KQED'S STEPHANIE MARTIN: After years of construction delays, Caltrans says it's finally ready to open a pair of tunnels at Devil's Slide -- that precipitous stretch of coastal Highway 1 that connects San Francisco to Half Moon Bay.

Since opening in 1937, the route has gained fame for its views of the Pacific -- and notoriety for its frequent rockslides and deadly accidents.

San Mateo County Board of Supervisors President Don Horsley represents the district where the slide is located.

Mr. Horsley, I understand you also spent about 14 years as county sheriff. What about that experience convinces you that drivers are going to be safer when the tunnels open on March 25?

DON HORSLEY: Well, there are a number of things. We had some really terrible accidents, and that's why it was called Devil's Slide.

MARTIN: You had both the threat of the cliff itself -- people went over, and then also, people drove into each other.

HORSLEY: That was true, too. The road has actually become worse over the years because it's like a roller coaster now. It's sort of dropped in certain areas. As you're going on the road you suddenly drop down, and you're back up. It's quite a scary ride.

MARTIN: And the last major rockslide that caused serious problems was back in 2006. It took four months to repair the highway, as you recall. And the result was that long detour affecting commuters, tourists and businesses. With that threat gone, what will the impact be on the local economy?

HORSLEY: Well, talking about that four-month stretch - it actually drove a lot of people on the north part of the coast out of business, because you can't really sustain a business when nobody comes there. And the other thing was that traffic problems were just horrific. We had to have officers from the California Highway Patrol, the sheriff's department and what used to be Half Moon Bay Police to be able to try and direct traffic.

MARTIN: As you know, the project cost $439 million in the end -- more than $100 million over budget, and also, it took two years longer than anticipated. What, from your point of view, were the biggest challenges of getting this done?

HORSLEY:  When Caltrans and engineers had to go through the mountain, they had to make sure they were hitting the most stable part of Montara Mountain, and they did.  But on the other hand when you're going through, you find there are different kinds of rocks - would have been nice if they found gold or something [laughs]. They did come up with different kinds of rock, and that's one of the reasons they had to do different drilling techniques, and that's what caused the delays.

MARTIN: Have you actually been inside it yet?

HORSLEY: Well, you know, I've been up to it, yes. But I haven't actually walked through the whole thing. It is really a gorgeous facility. It's kind of a faux rock that makes it look like it's actually the inside of a beautiful tunnel. It's really nicely done. And the other advantage of having this tunnel now is that the old road is going to become a park. So you'll still be able to go on the old Devil's Slide, but you have to walk or bicycle. And you'll still be able to see the views, but you're not going to have to drive through the fog, and it's not going to be something that is treacherous.

MARTIN: I understand plans are in the works for a very large celebration with dignitaries from all over the state. Why so much fanfare for this?

HORSLEY: Well, because I think it's one of the first tunnels that Caltrans built for many, many decades, and it was something that was fought over in this county. Originally it was going to go over the mountain, which would have destroyed one of our scenic areas - a park up there. And locals came up with a plan, and they actually got it on the ballot to have voters vote for a tunnel versus the bypass. And it was really a hot and contentious issue for a long time, but they prevailed. So, I think people felt that it was a great victory on their part that they were able to convince the powers-that-be and Caltrans and federal government and county politicians that it really was best to build a tunnel. So it was really the people's victory, and I think because it was a victory on the part of the people, I think they're really excited about it. So, not only are we going to have dignitaries, but we're going to have high school bands from Half Moon Bay as well as Pacifica.

MARTIN: Thanks so much for talking with us today.

HORSLEY: And thank you.

MARTIN: Don Horsley is President of the San Mateo County Board of Supervisors.