Busman's holiday.

On the whole, bus stations tend to be anonymous and depressing sheds, but Cruz and Ortiz'z poised new building in Huelva is a notable exception to the rule.

The categorisation 'organic machine' may at first appear as a contradiction in terms, but the new bus station at Huelva by architects Antonio Cruz and Antonio Ortiz is neatly described by this ostensible oxymoron. 'Organic' is apt because of the station's topographic posture, its fluidity of line, its contiguity of material and the central positioning of vegetation. 'Machine' is suggested by the critical role played by circulation, both vehicular and pedestrian. Essentially, the diagram of bus access and egress is expressed volumetrically, so that the building becomes a functional valve, with architectural presence.

At the scale of the city, the site is a triangular hinge between somewhat disparate blocks of apartment buildings and a gridded tract of scrub leading to industrial sheds and cranes perched along the river Odiel. The new building swells to the perimeter of its lot and caps it with a great lid of a roof. By bus, from one of the long-distance air-conditioned capsules that ply this sector of Andalusia, the station appears as a walled enclosure with curving flanks of horizontally-striated concrete. With a continuous clerestory above of ribbon windows (and a lower break containing a small area of retail space), the station presents itself as a homogeneous banded form until it is deftly pierced by the buses and (in traditional Spanish fashion) an inner world is revealed.

This controlled world uses the particular geometry of the site to accommodate the mechanical needs of long-distance bus travel. The fat end of the triangle is colonised by a gyratory system open to the elements, in effect a diagram of comfortable circular movement for the coaches, An inner structure, extruded curvaceously from the more solid apex, shades the loading berths into and out of which the larger vehicles slide and reverse with ease. The two remaining corners are fortified with lower flat-roofed structures - storage slots and a refuelling depot. A total analysis of the project might - as with fire stations or airports or tube stops necessitate a practical critique from literally the driver's seat, but within the constrained precinct at HueIva, one can at least say that the vehicles - up to 28 at a time, including articulated models - are neatly clustered or cloistered about a simple geometry.

The reverse, pedestrian experience of the station is a similar blend of homogenous fluidity and clever calculation. From town, the prospective traveller or party is met by the low apex of the new form inserted in the urban fabric like an unfolding dart. Where this hard-edged canopy meets the more sensuous walls of the principal mass, shade and the isolated lettering of 'AUTOBUSES' signal entrance, function and activity. In the heat of day, the solid enveloping forms create a soothing cave-like space, a haptic welcome, as the interior opens up into a double-height hall. Above and behind, a deep fronted fascia wraps around to service a balcony of offices. Overhead, the ceiling plane sweeps across into the recesses of these upper rooms and is punctured by cylindrical rooflights - three over the ticket booth and four above a coffee counter.

One's natural inclination to wander off and inspect is dynamised in the hall at Huelva by the architect's manipulation of plane and light. The sweeping interior walls direct the visitor past the ticket window, but more dramatically, out past the snack bar through infill sheets of glass to sunshine beyond. These minor and major exits are separated by a full-height silver of office accommodation - an island in a stream - with an information desk in the inward prow and, outbound, a butt-jointed double vitrine for manager observation. The principal exit and this subsidiary glazed protrusion lead inexorably to the heart of Cruz and Ortiz's plan, to the centre of the functionalist circle, where, surrounded by bus bays, the flat continuous soffit from the interior has curved out of it a secret cylindrical court.

'Organic' and 'machine': the optimal fluidity of buses and the efficient inclusion of the sensuous, the tectonic, the natural. Whereas the built fabric and fittings such as screens and benches (combinations of metal and concrete) are inevitably robust, the court's surprise is its containment of 37 orange trees beneath the Andalusian sky. Ringed by 24 rectangular concrete piers, the stark trunks reaffirm nature's role in the gritty context of the city. Above, dropping from the unitary 7 m high roof slab, is a concrete frame, vertically-proportioned and glazed as a kind of passive reflection mechanism. The public concourse flows out into the air of the courts before the individual voyager is redirected to the waiting necklace of clearly numbered coach bays.

In the 1980s, the Cruz and Ortiz partnership had a certain typological preoccupation with expressive inner-city housing, which developed into the more expressive volumetrics of Santa Justa station, in time for Expo '92 (AR June 1992). Now, two hours' bus journey away at Huelva, the architects' abstract exploration is again allied to programmatic particularities, but in an even more plastic way. On a superficial level, it seems uncharacteristic, until one recognises the project's symptomatic total unity and remembers, from almost 20 years ago, the firm's Dona Maria Coronel apartment complex with its fluid poche arrangement about a kidney-shaped court. But the really reassuring back-seat view from Huelva is that transportation and the city can be poetically integrated.