Light fantastic (without the tripping)

Not many English cities can claim to have inspired a number one single. Coventry has that distinction, but its depiction in The Specials' 1981 hit Ghost Town is not a happy one. The song was written amid race riots and a recession that knocked the stuffing out of the town's manufacturing industry. Although the ska tune may have been uplifting, the lyrics certainly were not.

Twenty years later, things are looking a lot brighter for Coventry. The commercial regeneration of the centre, blitzed during the Second World War, has giving the city the feel of a boom town once more. Central to the revival of the city's fortunes has been the completion of 22 millennium projects designed to add sparkle to the city centre.

One of the most important schemes was the creation of a new pedestrian bridge, which links historic sites in the city with a new public square called Millennium Place. Devised in 1999 and completed last Christmas, the £650,000 bridge snakes out of the square through a 360-degree spiral and takes pedestrians 3 m over a medieval city wall and the restored Lady Herbert Garden before making a gentle landing in the new Garden of International Friendship.

At the garden end of the 120 m long steel bridge is a viewing platform – in the square, the bridge lands near the new facade of the Museum of British Road Transport. The bridge lights up at night to ensure 24-hour use and the etched glass fins by artist Alexander Beleschenko gives the structure an extra architectural lift.

The design and specification of this important landmark was not as simple as its elegant appearance suggests. "It's a tortured story," says Toby Johnson managing director of architect MacCormac Jamieson Prichard. Back in 1999 Johnson says that large curved glass panels featuring Beleschenko's artwork were designed to sheath the structure, including the bridge underside.

After designing the structure with engineer Dewhurst McFarlane the client Coventry City Council decided the large glass panels had to go. "It was redesigned because of the fear of vandalism and to make cost savings,' he remembers. The necessary redesign involving engineer Whitby Bird meant that the lighting specifications for the flooring had to be totally revised.

On top of this, Johnson's graceful spiral ramp was being threatened by the requirements of Part M of the Building Regulations, which govern accessibility. The legislation states that access ramps with a gradient is greater than 1 in 20 must include resting points and landings. This is something that Johnson wanted to avoid. "The landings would have got in the way of the smooth line of the ramp," he says.

The structural strength of the bridge is derived from a 800 mm steel tube, which forms the shape of the ramp and bridge. Ribs are attached to the tube, and these support the steel grids and plates that form the walkway (see "Get a grip", for more on the walkway spec).

The walkway surface alternates every 600 mm between a steel grating and resin based aggregate finish. Under each steel grating is a 1500 mm long fluorescent tube, which has a control that automatically switches the light on at dusk and off at dawn. The tube is incredibly cost effective as it performs three functions. As well as providing safety lighting on the walkway, it also picks out the glass artwork and provides illumination to the underside of the bridge.

The fluorescent tube was not the first choice according to Philip Rose, lighting architect at Speirs and Major Associates. "Originally the light source was going to be a linear cold cathode, which would curve and follow the line of the bridge. This was when the glass was U-shaped, which would have protected the light." Once the large glass panels were eliminated from the design Rose had to think of another way to protect the light. "We would have had to create a case or provide clear polycarbonate, which would have had cost implications," says Rose.

The solution was something normally associated with office interiors. "After numerous designs and contributions we settled on linear fluorescent lighting in a polycarbonate casing [fluorescent tubes]," says Rose. The attraction of this approach was that the tube was a standard, inexpensive 50 mm batten from lighting manufacturer Encapsulite, and the product came with the waterproofing. Its specification was not straightforward, however; Rose had to adjust the tube to make it work.

The standard product has the lamp located at one end of the tube. To avoid the need for two fittings across the width of the bridge Rose asked for the lamp to be located at the centre of the tube. He also specified that two holes be punched in the metal reflector that dissipates light along the tube. This simple modification meant the underside of the bridge could be lit without additional lighting. With coloured plastic wrapped round the underside of the tube, the bridge supports are bathed in a striking shade of blue.

Pedestrians at the foot of the ramp in Millennium Place can use a lift to take them to the top of the spiral. This is how Johnson complied with Part M of the Building Regulations as he couldn't bear the thought of landings interrupting the flow of his spiral. "It has been accommodated quite successfully," he says. No lift was required at the other end where the gradient was below 1:20 and complied with Part M at the time.

Johnson made the decision to incorporate a lift following an access audit by consultant David Bonnett Associates. Bonnett remembers recommending to MJP that the spiral ramp gradient be made shallower to avoid the requirement for ramps. "To fit landings on a ramp is a nightmare," he says. Johnson avoided this approach, partly because the ramp would have to be much longer to achieve the shallower gradient, and this would have pushed up costs.

Though the lift was the most satisfactory solution in the circumstances Bonnett says it can lead to long-term maintenance issues. "Public lifts are difficult things to keep clean and secure," says Bonnett. He fears that the new version of Part M will see a proliferation of lifts as the regulation is now demanding that for a rise more than 2 m wheelchair users will have to be provided with an alternative means of access (see "Rampant discrimination" page 20, for more on Part M's impact on ramps and bridges).

The bridge is a stylish and functional addition to Coventry's urban environment, and with the other 20 projects including the creation of three gardens and the restoration of the 15th-century Swanswell Gate, has given Coventry a shot in the arm. A strong sign that Coventry is now doing quite nicely, thank you, is in the music originating from the town. There's no more songs about urban deprivation. Coventry's Pete Waterman, the svengali behind Kylie and Steps, is proof that the best music is borne out of adversity …