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Safety & Mobility

​North Carolina’s population has grown tremendously in recent years, making the state one of the fastest growing in the nation. This trend is predicted to continue in the coming years.

More people living, working and visiting North Carolina also means more people on the roads.

Using technology, new designs for intersections and interchanges and traffic signals as well as other traffic management tools, the N.C. Department of Transportation's Mobility and Safety Unit continuously looks for ways to improve traffic flow and safety for drivers – methods often at less cost than other alternatives.

Some of the measures currently being employed across the state or being studied are outlined in the below table.

​Measure​Description
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.
​Continuous Flow Intersection​Also known as a Displaced Left-Turn Intersection, this innovative intersection design separates left-turning traffic several hundred feet from the main intersection. The left-turning traffic is directed to a separate roadway that runs parallel to the main road. This design requires fewer traffic signal phases, which means traffic moving on the main highway stops less frequently. It is also safer, because left-turning traffic is separated from the main traffic flow.
Diverging Diamond Interchange​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.
Median U-Turn​This intersection design prohibits left turns from the main road and side streets. Instead, drivers wanting to turn left must drive straight or turn right and then make a U-turn at a median crossover. A median U-turn varies from a superstreet by allowing traffic on the cross street to go straight through the intersection instead of turning right.
​On-Ramp Signal​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.
​Roundabout​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.
​Square-Loop Interchanges​A “square-loop,” or quadrant, interchange operates similar to a traditional interchange, but its design eliminates the need for left turns. Instead of on- and off-ramps, a short roadway provides access from one street to the other. The roadway connects with both streets at a “T,’ forming a square shape with the two streets.
​Superstreet​A superstreet requires drivers from side streets to turn right, instead of turning left or going straight through an intersection. Drivers then make a U-turn at a designated opening a little further down the road. By eliminating left turns from side streets, safety is improved. It also allows drivers to pass through the intersection quicker, because the traffic signal cycles through quicker.
​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.
​Zipper Merge​As its name suggests, this type of merge works much like a zipper. When approaching the merge, drivers are directed to stay in their lane until they reach a specified point, then drivers in the open lane take turns allowing vehicles from the closing lane to merge in front of them. By taking turns at the merge point, drivers should experience smoother merging conditions, which reduces traffic backups and the amount of time it takes for all drivers to get through the merge.

7/10/2018 10:19 AM

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