19.5 inches seems too far. I'd estimate 14 or 15 from center to center at Monon High. I'll post a couple of pictures at end of the post. The gaps are considerably wider and the planks in worse shape at the beginning of the bridge, while it's over Deer Creek. Obviously for decades most bridge walkers sample that section only, before turning around. Maybe 40 feet out there is one prominent missing plank that stands out because the next plank is wearing out and insecure also. It's basically a requirement to step or jump over two plank sections. Then I believe there was another missing plank, but not as bad because the surrounding planks were secure.
Beginning is slow going and nerve wracking because so many planks are awful. They look awful and are awful. Fortunately there were videos prior to my visit that demonstrated that the worst section was the first 100 feet or so. Then it begins to improve. If I hadn't known that I probably wouldn't have ventured across because it is anything but evident while standing there at the foot. Subsequently the biggest problem I had were spongy planks that did not look spongy. Happened several times. Twice I got careless and had my weight leaning backwards while I stepped forward onto a spongy plank. That sent me whirlybirding to maintain balance. The first one was particularly scary because I had one or two seconds to wonder what would happen if I fell fully backwards onto worn planks at 6-3 and 205 pounds. It was 40 degrees and I was a Floridian burdened by a comparatively heavy jacket that I use maybe once or twice per year. In lighter more comfortable attire there's no question I would have felt more nimble and at ease.
Despite my two wobbles I'd say the difficulty and danger of crossing is wildly overstated by most followers of this case. That's because so many photos and videos are taken from below or above the bridge. Those angles lend toward human vulnerability. They also tend to exaggerate the gaps between planks. But once you're up there it's plenty wide enough and you focus on the task...one step at a time.
The end of the bridge where Bridge Guy was videotaped is a comparative piece of cake, with narrow gaps. That is a cruise control section. I could have walked with hands in pockets. The only issue in that area was lots of green moss on the planks. And smack in the middle of the planks. That moss must not be frequent because I have never seen it in other photos or videos but it was all over the place during my November 2019 visit, and quite slick. The plentiful moss was a contributing factor to my decision not to cross the bridge on the way back.
imgur.com
imgur.com