I'm not sure this makes a very convincing argument:
West Seattle is going to absorb more population density, one way or another, and if that creates traffic congestion along the neighborhood's main feeder arterial, which is inevitable as the population grows, then the solution is increasing mobility. It's more transit, it's street improvements, it's better transportation infrastructure. Its also requiring the development to make the streetscape better for pedestrians and access better for trucks. But I don't think that the threat of more traffic makes the case to stop dense, mixed-use development. But go to Getting It Right For West Seattle and decide for yourself.