This summer, Region Two began work on Redwood Road from I-80 to North Temple to rotomill and resurface the roadway with a thin bonded PCCP 6” overlay. One of the biggest challenges on the job was maintaining traffic through the work zone while also maintaining side-street and business access. This issue was complicated by the high number of large trucks in the area. These trucks not only utilize a significant amount of available queue space on the ramps, they also take more time to climb the incline at the interchange before clearing the signal. These factors required significant coordination to keep traffic moving.
Our contractor, Dry Creek Structures, and construction crew worked closely with the Traffic Signal Maintenance group to split phase signals and move detection zones to accommodate traffic through the work zone. We also worked closely with Grant Farnsworth at the TOC Traffic Signals Desk to adjust signal timing as the work zone configuration changed.
From a traffic safety perspective, our top priority was to minimize queuing on the
westbound I-80 ramp and prevent stopped traffic on mainline I-80. Despite the team’s best efforts, traffic was occasionally still backing onto mainline I-80 while waiting to exit at Redwood Road. To help address this queuing problem, working with Marge Rasmussen in Region Two Traffic and Safety, and Project Manager Peter
Tang, an Automated Queue Warning Detection System was change ordered into
the project and installed on the I-80 westbound off-ramp to Redwood Road.
With this system, the occupancy rate was monitored near the gore point of the off-ramp. When the system detected stopped cars at this location, a warning message was activated at a Variable Message Sign (VMS) upstream of the off-ramp alerting motorists of “STOPPED TRAFFIC AHEAD” and “PREPARE TO STOP.”
How it works: A sub-contracted vendor (Ver-Mac) installed a radar sensor, cellular
modem and solar panel on a highway lighting pole near the bottom of the off
ramp. They also placed a VMS equipped with a cellular modem upstream of the off
ramp. When the vendor’s software system (Jam-Logic) detected an occupancy rate greater than 10 percent at this location, a message was activated at the VMS alerting travelers to the stopped condition ahead. Once the queued traffic had dissipated, the VMS message was automatically turned off and remained off until ramp queuing was detected again.
In addition to the VMS message activating when a queue was detected, email messages were also sent to the TOC Operators, the Signal Timing Engineer and the Resident Engineer, alerting them to the situation. When possible, adjustments were made to the signal timing to help clear the ramp traffic.
Results: The project team is not aware of any accidents at this location after the automated queue warning system was installed. Typically, the system was activated 10 times each day throughout the week or an average of 13.4 times on weekdays. Even during low traffic volumes, just a few long trucks on the ramp can back up traffic and activate the system. While the system was live, the queue warning messages were displayed 256 times for a total of 2,327 minutes. The average display time was 9 minutes. The maximum display time was 56 minutes (on August 23 starting at 9:19 a.m.).
“Doing advanced queue warning is a great operational benefit, but what the TOC appreciated most was the communication between the project and the control room. When the control room knows what’s going on, we’ll help out in any way that we can. In this case, we monitored the queue system and helped ensure that it was functioning as advertised – which it was,” explained Glenn Blackwelder, Traffic Operations Engineer.
Future Applications: The automated queue warning detection system was a valuable addition to our “tool box” for managing traffic issues in the construction work zone on the Redwood Road project. In the future, perhaps other projects could benefit from this or other types of technology to help address traffic control issues within construction work zones.
This guest post was written by Bryan Chamberlain, Region Two Resident Engineer, and was originally published in the Region Two Fall 2014 Newsletter.