New subdivisions, major shopping centers and a projected increase in traffic along U.S. 17 from Brunswick County, NC, down to the South Carolina border had made it essential to upgrade the roadway and incorporate the superstreet design into its increasingly busy intersections.
According to Chris Baker, assistant District 3 engineer for North Carolina Department of Transportation (NCDOT), the agency compared several different designs for upgrading U.S. 17: intersection improvements, expressway system, freeway system and the superstreet design.
The $3-million superstreet design was selected because it is economical, increases the capacity at intersections and extends the life of the roadway.
“The superstreet design has the best cost benefit ratio of the four designs,” Baker said. “The superstreet doesn’t require expensive interchanges, excessive pavement or fill material [required for both freeway and expressway systems], and enhances efficiency at intersections beyond the capability of traditional intersection design. In addition, it decreases collisions at the intersections and reduces backups for turning movements.”
Design Created in Michigan
The superstreet design, also known as the Michigan left turn, was developed in Michigan in the 1960s as a way to reroute the interlocking left-turn movements along divided highways.
Superstreets can be incorporated at intersections where at least one road is a divided boulevard or highway. It is designed so that drivers on a divided highway cannot turn left directly (from the minor street onto the major street) at the crossing intersection. To accomplish the left turn, the driver must turn right at the intersection, move to the left lane, and perform a U-turn movement, usually between 800 to 1500 ft. from the intersection. In the case of U.S. 17, all turning movements will be signal controlled. Drivers on the major street wishing to turn left onto the minor street will do so in a traditional manner.
According to Baker, NCDOT determined that a 1.5-mi. section of U.S. 17, located between the Waterford and the Magnolia Greens subdivisions was most in need of upgrading. S.T. Wooten Company was hired as the primary contractor for the project.
“In addition to large subdivisions [more than 2,500 homes] a new Wal-Mart is being built along this section of U.S. 17, significantly increasing traffic,” Baker said.
According to Jonathan Bivens, vice president of the engineering and design-build group of S.T. Wooten Corporation, the firm will handle all grading, paving and storm drainage. Fulcher Electric Fayetteville Inc. of Fayetteville, NC, is subcontracted to handle all the electrical work including the installation of the new signal lights and Bost Construction was subcontracted by Fulcher to install the footing work for the signals.
Three intersections will be converted to the superstreet design.
Construction along this section of U.S. 17 will incorporate U-turns, bulb-outs (the additional turning lane for U-turns) and signal lights at both sides of each of the three intersections. The superstreet should not go beyond the current footprint of the road; therefore, grading and additional pavement will be minimal. Asphalt will be used on the road and concrete will be used for the curbs, islands and foundations of the signal lights. Some underground drainage will be needed, along with the laying of cables for traffic signals.
According to Baker, the state is not responsible for the costs of converting this section of U.S. 17 into a superstreet.
“Prior to approval for developments [commercial or residential]along U.S. 17, developers must submit plans to the DOT for review and determination if a superstreet conversion will be required,” Baker said. “If a superstreet design is required, the developer will be responsible for the costs.”
Heavy Traffic a Challenge
“Ensuring the safety of the workers and drivers during the busy morning and afternoon traffic has required substantial traffic control ” Baker said. “If this becomes too much of a problem we may shift the work to non-peak traffic hours, or night work.”
Work requiring daytime lane closures was to have been completed by May 25, the start of the peak tourism season. Additional construction, which should be complete by June 23, with allow only nighttime lane closures.
“Another section of U.S. 17 to be converted to a superstreet is at NC 211 in Brunswick County,” Baker said. “NC 211 is a major artery going from U.S. 17 to Southport. The anticipated increase in traffic volume is due to the approval of as many as 15 major developments along NC 211.”
Some Drivers Confused
“The main drawback to the superstreet design is that it can be confusing to drivers who must turn right, move to the left, and make a U-turn in order to make a left turn movement,” Baker said. “It can also be perplexing to drivers since not all intersections use the system, so drivers approaching an unfamiliar intersection don’t necessarily know to use this sequence in order to make a left turn.”
He said proper signage will be key in directing drivers for this type of movement.
“The advantage to the superstreet design is that it improves traffic flow and reduces accidents at intersections by controlling the turning movements of side streets accessing a four-lane divided highway,” Baker explained. “The superstreets have been very successful in Michigan; hopefully they will be as successful in North Carolina.” CEG
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