North Carolina’s population has grown tremendously in recent years, making the state one of the fastest growing in the nation. More people living, working and visiting North Carolina also means more people on the roads.
The N.C. Department of Transportation's Mobility and Safety Unit studies new designs for intersections, interchanges and traffic signals to help keep people moving safely and reaching their destinations more quickly.
In addition to the innovative designs, the unit also relies on technology, data and other traffic management tools to identify the best feasible solutions for improving the transportation network.
Some of the innovations and other measures NCDOT is currently employing across the state or studying are listed in the table below.
All-Way Stops
| An all-way stop is an efficient and cost-effective way to improve the safety of an intersection and reduce the risk of serious crashes. Converting intersections into all-way stops has been shown to reduce fatalities and injuries by 77 percent on average. They are recommended after a thorough evaluation and investigation.
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Bus on Shoulder
| When traffic moves at speeds below 35 mph, the Bus on Shoulder System allows trained public transportation bus drivers to travel on designated interstate and primary route shoulders. Buses driven on the shoulders can only travel 15 mph faster than traffic, with a maximum speed of 35 mph.
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Continuous Flow Intersections
| This design separates left-turning traffic several hundred feet from the main intersection. This shift allows left-moving traffic and opposing drivers going straight to pass through the intersection at the same time, reducing travel delays, improving safety and allowing people to reach their destinations more quickly. |
| Diverging Diamond Interchanges | Traffic on the right side of the road is transitioned to crossover, or diverge, to the left side of the road and then back again in a diamond pattern. This interchange design moves high volumes of traffic through an intersection quicker and safer because drivers turning left do not have to cross opposing traffic. |
On-Ramp Signals
| Also called ramp meters, on-ramp signals are stop-and-go signals used during peak congestion times to control, or meter, the number of vehicles merging onto an already congested freeway. The signals allow one or two cars every few seconds to merge onto the freeway, avoiding the congestion that occurs when large numbers of vehicles attempt to merge with traffic already on a highway. |
| Quadrant Left | This unique intersection design reduces congestion and travel time through busy intersections by prohibiting all left turns at the main intersection. Left-turning drivers are rerouted to a connector road that allows them to go left by making a series of right turns. The traffic signal only needs to allow for through traffic and right-turning traffic, which moves all traffic through the intersection quicker. |
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Roundabouts | A roundabout is a circular intersection that channels traffic around a center island without using traffic signals. Because roundabouts allow traffic to continuously move, vehicles pass through a roundabout more efficiently than traditional intersections. |
Reduced Conflict Intersections
| A reduced conflict intersection (also referred to as a superstreet) simplifies how traffic is moved through the area, reducing travel delays and improving safety. In the most common design, drivers on the side street turn right to enter the flow of traffic. To go in another direction, the drivers, after turning right, enter a nearby dedicated lane to make a U-turn.
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Speed Limits
| NCDOT sets the speed limit for all state-maintained roads and can adjust the speed limits after a careful review that is based on several factors.
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Thru-Cut Intersections
| A thru-cut intersection is a contemporary design to better manage traffic flow and safety. It’s a type of
reduced conflict intersection that decreases the potential locations where a crash can occur.
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| Turbine Interchange | This innovative interchange design circles all left-turning traffic around a central bridge in a counterclockwise direction, like a whirlpool, allowing a high volume of traffic to travel between two interstates at highway speed. Since it features smaller bridges with smaller supports and lower roadway profiles than a traditional interchange, a turbine interchange has less impact to traffic during construction, and costs less to build and maintain than other types of interchanges. |
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Dynamic Zipper Merge | As its name suggests, this type of merge is intended to work like a zipper. When traffic is heavy and slowed, signs direct drivers to use both lanes until reaching the work zone, where they merge into a single lane. By taking turns at the merge point, drivers experience smoother merging conditions, which reduces traffic backups.
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