3 Speed Management
3.1.2 Green Light Field Operational Test Truck Speed Warning System – Oregon
Impetus for the Activity
The problem that sparked the Oregon DOT (ODOT) to consider a technological treatment was a high number of truck crashes on Emigrant Pass.
Truck drivers, many of whom travel long haul and across country, are susceptible to fatigue-related conditions, such as speeding and lack of attention. When combined with hazardous environments, such as steep downgrades with sharp curves, traffic fatalities are almost inevitable. A single crash can cause millions of dollars of physical damage and related costs. Besides the direct damage, the intangible costs including death, injury, insurance, and economic consequences can be even more significant.
The Emigrant Pass has a 6 percent downgrade for 10 km with sharp curves. Between 1993 and 1996, there were a total of 40 truck crashes on I-84 at Emigrant Hill, resulting in 3 fatalities and 28 injuries.
Before considering a technological treatment, ODOT had implemented runaway truck ramps and fixed truck advisory signs at the pass location. Furthermore, ODOT had listed Emigrant Hill as a crash-intensified, high truck-crash corridor.
Seeking alternative methods to prevent truck crashes on steep sections of mountainous highways, the ODOT Motor Carrier Transportation Division (MCTD) planned a Downhill Speed Information System through the “Green Light” Project.
Criteria for System Selection (Hardware and Software)
ODOT, through its MCTD, is engaged in a multimillion dollar project called Green Light that seeks to demonstrate the benefits of using ITS to improve the efficiency and enhance the safety of commercial vehicle operations (CVO). One objective of the Oregon Green Light Project is the establishment of Downhill Speed Information Systems (DSIS) for commercial vehicles.
DSIS remind truck drivers of their gross vehicle weight and advise them of a safe speed for negotiating a steep downhill grade ahead. The system is especially helpful to the novice, or less-experienced truck driver who is unfamiliar with downhill grades and the potential for braking problems.
ODOT decided to give a “customized” message to the truck via vehicle identification using a transponder, rather than a “generic” message through traffic loop detection. The concern was that over time, a generic message (i.e., Truck: Steep Downgrade) would become familiar to truck drivers. A customized, speed-specific message was deemed to always be relevant to the truck driver whose weight may be different for each trip traveled down the Pass.
Description of the System
The system is part of a demonstration project and is a prototype of a truck-specific safety system. The hardware and software is installed and undergoing testing as of May 2000. The target operational date was July 2000, but has been changed to spring of 2002 due to some issues that arose when trying to integrate the Green Light system with an existing VMS. In order to reduce cost, ODOT had decided to use an existing VMS that they were already using for road and weather information. They now plan to install a separate dedicated VMS, as was called for in the original specifications.
The purpose of the system is to advise truck drivers of what speed they should travel to make it safely down Emigrant Hill (on I-84 between Pendleton and La Grande). The objectives of the system are:
- To reduce truck crashes on the steep downward slopes of Emigrant Hill,
- To reduce usage of runaway truck ramps on the steep downward slopes of Emigrant Hill,
- To reduce truck speeds on the steep downward mountainous slopes so that full control of the vehicle can be maintained, and
- To converge truck mean speeds on the steep downward slopes to advisory speeds.
The DSIS consists of high-speed, weigh-in-motion scales in the roadway and automatic vehicle identification devices that recognize in-truck transponder signals. In less than 1 s, a computer measures truck weight, reads the transponder signal (if the truck is equipped), and sends an appropriately customized message to a roadside VMS advising the driver of a safe range of downhill speed for that truck. Inputs are measured once per vehicle.
Properly weighed transponder-equipped trucks receive a truck-specific advisory message on the VMS. For example:
TRUCK ADVISORY
ABC TRUCKING
20MPH DOWNHILL
Improperly weighed transponder-equipped trucks receive a truck-specific generic message (without a suggested speed). For example:
TRUCK ADVISORY
ABC TRUCKING
STEEP DOWNGRADE
Trucks without a transponder do not receive a message. The message is displayed for 10 s and is updated for each interrogation of a transponder. The State can override the system to display emergency information.
System Performance
System performance and reliability are under evaluation.
System Effectiveness Evaluation
An evaluation of the established system is planned. Over the course of the evaluation study, the following steps will be conducted:
1. Collection of crash data – All recorded commercial motor vehicle crashes between the DSIS installation and the end of the downhill grade will be collected. Crash information will be requested from ODOT beginning in 1996 up until the date of DSIS installation. The crashes will be summarized by year and tabulated into Excel spreadsheets. All of the crashes will be examined and sorted by any identifying factors. Crashes after the system installation will be collected and recorded onto a separate Excel spreadsheet.
2. Collection of escape ramp logs – All escape ramp logs beginning in 1996 to present will be collected. Escape ramp incidents will be counted.
3. Collect and record speed data gathered with a radar gun sufficient to ensure a 95 percent degree of confidence – The speed data will be collected twice prior to DSIS installation and twice after DSIS installation via spot surveys. The spot surveys will use a radar gun and record speeds via a speed log.
A detailed analysis will be conducted using the data collected. The following steps will be performed:
1. Crashes will be placed in a matrix that quantifies the frequency of occurrence by various factors. In addition, a crash rate will be calculated for crashes occurring prior to the system installation, as well as after. The crash rate will be compared with rates calculated for I-84 and for all four-lane Interstates in Oregon over the same time period. This will allow researchers to note any general trends that may be occurring over the evaluation period.
2. Escape ramp incidents will be placed in a matrix that quantifies the frequency of occurrence. The escape ramp incident rate will be compared for rates calculated prior to the DSIS installation and after.
Speeds will be keyed into an Excel spreadsheet for analysis. The date, time, location, recommended speed, and weather and road conditions will be recorded for each survey conducted. Mean speed will be calculated from the data and then compared with the advisory speeds. Data sets collected prior to the installation will be coupled with the data collected from the same site and time after deployment and analyzed for changes in mean speeds.
Perceived “Hot Spots” for Rural ITS Deployment
The questionnaire response noted that steep downhill grades are “Hot Spots” for rural ITS deployment aimed at improving rural safety.