5 Intersections
The systems falling under the Intersections category are both safety warning systems.
5.1 Safety Warning Systems
5.1.1 Queue Detection System – Oregon
Impetus for the Activity
The problem that sparked Oregon DOT to consider a technological treatment was a sudden growth in traffic resulting in long queues, rear-end crashes, and a perceived high rate of near misses. A technological treatment was considered over a more conventional treatment due to the unpredictability of the condition.
The expected result of deployment of the system was a reduction in crashes.
Criteria for System Selection (Hardware and Software)
Several criteria were used in selecting the system. These included:
- Functionality,
- Cost,
- Ease of installation, and
- Use of available “tried and tested” components.
Description of the System
The system was installed in March 1999 and is currently active. The objective of the system is to provide advance warning of queues, and ultimately reduce crashes.
The system is deployed on Highway 99E at milepost 27.6 to milepost 28.2, south of Dundee. The first traffic signal in Dundee creates backups of almost 3 km, especially during the summer. The end of the queue is usually just downstream of a vertical curve with limited sight distance to the queue.
At milepost 27.6, there is a series of two loops, in each of the two lanes. This location provides stopping sight distance from the vertical curve. Milepost 28.2 has an overhead sign with beacons attached to it.
The system uses vehicle actuation as its input. This input is measured continuously, using the loop detectors mentioned above. System output is the flashing of the upstream beacons on the overhead sign. The beacons are activated when the detectors indicate the continuous presence of a vehicle for a predefined interval. The beacons continue to flash for a carryover period after the stopped vehicle is not present. The beacons turn on and off as input conditions change (i.e., queue detected, and queue not detected). The static sign tells drivers to, “Prepare to stop when lights flash.” This message is advisory.
System Performance
Oregon DOT noted that the system seems to have performed satisfactorily, but that they need a longer post-installation time period to make a valid assessment. The performance and reliability of the system has not been formally tested. The performance has been observed and tweaked informally at various time periods to evaluate if timing parameters are appropriate.
The issue that loop sensitivity may degrade over time was mentioned as a factor affecting system performance.
System Effectiveness Evaluation
There has been a preliminary evaluation of system effectiveness. The number of crashes was used as the measure of effectiveness. The preliminary analysis indicates a decrease in crashes in the 9-month post-development period. However, it was noted that it is not clear if other factors contributed to this decrease. A longer time (larger sample) will be required to make a statistical conclusion.
Perceived “Hot Spots” for Rural ITS Deployment
Rural intersections on high-speed roads with relatively large traffic volumes were noted as “Hot Spots” for rural ITS deployment aimed at improving rural safety.
Obstacles and Lessons Learned
An obstacle encountered was the interconnection between the cabinet and the upstream signs. The long distance made voltage drops to the sign a concern. Oregon DOT would have ideally liked to use a reliable solar system and wireless beacon activation system rather than running wires.