Dan's Excavating Constructs Michigan's First Flex Route
The problem on U.S. 23 north of Ann Arbor, Michigan, was clear: an old roadway at maximum capacity, with regular slowdowns and extreme congestion during rush hour. Due to narrow confines and the high cost of procuring additional right-of-way, though, the solution was harder to define.
To solve the dilemma, the Michigan Department of Transportation (MDOT) chose to install the state's first Flex Route using Intelligent Transportation System (ITS) technology. The active traffic management system will open an extra median shoulder lane on each side of the roadway as needed and promote safety by alerting drivers of delays and incidents ahead.
"We really just need to manage traffic during peak hours," said Jim Daavettila, Construction Engineer for MDOT's Brighton Transportation Service Center. "When we looked at the cost of expanding to three lanes, it made much more economical sense to go with this solution."
The Flex Route system resolves the part-time congestion problem while working within the existing infrastructure, resulting in a significantly lower cost. Prime Contractor Dan's Excavating of Shelby Township, Michigan, began construction of the 11-mile, $91 million project in Washtenaw and Livingston Counties last November, using numerous subcontractors and many simultaneous worksites throughout the corridor to meet the expedited, one-year schedule.
How the Flex Route Works
The new lane control system uses overhead digital signs, cameras, and electronic message boards mounted on a dozen large gantries built every half-mile on both sides of the road. Green arrows on the digital signs will indicate which lanes are open. During light traffic with no incidents, a red X will signal that the third lane is closed. The shoulder lane will open as needed for rush-hour traffic, seasonal travel, and other temporary conditions such as bad weather, traffic incidents, or construction.
Crews are building the two shoulder lanes in the existing median, with barrier wall and guardrails separating northbound from southbound traffic. Longitudinal lines will differentiate the new lane from the other two on each side of the road. The median lanes are built like the rest of the roadway, with concrete base course and an HMA surface over the top.
The ITS technology, overseen by MDOT's Statewide Transportation Operations Center, will continuously monitor for traffic slowdowns and post recommended speeds to reduce the potential for crashes. When an incident occurs, the electronic signs will provide information about blocked lanes ahead.
Six new crash investigation sites along the corridor will allow traffic to continue uninterrupted when incidents occur. If an accident happens when two lanes are open, "They'll keep the median shoulder lane closed until emergency vehicles get through so they have quick access to the accident," Daavettila explained. "Once those vehicles arrive at the scene, the computer program will adjust. One gantry will say, "˜Right lane closed ahead.' The next gantry sign will say, "˜Prepare to merge left,' then the next will say, "˜Right lane closed' and you'll get the green arrow for the left and center lanes. It'll really help traffic maneuver in the event of an incident on the freeway."
Before deciding on the Flex Route solution, MDOT researched similar systems in other locations. "In a lot of other states, motorists pay to use it," Daavettila said. "Here it will just be whether the lane is open or closed to help traffic flow."
To accommodate the flexible shoulder lanes and gantries, construction crews are widening bridges and shoulders. In total, the project includes eight bridges (repairs on two bridges and complete replacements alongside existing pairs of bridges at three other locations). With the roadway originally built in the 1950s and expanded in the 1960s, MDOT also incorporated pavement rehabilitation, upgraded acceleration and deceleration ramps, and improved drainage systems.
Tight Space and Schedule
As crews construct the new Flex Route, "The biggest challenge is trying to do all this work in such a tight area and maintain two lanes of traffic both northbound and southbound while we build it," Daavettila said. "We shifted traffic to the outside while we work in the median, then we'll shift traffic to the median while we work on the outside."
To accommodate the shifts, the project includes 15,000 square yards of temporary pavement for ramps and mainline. Because of the tight spaces, "A lot of our paving operations take place at night," said Dennis Rozanski, Vice President of Dan's Excavating. "During the day we have to maintain all the lanes of traffic in both directions."
The tight work area isn't the only challenge. "Our planners and designers looked at whether to complete the project in one year or two and decided on one to shorten the disruption," Daavettila said. "There was a lot of work we could do in the winter, and we just happened to have a really nice winter for construction activity."
To meet the expedited schedule, "On any given day, seven to 12 different contractors are working onsite," Rozanski said. "We have all kinds of different work going on at the same time - storm sewers, road building, electrical, curb and gutter, mainline paving, asphalt paving, bridges, and restoration work."
That means significant resources - both labor and equipment - onsite every day. Rozanski estimated that the corridor usually contains up to seven GPS dozers, a couple GPS graders, seven cranes, and 15 to 20 backhoes spread out across the 11 miles.
Dan's Excavating self-performs ITS, electrical, grading, and storm sewer work, as well as construction of two bridges. To manage all the subcontractors for the rest of the project, "Every Monday we schedule work for the following week to give our subs a heads-up of where they're going and where the project's going," Rozanski said. "All the contractors knew at bid time what the schedule was and when we would need them, so it hasn't been too much of an issue."
Accommodating Motorists and Farm Equipment
In addition to the many subcontractors, the project affects a large number of locals. "We're doing our best to address the obstacles this project has caused not only the motorists, but the residents, pedestrians, bicyclists, and businesses in the area," Daavettila said. "We communicate regularly with emergency responders, government administrators, and the schools to give as much advance notice as possible on scheduled closures. We also try to work around the University of Michigan football schedule and other events that draw commuters to the area."
Those efforts require some flexibility. For example, at the Joy and Warren Road bridges, "We were going to close half of each bridge and build them part-width, but a farmer who has fields on both sides of the freeway wouldn't be able to get his equipment across," Daavettila related. "We changed the staging a bit and kept one bridge open while we started work on the other. Once school got out and his farming finished for the spring, we could attack the job more aggressively - but we need to get the bridge done before the fall harvest."
MDOT expects to begin operation of the corridor's Flex Route system by the end of 2017. In other areas of the state, additional Flex Routes are being discussed as an option to manage temporary congestion and improve safety.