The High Five Interchange is one of the first five-level stack interchanges built in Dallas, Texas. Located at the junction of the Lyndon B. Johnson Freeway (Interstate 635, I-635) and the Central Expressway (US Highway 75, US 75), it replaces an antiquated combination interchange constructed in the 1960s. The $261 million project was started in 2002 and completed in December 2005. It was designed by the HNTB Corporation and built by Zachry Construction Corporation. The interchange is considered by Popular Mechanics to be one of "The World's 18 Strangest Roadways" because of its height (as high as a 12-story building), its 43 permanent bridges, and other unusual design and construction features. In 2006, the American Public Works Association named the High Five Interchange as "Public Works Projects of the Year". Description The High Five Interchange, north of downtown in Dallas, Texas, is a massive five-level freeway interchange. It is the junction of two major highways carrying heavy rush-hour traffic, the Lyndon B. Johnson Freeway (Interstate 635) and the Central Expressway (US 75), and is the first five-level stack interchange to be built in the city. It replaces the antiquated three-level modified cloverleaf interchange built in the 1960s, which caused a severe bottleneck by narrowing US 75 down to two lanes at the junction of the two highways. The looped ramps of the cloverleaf forced motorists to slow down drastically, backing up traffic. Left-hand exits contributed to the congestion. Further, its two frontage roads were not directly connected to each other, making local access difficult. Alluding to the celebratory gesture, the "High Five" name refers to the five flyover ramps that tower over the landscape, handling the left-turn movements. The interchange is as high as a 12-story building, and includes 43 bridges spread across five levels (the "High Five"), 710 support tiers, and 60 miles of additional highway. The highest ramps are above ground. The lanes of US 75, which are on the bottom level, are below ground level, giving the structure a total height of 120 feet from bottom to top. As part of the project, I-635 was widened to include four dedicated high-occupancy vehicle lanes (HOV lanes) that are barrier-separated and reversible. The roads on the five levels are: Level I: US 75, a six-lane highway, three lanes going each way Level II: The junction of the two six-lane frontage roads, each having three through lanes in each direction,