Freeway Interchange Research Articles

Assessing Corridor Safety Performance at Approaches to Freeway Interchanges Using Lane Change Data

Urban arterials near freeway interchanges are vital components of urban road infrastructure, connecting high-mobility freeway networks to the more accessible but lower-mobility urban network. In this study, the operational safety of these arterials is examined and the relationship between roadway geometry and safety performance is investigated. To assess operational safety, lane changes were considered as a risk factor, and the number of lane changes in each study subsegment was recorded. Segments were categorized as upstream or downstream based on their location relative to the intersection. The number of lane changes served as a safety performance measure, and was analyzed using linear regression models. The results indicate that downstream segments experienced decreased safety performance when median storages were present, while adding right running bays improved safety. Median openings and increased numbers of driveways negatively affected safety in these segments. For upstream segments, right turning bays were found to impair safety performance the most, followed by the number of driveways. The closer the driveways were to the interchange; the worse was the effect on the safety performance. In summary, this research highlights the importance of geometric design elements when considering the safety performance of urban arterials. It is crucial to consider geometric design elements, such as median storages, driveways, and other elements, as a part of a larger system rather than isolated elements, so as to provide safer arterials near freeway interchanges.

Connected Automated and Human-Driven Vehicle Mixed Traffic in Urban Freeway Interchanges: Safety Analysis and Design Assumptions

The introduction of connected automated vehicles (CAVs) on freeways raises significant challenges, particularly in interactions with human-driven vehicles, impacting traffic flow and safety. This study employs traffic microsimulation and surrogate safety assessment measures software to delve into CAV–human driver interactions, estimating potential conflicts. While previous research acknowledges that human drivers adjust their behavior when sharing the road with CAVs, the underlying reasons and the extent of associated risks are not fully understood yet. The study focuses on how CAV presence can diminish conflicts, employing surrogate safety measures and real-world mixed traffic data, and assesses the safety and performance of freeway interchange configurations in Italy and the US across diverse urban contexts. This research proposes tools for optimizing urban layouts to minimize conflicts in mixed traffic environments. Results reveal that adding auxiliary lanes enhances safety, particularly for CAVs and rear-end collisions. Along interchange ramps, an exclusive CAV stream performs similarly to human-driven ones in terms of longitudinal conflicts, but mixed traffic flows, consisting of both CAVs and human-driven vehicles, may result in more conflicts. Notably, when CAVs follow human-driven vehicles in near-identical conditions, more conflicts arise, emphasizing the complexity of CAV integration and the need for careful safety measures and roadway design considerations.

Study on Driver Behavior Pattern in Merging Area under Naturalistic Driving Conditions

To reduce the risk of traffic conflicts in merging area, driver’s behavior pattern was analyzed to provide a theoretical basis for traffic control and conflict risk warning. The unmanned aerial vehicle (UAV) was used to collect the videos in two different types of merging zones: freeway interchange and service area. A vehicle tracking detection model based on YOLOv5 (the fifth version of You Only Look Once) and Deep SORT was constructed to extract traffic flow, speed, vehicle type, and driving trajectory. Acceleration/deceleration distribution and vehicle lane-changing behavior were analyzed. The influence of different vehicle models on vehicle speed and lane-changing behavior was summarized. Based on this data, the mean and standard deviation of velocity, acceleration, and variable acceleration were selected as the characteristic variables for driving style clustering. To avoid redundant information between features, principal component dimensionality reduction was performed, and the dimensionality reduction data was used for K-means and K-means++ clustering to obtain three driving styles. The results show that there are obvious differences in the driving behaviors of vehicles in different types of merging areas, and the characteristics of different areas should be fully considered when conducting traffic conflict warnings.

Traffic Performance of Successive Freeway Merge Segments

At freeway interchanges with high entering flows, implementing two successive merges can improve traffic flow and capacity by distributing the merging maneuvers. The German Guidelines for the Design of Motorways define different types of successive (“double”) merges. According to the quality of service assessment procedure for freeway merge segments given in the German Highway Capacity Manual, successive merge segments can be evaluated separately. However, depending on the distance between the merges, the capacity of the second (downstream) merge might be affected by the entering traffic at the first (upstream) merge, which influences the lane-flow distribution. For a more precise evaluation of traffic flow performance and traffic safety depending on the geometric design characteristics, vehicle interactions, lane changes, the resulting capacity of successive merge segments, accident rates, and crash types were analyzed in the study. The research was based on loop detector data as well as trajectory data obtained from video measurements, which provide an insight into the interactions between mainline and entering vehicles. For the analysis of traffic safety, crash data were evaluated over a period of 3 years. Furthermore, successive merge segments with different geometric and traffic characteristics were modeled with the microscopic traffic simulation tool BABSIM to analyze the influence on traffic flow and capacity. As a result, capacity models and recommendations for the geometric design of successive freeway merge segments are provided.

Developing a time-series speed prediction model using Transformer networks for freeway interchange areas

This study investigates the lane-level speed distribution in the freeway interchange area and develops a time-series speed prediction model using Transformer networks. The full-sample real-time speed data from interchange areas under heavy traffic was extracted by the YOLO v3 detection algorithm and Deep-Sort tracking algorithm based on Unmanned Aerial Vehicle (UAV) videos. A short-term prediction model of lane-level driving speed was constructed using the Time-Series Transformer (TST) framework. Results showed that the greatest magnitude of speed change occurred during the process of switching from the passenger lane to the truck lane. The inner lane consistently demonstrated higher mean speeds compared to the outer lane. The TST model proposed in this study could achieve an accuracy of 98.35% in predicting lane-level driving speed. These findings suggest the need to consider the speed transition between passenger and truck lanes in freeway engineering design, marking setting, and optimization of safety facilities.

Integrated Real-Time Interchange Control System for Freeway Ramps and the Connecting Arterial

Contending with various recurrent congestion patterns on major freeway corridors has long been a prioritized task of the transportation community. Most of these patterns take place on a freeway interchange’s on-ramp and off-ramp segments where both exiting and merging flows often trigger a series of lane changes, resulting in significant freeway speed reduction and propagation of traffic queues to neighboring surface streets. To concurrently mitigate freeway traffic congestion and minimize any negative impacts on the nearby local arterials, this study has developed an Integrated Real-time Interchange Control (IRIC) system, which maximizes the benefits of both freeway and arterial users by fusing an integrated off-ramp signal control (IOSC) module, an off-ramp queue impact (OQI) model, a lane group-based (LGB) traffic model, and a ramp metering control strategy as well as arterial signal optimization modules. The proposed system with both ramp metering functions and local arterial signal design capabilities can determine whether to implement system-wide optimization or merely the ramp metering based on real-time detected traffic conditions. The evaluation results from experiments have confirmed the effectiveness of the developed real-time interchange control system, especially with respect to its ability of preventing ramp queue overflows to the neighboring arterials and minimizing the off-ramp spillback onto the freeway mainline.

Planning and design of the Gordie Howe International Bridge, North America

The Gordie Howe International Bridge project is providing a new modern border crossing between Windsor, ON, Canada and Detroit, MI, USA. The centrepiece of the project is a 2.5 km long cable-stayed bridge with 853 m main span over the Detroit River and 220 m tall towers on both sides of the river. In addition to the bridge, the project includes ports of entry on both sides of the border and a new freeway interchange with Interstate-75 in Detroit. The project was procured as a public–private partnership that allowed the proponents to propose either a suspension or cable-stayed bridge, with the ultimate selection creating the longest cable-stayed bridge in North America. The paper outlines the need for the new border crossing and results of the environmental assessment process, as well as describing the project evolution from planning through procurement and into detailed design. The scoping of the bridge design parameters is discussed, including: comprehensive geotechnical investigation; load study to develop project-specific live loading; the approach for durability requirements to achieve a service life of 125 years; special considerations for security; wind engineering; and compliance with both Canadian and US design codes. The paper also discusses the approach to achieving an aesthetically pleasing bridge design.

Transit “Pass-Through” Lanes at Freeway Interchanges: A Life-Cycle Evaluation Methodology

Transit “pass-through” lanes provide transit vehicle priority at freeway interchanges. “Pass-through” lanes allow a transit vehicle to exit the freeway at an interchange, cross straight through the intersecting arterial road, and re-enter the freeway. This treatment allows transit vehicles to bypass congestion on the mainline between the beginning of the off-ramp and the end of the on-ramp.This paper outlines a methodology to evaluate if transit “pass-through” lanes are economically justified at a given interchange and provides a method for prioritizing candidate locations. The methodology provides an objective and consistent decision making method, reduces the effort required for practitioners to assess the need for “pass-through” treatment at a given interchange, and helps ensure that limited resources are directed towards interchanges that are expected to experience the greatest benefit per dollar spent.The proposed methodology is based on an analytical approach that compares the value of travel time savings (for passengers and transit vehicles) with the construction and maintenance costs of the transit “pass-through” lane treatment.

Optimization of Dynamic Speed-Homogeneous Space Using Location-Based Vehicle Data

Road extent compared with the number of automobiles registered in South Korea is the lowest among OECD (Organization for Economic Cooperation and Development) countries. Currently, traffic information is provided based on nodes and links using the centerlines of the roads. However, detailed speed information is unavailable. This study presents an optimization method for space to represent a dynamic speed-homogeneous space. Vehicle directions were separated by route using azimuth data based on global navigation satellite system (GNSS) location information, and the time mean speed and space mean speed were used to determine the homogeneous space of vehicle speed through the gradual separation of space. The processing speed of large-capacity data was increased by using Geohash, which applied a quaternary basis segmentation method that split data into two directions of longitude and latitude. The numbers of homogeneous speed spaces along the two directions of the Gyeongbu Expressway were determined to be 127 and 170, respectively, by the 12-step segmentation method. Spaces not included in the range of homogeneous speed spaces amounted to 5.19% and 7.51%, respectively, along the northbound and southbound roadways of the Gyeongbu Expressway. These non-convergence spaces were analyzed by the influence of vehicles entering or exiting slowly from the merging and diverging areas of the freeway junctions and interchanges. In other words, these were analyzed by the difference of speed by lane and not the driving direction.

Real-Time Arterial-Friendly Ramp Metering System

To balance the benefits between the freeway and arterial users and also to prevent on-ramp queue spillbacks, the authors have developed an arterial-friendly local ramp metering control (AF-ramp) system for time-of-day operations during recurrent congestion. This study presents the real-time version of the AF-ramp (named RAF-ramp) system, with a lane-group-based macroscopic traffic module for predicting traffic state and for executing control strategies, aiming at maximizing the total throughput from the control area, comprising the ramp meter and nearby local intersection signals. Recognizing the discrepancy in the dynamic nature between ramp traffic and arterial flows, the RAF-ramp system with its embedded traffic state prediction and monitoring mechanism can trigger the concurrent optimization of both controls when justified to do so, or only dynamically adjust the ramp metering rate under the pre-optimized local signal environment. The results of extensive simulation experiments have confirmed that the proposed system outperforms the widely-applied real-time ramp control model, ALINEA/Q, under various experimental traffic scenarios, because the produced control strategies can effectively utilize the freeway’s weaving capacity and also best coordinate neighboring intersections’ signals to maximize the entire network’s performance. Such a real-time arterial-friendly ramp metering system, addressing both the time-varying freeway dynamics and the concerns of local traffic users, may well serve as an effective tool for contending with bottlenecks at freeway interchanges.

Diamonds, Cloverleafs, and SPUIs: The Geography of Freeway Interchanges in the United States

Freeway interchanges are a fundamental component of freeway networks and provide nodes for economic development. They take a wide range of forms, including diamonds, cloverleafs, and stacks, depending on traffic conditions and other factors. They have not been the subject of study or data collection, however, and their numbers are unknown. Their geography is examined using nationwide data that allow the location and type of every interchange to be identified. The results show that there are more than 25,000 freeway interchanges in the United States, with diamond configurations accounting for almost 61 percent of them. They are far more common in urban areas. Interchanges have been modified or replaced at a steady rate and continue to grow in number. Although frequently overlooked, they are some of the sites of greatest congestion in the country and some of the most expensive transport infrastructure elements ever built.

Driver Response to a Dynamic Speed Feedback Sign on Freeway Exit Ramps Based on Sign Location, Interchange Type, and Time of Day

A series of field evaluations was performed at three freeway interchange ramps in Michigan that possessed significant horizontal curvature to assess the impacts of a dynamic speed feedback sign (DSFS) on driver speed selection and brake response while approaching and entering the ramp curve. A DSFS with a 15 in. full-matrix display was temporarily installed at each of the three exit ramp locations. The sign was programmed to display the same feedback message at each location, which included the speed number for all approaching vehicles, which alternated with a “Slow Down” message for vehicles approaching above 40 mph. The effectiveness of the feedback sign was tested across various sign locations (at the point of curvature versus 350 ft upstream), interchange types (system versus service), time of day (peak versus off-peak), light conditions (daylight versus darkness), and vehicle types (passenger vehicles versus trucks). Compared with the pre-DSFS site condition, the DSFS reduced curve entry speeds and improved brake response at two of the three ramp locations. In general, the greatest beneficial effects on driver behavior were achieved when the DSFS was positioned at the point of curvature, during which curve entry speeds were reduced by approximately 2 mph. These findings were consistent between the system interchanges and service interchanges, and across all vehicle types. The DSFS was also found to be most effective during daytime off-peak periods compared with peak periods and at night. Further evaluation of DSFS at additional ramp locations, and considering an expanded set of conditions, is recommended.

Using single and multiple unmanned aerial vehicles for microscopic driver behaviour data collection at freeway interchange ramps

This paper presents a detailed methodological framework for collecting microscopic driver and vehicle behaviour data over a long road segment with an application to the entire stretch of a freeway ramp segment using single and multiple unmanned aerial vehicles (UAVs). The methodology allows users to collect reliable and complete trajectories of traffic movements in areas with challenging physical characteristics (long road segment, horizontal curvature, changing elevation, and presence of shadow), challenging traffic characteristics (high traffic volume, high speeds, and high-speed changes), and restrictive regulations (UAVs prohibited from hovering over the freeway or the right-of-way). Different UAV setups are recommended and can be used depending on the site conditions. Specific commercial software and procedures used to complete the data collection are explained. The methodology was applied at two ramps and verified with speed data acquired from differential GPS receivers using three different error metrics. The results showed good performance of the proposed methodology, including when aerial videos were taken from oblique angles.

Layered Landscapes: Links between Brazil and Australia after the Second World War

ABSTRACT The modern garden in Australia after the Second World War reflected international design movements along with new appreciations of the country’s indigenous landscapes. Conservation activities and concern for environmental quality expanded in the face of the development boom’s insatiable quest for resources and unprecedented threats to natural systems. The Australian profession of landscape architecture, institutionalised in 1966, emerged in response. An uneasy association of planners, architects, horticulturalists, foresters and others stemmed from sometimes vastly different standpoints that remarkably coalesced around singular points of reference. One possible source requiring clarification is the work of Brazilian landscape architect and artist, Roberto Burle Marx (1909–94). Evidence suggests that Burle Marx’s alluringly graphic landscape designs struck a chord, sometimes very clearly, influencing Australian designers such as John Oldham (1907–99), John Stevens (1920–2007), and Karl Langer (1903–69) in their landscape designs surrounding freeway interchanges, atop office block car parks, and for tourist resorts alike. This gave their practices a leading edge. In other instances, connections between Burle Marx and Australian founders of the profession were merely subtle traces, and the subliminal influence instead sheds light on the character of the Australian profession rather than overt derivations.

How do dutch drivers perceive horizontal curves on freeway interchanges and which cues influence their speed choice?

Operating speeds in Dutch freeway curves differ often by 20 km/h compared to their design speeds. Operating speed is thought to be influenced by how drivers perceive curves when approaching a curve. This explorative research explores which curve cues and other variables influence drivers’ speed choice in curves. For this purpose, a survey was designed with 28 sets of curve comparisons. The curves were chosen from interchanges in the Netherlands and were compared to each other. To avoid direction bias, the curves were right turning only. In each set illustrations of two different curves out of a total of 8 curves were shown, and the participants were asked in which curve they would drive faster. In total 819 participants in the age range of 18 and 78 (mean=41.3; Std.=11.9) completed the survey. The survey data showed four common categories of curve cues and variables influencing the decision to drive faster, of which those in the category of the road environment and its surroundings were mentioned the most. The top three variables influencing speed choice are visibility of curve characteristics, “overview” as a holistic but as such hard to measure variable, and number of lanes. Variables such as presence of signage and trees were also mentioned frequently by the respondents. Geometric road characteristics such as curve radius and deflection angle were identified by the respondents as influencing variables, but only showing to affect speed selection when these are visible to the driver and not obscured by trees or other elements. This suggests combinations of geometric and surrounding elements are needed to get a better understanding of speed selection by drivers.

Evaluation of Alternative Messages and Sign Locations on Driver Response to a Dynamic Speed Feedback Sign on a Freeway Interchange Ramp

Research was undertaken to determine effective messaging strategies and sign positions for dynamic speed feedback signs (DSFS) when used for speed management at freeway ramp curves. A field evaluation was performed in this setting to assess the impacts of a DSFS on driver speed selection and braking characteristics while approaching and entering the curve. Three feedback messaging strategies were evaluated at three sign positions in advance of the curve. Compared with the existing site (without the DSFS), the DSFS reduced curve entry speeds and improved brake response across all test conditions, particularly for heavy trucks. Overall, considering the combination of both sign position and feedback messaging strategy, the greatest benefits to driver behavior were attained when the DSFS was positioned 255 ft upstream of the curve and the feedback message included the speed number alternating with a SLOW DOWN message. The inclusion of an advisory speed panel with the DSFS did not have a substantive impact on driver behavior. Based on the findings, the continued use of DSFS as a speed reduction treatment at freeway ramp curves is recommended. Specifically, the sign should be positioned to provide adequate time for drivers to perceive and react to the message, such that comfortable braking can be accommodated while approaching the curve. However, the sign should not be placed too far in advance of the curve, as drivers may be more likely to disregard such a premature warning message. Further evaluation of DSFS under various alternative ramp configurations is recommended.

How Firms Absorb Demand Side Shocks: Evidence from a Natural Experiment

We analyze impact of the freeway interchange collapse in San Francisco Bay area on difference in airfare quotes for travel into the area's three main airports. The incident temporarily made Oakland airport a less attractive choice for traveling to San Francisco, so we hypothesize that fares for travel into Oakland will be relatively lower while the freeway interchange was out of service than afterwards. We test our contention using the sample of fare quotes collected on-line, and find the expected effect in the magnitude of 6-7 percent. Our results imply the following conclusions. First, the demand-side shock was well absorbed by the supply side. Second, return to status quo once the shock vanished was swift.

Safety evaluation of freeway interchange merging areas based on driver workload theory.

Prior safety evaluations of interchange merging areas have mostly focused on traffic conflicts and operating speeds, without considering how these factors can influence the driver workload. Researches regarding the level of driver workload have largely concentrated on urban roads, tunnel sections, and basic freeway segments, without considering the impact of merging traffic flows on safety. Therefore, this study has investigated how merging vehicles can impact through-driver workload and safety. Three independent field experiments were conducted on freeways, involving 18 drivers and 17 interchanges. The results showed that the vehicles merging onto freeway impact driver workload and driving performance, generating potential risk that cannot be ignored. Merging into the mainline traffic flow increases the through-driver workload to a higher level or even exceeds the safety threshold, despite there being better geometrical conditions of interchanges than those of basic freeway segments. When the volume of merging vehicles exceeds 564 pcu/h or the traffic saturation is above 0.485, driver workload rises above the safety thresholds and the driving risk is elevated, which potentially would lead to crashes. This study offers insights for more effective segment division of operating speed prediction, and dynamic risk management with regard to interchange safety.

Impacts of Directional Rumble Strips on Vehicle Speeds and Driver Behavior at Freeway Off-Ramps

AbstractDrivers have an increased crash or incident risk when driving on freeway interchange ramps compared with the other interchange-related segments. Directional rumble strips (DRS), a pattern s...

Application of the speed prediction model (V85) (V85) in the design of freeway interchanges

The design of freeway interchanges is performed on the basis of technical and economic comparison of options for a large number of indicators. Design decisions depend on a large number of factors: the class of intersecting streets and roads, the level of service, traffic intensity, the estimated speed at the ramps, terrain, urban development, hydrogeological conditions of construction, etc. An integral indicator of the quality of design decisions is the maximum safe speed. In most countries of the world, the speed of single passenger cars is 85 % of the security (V85), which may differ from the calculated speed at the maximum safe speed. In the article, on the basis of experimental data, empirical models for calculating speeds (V85) are obtained at freeway interchanges with directional ramps. Experimental studies were performed at freeway interchanges in the city of Moscow using a car laboratory according to the method of following the leader, as well as by processing video from a quadrocopter. The results of the study make it possible to predict the speed of movement (V85) at the ramps of freeway interchange and to compare the freeway interchanges schemes according to the criterion of speed, loss of time, relative safety and traffic capacity.