Those of you that have driven in the great state of Utah know that things are a little different here. The streets are generally wide, the blocks enormous and the drivers all have
four wives someplace to be right now. The first two can be traced back to Mormon leader Joseph Smith’s plat for the city of Zion – a piece of city planning that recently won an award from the American Planning Association. When the Mormon pioneers settled in Utah, they implemented that plan in nearly every settlement from Logan to St. George.
From a planning point of view, the plat has good aspects and bad – the good being the easy access to all points of the city because of the regular grid pattern – the bad being the utter misery inflicted on pedestrians by massive street crossings and lengthy blocks.
Of course, as in many American cities, the plan kinda fell apart as suburbs developed. Big blocks became HUGE blocks – a mile or more in length – and the streets in turn became congested as all traffic funneled onto a few major roads.
But the pioneering nature of Utahns seems to have found a few potential solutions. Well, pioneering if you mean stealing ideas from other places…
The key component of all of these alternative intersections is to reduce the impact of left turn movements on the ability of straight-line traffic to move through an intersection.
Let us first visit the intersection of Bangerter Highway and 3500 South Street (yeah, so that’s a weird street name – here’s an explanation). Bangerter Highway is a major north-south artery on the west side of the Salt Lake Valley. It probably should be a limited-access freeway, but the money apparently wasn’t in the budget for that, and instead the highway is saddled with numerous at-grade intersections. These intersections caused significant delays and accidents.
Channeling that aforementioned pioneer spirit, the Utah Department of Transportation (UDOT) stole an idea from Mexico (or New Jersey – no one is certain) known as the Continuous Flow Intersection (CFI). Implemented at 3500 South and Bangerter Highway, this is the first of several “alternative” intersections in Utah, and has the first in a series of fun little animations produced by UDOT. I like to watch these with a jaunty Super Mario Brothers-esque synthesizer soundtrack playing in my head.
Here, the left turn is moved ahead of the intersection, placing left-turning drivers on the “wrong” side of the intersection. This allows straight traffic to move at the same time as the left-turning traffic.
Moving south in the Salt Lake metro area, we find the Pioneer Crossing interchange in American Fork. Here, UDOT took a formerly rural 2 lane crossroad with on- and off- ramps and completely overhauled the facility with multiple lanes crossing to create an intersection known as the Diverging Diamond. Not surprisingly, this particular form had been used before – in the wilds of France. At a transportation engineering conference in 2003, the idea was introduced in the United States and implemented in Missouri and Utah by 2010.
In this case, instead of placing just left-turners on the wrong side, all traffic is inverted. Using two intersections – one at each end of the overcrossing – engineers have allowed left-turning traffic to continue to the freeway unimpeded.
Note the realism in this video – the Mini Convertible driver never once used a turn signal.
And finally, something that our industry friends in Detroit may recognize – UDOT calls it the ThrU-turn, but let’s be honest, it’s a Michigan Left. Like the CFI, the ThrU-turn is designed to separate left-turn movements from the through traffic to allow for greater and more efficient flow – left-ers continue through the intersection, then make a U-turn after the light (get it – ThrU-turn?). This particular design has been around significantly longer than the previous two examples, first being used on 8 Mile Road in Detroit in the early 1960s.
Now, back to that thing about Utahns being fast drivers – I have no idea where it comes from, other than ever since that months-long journey across the Plains to get here, those pioneer types are thrilled to be moving at a more urgent pace – these alternative intersections will hopefully allow that pace to continue.
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