It happens to all of us: We are sitting in the car in stalled traffic and wondering what the delay is and how long will it be?
Most of the time it is some sort of construction or maintenance activity on the roadway ahead that restricts the number of vehicles that can get by. If only we had better notification of this work that would give us the option to choose an alternate route to avoid the roadwork, or to leave a bit earlier to ensure that you get to your destination on time. There are solutions to this problem, and it involves the use of portable intelligent transportation systems (ITS) technology applications that support work zone safety and mobility. This so-called “smart work zone” technology brings motorists more accurate and timely information to mitigate the impacts that construction and maintenance projects create. This article will provide an insight into how the Massachusetts Department of Transportation (MassDOT), an avid smart work zone user, was able to think outside the box and bring in an application of smart work zone technology to address an issue that a unique infrastructure maintenance project created.
Anyone who has ever traveled to Massachusetts to beautiful Cape Cod most likely crossed the Bourne or Sagamore Bridges that span the Cape Cod Canal. Both bridges are under the control of the U.S. Army Corps of Engineers and were built in 1933-1935. Each bridge covers a span of more than 600 ft and is over 130 ft above the water to allow large vessels to cross through the canal. But these structures were certainly not built to carry the level of vehicular traffic that they handle today. The bridges are identical in design—approximately 48 ft in width providing only four 10-ft-wide traffic lanes with two lanes in each direction and no paved shoulder.
Finding an ideal time to maintain these two large bridge structures is difficult due to the high traffic volumes and the pure lack of pavement width to take lanes out of service for temporary traffic control. Looking at the Sagamore Bridge, it is owned and maintained by the Army Corps but the roadway on top is U.S. Route 6 and controlled by MassDOT. As one could imagine, any project that requires temporary travel lane closures on a four-lane highway is going to create impacts to traffic flow that will need to be managed.
This brings us to 2018 when the Army Corps approached MassDOT with a need to address some structural maintenance of the Sagamore Bridge. The proposed Route 6 traffic management plan called for permanent lane closures that would provide only two opposing 10-ft lanes immediately adjacent to the work area, closing half the bridge. The Sagamore Bridge carries just shy of 62,000 vehicles per day (vpd) during the off-season, with a summer peak of 80,000 vpd. As one would expect, with the high traffic demand on the bridge and only half the lane capacity available, the result was significant congestion on the single-lane approaches to the bridge.
On the Cape side of the canal is the Exit 1 (now Exit 55) interchange junction to Route 6A (Cranberry Highway) which is located just a quarter mile from the end of the bridge. During normal day-to-day operations, the proximity of the interchange creates additional friction in traffic flow with the merge and diverge activity at the exit’s on and off-ramps. What complicates traffic operations is the Route 6 westbound on-ramp from Route 6A that is just 810 ft from the actual bridge and right in the middle of the lane closure area needed for the bridge deck repairs. This on-ramp from Route 6A is historically busy throughout the year with people looking to depart the Cape during all periods of the day.
The construction project went live on a Sunday night and one day later the complaints of severe traffic congestion and frustration among motorists came pouring in. On Tuesday morning, MassDOT had a meeting with the local Army Corps unit to request some minor adjustments to the Temporary Traffic Control Plan (TTCP). However, it was not enough to relieve the congestion issues that the project was creating. MassDOT suggested police details try to mediate the traffic streams and essentially create a ramp meter at the on-ramp to Route 6 west. Unfortunately, there was difficulty in filling the detail slots and a desire to avoid adding significant costs to the project due to overtime expenses. The team had to find a different answer to solve this issue.
Working with the District Office to find a solution that would address the significant delays and chaos that was happening with the existing TTCP, it was clear that we wanted something that could be flexible enough to address the variable traffic demand. The team decided to pursue the use of unique technologies to enhance a traditional portable traffic signal (PTS) system, which was a bit outside the box for MassDOT. The proposed solution was demonstrated at the American Traffic Safety Services Association (ATSSA) Convention earlier that year and would provide a “smart” signal system that we felt would better manage the traffic and reduce the safety concerns created by the forced merge condition.
On Thursday, we reached out to a manufacturer that had the ability to deliver what was needed and contacted a local traffic control contractor who would be willing to work with us in such an accelerated time frame. The manufacturer was Horizon Signal Technologies based out of Pennsylvania, and the local contractor was Northeast Traffic Control from Plymouth, Massachusetts. A conference call between the parties set the game plan into action, and we needed a super quick turnaround. The equipment would be put on a truck in Pennsylvania for delivery that Saturday, and we would meet early on Sunday to configure the system and deploy it later that day.
So what makes a portable traffic signal system “smart”? For this project we were adding a traffic signal on U.S. Route 6 in the westbound direction, which is a two-lane freeway and would bring people to a complete stop. This would allow the on-ramp from Route 6A to have dedicated “green time” to access the bridge without having to force their way into the signal travel lane. To prevent any potential issues with placing a signal where it did not already exist—never mind that it is on a high-speed roadway—we wanted to provide advance notification to approaching motorists. This was done via a wireless communications interface between the portable traffic signal controller at the “temporary” intersection and portable changeable message signs located a quarter-mile upstream. This allowed us to broadcast that there is a signal ahead, but to also warn motorists when it was “red”. During congested periods this was not as much of an issue, but off-peak when traffic volumes are lower and speeds are up, it was a necessary safety countermeasure.
The other key technology that the PTS system uses is built-in video detection that allows for the traffic signals to utilize custom detection zones—much like what is found in most permanent signalized intersections. Rather than run the signal on a fixed timing plan which would be inefficient during lower traffic volumes, we could use an “actuated” timing plan that would provide “green” time for the Route 6A ramp when there was traffic demand. In addition, due to the longer “yellow” clearance times needed to ensure that we were not having traffic merge together unnecessarily, we wanted a mechanism to give feedback to drivers who were waiting near the stop line. The last thing that we wanted to see happen is a driver think that the signals were broken due to the long period of stopped traffic sitting at the “red” light, and have them run the light. We added a small message sign on the mast arm of the temporary signal which provided a wait-time display that gave motorists a series of messages about the signal operation and a countdown of the time they had to wait on the “red” cycle while the opposite approach had the “green” movement. This helped to prevent drivers from running the red light during the long wait times, and to keep drivers more engaged and aware of their surroundings.
The temporary signals also had a built-in integrated conflict monitoring system that would ensure that the two separate trailers would work in unison and not fall into a conflict mode where the potential for “green” on both approaches could occur. In addition, the other benefit of the portable system is that they are fully solar powered with enough on-board battery backup to support up to 30 days without sunlight. The equipment meets all the Federal Manual on Uniform Traffic Control Devices (MUTCD) standards and NEMA communication requirements for portable traffic signals, which provides a level of comfort to DOTs looking to use these devices.
Back to the million-dollar question: How did it operate? We were very transparent with the MassDOT Public Affairs Office that we were not installing the portable traffic signal to make traffic go away, but rather this was a measure to provide safe and orderly traffic control for the forced merge of two approaches into one travel lane. Before we introduced this situation things were chaotic, and we had several near collisions that would have further exacerbated the congestion out there. By providing for the orderly flow of traffic, we were able to smooth out conditions and in return, process more vehicles at this junction point. There were no reported crashes while the temporary signal was in operation.
MassDOT felt this was a success, however, there were some portions of the motoring public and the local news outlets who needed a reminder that signals do not reduce the number of vehicles on the road. The truth is the signals provided controlled and safe access at the merge point that was previously a much more chaotic situation. We did get local public officials and police support for the operation as it was providing a safer alternative than what was set up before. The positive results experienced with this application has encouraged MassDOT to utilize this smart technology for more outside-the-box, low-cost applications. In fact, we reinstituted this same portable traffic signal control at the Sagamore Bridge for another one-lane each direction application this past April 2021. Same result, no loss of traffic volumes, but a far more organized and safe movement of traffic.