Due to the policy of building freeways through communities and the resulting highway revolt, most U.S. metro areas now have unfinished freeway networks. With the economy and traffic congestion growing, it is time to consider filling the missing links in these freeways. Fortunately, with the advent of tunnel boring machines (TBMs), it is now possible to cost-effectively build tunnels under densely populated neighborhoods. These tunnels can help complete unfinished freeways. These tunnels can also encourage transit service by offering free usage of premium lanes at no charge. Most importantly, these tunnels will have no adverse impacts on the neighborhoods above them.
Tunnels have proven an effective alternative to surface freeways across the world. For example, to protect Versailles, the French built a highway tunnel under the historic estate. The tunnel keeps traffic flowing while protecting the national landmark. The Port of Miami built a tunnel, allowing trucks to access the Port of Miami and bypass city streets. This tunnel reduced cut-through traffic and helped rejuvenate city neighborhoods. In Washington State a tunnel is being constructed to replace the seismically deficient SR 99. In addition to providing a better travel alternative, the tunnel will allow better connections between Seattle’s neighborhoods and Puget Sound waterfront. While Seattle TBM broke last year delaying the project, the TBM has been fixed and construction is progressing.
Building tunnels is not cheap. Costs typically range from approximately $100-$500 million per lane mile. However, building surface roads in such areas can often reach $50 million or more per lane mile to build an elevated section if right of way is needed. Further, the lost economic costs of congestion are much higher than $500 million. In Chicago alone, reducing congestion by 10 percent would save business $1.3 billion per year in business-related expenses and $455 million in labor market expenses. This assumes a 10 percent improvement; 20 percent would double the benefits.
Which metro areas in the U.S. could benefit from tunnels? The largest metro areas such as Chicago and Los Angeles could benefit from multiple tunnels, between 2 and 7, depending on the cost-benefit analysis. Other large regions such as Atlanta, Dallas, Houston and Washington D.C. could benefit as well. Tunnels are not appropriate in all situations but they are an important key to reducing urban congestion.