A field study performed at Virginia Tech Transportation Institute tested the effectiveness of the “School Bus Stopped Ahead” message.
School buses are frequently touted as the safest way to transport students to and from school. Overall, school buses account for only 2% of all fatal motor vehicle crashes; however, they are considered to be a contributing factor to approximately 140 school-aged fatalities and 85,000 injuries each year. Advanced vehicle safety systems have shown great promise for improving safety and reducing crashes in real-world and staged research experiments. A natural next step was to develop an advanced vehicle safety system to specifically address the concerns and issues surrounding school bus safety.
Connected-vehicle communication is a system of sending coded messages between vehicles, then displaying important messages directly to a driver through in-vehicle or roadside displays. This system has been undergoing research and development for nearly a decade to establish and prove the benefits of near-instantaneous wireless communication between an unrestricted number of road users and roadside devices. Connected-vehicle technology is the foundation for the development of the following school bus applications to warn drivers as they approach an unexpected school bus stop.
School bus stop applications
The developed application of the connected-vehicle system covers a wide range of school bus-related situations including:
- Warning of students waiting at a school bus stop ahead: This application is intended to warn drivers that they are approaching a school bus stop where students are waiting on the roadway. The application aims to increase driver awareness and the expectancy that students will be loitering near the roadway. This application also can be used to reduce speed limits around the bus stop.
- Warning of a stopped bus ahead/collision warning: This message is intended to warn drivers that a bus is stopped ahead of them so they can slow down and/or prepare to stop. The mechanics of the system will be similar to previous studies on the topic of activated school bus warning signs and messages.
- Emergency crash notification: This message is similar to the OnStar system or other emergency-management systems available to school buses. It is intended to provide increased communication with first responders in the case of a school bus crash.
These applications can all operate during various stages of the connected-vehicle implementation, benefiting early adopters of the technology with accurate roadside messages while still ensuring a future benefit when the technology becomes more focused on vehicle-to-vehicle interactions.
An extended school bus stop sign.
Benefits of an incremental approach to implementation
Near-term: A focus on active roadside messages using vehicle-to-infrastructure (V2I) communication
The near-term case assumes that very few vehicles will have the required equipment to facilitate direct vehicle-to-vehicle (V2V) messages. The concepts described in this section assume that school buses would be capable of transmitting messages to specialized roadside displays, which can then present real-time messages to other road users.
Students at School Bus Stop Ahead: In the early stages of the “Students at Bus Stop” application, existing infrastructure signs can be equipped with actuated flashing beacons or variable speed-limit signs. These signs may initially be time-sensitive based on the expected times in which students will occupy the school bus stop area. A time-based system, however, may have reliability issues in circumstances where the school has an unplanned early release (such as a weather event) or when students are not at the bus stop, thus decreasing drivers’ trust in the system.
Another option for the V2I school bus stop ahead system is to apply a geo-fencing protocol or track the school bus’ location along the route through an external GPS tracking system. Once a school bus enters the geo-fenced area or reaches a certain point along the route, the system can activate the flashing beacons along a “School Bus Stop Ahead” sign to indicate that students may be at the bus stop. This system addresses the issue of unplanned early releases or late starts, but it is still subject to reliability concerns if students are not actually present at the bus stop when the system is active.
Stopped School Bus Ahead: In the near-term, the “Stopped School Bus Ahead” message is expected to be accommodated as part of the “School Bus Stop Ahead” sign. The presence of the school bus may be used as a trigger to activate or deactivate the flashing beacons. Based on the time of day, the school bus can deactivate the sign when it leaves the geo-fenced location after picking up students, or activate the sign when it enters the geo-fenced location during morning pickup routes. Additionally, simple programming logic also can be applied to trigger the sign to activate or deactivate based on the time of day, status of the stop arm and speed of the school bus.
Emergency crash alerts: The near-term focus of emergency school bus crash alerts is to utilize commercially available systems to live-stream videos of the bus’ interior compartment. Should a crash occur, the interior video surveillance system can provide a live feed of the students to school bus dispatchers, who can then notify emergency personnel. The live video feed can provide information such as the orientation of the school bus (upright or rolled), the approximate number of students on the bus, and a subjective estimate of the overall severity of the crash and occupant injuries. In an emergency situation, these systems may be called upon to evaluate the initial extent of the emergency in order to deploy an appropriate number of first responders.
A V2I system also could be utilized to display a crash notification on a roadside variable-message system that warns drivers to be prepared for slow or stopped traffic due to a crash ahead. In extreme cases, this type of system also could recommend that drivers reroute to avoid the crash scene, provided that a control center confirms that an alternate route is a feasible detour.
This “School Bus Stopped Ahead” message shows how the in-vehicle messaging system was set up in the test vehicle.
Intermediate-term: A continued focus on infrastructure and early V2V communications
The intermediate-term approach to integrating school bus-related messages into the connected-vehicle system assumes that the connected vehicle system has reached a reasonable market penetration that enables direct V2V communication between equipped vehicles. The concepts described in this section assume that the school bus is equipped with the technology that can transmit messages to specialized roadside equipment in addition to sending messages directly to other equipped road users.
Students at School Bus Stop Ahead: Similar to the earlier form of the application, activation of the direct V2V messaging may be controlled by the school bus’ progress along the route or via passive image-detection software that identifies student presence at the bus stop. Another intermediate-term option is utilizing smartphone technology to identify whether students are present at a bus stop. When communicating directly with other vehicles, an occupied bus stop could provide messages directly to the vehicles that are approaching the bus stop. These messages may contain advisory speed limits and information such as the location of the bus stop (distance to the stop) or how many students are at the bus stop (provided that all students can be accounted for).
To accommodate vehicles that are not equipped with connected-vehicle technology, this system could utilize the previously discussed infrastructure-based technology.
Stopped School Bus Ahead: The message is intended to be used as a warning that a school bus is stopping or stopped; however, it also could assist in preventing collisions by presenting itself as an imminent collision warning for vehicles that are not slowing down for a stopped school bus. Part of this message will rely on the ability to reference roadway design features, such as number of lanes and presence of a median, to determine whether vehicles need to stop based on the geometric design of the roadway and the state laws of the subject location.
Although collision-warning systems currently exist, these systems are unable to accommodate the unique collision scenarios that could occur near school buses, such as students crossing the road at mid-block. The imminent collision-warning system also would need to consider that students are not immediately present on the road when the stop sign deploys since it takes time for students to exit the bus and cross the road. In this case, the authors propose one of two possibilities to avoid heavy braking when the hazard does not exist:
1. Accounting for buffer time, similar to an all-red phase of a traffic signal, that deploys the “STOP” message after a certain amount of time (time TBD); and
2. Equipping school buses with a radar or image-detection software to determine whether a student is crossing the road and entering a dangerous situation.
Emergency alerts: In the intermediate-term, the detailed information in the emergency school bus alerts will likely remain as secure communication between school buses, school bus dispatchers and emergency personnel (as described in the previous section); however, generic warnings could be presented to connected vehicles to warn of a delay or advise rerouting.
The R.E.S.C.U.M.E. (Response, Emergency Staging and Communications, Uniform Management and Evacuation) project is a likely partner in the V2V approach to incident response and scene management. The R.E.S.C.U.M.E. applications provide approaching vehicles with in-vehicle messages and alerts related to speed reductions and lane closures. The applications allow for situational awareness and collaboration among dispatchers and first responders, as well as providing in-vehicle messages that inform oncoming drivers of the incident.
The speed-reduction sign is the message for reducing speed limits at bus stops along high-speed roads.
Long-term: A focus on autonomy
The long-term assumption of the connected-vehicle system is that it will evolve into a fully connected autonomous-driving environment and that individual messages will be less necessary. This section covers the features that are predicted to improve school bus and school bus stop safety under these conditions.
Students at School Bus Stop Ahead: In addition to the features in the previously discussed sections, the autonomous system could utilize a speed-control mechanism to ensure a reduced speed in the area surrounding the occupied bus stop in order to improve pedestrian survivability in case of a crash. Speed control and speed-related messages have been demonstrated as part of several connected-vehicle studies involving the topics of speed harmonization, work-zone speed compliance and various intersection applications. While it is expected that some school bus locations may not require speed reductions or speed control, such as neighborhoods with low speed limits, bus stop locations on high-speed and/or high-volume roads could benefit from this system.
Stopped School Bus Ahead: A fully autonomous driving environment will reduce the need to warn drivers about a stopped school bus ahead since the position of all vehicles will be inherently known. Furthermore, if students are provided with DSRC-enabled devices that can broadcast their exact location relative to the traffic stream, the requirement for other vehicles to stop for stopped school buses may be relaxed since the location of all students will be known at all times. Autonomous vehicles that are fully aware of their surroundings will not need to stop if students are not actively crossing the roadway. However, researchers recognize that this level of complete autonomy is highly unlikely, even in the long term.
Emergency alerts: The long-term emergency alert application for school buses will utilize information similar to what was described in the near-term and intermediate-term sections. It is expected that a fully autonomous environment will continue to partner with emergency and response applications such as R.E.S.C.U.M.E. Future capabilities may include the ability to automatically reroute oncoming traffic onto an alternate route or to clear a lane for emergency vehicle staging and transport.
The “School Bus Stopped Ahead” warning is the message displayed to drivers on the in-vehicle display system. The message is accompanied by an audible beeping sound.
Within the framework of further developing a successful message set, a multi-staged approach for utilizing the connected-vehicle system to improve safety around school buses and school bus stops could have significant benefits. When the connected-vehicle system first becomes available and market penetration is low, this first stage for utilizing the connected-vehicle system focuses mostly on disseminating reliable information through infrastructure-based communication between school buses and active roadside signing. As market penetration increases, the system can incorporate direct vehicle communication between school buses and other road users. Once the connected-vehicle system approaches full market penetration, it can assume fully autonomous driving abilities. This long-range plan for improving safety around school buses and bus stops can lead to the prevention of future school bus-related crashes and pave the way for researchers to focus on a trans-disciplinary approach to developing a connected-vehicle system that encompasses the needs of the future transportation system.
Palframan is a consultant with Focus Forensics LLC.