Staying Connected Above or Below – Seattle SR-99 Tunnel

Over 134.7 million U.S. business travelers pass through transportation hubs every year including airports, light rails, and highway tunnels when commuting. Exactly half of those travelers use a cell phone during their commute, revealing the importance of connectivity during travel.

A few years ago, periodic wireless dead zones during transit were accepted by consumers but now the expectation for seamless connectivity has risen significantly. Currently, densely populated indoor and outdoor open areas are typical characteristics of many airports and transit systems which pose challenging problems in providing commuters with uninterrupted coverage. Luckily, many of the new mass transit construction projects are keeping pace with these expectations, baking connectivity directly into the design.

The Alaskan Way Viaduct replacement tunnel, also known as SR-99, is a perfect example of how cities are rising to the occasion in providing excellent transportation capabilities and coverage despite being 200 feet below ground and two miles long. The tunnel also features 13 miles of fiber optic cables, 95 miles of electrical wiring, 15 miles of lights, and 8 miles of heat detectors constantly monitoring air conditions within the tunnel for an incredible transit experience. The double-deck highway tunnel carries two lanes of traffic in each direction and almost 110,000 vehicles each day. In order to keep SR-99 commuters safe and connected, the tunnel needed to be one of the “smartest” ever built.

With strong connectivity for commuters a top priority in the $1.4 billion tunnel, the Washington State Department of Transportation (WSDOT) relied on ADRF’s ADXV distributed antenna system (DAS) to enhance coverage for all major carriers on the network. ADRF’s DAS system provides travelers with strong LTE connection for cellular calls, allowing them to avoid dropped calls upon entry and maintain service inside the tunnel in the event of an emergency. WSDOT has prioritized cellular connectivity for travelers by building smart systems capable of utilizing DAS networks to keep travelers safe and connected within every inch of the expansive underground tunnel.

ADRF’s ADXV DAS solution helped make SR-99 one of the greatest early infrastructure advancements in a smart city to date, supporting subscribers of all wireless service providers with a compact, simple design that allows for modular, future proof solutions should any improvements need to be made in the future.