The interchange where I -25 crosses I - 40 in Albuquerque was originally designed in the 1960's to handle 40,000 vehicles per day. By the late 1990's, the interchange was handling nearly 300,000 vehicles per day and was completely overloaded, as well as being physically worn out. Being in the middle of a major metropolitan area, the interchange could not be kept out of service for a long time. After discussing various closure options, the city and state decided to allow night time closures only for a two year period and completely reconstruct the facility within that ambitious time frame. A complete redesign of the interchange was undertaken, which increased the number of bridges in the interchange from 15 to 45. Eight of those bridges were high-level flyover ramps. The ramps had to be built while the interchange stayed in service beneath them.

The physical constraints for the bridges included very constrained opportunities for pier locations, the need to work over traffic and to meet the tight time frame. The visual environment is dominated by the roadways and graded slopes of the interchange itself. In keeping with the desert climate, it was anticipated that most of these slopes would be covered with desert vegetation or slope paving of crushed stone. The interchange is surrounded on all sides by the city's street grid, which interconnects with the interchange through a series of frontage roads. The nearby uses include low level commercial and residential buildings and one mid rise hotel. It is close to the downtown buildings, and from many locations appears to be part of the city's central core (Figure 6-56).

Since the interchange is the hub of vehicular travel in the Albuquerque region, most people in the region pass through it regularly, many daily. It forms a big part of everyone's life and asserts a strong influence on the image of the city. Together with its frontage roads the interchange's structures extend for long distances along the two interstate corridors, making it hard to designate a place where the interchange ends.

The design intention/vision was dominated first by the need to get the interchange rebuilt within the time available and keep traffic moving in the meantime. However, the city and state also wanted to take this once-in-a-lifetime opportunity to create a civic asset for the community, to make it an attractive part of the cityscape.

The geometry of the ramps was adjusted to keep the flyover ramps at two constant widths, one carrying one lane with shoulders and the other carrying two. Concrete box girders were chosen for the ramps for several reasons. The concentration of reactions at the centers of the boxes kept the piers narrow and eliminated the potential clearance problems of hammerhead pier caps. That plus the long spans available with concrete box girders gave much flexibility in the placement of piers. Finally, the girders could be manufactured offsite in advance and erected with minimal interference to traffic using the balanced cantilever method. Piers were placed to keep them as clear as possible of undercrossing roadways, mainly for construction reasons. However, the result was to provide generous vistas through the interchange. (Figure C 6-57) Abutments were placed to minimize wall lengths and heights. The box girders are slightly trapezoidal in shape, which narrows the bottom flange and makes the boxes seem smaller and lighter. The parapets are uniform throughout and have a continuous inset strip. There is no railing and no pedestrian screen.

The piers are an elongated octagon in plan, giving them a faceted appearance which makes them seem thinner and taller. Those with two bearings flare outward slightly at the top to accommodate the bearings. Most abutments are small and simply facilitate the transition to embankment. Some tie into retaining walls. The same parapet detail continues across both types and also forms a continuous coping along all retaining walls.

It is with its color that the Big I makes its major statement. All of the surfaces of all of the bridges, piers, and parapets are coated with the same rosy tan color, except for the inset strip of the parapets, which is coated with a bright blue (Figure C 6-58). The color ties together all of the disparate shapes of the ramps as well as the conventional underpass girder bridges that also form a big part of the interchange. The blue stripe acts even more strongly to tie the whole complex together. At the same time, when seen against the sky, it seems to unite with the sky, fuzzing the upper edge of the structures and making them seem thinner.

The rosy tan seems to come right out of the New Mexico desert. Even the gravel slope paving shares the hue. Because of the color, the interchange seems to fit right into the Sandia Mountains and nearby developments, as if it had always been there (Figure C 6-59).

The retaining walls are all faced with a rock-patterned form liner, recalling desert sandstone and coated in a compatible tan color. With the box girders there are no visible bracing, conduit, or other piping to interrupt the curved surfaces of the bridges. The sign structures are simple, single bent tubes, and accommodated on the structures by thickening the parapets. The lighting is ground-mounted high-mast lighting, so no poles appear on the bridges.

The Big I clearly met the first part of its design intentions, finishing within the two-year period while keeping traffic moving throughout. The interchange met its second part as well, creating a new visual asset for its region.

The Big I was designed by the URS Corp, with Steve Stroh as the design manager, under the direction of the New Mexico Highway Department.