Hector Woodhouse knows the Forth Road Bridge like the back of his hand.

As a young civil engineer in the late 1950s and early 1960s, he was one of hundreds of people who worked on the construction of this iconic suspension bridge. Now, as the Forth Estuary Transport Authority prepares to mark its 50th birthday with a series of celebratory events under the banner of The Forth Bridges Festival, he stands proudly beside one of Kate Downie's large ink paintings of the North Side Tower.

This majestic drawing, informed by Downie's ongoing love affair with traditional Chinese ink painting techniques, is currently on show as part of a new exhibition at nearby Hopetoun House. It bears all the hallmarks of a Downie classic. Bold brushstrokes and a bravura sense of scale are underpinned by a restless energy and an eye for the tiny telling details; a curved Portacabin at the giant tower's foot has a lick of neon on its roof, while miniscule studs of glittering steel are depicted embedded into one of its legs.

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This hard-working edifice stands 150m above the water. "This was my tower," Woodhouse grins as he poses for a photograph beside the drawing for its creator. "But looking at it here alongside Kate's other work, I'm seeing it all with different eyes. She's done an amazing thing here."

Since being appointed Forth Road Bridge artist-in-residence last December, Downie has immersed herself in creating an intimate portrait of the bridge, which was opened on September 4, 1964, by The Queen. She has also painted a vivid picture of its near neighbours, the work-in-progress Queensferry Crossing, due to open in 2016, and the Victorian railway bridge with its distinctive cantilever structure and red paint.

There are never any half measures with Downie. During the summer months, the Edinburgh-based artist even found herself a billet beneath the bridge in an old boat house, where she created a temporary studio. From this vantage point, she set about befriending bridge workers and hearing their stories as she worked from an access-all-areas standpoint.

Not every artist would be comfortable sitting in a cherry-picker 40m above the ground, but it's meat and drink for Downie. "I've always wanted to go up in one of these things," she says. "I love heights!"

No experience on the bridge was wasted, and one of the stand-out works in the show, a monoprint called Four Lane Estuary, depicts an abstract bird's-eye view of the lanes on the bridge interspersed by glimpses of water below.

The drawing and accompanying story charting the cherry-picker lift and other adventures are now part of The Road Bridge Diary, a handmade book which unfolds like a Chinese scroll painting. Hector Woodhouse's story will also be included in this unique record of Road Bridge experiences.

One entry records a sad tale told to Downie by a bridge worker called Sean, of how he was summoned at 3am one cold rainy night to attend an incident involving a stationary car on the southbound carriageway. "When he got to it," she writes alongside a sketch depicting the happening, "he found the door hanging open, the headlights blazing, the engine running, but empty."

Sean found a suicide note from a mother to her children, written just before she had headed into the oblivion of the dark waters below. He then had to drive the car off the bridge. "Once that story is in your head, it's hard to shift the image," says Downie. "But I think it's important to include stories like that to create the bigger picture."

There are more than 30 artworks in this exhibition, including a soundscape Downie made with her partner, architectural photographer Michael Wolchover, filmed and recorded underneath the bridge on the maintenance deck. This work speaks volumes - literally - about the rush of traffic on the bridge.

Many of the works are for sale, including a group of 50 etchings called The Art Of Crossing, commissioned to commemorate the 50th year of the bridge. "What I love about doing this residency is I'm learning so much," says Downie of the experience. "It's not just about a bridge. It's about all the people who worked on it."

Zero To Fifty: The Road Bridge Diaries, Hopetoun House, South Queensferry (0131 331 2451, www.zero-fifty.co.uk) until September 13