Welcome to Thursday Trivia where we offer up a historical automotive trivia question and you try and solve it before seeing the answer after the jump. It’s like a history test, with cars!
This week’s question: What iconic freeway structure nicknamed “The Stack” is a designated Civil Engineering Landmark?
If you think you know the answer, make the jump and see if you are right.
If you’ve been driving for any length of time at all you’ve no doubt come across feats of highway engineering both laudable and laughable. When it comes to the U.S. system of highways and freeways, that engineering isn’t all that old. Here in what’s considered the most auto-centric city in the country, Los Angeles the first freeway was the Arroyo Seco Parkway, which opened in 1940 replacing Figueroa as the main conduit between downtown and Pasadena.
That snake-like ribbon of concrete hasn’t changed much in its 75 years of existence, still featuring treacherous on and off ramps and roller coaster-like curves. It’s a blast to drive and appreciably scenic for much of its length, although your probably won’t want to do much reflection on the chaparral covered Monterey Hills that border the Parkway as you’ll need to pay attention to those curves and the merging traffic.
The Parkway itself is a marvel, however its southernmost terminus, where it becomes the Harbor Freeway, there lies an even greater achievement, one that has gained a number of nicknames, and which was such an impressive feat of engineering and design that it has been designated a Civil Engineering Landmark by the Society of Civil Engineers. That of course is the tangle of transitions known officially as the Four-Level.
From KCET.org:

The Four Level, also known as the Stack, gets its name from its multi-tiered structure that separates traffic heading in each direction into dedicated lanes. On the bottom level are curved ramps for those changing from the 110 freeway to the 101. One level above is the main trunk of the 110 freeway, named the Arroyo Seco Parkway north of the interchange and the Harbor Freeway south of it. On the third level are the arcing flyover ramps carrying traffic from the 101 freeway to the 110. Finally, on the fourth and top level is the main trunk of the 101 freeway, named the Hollywood Freeway to the west and the Santa Ana Freeway to the east.
This design, now the basis of freeway interchanges around the world, was a marked improvement over the previous model. Older cloverleaf interchanges were less expensive and kept a lower profile, but they also tended to slow traffic and were more dangerous. They required motorists both entering and exiting a freeway to merge into one lane. (The 405 freeway’s interchange with Wilshire Boulevard in Westwood is an example.) Stack interchanges, on the other hand, kept the eight directions of traffic separate until the final merge.

Plans for The Stack were unveiled in 1944 and the $5.5 million project was completed five years later. It wasn’t immediately put to use however as the connecting Hollywood, Harbor and Santa Ana freeways weren’t yet completed. In 2006 it was officially named the Keene Interchange in honor of former KNX traffic and weather reporter Bill Keene, however locals still refer to it as either the Four-Level, or just The Stack.
Image: KCET.org