ddi

A busy Upstate bridge has temporarily closed as work for the new "diverging diamond interchange" nears completion.

The SC-290 bridge in Duncan, South Carolina, closes on Friday, May 16, at 7 p.m. to finish the new traffic pattern. The bridge is set to reopen on Sunday, May 18, at 6 a.m.

Detours

Officials said all cross-bridge traffic will be detoured to SC-129 or US-101 depending on direction of travel.

Northside of the Intersection

Drivers will use the following detour:

East on SC 290 to I-85 Southbound ramp. I-85 to SC 101. Take exit to SC 101. Left to SC 101 Eastbound. East on SC 101 to I-85 Northbound ramp. North on I-85 to SC 290. Take exit to SC 290 Eastbound.

This detour is an estimated length of 7.4 miles.

Southside of the Intersection

Drivers will use the following detour:

West on SC 290 to I-85 Northbound ramp. I-85 Northbound to SC 129 . Take exit to SC 129. Left to SC 129 Westbound. West on SC 129 to I-85 Southbound ramp. South on I-85 to SC-290. Take Exit to SC 290 Westbound.

conventional diamond

This detour is an estimated length of 9.3 miles.

What is a Diverging Diamond Interchange?

A diverging diamond interchange (DDI) is a rare interchange where traffic crosses to the other side of the roadway between the freeway ramps.

diverging diamond interchange

According to the South Carolina Department of Transportation, a DDI is statistically proven to improve safety and mobility of traffic often at a much lower cost.

SCDOT says a DDI has 14 ways vehicles can collide within the interchange, compared to 26 different ways vehicles can collide in a conventional interchange.

Additionally, U-turns are accommodated well on a DDI as a vehicle would not have to cross opposing traffic.

How to Navigate a DDI

Navigating a DDI can be intimidating for a driver who has never encountered the interchange before, however, signage, pavement markings, and traffic signals make the traffic pattern relatively easy to navigate.

SCDOT provided the following information:

Drivers will follow signage and pavement markings to a signalized intersection. Traffic will appear as if on a one-way street that crosses them to the opposite side of the roadway.

All left turns onto the freeway are free flow, which means that they do not have to stop to access the ramp.

northside detour

All vehicles that are going straight simply continue through the second set of traffic lights that crosses them back to the original side of the roadway.

southside detour

ddi

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