s<sup>2</sup>, implying that any conflict with more than this value may lead to a fatal crash. Further, the Delta<em>V</em> values deduced for the study corridor on interurban curve sections catering to heterogeneous traffic movement is 4.1 m/s. Again, any conflict more than this value can turn into a potential crash.</p>

Assessment of Deer–Vehicle Crash Mitigation Structures on the US 33 Nelsonville, Ohio, Bypass

The US 33 Nelsonville Bypass project involved construction of a new four-lane divided highway through the Wayne National Forest in southeastern Ohio, an area high in species diversity and home to several threatened and endangered species. The project included three wildlife underpass structures to promote habitat connectivity, 16 jump out structures to allow wildlife to exit the highway right-of-way (ROW), and 2.44-m (8-feet) tall exclusion fencing along the ROW boundary to discourage entry. This paper reports the results of a comprehensive research study undertaken to determine if these features were effective at reducing collisions between vehicles and wildlife (specifically, white-tailed deer). A multi-season camera-based monitoring plan was deployed to track the movement of animals within and around the highway ROW. The results of the analysis showed that the crossing structures were heavily used and that the tall fencing was effective at excluding deer from the highway area. Approximately 43% of deer that approached the jump out structures used them to successfully exit the ROW. Analysis of traffic crash data from six years after the opening of the highway suggests that the prevalence of deer crashes on the highway is lower than other highways in the region, indicating that the mitigation features appear to be successful at reducing such collisions. Considering the additional costs of constructing the mitigation features and the economic benefits of the associated deer crash reductions, the incremental cost-benefit ratio of the complete installation is estimated to be 1.65, indicating a net positive benefit realized by the mitigation plan. The results of this study suggest that wildlife mitigation structures can be effective in supporting highway development in wildlife-sensitive areas, particularly if the placement of the structures relates to existing wildlife patterns and the features are maintained post-construction.

Evaluation of reverse curves focusing on the lateral friction demand on four-lane divided highways

Horizontal curves on mountainous roads are highly crash-prone and geometric consistency is vital in their design. The drivers' lateral friction demand will be significantly affected if there are a substantial number of successive horizontal curves on these roads due to design limitations. This study is aimed to evaluate the safety of reverse curves using the lateral friction demand as a design criterion. Using a UAV, the required data were collected from ten reverse curves on a mountain highway in Iran for a multiple linear regression model to investigate the effects of geometric variables and speed of vehicles on the average lateral friction demand (fd,mean). According to the results: (1) the length of the common tangent and the ratio of the curves’ radii affect fd,mean, (2) the road longitudinal grade and the vehicle speed have positive effects on fd,mean, but the curve superelevation affects it negatively and (3) when the length of the common tangent is ≈ 400 m and the curves’ radii are close, the vehicle trajectories are close to the expected trajectory based on the design. These results can help reverse curves to be designed more safely.

Effect of vehicle size on crash risk in a heterogeneous traffic scenario: a bivariate extreme value approach

ABSTRACT Most traffic conflict indicators are defined for car-following scenarios where a follower vehicle interacts with a leader vehicle in one-dimensional space. However, vehicles do interact in a two-dimensional space especially in a heterogeneous traffic environment. Further, designating an interaction as risky depends on the interacting leader-follower (LF) pairs. Conflict indicators namely Time-to-Collision (TTC) and lateral gap which quantifies longitudinal and lateral interactions respectively, were computed from video recordings at four accident black spots on four-lane divided highways. Conflict in two-dimensional space was modelled for various LF-pairs using the Bivariate Extreme Value function of these two conflict indicators. Crash risk was estimated for each LF-pairs separately. Results show that cars and light commercial vehicles exhibit higher crash risk as compared to two-wheelers and motorized three-wheelers. The proposed framework can be used for more accurate risk assessment and calibration of collision warning systems in lane free mixed traffic conditions.

Effectiveness of the Overtaking Ban for Heavy Vehicles on the Four-Lane Divided Highway in Different Weather Conditions

In many European countries and also in Slovenia, the highway network was rapidly built in order to reduce congestion and to increase the level of traffic safety on congested sections of the road network, thus enabling a higher level of service and accelerating polycentric development. Unfortunately, traffic demand is growing over all limits, be it tourist car traffic or transit-heavy vehicle traffic. Thus, countries are forced to actively manage road freight traffic, which is present all year round. Accordingly, in Slovenia, permanent and timed restrictions were introduced for trucks regarding overtaking on highways. Overtaking is prohibited during the day but trucks are allowed to change lanes at night. It should be noted, however, that there may be circumstances that can restrict the normal travel of heavy vehicles in all lanes in one way or another, whether at night or during the day. We would like to convince highway traffic managers that weather-responsive adaptive traffic control could be more efficient when weather conditions are considered. This article presents an approach to simulate traffic flow on a short section of a two-lane unidirectional carriageway under various weather conditions. Using two scenarios for lane traffic control, i.e., with and without a truck overtaking ban, as examples, we show that knowledge of the traffic characteristics of each lane in different weather conditions is important for decision-making and for the timeliness of traffic management. We found that under certain traffic and weather conditions, prohibiting vehicles from overtaking with limited speed limits on four-lane divided highways or proper traffic lane control has a positive effect on the traffic fluency or available conditional capacity of the highway. To some extent, this confirms that the decision of the operator of the Slovenian highway system regarding the driving regime for heavy vehicles was correct. Through our research, we found that dynamic bans can be more effective when we include the dynamics of traffic demand, and environmental and weather conditions.

Safety effects of paved shoulder width on a four-lane divided rural highway in India: A matched case-control study

Research has revealed the safety benefits of shoulder improvements on highways are significant. The study aimed to assess the impact of paved shoulder width on the frequency of fatal crashes in case of heterogeneous traffic on a rural four-lane divided highway in India. A matched case-control design was employed to evaluate the safety effectiveness of the paved shoulder width on fatal crashes. The impact of shoulder widths on victims of motorized two-wheelers (MTW) users, slow-moving vehicles and rear-end fatal crashes were also analyzed. The study stretch was divided into segments of 100 m. Each segment was linked to the traffic volume, speed, geometric characteristics, and roadside hazards characteristics. Analysis of the crash data revealed that 39% of the total crashes are due to rear-end collisions, mostly occurring at nighttime. The model results are interpreted concerning segments with no shoulder as the baseline category. Model results suggest that paved shoulder has safety benefits for all road users up to 1.5 m shoulder width. The provision of paved shoulders reduced the risk of all fatal crashes and improved the safety of pedestrians and slow-moving vehicles. However, the safety of MTW users reduced on segments having paved shoulder width more than 2 m. Also, segments with a paved shoulder width of more than 1.5 m have a higher risk of rear-end fatal crashes than no shoulder segments. This study findings have a direct bearing on the geometric standards recommended by the road authorities in India.

Investigations on development of early distresses on bituminous pavement in India and remedies

In the present study, reasons for early distresses noticed on the bituminous pavement of a four-lane divided highway between the Pardi and Agrasen sections of National Highway 6 from km 498.000 to km 544.000, in India, were investigated. The total length of the road project is 46 km. A detailed pavement condition mapping was carried out, and various distresses were noticed on the surface. To assess the reasons for the distresses, combined cores of the bitumen surface course and the base course were taken from 57 locations, 29 on the left-hand side and 28 on the right-hand side of the carriageway, and mix properties were evaluated in the laboratory. The investigation on the mixes revealed that bituminous cores collected from both the surface course and binder course have no resemblance to the job mix formula. Non-homogeneity of layer thicknesses, variation in mix properties, variation in aggregate gradation and high filler–binder ratios were observed. Aside from the laboratory investigation, the physical condition of bitumen cores was studied and the conditions of the pavement layers were assessed based on the deflection basin parameters. This paper presents a systematic procedure adopted for identifying the causes of early distresses, and appropriate treatments are suggested for rectification.

Effects of Inter-Vehicle Interaction on Speed and Lateral Position for Reviewing Free - Flow Condition

Speed and lateral position of free-flowing vehicles are the performance measures of roadway geometric elements. Most of the earlier studies evaluated a threshold headway based free-flow criteria at an observation station and considered the relevant vehicles for estimation of speed and lateral position. However, evaluation of free-flow at one observation station cannot guarantee the same in the entire segment, due to the possible inter-vehicle interactions prior to the observation station. It can cause inappropriate performance evaluation of the roadway geometric element. Moreover, horizontal curve is one of the critical geometric elements of four-lane highways. Hence, in this research, all the possible inter-vehicle interactions of passenger cars prior to a curve center of four-lane divided highways were identified and analyzed for the effect of inter-vehicle interactions on speed and lateral position. The analysis indicates that speed and lateral position are dependent on the location of inter-vehicle interactions prior to a curve center. Vehicles, which did not interact with other vehicles until the curve center, remains uninfluenced and should be considered for geometric evaluation. This finding is useful to identify the relevant free-flowing vehicles and in-turn, improve the evaluation of horizontal curve geometry.

Modeling 85th Percentile Speed Using Spatially Evaluated Free-Flow Vehicles for Consistency-Based Geometric Design

AbstractThis paper investigates the free-flow condition suitable for four-lane divided highways and proposes spatial free-flow speed–based operating speed prediction models. The 85th percentile spe...

Effect of horizontal curve geometry on vehicle speed distribution: a four-lane divided highway study

ABSTRACT Poor coordination between geometric elements of horizontal curves can lead to unsafe speed. This study evaluated the effect of horizontal curve geometry on vehicle speed distribution for a four-lane divided highway and developed prediction models for mean speed and standard deviation. Spot speed data of passenger cars (PC), heavy commercial vehicles and light commercial vehicles were collected at 24 horizontal curves. Statistical analysis of the speed data of randomly selected 10 sites revealed PC as the critical vehicle category. Hence, the effects of horizontal curve geometry on PC speed were analyzed and radius was identified as the most influencing parameter. Radius beyond 400 m had similar influence on speed distributions. Appropriate models were developed using regression analysis. Degree of curvature was found as the most significant predictor. Benefits of the proposed models over traditional 85th percentile speed in designing and evaluating horizontal curves for consistency and safety were discussed.

Mega elliptical roundabouts versus grade-separation interchange

The mega elliptical roundabout is a new idea for intersections on rural multilane highways in the form of an elongated ellipse. Basically, there are no procedures or guidelines for designing the mega elliptical roundabout in the Highway Capacity Manual, Federal Highway Administration guides or the American Association of State Highway and Transportation Officials' ‘Green Book’. This research therefore presents the best geometric design scenarios of mega elliptical roundabout intersections at various traffic flows for all intersection entrances. The basis for selecting the best scenarios is to achieve minimum delay time, minimum emissions and minimum fuel consumption. This was studied at the intersection of a six-lane divided highway with a four-lane divided highway when the traffic enters from four approaches. Moreover, this research proposes the cases in which the mega elliptical roundabout is better than an interchange (full cloverleaf), and suggests the best time to make a decision to change from a mega elliptical roundabout to an interchange (full cloverleaf). The study was conducted by using Vissim software (version 10.00-02). In total, 1134 scenarios were analysed.

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

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.

Automated Highway Sign Extraction Using Lidar Data

Traffic signs are integral elements of any transportation network; however, keeping records of those signs and their condition is a tedious, time-consuming, and labor-intensive process. As a result, many agencies worldwide have been working toward automating the process. One form of automation uses remote sensing techniques to extract traffic sign information. An algorithm is proposed that can automatically extract traffic signs from mobile light detection and ranging data. After the number of signs on a road segment has been determined, the coordinates of those signs are mapped onto the road segment. The sign extraction procedure involves applying multiple filters to the point cloud data and clustering the data into traffic signs. The proposed algorithm was tested on three highways located in different regions of the province of Alberta, Canada. The segments on which the algorithm was tested include a two-lane undivided rural road and four-lane divided highways. The highway geometry varied, as did vegetation and tree density. Success rates ranged from 93% to 100%, and the algorithm performed better on highways without overhead signs. Results indicate that the proposed method is simple but effective for creating an accurate inventory of traffic signs.

Development of Comprehensive Crash Models for Four-lane Divided Highways in Heterogeneous Traffic Condition

Traffic safety is of prime concern worldwide. Highway geometry should be designed for vehicle safety and efficiency. Several researches have been carried out to identify the factors contributing to road crashes and for finding measures to reduce the crash rate. One of the critical gaps in the management of highway safety is the lack of a reliable method for estimating the safety of an existing roadway with, widely varying road geometrics and vehicle mix. The focus of this work is mainly to quantify the relationship between geometric design characteristics and level of safety of intercity highways under heterogeneous traffic conditions. Study was carried out in a four-lane divided rural highway in Tamil Nadu, India and a relationship was established using statistical modeling technique. Crash Prediction Models (CPM) were developed by Poisson regression, Poisson-gamma and negative binomial modeling approach for three categories, namely, current (ith) segment, with preceding (i-1th)segment and with succeeding and preceding (i+1&-1th) segments. Results showed the significance of identified variables and the effect of preceding and succeeding segments on the current segment in the case of CPM. Attempts were also made to develop operating speed models for curve and tangent elements. From the developed models, the effect of contiguous element on the operating speed could be understood.

Highway capacity through vissim calibrated for mixed traffic conditions

The present study demonstrates applicability of VISSIM software to determine capacity of multilane highways under mixed traffic flow conditions. Traffic flow data collected on a section of four-lane divided highway are used to develop the speed-flow curve. The same set of field data is used in VISSIM and simulated speed-flow curve is compared with field curve. It was found that VISSIM in its original form overestimates both speed and capacity of the highway. Driver behaviour parameters CC0 and CC1 are first determined for homogeneous traffic conditions having only one of the four types of vehicles in the stream and then results are aggregated to get the values of these parameters for a mixed traffic stream. Further analysis of field data with calibrated values of CC0 and CC1 indicated a good match between field and simulated capacity. The procedure is shown to work on another section of four-lane divided highway with paved shoulders, where simulated capacity was 5329 pcu/hr against the field capacity of 5277 pcu/hr.

Major roadwork impacts the space use behaviour of gray wolf

Roads are known to impact wildlife in numerous ways and wolf response to roads was shown to vary with human activity level and road type. We assessed the impacts of increased road-disturbance intensity associated to a major roadwork on wolf movements and space use in eastern Canada: from 2006 to 2010, the provincial two-lane Highway 175 has been enlarged to a four-lane divided highway. We hypothesized that the level of human activity relative to the construction was the most important factor driving wolf response to road enlargement because of the risk of human encounter. We tracked 22 wolves belonging to nine packs using GPS telemetry, focusing our efforts on individuals with territories encompassing a part of the highway being modified or a similar but unmodified highway (control). Impacts of the road enlargement were assessed using resource selection functions and highway crossing events by wolves as roadworks progressed. During the denning period, crossing rate decreased from the beginning to the completion of the road enlargement (0.66±0.16 (SE) to 0.15±0.11crossing/km/100-days). Wolves stayed ca. 300m farther away from active road construction sites than from segments without roadwork or where roadwork activity had temporarily stopped, except during nomadic period. Negative impacts of road modification on crossing rate and space use were more noticeable during the denning period and faded as pups aged. We then demonstrated the wolf capacity to adjust its behaviour to local disturbances and the importance of human activity level in explaining response to anthropogenic disturbances.

Calibration and Development of Safety Performance Functions for Alabama

One critical component of the Highway Safety Manual (HSM) statistical methods is the safety performance function (SPF). SPFs are essentially regression models that correlate quantitatively the expected number of crashes with traffic exposure and geometric characteristics of the road. As part of a project performed by the University of Alabama to facilitate implementation of the new HSM procedures in the state, this study aims to evaluate the applicability of HSM predictive methods to Alabama data and to develop state-specific statistical models for two facility types: two-lane, two-way rural roads and four-lane divided highways. This study first calibrates HSM base SPFs by using two approaches: the method recommended by the HSM and a newly proposed approach that treats the estimation of calibration factors as a special case of a negative binomial regression. In addition, new forms of state-specific SPFs are further investigated by using Poisson-gamma regression techniques. Four new functional forms are studied in this project. The prediction capabilities of the two calibrated models and the four newly developed state-specific SPFs are evaluated with a validation data set. Five performance measures are considered for model evaluation. The study is able to identify a particular state-specific SPF that fits the Alabama data well and outperforms other models, including the calibrated SPFs. The best model describes the mean crash frequency as a function of annual average daily traffic, segment length, lane width, year, and speed limit. The study finds that the HSM-recommended method for calibration factor estimation also performs well.

Overtaking Behavior on Divided Highways Under Mixed Traffic Conditions

The acceleration and overtaking characteristics of different types of vehicles on four-lane divided highways in India are evaluated in this paper. The floating car method was used to record the time of different events in an overtaking process. It is observed that the shoulder condition (paved and unpaved) influences the acceleration behavior during overtaking. In the case of highways with paved shoulders, two-wheelers rarely overtook the test vehicle as they mostly used shoulder lane for their movement. An inverse correlation is observed between the overtaking speed and the acceleration rate. Graphs are plotted between the relative speed of the overtaking and overtaken vehicles against the overtaking time for flying overtaking.

Real-time Traveler Information Performance Measures for Work Zone Congestion Management

This study evaluates the use of an advanced traveler information system (ATIS) to promote the use of alternative routes and improve local road network performance during work projects. The ATIS system was implemented on a four-lane divided highway in Edgerton, Wisconsin during a bridge reconstruction. Field comparisons between ATIS presence and absence showed different diversion patterns in northbound and southbound directions associated with traffic delay. Drivers remained on the freeway when the displayed delay was less than 15 minutes while more drivers chose to leave the freeway with displayed delay greater than or equal to 15 minutes. A linear regression analysis showed that freeway volume, ramp exiting volume during normal days, and delay time were significant variables associated with a high diversion rate. The ATIS also was shown to perform effectively in increasing the work zone operational capacity.