Service Patrol Research Articles

Improving Effectiveness of the Safety Service Patrol Programs: A Discrete Event-Based Simulation Approach

Safety service patrols (SSPs) play an important role in incident management on highways. It is critical to respond to incidents in a timely manner as this can significantly reduce nonrecurrent congestion and improve safety. Therefore, it is essential to allocate available SSP vehicles to highway segments such that their effectiveness is maximized. This study aimed to develop a simulation-based framework to assist with SSP service optimization. More specifically, a discrete event-based simulation tool (i.e., SSP-OPT) with customizable parameters was developed to help plan the optimum patrol routes based on available SSP resources and predicted incidents. The developed tool was tested with roadway traffic and incident data from the Virginia highway network. After model calibration, the simulation results showed that the developed SSP-OPT tool could replicate the patrol routes with similar performance to the field observations, validating the tool. Further, adopting the tool for corridor-level optimization could help to identify the best patrol plan to minimize SSP response time and maximize SSP response rates for a given number of SSP vehicles. The SSP-OPT tool requires minimal user input (e.g., segment lengths, annual average daily traffic) and has the flexibility to be easily applied to any highway corridor once calibrated. The tool generates various performance metrics to enable more informed decision making in SSP route planning.

A Data-Driven Approach to Estimate Incident-Induced Delays Using Incomplete Probe Vehicle Data: Application to Safety Service Patrol Program Evaluation

This paper presents a data-driven approach to estimate incident-induced delays (IIDs) using probe vehicle data while accounting for missing data. The proposed approach is applied to evaluate the effectiveness of a safety service patrol (SSP) program. Existing data-driven methods for IID estimation usually rely on complete data sets. The proposed approach employs a random forest-based classification model and an interpolation method to estimate IIDs when real-time data are completely or partially missing during the incident-impacted time period. It also identifies reference profiles from the closest spatial-temporal road segments to improve data availability. The case study shows that the SSP program in the Quad Cities area of Iowa reduces IIDs associated with various incidents by 15%–91%. This data-driven evaluation framework can be applied to other traffic incident management programs, allowing more accurate and objective evaluations of their effectiveness.

The integrated analysis of primary and secondary incident characteristics: Focusing on the impact and scope of the safety service patrol program in Iowa

Secondary incidents are considered a major risk in terms of traffic management due to dangerous ramifications, such as reduced capacity, additional traffic delays, and serious injuries. Therefore, it is necessary to examine what causes a secondary incident to occur after a primary incident and prepare countermeasures to reduce the possible damage to human and property from primary and secondary incidents. In Iowa, a safety service patrol program is being implemented on major highway routes to respond to both types of incident efficiently. However, research on when, where, and under what conditions these incidents occur and how the program can deal with incidents must be conducted to determine the major characteristics of primary and secondary incidents and to estimate the program's performance. Consequently, statistical and spatial analyzes were performed on traffic incidents in a 5-year period (2016–2020) in Iowa. A survival analysis confirmed that the program could decrease the probability of secondary incident occurrences, and 99.9% of secondary incidents occurred within 4 h of the primary incident. Additionally, the binary logistic regression analysis of primary incidents affirmed that a longer incident clearance time and a higher severity of incidents could increase the probability of secondary incidents occurrence. Furthermore, a spatial analysis evaluated that the Iowa DOT safety service patrol program adequately covered areas where primary and secondary incidents are focused. This study is expected to be used to develop countermeasures in both incident cases by identifying the characteristics of secondary and primary incidents in Iowa.

Evaluating the impacts of vehicle-mounted Variable Message Signs on passing vehicles: implications for protecting roadside incident and service personnel

This study aims to evaluate the Variable Message Signs (VMS) mounted over the cab of emergency vehicles as a safety countermeasure to protect roadside incident and service personnel. The research team collaborated with the Alabama Department of Transportation’s Safety Service Patrol (SSP) program, specifically the Alabama Service Assistance Patrol (ASAP) in the West Central Alabama region, to collect video data from their service vehicles. Deep learning techniques were employed to detect vehicles in the recorded videos. A total of 11,338 passing vehicles were detected in 135,946 frames of video footage, and their trajectories were extracted for analysis. The study focused on examining the behaviors and movements of passing vehicles, including their speed and lane change behaviors, and developed statistical models to systematically investigate the impact of VMS on these behaviors. Random intercept models were utilized to account for unobserved factors associated with different stop locations. The modeling results revealed significant relationships between the use of VMS and the behaviors of passing motorists. When the VMS was active, drivers were more likely to change lanes and reduce their speed compared to situations where the VMS was not active. The odds of a vehicle changing lanes were found to be 95% higher when the VMS was in use. These findings suggest that the utilization of VMS can have a positive impact on traffic, particularly for passenger vehicles. The study outcomes imply that the use of VMS could be an effective countermeasure in protecting roadside incidents and ensuring the safety of service personnel.

Evaluation of Two Regional Transportation Systems Management and Operations Strategies for Improving the Response to Disabled Vehicles

Disabled vehicles are a common issue faced by agencies which can negatively affect traffic operations and safety. A wide range of response strategies exist, but determining which are best for a region can be challenging. After surveying 60 U.S. traffic incident management stakeholders, two commonly suggested improvements to disabled vehicle response strategies were: 1) expanding safety service patrols (SSPs) and 2) increasing towing capabilities. This paper develops a congestion-based methodology for quantifying the congestion reduction benefits of implementing these improved strategies for addressing disabled vehicles, specifically expanding SSP patrol hours and implementing instant dispatch tow (IDT) programs. Using 2019 incident data from three Florida, U.S., limited access roadways, the estimated congestion costs caused by disabled vehicles on the studied roadways were over $20 million. The estimated congestion savings for expanding Road Rangers (Florida’s SSP) ranged from $196,315 to $1,413,641 ($14,023 to $20,488 per incident). Implementing an IDT program had estimated congestion savings ranging from $398,353 to $3,910,299 ($9,264 to $76,485 per incident). IDT programs would address more disabled vehicle incidents than Road Ranger expansions, making the benefits substantially higher, especially on urban roadways. Based on the results, it is recommended that agencies prioritize IDT deployment on urban roadways with long incident durations for the most immediate benefits. An IDT program would also be able to address other types of incident, likely making the benefits greater than those estimated in this paper. Agencies nationwide can use this paper’s methodology and results to help identify effective regional disabled vehicle transportation systems management and operations strategies.

Evaluating the Impact of Freeway Service Patrol on Incident Clearance Times: A Spatial Transferability Test

Freeway service patrol (FSPs) programs have been considered as an effective tool for traffic incident management in minimizing the adverse effects of traffic incidents. In this study, random parameters hazard-based duration modeling method was used to evaluate the impact of the newly implemented Alabama Service and Assistance Patrol (ASAP) program, using incident clearance time as a performance measure. It was determined that there is a statistically significant difference in the factors that influence incidents clearance times between incidents that occurred inside and outside the ASAP regions. A total of five variables (on-road, nighttime, peak hours, rain, and fire response present) were observed to have random effects along with ten fixed effects variables on incidents occurring inside the ASAP regions. On the other hand, incidents that occurred outside the ASAP regions were found to have three random effects variables (on-road, nighttime, and fire response present) and seven fixed effects variables. The estimation results indicate a significant association of incident clearance times to incident related variables such as involvement of CMVs, fatality, vehicle towing, seat belt indicated as involved, and on-road incidents that occurred both inside and outside the ASAP regions. The results also reveal that incident clearance times are influenced strongly by temporal variables (e.g., nighttime), traffic factors (e.g., AADT), and operational variables (e.g., fire response present) for incidents both inside and outside the ASAP area models. Overall, it was observed that the incident clearance times recorded in the regions where the ASAP program is in effect are significantly different. The findings of this study are expected to be useful for the state traffic incident management (TIM) agencies in developing and executing strategies to minimize incident clearance times. Ultimately, the study provides a data-driven evidence-based assessment of the ASAP program in the state.

Methodology for Predicting MAP-21 Interstate Travel Time Reliability Measure Target in Virginia

This study develops a target setting methodology for the (Moving Ahead for Progress) MAP-21 Interstate Travel Time Reliability Measure of “Percent of the Person-Miles Traveled on the Interstate that are Reliable” (PMTR-IS). The study uses data specific to Virginia for a set of independent variables (Hourly Volume, and Volume/Capacity Ratio, Truck Percentage, Equivalent Property Damage Only Rate, Lane Impacting Incident Rate, Number of Lanes, Presence of Safety Service Patrol, Terrain, Urban Designation) to predict whether a MAP-21 reporting segment is reliable. This is used to estimate predicted PMTR-IS with the MAP-21 specified formula. CART (classification and regression trees) models were used with 1,536 different configurations. Of the four best performing models, one was selected using engineering judgement. Datasets from 2017 and 2018 were used for training, and from 2019 and 2020 for testing. The predicted and calculated PMTR-IS were compared, and the error percentage was lower than 1% for 2019, which can be considered negligible. The 2020 error rate was higher and can perhaps be attributed to unusual reliability because of the impacts of the pandemic on travel. Sensitivity analyses revealed that the predicted PMTR-IS is reactive to capacity increase in unreliable sections at a local level, slower to respond to local AADT (annual average daily traffic) increase, and stable to small statewide AADT oscillations. The authors recommend using this methodology for target setting, taking into consideration the state authorities’ other strategic priorities.

Analyzing Disabled Vehicle Incident Durations and Crash Response to Identify Service Patrol Expansions and Reduce the Need for Law Enforcement Involvement

Florida’s Road Rangers (RRs) are the state’s safety service patrol. Over 60% of RR responses are for disabled vehicles. This paper investigates the impact RRs have on disabled vehicle events and identifies roads with potential for expansion of RR patrol hours by analyzing 2019 incident and crash data. Over 213,000 disabled vehicle incidents occurred on roadways with partial RR coverage, with 20% occurring during RR inactive periods. The average incident duration more than doubled during inactive periods from 49 min to 100 min. After analyzing several factors, such as incident duration differences and percentage of inactive events, I-10 in Florida’s panhandle was identified as the roadway which would most benefit from increased patrol hours. Ninety-five disabled vehicle crashes occurred on roadways with partial RR coverage, with 56% occurring during inactive patrol hours; these inactive period crashes resulted in 70% of the injuries and 67% of the fatalities. The Tampa area had many crashes (especially during inactive periods), so roadways in this area would benefit from increased patrol hours. A significant relationship between RR presence and response activity duration was found, with an average response activity duration of 106 min during inactive periods and 71 min during active periods. These results show the importance of increasing the periods of RR coverage and how RRs assist law enforcement by responding to disabled vehicle events and their associated crashes, allowing law enforcement to focus their efforts on more severe crashes or other traffic-impacting events.

Evaluating the impact of Road Rangers in preventing secondary crashes

Many transportation agencies utilize freeway service patrols (FSPs) to quickly identify and respond to incidents. The objectives of FSP are to minimize the incident duration and increase safety at the incident scene. The current research explored the safety benefits of Florida’s FSP program known as Road Rangers – harnessed from lowering the likelihood of secondary crashes (SCs) – compared to other responding agencies. The analysis was done on 6088 incidents that occurred on freeways in Jacksonville, Florida, from 2015 through 2017. Since SCs were not explicitly identified in the SunGuide® incident database, the study adopted a data-driven technique that used BlueToad® speed data to identify them. Once SCs were identified, a model was developed to identify factors influencing their occurrence. Factors such as an increase in equivalent hourly traffic volume, incident impact duration, and the percent of lanes closed significantly increased the likelihood of a SC. Besides, moderate/severe incidents, crash events, weekdays, peak hours, shoulder blockage, and incidents involving towing showed a high likelihood of resulting in a SC. Of practical importance, the model results revealed that a minute increase in incident impact duration increased the SC probability by 1.2 percent, with other factors held constant. Based on a 16-minutes decrease in incident impact duration, the Road Rangers program could lessen the probability of SCs by 21 percent, compared to other agencies. These findings could be beneficial to incident managers, responders, and researchers in evaluating the program’s performance.

Impact of Freeway Service Patrols on Incident Clearance Duration: Case Study of Florida’s Road Rangers

AbstractFlorida’s Road Rangers monitor the freeways for incidents to minimize incident clearance duration. The objective of this study was to evaluate the extent to which Road Rangers reduce incide...

Safety Service Patrol Uniforms: Technology, National Practices, and Operator Preferences

Safety service patrols operate in more than 40 states and territories in the United States and each program operates with unique vehicles, uniforms, and equipment. Despite the variety of operator uniforms, legal and technical requirements at a national level dictate some choices, though color and style are largely at the discretion of states. Past research confirms that high-visibility safety apparel (HVSA) increases visibility. Biomotion markers on the joints further enhance visibility. The Manual on Uniform Traffic Control Devices specifies that personnel working in the right-of-way wear a Class 2 or 3 HVSA. A survey of states where service patrols operate found the majority use high-visibility yellow-green over red-orange, and Class 3 garments are preferred over Class 2. In relation to the base uniform, there is a mixture of maintenance-type uniforms, polo shirts, and no uniform specification at all. In a survey of Florida service patrol program managers and operators, conveying professionalism, comfort, and safety were the most valued aspects of uniforms. Operators understand the need to care and maintain HVSA, but may overestimate their ability to be seen at night by between two and four times the actual distance they are visible. When given a choice, operators preferred dark trousers with biomotion markers, though they were roughly split between the polo shirt/vest option and the integrated HVSA shirt that does not require use of a vest. A uniform protective outerwear was favored by almost all operators, and a ball cap was the headwear of choice.

Genetic Algorithm for Optimizing Routing Design and Fleet Allocation of Freeway Service Overlapping Patrol

The freeway service patrol problem involves patrol routing design and fleet allocation on freeways that would help transportation agency decision-makers when developing a freeway service patrols program and/or altering existing route coverage and fleet allocation. Based on the actual patrol process, our model presents an overlapping patrol model and addresses patrol routing design and fleet allocation in a single integrated model. The objective is to minimize the overall average incident response time. Two strategies—overlapping patrol and non-overlapping patrol—are compared in our paper. Matrix encoding is applied in the genetic algorithm (GA), and to maintain population diversity and avoid premature convergence, a niche strategy is incorporated into the traditional genetic algorithm. Meanwhile, an elitist strategy is employed to speed up the convergence. Using numerical experiments conducted based on data from the Sioux Falls network, we clearly show that: overlapping patrol strategy is superior to non-overlapping patrol strategy; the GA outperforms the simulated annealing (SA) algorithm; and the computational efficiency can be improved when LINGO software is used to solve the problem of fleet allocation.

Safety of Freeway Service Patrol Operations: Case Study of Florida Road Rangers

Safety service patrols are a proven strategy to mitigate the effects of traffic incidents through quick clearance, incident management, and assistance to other incident responders like police, fire, emergency medical services, and towing. As encountered by other responders, working on or near roadways presents unique hazards for safety service patrol vehicles and operators. Road Rangers are Florida’s branded safety service patrols and, as a mature program with over 100 beats, a suitable case study for safety. This research combined an analysis of Road Ranger traffic crash data for 3 years with a comprehensive safety survey of more than 200 operators to determine safety characteristics related to service patrols. Comparing 200 Road Ranger traffic crashes from 2014 through 2016 with all Florida freeway crashes for the same time period revealed that Road Ranger crashes are five times more likely to involve a parked vehicle, and involve two or more vehicles 95% of the time. Pedestrian involvement, nighttime, shoulder locations, and work zones have higher representation for Road Ranger crashes, but weather is not a factor. Alcohol is three times more likely, drug use five times more likely, and distraction slightly higher when Road Ranger vehicles are struck. A survey of 217 Road Ranger drivers revealed that they are keenly aware of important safety topics like high-visibility safety apparel, non-traffic side vehicle approaches, and the dangers of working where there is limited lateral buffer space. Drivers overwhelmingly believe that they have the training and equipment necessary to do their jobs safely.

Methods for the Design of Safety Service Patrol Beats: The Florida Road Ranger Case Study

This paper introduces a framework for the design and deployment of safety service patrols (SSP) on freeways. Three mathematical programming models are proposed, with the targets of minimizing fleet size and total average response time and maximizing social benefits to accommodate various design objectives. Fast heuristic algorithms based on neighborhood searching techniques are presented for solving the optimization problems. In addition, a computer tool with a graphical user interface has been developed that takes roadway segments information as the input and provides real-world recommendations for deployment. The tool was tested using nearly 800 unique Florida roadway segments, totaling over 2,000 centerline freeway miles. The results were consistent with more than 100 current beats of Florida Road Ranger service patrols, and will be used for budget forecasting for the state.

Routing design and fleet allocation optimization of freeway service patrol: Improved results using genetic algorithm

Freeway service patrol (FSP), is considered to be an effective method for incident management and can help transportation agency decision-makers alter existing route coverage and fleet allocation. This paper investigates the FSP problem of patrol routing design and fleet allocation, with the objective of minimizing the overall average incident response time. While the simulated annealing (SA) algorithm and its improvements have been applied to solve this problem, they often become trapped in local optimal solution. Moreover, the issue of searching efficiency remains to be further addressed. In this paper, we employ the genetic algorithm (GA) and SA to solve the FSP problem. To maintain population diversity and avoid premature convergence, niche strategy is incorporated into the traditional genetic algorithm. We also employ elitist strategy to speed up the convergence. Numerical experiments have been conducted with the help of the Sioux Falls network. Results show that the GA slightly outperforms the dual-based greedy (DBG) algorithm, the very large-scale neighborhood searching (VLNS) algorithm, the SA algorithm and the scenario algorithm.

Development of Guidance for Deployment Decisions on Safety Service Patrols in Florida

This research had the objective of providing a decision support system for managers who must decide whether a roadway warrants the addition of a safety service patrol (SSP). Unlike the familiar signal warrants that guide the installation of traffic signals at candidate intersections, no such guidelines exist for decisions on SSPs. A proven framework for deploying intelligent transportation system equipment is adapted for this purpose. Meetings with managers from the service patrol program of the Florida Department of Transportation and a survey of national state points of contact for service patrols provided insight into critical factors that might contribute to guidelines. Historical incidents from Florida fed models that predict incidents and crashes on candidate roadways by using proven negative binomial regression models like those found in the Highway Safety Manual. Qualitative and quantitative thresholds for critical factors were established in the form of rules in decision tables that, when evaluated, render recommended actions for decisions on SSPs. The critical factors, thresholds, and use of decision tables proved to be an effective means by which to guide deployment decisions on SSPs, as evidenced by testing with a candidate roadway in Florida. Ultimately, computer software, with a graphical user interface, facilitated the collection of needed information, analysis, and recommendations in implementation of the guidelines.

Evaluation of the Benefit-to-Cost of Freeway Service Patrol in Advanced Video Surveillance System Environment: A Case Study in China

Abstract With the growing traffic incidents led by the rapid increase of traffic volume on freeways, Chinese government is facing how to ensure the efficiency and safety of the freeway system. One of the hot debates is the efficiency of Freeway service patrols (FSPs) technology in the advanced video surveillance system environment, namely dense video-based surveillance system (DVBSS). To help making a correct decision, this paper develops an effective approach to assess the effectiveness of FSPs in the DVBSS environment. This paper proposes a simulation method to measure the B/C ratios of FSPs in advanced VSS environment. B/C ratios are evaluated under four scenarios namely basic scenario, FSP1, FSP2, and FSP3. All scenarios were simulated in the 9.4-kilometer segment and data were collected from the working log of traffic monitoring center. Among all scenarios, B/C ratio of FSP1 is lowest, sometimes less than1, indicating that not all the FSPs scenarios are effective in the advanced VSS environment. However, the B/C ratios of FSP2 and FSP3 in mean cost scenarios exceed 1, represent as 4.33:1 and 3.47:1 respectively. It indicated that FSPs technology is still an effective way for traffic incident management in VSS environment. To explore the robustness of the results, authors extended the length of patrolling segment to 13.4 kilometers.

User-Friendly Benefit–Cost Estimation Tool for Traffic Incident Management Programs

Traffic incidents contribute significantly to deterioration in the level of service on freeways and arterials. Traffic incident management (TIM) programs have been introduced worldwide to mitigate the effects of traffic incidents on safety and roadway performance. These programs support quick incident response and thereby shorten incident duration, and control traffic demand around the incident scene. Some TIM programs can be costly to taxpayers. Thus, it is important to be able to evaluate benefits and determine associated returns on investment. Although benefit–cost (B/C) estimation studies have been conducted for numerous Safety Service Patrol programs, these studies use a wide range of estimation methods and monetary equivalent conversion factors. Consequently, the resulting B/C ratio estimates vary widely and have been shown to be sensitive to these choices. Moreover, these studies can be quite costly. Therefore, this paper is aimed at developing a user-friendly TIM-BC tool with a standardized method that can be universally and equitably used in such a B/C ratio estimation for TIM programs, essential to creating consistency and, therefore, greater confidence in the validity of estimation results. With access to the method in the form of a simple-to-use, less data-intensive tool, TIM programs and taxpayers alike can benefit from cost-effective evaluations. A New York State case study compared the effectiveness of implementing three selected TIM strategies, namely, Safety Service Patrol, driver removal laws, and dispatch colocation. The case study also helps in understanding the need for a standardized B/C ratio estimation tool and the effectiveness of the developed TIM-BC tool.

Deriving a surrogate safety measure for freeway incidents based on predicted end‐of‐queue properties

Incidents can significantly impact freeway operations and deteriorate mobility and safety. This study quantified their safety impacts through inspecting queue properties. Specifically, the end-of-queue (EOQ), where severe rear-end collisions commonly occur, is employed for safety assessment based on vehicles' trajectories. Since detector data is typically available, this study applied such data for EOQ identification, as opposed to vehicle trajectories that are difficult to collect and process. Three measures related to queue duration, impact area and vehicle number exposed to the EOQ are presented as surrogates. To understand the applicability of these measures, a systematic set of incident scenarios is replicated with VISSIM. Quantitative results are used to estimate regression models, and significant variables are identified. The proposed methods can be used to evaluate safety impact of traffic incident management programs such as freeway service patrol, as well as to determine optimal plans for prearranged incidents such as pothole repair.

Analysis of freeway service patrol with discrete event-based simulation

As an efficient incident management program, freeway service patrol has gained wide popularity. There is increasing need for developing systematic procedures of planning the program to ensure efficient resource allocation and to achieve maximum benefits. A discrete event-based simulation model is developed to replicate the patrol process that includes districting, incident generation, response vehicle dispatching and routing, and incident clearance. Model validation proves its capability to accurately replicate the incident generation/distribution process. Later, the Interstate-95 freeway in south Florida is used as a model application example to test alternatives, and the improved alternative shows better performance compared with the previous even-length districting method and the currently used even-activity districting approach. Besides traditional roving scheme, the simulation model also has the capability to evaluate the prepositioning schemes. Furthermore, sensitivity analysis is performed to examine the impact of operational parameter settings, such as beat districting, incident detection rate, and incident frequency. Although continuous efforts are needed to develop a more comprehensive simulation model for the freeway service patrol program, the application example presented in this study reveals promising application results, and provides an insight into the patrol process as well as a better understanding of the impact of parameters on performance.