Multiple Sources of Safety Information From V2V and V2I: Redundancy, Decision Making, and Trust - Safety Message Design Report

Chapter 2. Overview of CV Applications

CV Communication Architecture

This chapter provides definitions of key terms used in the current report to describe the CV communication architecture. This chapter also provides an overview of the operation, collision types addressed, and target-site characteristics for the CV safety applications discussed in this report. The following applications are described in this chapter:

• Stop sign assist (SSA).
• Signalized left turn assist (SLTA).
• Red-light violation warning (RLVW).
• Curve speed warning (CSW).
• Spot weather information warning—reduced speed (SWIW-RS).

Additional CV safety applications have been developed under the CV program. These include applications such as overweight vehicle warning (OVW) and railroad crossing warning. These applications, however, are not discussed in this report.

V2V

V2V communication is the dynamic wireless exchange of anonymous, vehicle-based data using dedicated short-range communication (DSRC) protocols. The minimum transmitted data package from a vehicle is referred to as the “basic safety message” and contains information regarding the vehicle’s current position, speed, heading, acceleration, braking status, and vehicle size.⁽¹⁾ This information is broadcast to and received from surrounding vehicles. This communication enables a vehicle to sense the position of other vehicles and the threat or hazard they present with a 360‑degree awareness, calculate risk, issue driver advisories or warnings, or take preemptive actions to avoid and mitigate crashes.

V2I

V2I communication is the wireless exchange of safety and operational data between vehicles and the highway infrastructure (via roadside equipment (RSE)) using DSRC protocols. V2I communication is intended to prevent or reduce the severity of vehicle crashes; however, it can also provide system mobility and environmental benefits by supporting applications such as speed harmonization and traffic optimization.⁽²⁾

Vehicle-to-Infrastructure, Vehicle-to-Vehicle, and Vehicle-to-Device (V2X)

V2X communication is a term collectively referring to any type of CV communication, including V2V, V2I, or vehicle-to-device communication.

DII

DII is a changeable information display located externally to the vehicle that provides information to drivers and other road users. CV safety application DIIs use V2X information to identify roadway conditions and provide appropriate safety messages, which are typically visible to multiple roadway users, as long as the DII display is pointing towards them. DIIs include a range of equipment, such as changeable message signs (CMSs), blank-out signs, triggered beacons accompanying static signs, dynamic signals, traffic control devices (TCDs), and in-road/in-path lighting.

DVI

DVI is an in-vehicle display (or set of displays) and controls that a driver uses to obtain information from a vehicle.⁽³⁾ Messages provided via DVI can be targeted to the individual vehicle. A variety of DVIs can support CV safety applications, including dash- or instrument panel-mounted screens, head-up displays, auditory displays, and vibrotactile or haptic displays (i.e., seat pan vibrations or steering wheel torques). Throughout this report, the display element is typically the focus of discussions regarding DVIs for CV safety applications. CV safety application DVIs provide warning information to the driver using information acquired through V2X communication. Not all vehicles will support all CV safety applications; some vehicles may only support specific CV safety applications.

RSE

RSE is roadside-installed hardware used to relay messages using DSRC protocols. RSE may receive messages from vehicles, other RSEs, or from back offices that monitor traffic system performance (i.e., a traffic management center). RSEs may be permanently or temporarily installed, allowing their use for either long-term or short-term (e.g., work zones) applications.

Summaries of Safety Applications Discussed in this Report

The following section presents a brief summary of each of the five CV safety applications listed in the previous section, along with an overview of the application’s operation, collision types it may address, and its target-site characteristics.

SSA

SSA is a system that supports drivers on minor roads who are attempting to either cross or enter the intersecting major road. SSA provides drivers with information about oncoming vehicles traveling on the major road. The objective of this system is to help drivers safely travel through or turn onto a highway from a stop-controlled intersection. This system is related to the Cooperative Intersection Collision Avoidance System-Stop Sign Assist (CICAS-SSA).

SSA has the following attributes:

• Operation:Identifies the location and speed of vehicles traveling on the major road and provides the driver on the minor road with information via DII to assist in selecting an adequate gap when turning or going through the intersection.
  
  
• Collision Types:Includes left/right turn into path (rear-end), sideswipe (same direction), and right-angle crashes with vehicles travelling on the major road.
  
  
• Target-Site Characteristics: Includes rural stop-controlled/through-stop intersections where lower speed/volume minor roads intersect higher speed/volume median divided highways. The DII is positioned where it can be easily seen by stopped drivers on the minor road.

Figure 1 provides an example of a CICAS-SSA (DII) protype.

Source: National RITS Conference.
Figure 1. Photo. CICAS-SSA (DII) prototype implemented by Minnesota.⁽⁴⁾

SLTA

The SLTA system supports drivers who are making permissive left turns at signalized intersections. The system provides information to left-turning drivers about the presence of oncoming vehicles based on proximity or available gap size. The objective of this system is to help reduce driver errors related to detecting traffic and judging gaps. This system is related to Cooperative Intersection Collision Avoidance System-Signalized Left Turn Assist (CICAS-SLTA).

SLTA has the following attributes:

• Operation:Identifies the location and speed of approaching vehicles and informs the turning vehicle about their presence by displaying a message on a DII and/or DVI to discourage drivers from making left turns when a gap is inadequate. The SLTA system can also be combined with other systems to provide information about the presence of pedestrians and bicyclists in the left turning driver’s path. However, the design information in the current document provides information about SLTA systems for oncoming vehicles only—pedestrian detection/warning is not addressed.
  
  
• Collision Types: Includes vehicle head-on and sideswipe with on-coming traffic from opposite direction (left turn across path—opposite direction (LTAP-OD)).
  
  
• Target-Site Characteristics: Includes intersections with a high volume of oncoming traffic and limited sight-distance/visibility for oncoming traffic. The DII may be collocated with existing TCDs to support drivers seeing the display.

Figure 2 provides an example of a CICAS-SLTA at a signalized intersection.

Source: University of California, Berkeley.
Figure 2. Photo. CICAS-SLTA implemented at a signalized intersection.⁽⁵⁾

RLVW

The RLVW system supports drivers in safely traveling through signalized intersections. The system provides a warning to drivers who may potentially enter the intersection in violation of the TCD. The objective of this system is to reduce the frequency of red light violations. This system is related to Cooperative Intersection Collision Avoidance System to Prevent Violations (CICAS-V).

RLVW has the following attributes:

• Operation: Identifies vehicles that will enter an intersection in violation of the TCD based on vehicle speed and heading (contained in the vehicle’s basic safety message) and the TCD signal phase and timing (SPaT) information. Warnings are provided using DVI and/or DII.
  
  
• Collision Types: Inclues single and multivehicle collisions occurring within the intersection, including sideswipe (angle), broadside, and rear-end crashes.
  
  
• Target-Site Characteristics: Includes signalized intersections, especially when sight distances are limited or red light violation crashes are problematic. The DII may include displays collocated with the TCD, signs at the intersection, or in-pavement lighting.

Figure 3 provides an example of a CICAS-V DII.

Figure 3. Photo. Example of a CICAS-V DII. Adapted from previous research implementation.⁽⁶⁾

CSW

The CSW application supports drivers in traversing a roadway curve at a safe speed. The system provides an alert/warning to drivers if their current travel speeds exceeds a safe/advisory speed for the curve. The objective of this system is to reduce the occurrence of rollover or run-off-road crashes owing to unsafe speed in curves.

CSW has the following attributes:

• Operation: Identifies vehicles approaching a curve traveling at a speed above the safe or advisory speed and provides a warning to the driver via DVI and/or DII and advisory speed information.
  
  
• Collision Types: Includes single-vehicle rollover and run-off-road at road curvatures.
  
  
• Target-Site Characteristics: Includes horizontal and complex curves. The DII placement should be in accordance with the Manual on Uniform Traffic Control Devices (MUTCD) standards and far enough in advance of the curve to allow drivers to make appropriate speed corrections prior to encountering the curve.⁽⁷⁾

Figure 4 provides an example of a dynamic curve warning system (DCWS) on a freeway.

Source: Oregon Department of Transportation.
Figure 4. Photo. DCWS.⁽⁸⁾

SWIW-RS

The SWIW-RS system supports drivers who may encounter adverse weather conditions on their travel route. The SWIS-RS system provides drivers with information about potential weather-related hazards and appropriate precautions, such as reduced travel speed. The objective of the system is to reduce the risk of crash under adverse weather conditions.

SWIW-RS has the following attributes:

• Operation: Identifies vehicles traveling on roadways that will be or are affected by near-term, adverse weather conditions and provides an alert message via DVI and/or DII with information on the weather event and necessary actions (i.e., reducing speed).
  
  
• Collision Types: Includes single and multivehicle crashes owing to weather, including pre-crash control loss caused by high winds, flooding, adverse road surface conditions, and reduced visibility.
  
  
• Target-Site Characteristics: Includes roadways that encounter frequent adverse weather conditions and localized road-weather hazards (e.g., icy bridge).

Figure 5 provides an example of a two-phase CMS message.

Figure 5. Illustration. Two-phase CMS display showing weather advisory.⁽⁹⁾