PHOENIX (3TV/CBS 5) - On a normal day, about 25,000 cars travel the Interstate 17 north of Phoenix.

On a busy weekend, that number can double.

"We've always faced this challenge of I-17 in that Black Canyon City region being such a mountainous, winding area and it's prone to fender benders, to crashes, to even disabled vehicles," said Doug Nintzel, spokesman for the Arizona Department of Transportation.

[WATCH: ADOT plans to start I-17 'flex lanes' construction in 2021]

Drivers often find themselves stuck as the I-17 turns into a parking lot.

Since last year, ADOT has been working on a solution and is getting closer to building "flex lanes" to handle the extra traffic.

"They will line up with the current southbound lanes, but they will be separated by barrier lanes in either direction, depending what the traffic need is," said Nintzel.

A new computer rendering shows how on a busy Friday, for example, the extra lane would be opened, taking some of the traffic heading north.

Then on Sunday, when weekend travelers return south, that same lane could be reversed.

To prevent wrong-way drivers, gates would close the flex lane to opposing traffic.

"So we're getting there and this would be a really positive step in terms of the challenges we face and drivers face on I-17 in that Black Canyon City region," said Nintzel.

The project would be a major feat of engineering.

ADOT has already secured $120 million to build the 8 miles of the new road.

"It's going to make a world of difference as we look to things like busy holiday weekends when traffic may come to a standstill, the summer months and summer weekends, the ability to have this extra traffic capacity it will make a big difference. especially if you had an incident out there," said Nintzel.

ADOT expects to have the final design by 2020, with construction to start in 2021, and the project completed in 2023.


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