Freeway Exit Ramps Research Articles

Do Dynamic speed feedback signs impact drivers differently based on speeding tendencies? Insights from applications at select critical roadway contexts

The effects of a traffic control devices on drivers at different speed percentiles, particularly on the faster drivers, are of specific interest due to their higher likelihood of crash involvement. A study was designed to evaluate how the dynamic speed feedback signs (DSFS) affect drivers while transitioning from a high-speed to a low-speed environment. A total of 5 sites were selected, which included a freeway exit ramp, two speed transition zones, and two high-speed rural highway curves. Vehicle speed profiles approaching and entering these critical locations were collected before and after installing the DSFS. Based on the tracked speed of the free-flowing vehicles before the influence area, drivers were categorized as slower drivers, average drivers, and faster drivers using the 15th and 85th percentile speed at each site. Overall, installing the DSFS resulted in a significant reduction in speed across all locations for all sites. Drivers were found to reduce their speed while approaching the curve, traversing through the speed transition zones, and entering the curves or reduced speed limit areas. Results showed that faster drivers tend to reduce speed more than the average or slower drivers at every location. The faster drivers also reacted to the sign earlier compared to the slower or average drivers. The overall results are encouraging as they indicate that DSFS impact faster drivers more, which can ultimately reduce speeding-related crashes when transitioning from a high-speed environment. Based on the findings, the continued use of DSFS as a speed reduction strategy is recommended.

Driver Behavior Performance at Freeway Exit Ramp Terminals: Investigation and Modeling

Driver Behavior Performance at Freeway Exit Ramp Terminals: Investigation and Modeling

Research on Influencing Factors of Traffic Conflicts in Freeway Diverging Area during the Maintenance Period

Based on the traffic conflict techniques, a microscopic safety analysis framework is presented to study traffic conflicts in the freeway exit ramp diverging area (FERDA) during the maintenance period. A manual–software combination data processing approach was used to extract trajectory data from aerial videos and identify actual conflicts. Simulation conflicts were obtained from the VISSIM simulation model. Firstly, the conflict features of maintenance and normal operation periods were compared. Subsequently, conflicts were classified as lane-change conflicts or rear-end conflicts to investigate their spatiotemporal characteristics during the maintenance period. Finally, a random parameters multinomial logit model was developed to study the influencing factors and heterogeneity of conflicts. The results revealed that the FERDA has a higher collision risk during the maintenance period compared with the normal operation period. Additionally, lane-change conflicts have a higher occurrence probability than rear-end conflicts, but a shorter duration. Besides, the conflict density heat map showed that the lane-change conflicts and rear-end conflicts are densely distributed at 0–150 m and the middle lane of the FERDA, respectively. The model results indicated that the factors that significantly influence conflicts include velocity, acceleration, type, position, and destination of vehicle, the heavy vehicle percentage, total number of vehicles in the FERDA, and the velocity and destination difference between vehicles. Among these factors, the type of vehicle, destination difference, and the position of vehicles (at 150–270 m of the FERDA) were found that have significantly heterogeneous impacts on the two types of conflicts. This study is expected to provide safety analysts with an effective analysis method for evaluating the risk of the FERDA during the maintenance period. Additionally, the concluded influencing factors can potentially help develop different and effective safety countermeasures for different types of conflicts.

Optimizing the guiding sign system to improve drivers’ lane-changing behavior at freeway exit ramp

A high incidence of traffic accidents is often observed in freeway exit ramp areas. Slowing down, wandering, and changing lanes suddenly and continually in a short interval near the exit ramp are important reasons for accidents. Helping drivers start changing lanes sooner and more efficiently in freeway exit ramp areas is a feasible solution to vehicle interweaving. This paper aims to optimize the current guiding sign system and improve drivers’ lane-changing behavior before the exit ramp. Three guiding sign optimization measures (sign symbols, ground signs and voice prompts) had been considered before five guiding sign plans were made for driving simulation experiments: original sign (OS) plan, new type sign (NTS) plan, ground guiding sign (GOS) plan, voice prompt (VOS) plan, and voice-ground sign (VGOS) plan. The decisions, reactions, and operation processes of 43 Chinese drivers were compared to confirm the optimal guiding sign plan. The results showed that updating sign symbols, adding ground signs and voice prompts all contributed to the drivers’ shorter response time, earlier arrival at the lane-changing location, higher average speed and greater longitudinal distance of lane-changing. These findings can help freeway designers optimize the guiding sign system for freeway exit ramps.

Driver Response to a Dynamic Speed Feedback Sign at a Freeway Exit Ramp Considering the Sign Design and Installation Characteristics

Research was conducted at a freeway exit ramp with significant horizontal curvature to evaluate the effectiveness of dynamic speed feedback signs (DSFSs) as a speed reduction countermeasure. Several aspects of the DSFSs were evaluated, including display size, border type, lateral installation position, and vehicle detection range. Three different full-matrix DSFSs were utilized, which included 15-in. display panel with yellow border, 18-in. display panel with yellow border, and 18-in. display panel with no border. Each sign was individually installed and tested at identical locations near the start of the exit ramp curve, in both the traditional right-side-mount and an alternative forward-mount within the exit gore area. Speed data and message activation location were collected for vehicles approaching and entering the curve across the various sign test conditions. Overall, the presence of a DSFS positioned near the start of the curve resulted in curve entry speeds that were, on average, 3.5 mph lower than without a DSFS present. The lowest curve entry speeds were observed for cases in which the message activated when vehicles were within 250 to 400 ft of the curve. Interestingly, earlier message activation did not contribute to further speed reductions, although later activation substantially diminished the speed reduction effects. With regard to DSFS lateral position, both the side-mounted and forward-mounted DSFS installations resulted in similar curve entry speeds. Furthermore, there were no discernable differences in curve entry speeds between the 15- and 18-in. display panels, although the inclusion of a yellow sign border had greater speed reduction effects.

Evaluation of Enforcement and Messaging Campaign Focused on Reducing Cell Phone-Related Distracted Driving

Cellular telephone use has increased significantly in the United States as 97% of residents now own some type of cell phone. The ubiquity of cell phones has introduced concerns with respect to traffic safety as cell phone-related distractions have been shown to affect driving ability and increase crash risk. Various countermeasures have been implemented to address this issue, including public outreach campaigns and targeted enforcement activities. However, the efficacy of such strategies has been the subject of limited research. This paper examines cell phone use rates in consideration of enforcement activities in conjunction with targeted safety messages on roadside dynamic message signs. Two phases of enforcement were conducted in two urbanized areas of Michigan. Data were collected before, during, and after the enforcement period. A two-way random effects logistic regression model was estimated, and the results showed that cell phone use rates were lower during and, particularly, after the enforcement activities were conducted. Use rates were also found to vary based on age, gender, and race, allowing for the identification of target groups for public awareness and outreach campaigns. Use rates were also lower at freeway exit ramps as compared to signalized and stop-controlled surface street intersections. Lastly, cell phone-specific safety messages were associated with lower use rates compared with other message types, suggesting a potential synergistic effect.

Safety Evaluation of Freeway Exit Ramps with Advisory Speed Reductions

Posted speed limits inform drivers of the legal maximum allowable speed. In contrast, advisory speeds provide recommendations to drivers based on highway design, operating characteristics, and conditions. Various studies have investigated the safety impacts of speed limit changes, particularly on high-speed rural highways. One area of particular concern on such roadways is the approach to exit ramps that require substantive speed reductions, such as loop ramps. To date, there has been limited research examining the safety impact of the differential between the mainline speed limit and the lower exit ramp advisory speeds. This study aims to evaluate this relationship through the estimate of a series of safety performance functions. Random effects negative binomial regression models were estimated using data from 187 exit ramps where advisory speed signs are present throughout Michigan. The analyses were conducted based on a five-year period from 2014 to 2019, excluding 2017 data because of speed limit increases. In addition to speed differentials, various roadway characteristics such as deceleration lane length and curve radius were also evaluated. Results indicate that crashes increased as the difference between mainline and ramp speed increased. Crashes were also shown to decrease on ramps where the upstream deceleration lane length was greater than the minimum recommendation as per current design guidance.

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.

Systematic Safety Evaluation of Diverging Diamond Interchanges Based on Nationwide Implementation Data

Diverging diamond interchanges (DDIs) are designed as an alternative to the conventional diamond interchanges to enhance operational and safety performance. As the popularity of the DDI is increasing and more DDIs are being constructed and proposed, the need has arisen to measure the actual safety benefits of DDIs as compared with the traditional diamond interchanges. This study evaluates the safety of DDIs using three methods: before–after study with comparison group, Empirical Bayes before–after method, and cross-sectional analysis. This study collected a nationwide sample of 80 DDIs in 24 states. The estimated crash modification factors indicated that converting conventional diamond interchange to DDIs could significantly decrease the total, fatal-and-injury, rear-end, and angle/left-turn crashes by 14%, 44%, 11%, and 55%, respectively. Moreover, the developed safety performance functions implied that a longer distance between crossovers/ramp terminals and a lower speed limit on freeway exit ramps are significantly associated with lower crash frequency at diamond interchanges. This study contributes to the existing literature using a relatively large representative sample size, which provides more reliable evaluation results. In addition, this study also explored the effects of different traffic and geometric characteristics on the safety performance of DDIs.

Statewide Application of Wrong-Way Driving Crash Risk Modeling and Countermeasures Optimization Algorithm to Identify Optimal Locations for Countermeasure Deployment on Florida Limited Access Facilities

Wrong-way driving (WWD) crashes can have significant impacts on freeway safety and operations. Deploying intelligent transportation systems (ITS) WWD countermeasures at freeway exit ramps can effectively reduce WWD crash risk (WWCR), but these countermeasures are expensive. In this paper, a WWCR segment model and WWD countermeasures optimization algorithm are developed for all Florida limited access facilities (56 roadways with 1,375 exits) to identify the optimal locations for ITS countermeasure deployment. These were previously developed for specific toll-road networks within Florida, but never for a statewide network. Multiple WWCR models were investigated, with the final Poisson model using four-exit segments and 5 years of WWD event data. This model showed that more WWD events and higher crossing road traffic volumes increased WWCR, while certain interchange designs increased or decreased WWCR. Sixty-three segments containing 169 exit ramps without ITS WWD countermeasures were identified as WWD hotspots; these ramps were compared with the 169 ramps with the highest WWCR selected by the optimization algorithm. The algorithm selected 96 ramps not in the hotspots (improved resource utilization of 56.8%) and provided a 38.6% increase in WWCR reduction. Comparing WWD detection and turnaround data from 31 sites with rectangular flashing beacon ITS countermeasures to the optimization indicated a significant positive association between WWCR and turnaround percentage (higher WWCR at sites with lower turnaround percentage), verifying the accuracy of the optimization. By showing the transferability, scalability, accuracy, and benefits of this approach, this paper can help agencies reduce WWD and improve freeway safety and operations.

Comparative Analysis of Freeway Exit Ramp Terminal Design Practices to Deter Wrong-Way Driving in Different States

Although wrong-way driving (WWD) crashes are rare compared with other crashes, the severe outcomes resulting from these crashes make them an important traffic safety issue, especially on freeways. The initial point of origin for the majority of WWD crashes is the exit ramp terminal. During 2009–2013, the exit ramp terminals of full diamond and partial cloverleaf interchanges in Alabama experienced considerably higher frequency of wrong-way entries compared with those in Illinois. In this study, a comparative analysis is conducted between these two states to compare the differences in exit ramp terminal design practices and determine the differences that might have caused the relatively higher frequency of wrong-way entries at the exit ramp terminals in Alabama. The comparative analysis revealed that there is relatively higher usage of certain geometric design features and traffic control devices in Illinois, which contributed to deterring WWD. The lessons learned from this study can potentially benefit the 4E community (i.e., enforcement, education, emergency response, and engineering) in further understanding the best practices on off-ramp terminal design and traffic control devices features that have the potential to reduce WWD crashes on freeways.

Impacts of experimental advisory exit speed sign on traffic speeds for freeway exit ramp.

Many crashes occur around freeway exit ramp areas in China due to excessive speeds and large speed variances. Traditionally, a single posted ramp speed limit sign is installed around the physical gore area to manage the speed. To address this issue, the study presented in this paper proposes the use of an advisory exit speed sign (AESS), which is an additional exit speed limit sign positioned along the deceleration lane to accommodate the speed changes ahead of the physical gore. The study selected three sites with similar exit ramp configurations and two scenarios (with AESS/without AESS) to quantify the influences of the AESS on the speed of exiting vehicles. The speed profiles of 480 vehicles were obtained based on 12 hours of data collection. A t-test was applied to verify the reduction in mean speed between the two scenarios. The results show that the AESS in this study was effective in reducing the mean speed and 85th percentile speed, especially in the taper and deceleration lane. It was clearly seen that drivers began to decelerate in advance when the AESS was installed, which led to a smooth deceleration process, especially on the segment between the theoretical gore and the physical gore. The AESS was also helpful in reducing speeding to some extent. Although the effects of the AESS on speed reduction at curved ramps were not ideal, the speed fluctuation range tended to be more contracted when the AESS was installed. This paper provides useful information for researchers, managers, and engineers when considering the implementation of AESS.

Methods of dropping auxiliary lanes at freeway weaving segments

ABSTRACTAuxiliary lanes connecting freeway entrance and exit ramps provide additional space for entering and exiting vehicles to change lanes. The method of dropping auxiliary lanes is critical in the design of freeway auxiliary lanes. This study investigates the performance of different methods of dropping auxiliary lanes. Case studies were conducted at two selected freeway segments with successive entrance or exit ramps in the City of Houston. Traffic simulation analysis results of these two case studies show that additional operational benefits can be achieved by extending an auxiliary lane beyond the freeway weaving segment. The study also found that if the weaving segment is followed by an entrance/exit ramp and this ramp has high traffic volume, it can be less operationally favorable to extend and terminate the auxiliary lane at this entrance/exit ramp location. Instead, dropping the auxiliary lane before this entrance/exit ramp represents a more operationally effective option.

Factors influencing the patterns of wrong-way driving crashes on freeway exit ramps and median crossovers: Exploration using ‘Eclat’ association rules to promote safety

Abstract Wrong-way driving (WWD) has been a constant traffic safety problem in certain types of roads. These crashes are mostly associated with fatal or severe injuries. This study aims to determine associations between various factors in the WWD crashes. Past studies on WWD crashes used either descriptive statistics or logistic regression to identify the impact of key contributing factors on frequency and/or severity of crashes. Machine learning and data mining approaches are resourceful in determining interesting and non-trivial patterns from complex datasets. This study employed association rules ‘Eclat’ algorithm to determine the interactions between different factors that result in WWD crashes. This study analyzed five years (2010–2014) of Louisiana WWD crash data to perform the analysis. A broad definition of WWD crashes (both freeway exit ramp WWD crashes and median crossover WWD crashes on low speed roadways) was used in this study. The results of this study confirmed that WWD fatalities are more likely to be associated with head-on collisions. Additionally, fatal WWD crashes tend to be involved with male drivers and off-peak hours. Driver impairment was found as a critical factor among the top twenty rules. Despite several other studies identifying only the WWD contributing factors, this study determined several influencing patterns in WWD crashes. The findings can provide an excellent opportunity for state departments of transportation (DOTs) and local agencies to develop safety strategies and engineering solutions to tackle the issues associated with WWD crashes.

Development of a new conflict-based safety metric for freeway exit ramps

In this article, the safety implication of freeway exit ramps is examined using a newly developed conflict-based safety metric. A multi-step Monte Carlo simulation procedure is proposed to estimate...

Driver performance and attention allocation in use of logo signs on freeway exit ramps

The objective of this research was to quantify the effects of driver age, ramp signage configuration, including number of panels, logo format and sign familiarity, on driver performance and attention allocation when exiting freeways. Sixty drivers participated in a simulator study and analysis of variance models were used to assess response effects of the controlled manipulations. Results revealed elderly drivers to demonstrate worse performance and conservative control strategies as compared to middle-aged and young drivers. Elderly drivers also exhibited lower off-road fixation frequency and shorter off-road glance durations compared to middle-aged and young drivers. In general, drivers adopted a more conservative strategy when exposed to nine-panel signs as compared to six-panel signs and were more accurate in target detection when searching six-panels vs. nine and with familiar vs. unfamiliar logos. These findings provide an applicable guide for agency design of freeway ramp signage accounting for driver demographics.

Safety and Capacity Performances of Single-lane Right Exit Ramp on Freeway: A Case Study in Jiangsu Province, China

Growing traffic in China has resulted in a demand for freeway exit ramps with higher capacity in order to avoid congestion. The right single-lane exit ramp is the most common style of the freeway exit ramp which can be divided into two types: taper-type single-lane exit ramp and parallel-type single-lane exit ramp. The main objective of the paper was to elaborate recommendations about the best single-lane exit ramp layout according to different parameters by evaluating safety and capacity. 6 taper-type and 4 parallel-type exit ramps were selected in Jiangsu Province and the space mean speeds (SMS) of the 200 vehicles on the deceleration lane of each sample were observed. The average SMS standard deviation of taper-type was 8.0 kmph comparing with 4.6 kmph of parallel-type, which indirectly indicated that parallel-type single-lane exit ramp was safer than the other one. The capacities of the two exit ramp types were analyzed using the FHWA's Traffic Software Integrated System (TSIS). Two microsimulation models were constructed and the vehicle input varied from 0 to system alert “backed up” by each increment of 100 pcph. The capacity was defined as the input value before the system “backed up”. The results of the two exit ramp types were 1800 pcph and 2100 pcph, which meant the capacity of parallel type was more than the taper type.

Selection for optimal exit ramp type on Florida’s freeways based on operational analysis

In the State of Florida, several types of exit ramps are used, including single-lane exit ramp with a taper, single-lane exit ramp without a taper, two-lane exit ramp with an optional lane, and two-lane exit ramp without an optional lane. Drivers exiting freeways need to make maneuver decisions (lane change, lane merge, and decelerate) prior to exit ramps in order to access cross roads at interchanges. Different exit ramp types lead to varying driving maneuvers when exiting, affecting the operational and safety performance on freeways. Based on the facts, there are several issues that need to be addressed in selecting the most optimum types of freeway exit ramps. This article mainly focuses on the comparison of operational performances of different ramp types and tries to present a method for choosing the optimal one. A data collection of 24 sites in Florida were conducted, and traffic simulations by Traffic Software Integrated System: Corridor Simulation were employed. Mathematical models were built to evaluate impacts of these ramps based on simulations. And an analytical hierarchy process method was applied to assign significance weight for all selected measures of effectiveness in terms of Florida questionnaire. Finally, an aggregate numerical evaluation was provided according to calculated data.

Concept of controlling the usage of nomadic devices in highly automated vehicles

Today, the automobile industry and several research institutes develop automated vehicles for several driving applications. With increasing capabilities of automation, the driver can be more and more dispensed from the driving task and might want to use his nomadic devices to get entertained, read the news or do office work while driving. However, in some complex driving situations (such as road works, freeway exit ramps or lane closure because of car accidents), the automation still needs to safely hand over the control to the driver. These situations require a lot of attention by the driver who must not be tempted to ignore the warnings of the assistance system and to continue any task on the nomadic device until a critical situation originates. This study describes a method to link nomadic devices to vehicles to support a safe usage during highly automated driving and a first approach to ensure a safe transition between different automation modes. Therefore the automation system is connected to the nomadic device in the vehicle and has the ability to actively control the content on the screen. The proof of concept is demonstrated in a research vehicle that drives on a simulated motorway.

Analysis of Crash Risks by Collision Type at Freeway Diverge Area Using Multivariate Modeling Technique

AbstractCrashes present different collision types at freeway diverge areas. The research reported in this paper applies the multivariate modeling technique to evaluate the crash risks by collision type. Three years crash data are obtained from 282 freeway exit ramps. Three types of crashes are considered [i.e., (1) rear-end, (2) sideswipe, and (3) angle collisions]. A multivariate Poisson-lognormal (MVPLN) model is estimated to jointly evaluate the impacts of explanatory variables on different collision risks. For comparison purpose, univariate negative binomial (NB) models are also estimated based on the same dataset. The results show that the MVPLN model successfully captures the correlation of latent effects among the crash counts of different collision types. Thus, the MNPLN model estimates the impacts of variables more accurately than the NB model. The MVPLN model is found outperform the NB models in predicting the crash count of each collision type. Findings of this paper can help better understand ...