3 Speed Management
3.3 Dynamic Curve Speed Warning
3.3.1 Sacramento River Canyon Curve Warning System – California
| Impetus for the Activity The problem that sparked Caltrans to consider a technological treatment was a high crash rate, particularly with trucks. The freeway was often closed for several hours following a truck crash for cleanup and investigation. Caltrans considered a technological treatment over a more conventional treatment because all of the conventional static signing treatments had been placed and there was still a crash concentration. The area was becoming a highly publicized crash location and Caltrans wanted to try something new. The expected result of deployment of the system is a reduction in crashes, particularly truck crashes. |
 Figure 5: Sacramento curve speed warning system - measured speed displayed on CMS. |
Criteria for System Selection (Hardware and Software)
The system was selected by bid. The contract specifications detailed several systems for the contractor to bid – all performed the basic function adequately. Each system was reviewed to determine how it would perform and if it would serve the basic function before it was included in the contract.
Description of the System
The system began operation in March 1999 and remains active. The objective and basic function of the system is to reduce crashes. There are five locations where these signs have been installed.
The system’s primary input is radar speed data, which is displayed on the CMS (see Figure 5). The CMS can also be operated remotely with inputs from the TMC or remote locations. Inputs are obtained through a radar gun and through remote PCs via a modem. Inputs are sampled several times a second.
The primary output is a message to the motorist of their speed and the suggested speed for the curve ahead. This information is updated several times per second and is displayed on the CMS. There are also CCTVs installed at the locations, the output of which is video images and vehicle speed and count data.
The system’s output is advisory, but it will trigger radar detectors, which may give motorists the impression that the system is used for enforcement.
System Performance
Caltrans considers the system to have generally performed very well. Caltrans has not experienced any problems with the performance or reliability of the system.
System Effectiveness Evaluation
The system is being evaluated by Western Transportation Institute (WTI). The primary measure of effectiveness being used is the reduction in crashes. Several other factors are being studied, but from the preliminary data, it does not appear that these other factors can be adequately evaluated.
While the evaluation was not complete at the time this document was prepared, the preliminary data is very encouraging. There were 30 plus truck crashes in the 5 years preceding installation, and only one truck crash since the system was installed, a little over a year before this report was prepared.
Perceived “Hot Spots” for Rural ITS Deployment
Highway curves with high crash concentration locations were identified as a general Hot Spot for rural ITS deployment.
Obstacles and Lessons Learned
It has been noted that lessons are still being learned, but that one design feature that could be done differently is to install a directional radar gun. The radar gun currently being used measures vehicle speed in both directions, and sometimes displays speed information for vehicles traveling in the opposite direction.