Carlos Llorca

Evaluation of Passing Process on Two-Lane Rural Highways in Spain with New Methodology Based on Video Data

Drivers need sufficient passing sight distance (PSD) to pass slower vehicles with safety. This distance can help to improve traffic operation on two-way, two-lane highways. Existing models propose different values of PSD because of different assumptions. In only some cases were these models based on field data of passing maneuvers. This research proposed the design of a methodology to observe passing maneuvers on existing highways with the help of six video cameras installed at a fixed point next to passing sections. The use of more cameras allows complete registration of trajectories along the entire passing zone, with uniform image resolution. The methodology was applied to register a sample of 234 maneuvers on four passing zones. Trajectories of 58 maneuvers were completely described and analyzed with specific restitution software. Results were compared with those from existing PSD models. The distances traveled proposed by the AASHTO model on the left lane were (a) similar to average observed distances when the passed vehicle was one truck and (b) between 50 and 100 m higher when one passenger car was passed. Higher differences, greater than 100 m, were found between measured data and the PSD model (published previously), especially at high design speeds. The observed average speed difference between passing and impeding vehicles was significantly higher than that in any model. Variables with the strongest influence on the time and distance traveled on the opposing lane were the type and speed of the passed vehicle and the length of the passing zone. Left-lane time and distance increase with this length.

Operational Effectiveness of Passing Zones Depending on Length and Traffic Volume

Most studies on two-lane highway operations have focused on the percentage of following vehicles or the adjustment of the Highway Capacity Manual (HCM) procedure to local data. The HCM proposes the length of no-passing zones as a model parameter; however, the distribution and characteristics of passing zones are not addressed. In fact, only a few studies on the expected number of passes in a passing zone have been carried out. This research presents an analysis of the effectiveness of passing zones in terms of their length and traffic volume. Data were collected from four passing zones on a rural highway in Spain. The two-way traffic volumes ranged from 100 to 900 vehicles per hour (vph), and the passing zone lengths ranged from 265 to 1,270 m. More than 1,600 passing maneuvers were recorded. The operational effectiveness of the passing zones was obtained from the passing frequency and the passing rate. The results indicated that the longer the passing zone, the higher the passing frequency; however, the results stabilized with lengths above 1,100 m. Balanced flows with two-way traffic volumes between 600 and 700 vph optimized the number of passes. Nevertheless, the increase in the passing frequency with the traffic volume was lower than with the increase in following vehicles. The results were validated with data from another 12 passing zones. Finally, HCM adjustments based on the percentage of no-passing zones did not reliably represent the effectiveness of passing zones. Therefore, the effectiveness of every passing zone should be considered, and adjustment factors should be modified to maximize the passing opportunities for traffic volumes between 600 and 700 vph.

Daytime and Nighttime Passing Maneuvers on a Two-Lane Rural Road in Spain

Passing is one of the most complex driving maneuvers performed on two-lane rural roads and has important effects on road safety and traffic operation. Passing is affected by driving behavior, road geometry, traffic volume, and traffic composition as well as external factors. Research was developed to compare the passing process under daytime and nighttime conditions. An experimental method was designed to collect video data of passing maneuvers on a two-lane rural road segment located near Valencia, Spain. Two methods were used: (a) external observations of four passing zones with six video cameras and (b) an instrumented vehicle equipped with video cameras and laser rangefinders, driven slightly below the operating speed along a segment of the same road so it would be passed by other vehicles. A total of 291 maneuvers were observed, up to 20% of which were at night. Macroscopic analysis results indicated that approximately 17% of passes were at night, even though passing frequency and passing demand decreased at night. Also, the behaviors of individual drivers who passed other vehicles were different at night and during the day. Maneuvers limited by the presence of an opposing vehicle were performed more quickly at night, even if the accepted gaps were longer. In this case, a more difficult perception of distances to opposing vehicles and of vehicle speeds explained the differences. In contrast, maneuvers limited by sight distance (without a visible opposing vehicle) were slower at night. This observation matched a traditional hypothesis: passing at night is safer because the headlights of an opposing vehicle allow a driver to anticipate the vehicles position before it becomes visible.

Sight distance standards based on observational data risk evaluation of passing

The paper presents an application of a reliability analysis for evaluating the risk associated with passing sight distance (PSD) standards in terms of the expected probability of noncompliance. Calculation of PSD is required to determine where drivers can safely execute passing maneuvers. Traditional PSD standards are based on deterministic, theoretical models, which are calibrated with conservative percentile values for uncertain design inputs to account for uncertainty. The PSD standards do not provide information about the risk of deviation from them. Reliability analysis is a technique that is based on limit state design and that accounts for the propagation of variability from input random parameters to the design outputs. A total of 1,098 passing maneuvers were observed on several two-lane highways in Spain; two data collection methodologies were used: external observations and an instrumented vehicle. The most significant factors affecting PSD were impeding-vehicle speed, passing-vehicle acceleration, and headways between impeding and passing vehicles. A uniform acceleration model described the passing-vehicle trajectory. The characterized input parameters and the passing model were used to perform a reliability analysis. The results showed the probability of noncompliance in different scenarios, defined as the proportion of cases in which the required PSD would exceed the available sight distance. American and Spanish PSD standards were evaluated. Geometric design standards presented a probability of noncompliance of about 0.15, whereas some marking standards had a probability of noncompliance exceeding 0.85. These standards may be associated with higher risk levels if they are followed by drivers. As well, PSD risk levels were not consistent for different design speeds, since they underestimated operating speed at some locations.

Design Criteria for Minimum Passing Zone Lengths: Operational Efficiency and Safety Considerations

Passing zones are provided to improve operational efficiency of two-lane highways. Minimum passing zone lengths of 120 m were established by FHWA and AASHTO. Some studies indicate that lengths may need to be increased, but no changes have been recommended, pending further research. The objective of this study was to develop design and marking criteria for minimum passing zone lengths, with traffic operational efficiency and safety taken into consideration. First, a traffic microsimulation was conducted with AIMSUN software. The calibration and validation included the observation of 1,750 passing maneuvers in Spain. Results indicated that passing zones shorter than 250 m added little to operational efficiency. Second, a reliability analysis was applied. The analysis quantified the probability that a passing maneuver was completed beyond the end of the passing zone (noncompliant passing maneuver). Then the number of noncompliant passing maneuvers was calculated. Traffic flow and passing zone length were contributing factors. Findings from the analysis indicated that the minimum passing zone length should be increased to a minimum of 275 m for high traffic volumes, 300 m for medium traffic volumes, and 350 m for low traffic volumes. With these lengths, noncompliant passing maneuvers decrease. The marginal increase in the minimum length of passing zones can potentially improve safety without significantly reducing operational efficiency. The results can be used by practitioners to establish minimum passing zone length on the basis of hourly volumes and level of risk.

Effect of width and boundary conditions on meeting maneuvers on two-way separated cycle tracks

Cycle track design guidelines are rarely based on scientific studies. In the case of off-road two-way cycle tracks, a minimum width must facilitate both passing and meeting maneuvers, being meeting maneuvers the most frequent. This study developed a methodology to observe meeting maneuvers using an instrumented bicycle, equipped with video cameras, a GPS tracker, laser rangefinders and speed sensors. This bicycle collected data on six two-way cycle tracks ranging 1.3-2.15m width delimitated by different boundary conditions. The meeting maneuvers between the instrumented bicycle and every oncoming bicycle were characterized by the meeting clearance between the two bicycles, the speed of opposing bicycle and the reaction of the opposing rider: change in trajectory, stop pedaling or braking. The results showed that meeting clearance increased with the cycle track width and decreased if the cycle track had lateral obstacles, especially if they were higher than the bicycle handlebar. The speed of opposing bicycle shown the same tendency, although were more disperse. Opposing cyclists performed more reaction maneuvers on narrower cycle tracks and on cycle tracks with lateral obstacles to the handlebar height. Conclusions suggested avoiding cycle tracks narrower than 1.6m, as they present lower meeting clearances, lower bicycle speeds and frequent reaction maneuvers.

Estimation of a Long-Distance Travel Demand Model using Trip Surveys, Location-Based Big Data, and Trip Planning Services

Long-distance trips are less frequent than short-distance urban trips, but contribute significantly to the total distance traveled, and thus to congestion and transport-related emissions. This paper develops a long-distance travel demand model for the province of Ontario, Canada. In this paper, long-distance demand includes non-recurrent overnight trips and daytrips longer than 40 km, as defined by the Travel Survey for Residents in Canada (TSRC). We developed a microscopic discrete choice model including trip generation, destination choice, and mode choice. The model was estimated using travel surveys, which did not provide data about destination attractiveness and modal level of service. Therefore, a data collection method was designed to obtain publicly available data from the location-based social network Foursquare and from the online trip planning service Rome2rio. In the first case, Foursquare data characterized land uses and predominant activities of the destination alternatives, by the number of user check-ins at different venue types (i.e., ski areas, outdoor or medical activities, etc.). In the second case, the use of Rome2rio data described the modal alternatives for each observed trip. Combining data from travel surveys, Foursquare, and Rome2rio, coefficients of the model were estimated econometrically. It was found that the Foursquare data on number of check-ins at destinations was statistically significant, especially for leisure trips, and improved the goodness of fit compared with models that only used population and employment. Additionally, Rome2rio mode-specific variables were found to be significant for mode choice selection, making the resulting model sensitive to changes in travel time, transit fares, or service frequencies.

Shared Autonomous Vehicles Effect on Vehicle-Km Traveled and Average Trip Duration

Intermediate modes of transport, such as shared vehicles or ride sharing, are starting to increase their market share at the expense of traditional modes of car, public transport, and taxi. In the advent of autonomous vehicles, single occupancy shared vehicles are expected to substitute at least in part private conventional vehicle trips. The objective of this paper is to estimate the impact of shared autonomous vehicles on average trip duration and vehicle-km traveled in a large metropolitan area. A stated preference online survey was designed to gather data on the willingness to use shared autonomous vehicles. Then, commute trips and home-based other trips were generated microscopically for a synthetic population in the greater Munich metropolitan area. Individuals who traveled by auto were selected to switch from a conventional vehicle to a shared autonomous vehicle subject to their willingness to use them. The effect of shared autonomous vehicles on urban mobility was assessed through traffic simulations in MATSim with a varying autonomous taxi fleet size. The results indicated that the total traveled distance increased by up to 8% after autonomous fleets were introduced. Current travel demand can still be satisfied with an acceptable waiting time when 10 conventional vehicles are replaced with 4 shared autonomous vehicles.

Impact of bicycle highways on commuter mode choice: A scenario analysis

The Dutch concept of ‘bicycle highways’ is increasingly being adopted by urban planners owing to rising environmental and health consciousness, and the growing popularity of electric bicycles. Bicycle highways differ from other types of cycling infrastructure in that they avoid intersections with motorised traffic, and are wide enough to allow for safe overtaking, thereby increasing cycling speeds. While many studies investigate the feasibility of constructing bicycle highways, few explore their effect on users’ travel preferences. In this context, our study aims to assess the potential impact of bicycle highways on commuter mode choice. We built a discrete choice model based on individual commute data from a national household travel survey, Mobilität in Deutschland 2008. The model was estimated in a logit modelling framework using Biogeme. We estimated multinomial logit and nested logit models and found nested logit to be more appropriate. The model estimates were then applied to forecast mode shares in scenarios with the pilot bicycle highway proposed in the Munich region. The variation in mode shares across scenarios with increasing average cycling speeds was analysed in areas with varying proximity to the infrastructure. The results suggest that bicycle highways reduce motorised travel and increase cycling. The effect is stronger as proximity to the corridor increases. The analysis helps to quantify the potential impact of bicycle highways on commuter mode choice even without considering further benefits beyond travel time reductions, such as increased safety, convenience, comfort, and reduced risks due to fewer interactions with motorised traffic.

Passing Behavior on Two-Lane Roads in Real and Simulated Environments

Passing maneuvers allow faster drivers to continue driving at their desired speeds without being delayed behind impeding vehicles. On two-lane rural roads, such maneuvers require the passing driver to occupy the opposing lane; this condition has tremendous implications for the safety and operation of two-lane roads. Several studies have investigated the passing behavior of drivers, and some studies have used driving simulators to analyze drivers’ behavior during following and passing maneuvers. However, the validity of simulators has not been ensured, because their results have rarely been compared with real data. The objective of this study was to compare drivers’ passing behavior as observed in the field with passing behavior in a driving simulator. For this purpose, data on passing performance and passing gap acceptance decisions were required. The study carried out a comparative analysis of the most significant variables related to passing behavior. The results showed similarities between passing time and passing distance of completed maneuvers (during the occupation of the opposing lane). However, drivers passed faster in the driving simulator and maintained greater clearances. Gap acceptance decisions were found to be similar, as the distributions of accepted and rejected gaps were similar, although critical gaps were found to be lower in the driving simulator. This finding might be explained by the absence of objective risks. The applicability of driving simulation seems reasonable, although some improvements are still possible, to account for sight distance limitations, replicate age and gender distributions, and reproduce the opposing traffic flow.