Proponents of a controversial concrete expressway bridge, known as the Three Sister's bridge, to be built across the Potomac River in Washington, D. C. have won a critical round. Engineering studies performed on a 30 ton scale model of the unique bridge structure support engineers' contentions that the new bridge would be structurally sound and easily capable of carrying peak traffic loads. The new structure will be located about half a mile upstream from Georgetown and will carry six lanes of traffic between Virginia and Washington, to permit direct access of I-66 traffic to the Capital by way of the new I-266 extension. The CCRI model was built of precast, three foot long segments which were sequentially grouted in position and post-tensioned together to form the complete bridge half. As construction proceeded, forces were applied to simulate the dead load of the prototype. Observed reactions, strains, and deflection were within anticipated limits in all cases. The model responded elastically as each new segment was added and dead load was applied. Also, no cracks attributed to applied load were found. After testing for safety of the bridge under anticipated traffic loads, test were made for safety under extreme overload. While such overloading would be impossible in actual use, it was found that the structure was capable of supporting 13 layers of heavy, bumper-to-bumper traffic filling all six traffic lanes and two emergency lanes. Clearly, the tests show the proposed design to satisfy serviceability requirements of the American Association of State Highway Officials Specifications.