5 Intersections
5.1.2 Intersection Collision Warning System –Virginia
The information for the Intersection Collision Warning System (ICWS) was obtained from an FHWA Tech Brief entitled, Intersection Collision Warning System.(10 )
Impetus for the Activity
The general problem that sparked development of the ICWS was safety at unsignalized intersections. The conventional treatment of signalization can be hard to justify in rural areas due to installation costs, maintenance, and delay to main line traffic. The ICWS offered an innovative and potentially less expensive means of improving safety at rural unsignalized intersections. The intersection at which the system is being demonstrated has extremely limited sight distance on the minor road segments, creating a large crash potential.
Criteria for System Selection (Hardware and Software)
This system is the first of its kind and was designed for use at the intersection of a major road with a stop-controlled cross street.
Description of the System
The system is installed at the intersection of Fleetwood Drive and Aden Road near rural Nokesville, Virgina, and is currently active. Sight distance on the minor approach (Fleetwood Drive) is extremely limited by buildings. The purpose of the ICWS is to enhance driver awareness of traffic at the intersection by providing timely and easily understood warnings of vehicles entering or waiting at the intersection.
Drivers traveling along Aden Road receive a warning when a vehicle is at either of the Fleetwood Drive approaches. Drivers stopped at either of the Fleetwood Drive approaches receive a warning when there is traffic on Aden Road. A schematic of the system is shown in Figure 7.
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System inputs include the presence of vehicles at the minor approaches and speed of vehicles on the major approaches. These inputs are measured by sensors embedded in the pavement and sent to a computer controller at the intersection. This controller estimates the various vehicles’ arrival times and activates the warning signs accordingly. Outputs are displayed on the active warning signs. Drivers on the minor approaches receive a crossing traffic alert with an animated car symbol to show the direction and relative speed of the crossing traffic. Drivers on the major approaches receive a flashing car symbol to show which minor leg of the intersection has traffic preparing to enter the intersection. Outputs are updated with changing traffic conditions. |
| Figure 7: Intersection collision warning system [from (10)]. |
System Performance
No information was available on system performance.
System Effectiveness Evaluation
A formal system effectiveness evaluation of the system was performed. The evaluation consisted of three phases – before, acclimation, and after (4 months after installation). Measures of effectiveness included:
- Drivers’ ICWS speed responses in the presence of cross traffic,
- Intersection approach speed reductions, and
- Projected times to collision (elapsed time to which an approaching vehicle would collide with a vehicle in its path in the absence of timely avoidance response).
The evaluation showed that:
- Intersection approach speeds were lower in the acclimation and after phases,
- The vehicle group at greatest risk of collision (shortest 10th percentile projected time to collision) in the before phase averaged longer projected times to collision and lower intersection approach speeds during both the acclimation and after phases, and
- Targeted high-speed vehicles demonstrated initial speed reductions in the acclimation period that were not generally sustained in the after period. However, fewer speed violators exhibited critically short projected times to collision in the presence of cross traffic in the after condition, indicating reduced crash potential.