I-30 Little Rock to Benton, Arkansas
In 1999, Arkansas decided to undertake the rehabilitation of over 50 percent of their Interstate highway infrastructure. As a result, the Arkansas Highway and Transportation Department (AHTD) began construction in 2000 on more than 350 miles of roadway. Most relevant to the study of ITS in work zones are the three work zones that utilized ITS with the goal of improving traffic safety and mobility during the time of construction. One of these three Arkansas projects using ITS included the widening of approximately 17 miles of I-30 from Sevier Street in Benton (mile marker 115) to Geyer Springs Road in Little Rock (mile marker 133). A key portion of the work zone is shown in Figure 5.
Figure 5. Arkansas I-30 Work Zone Location
Prior to the beginning of construction, this section of I-30 had an Annual Average Daily Traffic (AADT) of 63,000 vehicles. In 2001, as documented by the Highway Performance Monitoring System, sections of this stretch of I-30 experienced greater than 20 percent truck traffic. According to personnel at AHTD, when this I-30 project was constructed in 2004, there was an average of approximately 40 percent truck traffic during the day increasing to 75 percent at night. The large volumes of truck traffic created the potential for large work zone impacts due to their size and impact on mobility.
To improve the safety of travelers, the AHTD installed an Automated Work Zone Information System (AWIS) covering the entire I-30 Little Rock to Benton work zone corridor. AHTD procured the system from a vendor through the construction contract.
The complete system of monitoring equipment for the I-30 smart work zone included 47 vehicle detector sensors, 4 radio transmitters, 15 dynamic message signs (DMS) and 8 stationary video cameras mounted on trailers in and around the work zone. After detecting a change in Interstate traffic speeds, the AWIS system evaluated its own accuracy by performing a system check of other sensors. Within approximately 5 minutes, computers determined whether one of nine levels of severity warranted communication with the message boards and radios to report the situation. When the sensor system detected significant delays, flashing beacons on highway advisory radio (HAR) alert signs advised motorists entering the broadcast area that the message was, "Urgent when flashing, tune to 1490 AM."
While the roadside message boards and radios required the 5-minute relay time, sensor-recorded traffic speeds transmitted almost instantaneously to the website (www.arkansasinterstates.com). By clicking on the Central Arkansas Projects icon on the ArkansasInterstates.com home page and then on the I-30 project on the Central Arkansas map, site visitors could see a complete view of traffic conditions throughout the work zone. Color-coded roadway segments (green, yellow, red) between sensors indicated whether traffic was flowing well, slowed, or stopped. Hovering the mouse over any of the equipment icons revealed a live video image (for the cameras) or displayed the text and audio messages motorists were receiving on the road (for the DMS and HAR).
The main objective for this system was to improve the safety of travelers by providing advance warning of slowed traffic or congested downstream conditions. Based on this system objective, the study team conducted a driver survey and used the driver surveys and traffic volume data to assess several hypotheses. A total of 297 commercial vehicle drivers (CVD) and 319 private vehicle drivers (PVD) participated in the surveys. The study team collected traffic and survey data from May 17, 2004 through June 20, 2004.
The study team also conducted an initial review of the available crash data but determined that it was not feasible to use the crash data for this study. The level of detail available in the crash records did not support the level of analysis needed for this study and converting the hard copy crash records to an electronic database was cost prohibitive. The study team also held an in-person interview with the contract manager for the work zone to assess a hypothesis regarding the impact of ITS on contractor productivity.
Of these, 286 CVD and 306 PVD surveys were suitable for further analysis. The 24 surveys not used were discarded due to incomplete responses pertaining directly to the ITS devices. The study team observed the following findings (highlighted in Table 2) for selected hypotheses.
|The use of ITS in the work zone will reduce travelers' exposure to hazard.||Drivers agree that the use of ITS in the work zone reduces their exposure to hazard.||A large percentage of the surveyed drivers (82%) agreed that the ITS system
improved their ability to react to slow or stopped traffic.
A large percentage of surveyed drivers (49%) agreed that they felt safer traveling through the work zone because of the electronic messages. 17% were neutral, 32% disagreed, and 2% did not answer.
|The use of ITS in the work zone will enhance the safety performance of the highway.||The police officer and construction manager in the work zone agreed with this hypothesis.||People working within the construction zone felt that the ITS improved the safety of both the workers and the travelers.|
|Travelers will use the work zone ITS.||Travelers used the components of the ITS that were most available. The highly-used DMS were present in the work zone making them readily available to drivers to read. HAR was used moderately. The web site had a low utilization among the surveyed drivers.||DMS were observed by 95% of surveyed drivers.
HAR was used by 24%.
Web site was used by 5%.
|The use of ITS in the work zone will improve traveler tolerance of work zone delays.||ITS improves tolerance for at least some drivers.||About 1/3 of the drivers said the use of ITS made them feel less bothered in the construction zone.|
|The ITS system will improve the productivity of contractors and travelers.||
Work zones are highly variable environments. As a result the ITS system must be similarly flexible. For example, the work zone examined here was large, complex (included 7 separate projects by 2 contractors), and had a constantly changing configuration. As a result, the calibration of the ITS system became a major issue - requiring one full-time employee working long hours to maintain all sensors.
ITS is only one part of a successful work zone. The aim of outfitting this work zone with ITS was to improve safety. While there is some indication that the ITS system reduced travelers' exposure to hazard and made the work zone safer, fatal crashes in the I-30 work zone were not fully avoided. ITS can be a valuable part of effective work zone management, but other safety and mobility strategies should also be used as part of a coordinated transportation management plan (TMP).Previous | Next