Tag Archives: intersection

What Do I Think of the Diverging Diamond Interchange?

 

By Dom Nozzi

Febuary 2, 2017

Superior, Colorado built a “diverging diamond” interchange that opened in October 2015. It was only the second such interchange to ever be built in Colorado. Traffic engineers are imagessinging its praises throughout the nation. A newspaper article appearing in the February 2, 2017 edition of the Boulder Daily Camera fawned over the fantastic new addition to the region’s transportation system.

I am not joining the engineers or the newspaper in their love affair with the design.

Instead, I find such designs a colossal waste of money – money that could have been used for, say, transit. They are also a colossal waste of land. An entire city could fit inside one of these intersections.

The diverging diamond is a boondoggle for those reasons. But it is also a blunder because they promote increased per capita car travel. Why? In part because they are nearly 51df393d218c6-imageimpossible to cross by foot or bicycle. And in part because in the long run they will further disperse land development in a more sprawling way. Those increased distances will make it increasingly impractical to walk, bicycle or use transit.

Ironically, the major justification for the car-only design is that it briefly reduce intersection congestion, which will initially save a few seconds of motorist time (think of the fiscal irresponsibility of spending millions of public dollars spent to save a few seconds temporarily). Ironic because by artificially inducing more car trips than would have occurred had the diverging diamond not been built, the design will lead to MORE traffic congestion and MORE time delay for motorists in the long term (both at their location and areas in the region).

To hide the embarrassing fact that the millions spent ($14 million in this case) to briefly save a few seconds of time, the publicly proclaimed explanation is that it will improve safety. For the conventional traffic engineer, “improved safety” actually means that motorists can now drive faster and more inattentively with less fear of crashing. No mention is made of the fact that the intersection is much less safe for pedestrians or bicyclists, or that faster, less attentive driving is very dangerous for everyone.

The diverging diamond, therefore, is an excellent example of the century-long failure by conventional traffic engineers to understand induced car trips that are created by (briefly) reducing traffic congestion with these designs. There is a reason, after all, that many researchers repeatedly urge us to understand that it is impossible to build our way out of congestion. It is like loosening your belt to solve obesity.

But wait. There’s more.

Not only is the diverging diamond a boondoggle in the above mentioned ways. It also damages our world by adding more auto emissions into our air (by increasing per capita car trips) and reducing potential tax revenues in the region (by encouraging dispersed rather than compact land use patterns).

Future generations will shake their heads in disbelief over why our generation built these monstrosities.

There is one tiny upside to this overwhelmingly negative idea: it produces future jobs for people hired to remove these mistakes after we regain our senses.

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How Do We Preserve Small Town Ambiance?

By Dom Nozzi

May 15, 2015

The most sought after, popular form of community for Americans today is the small town.

When we ask many community activists to describe what they seek for their community, they state that they are trying to preserve or restore a “small town feel.”

How do we do that?

For most NIMBYs and assorted anti-development champions of happy cars, it is to fight against density, tall buildings, and congestion.

But I believe this is counterproductive in creating a small town ambience.

I agree we shouldn’t allow skyscrapers. My limit is five stories.

beacon hill bostonBut the most effective way to preserve or restore the small town feel is to keep roads and intersections modest in size, and avoid sprawling low density.

Pushing for lower densities and fighting to reduce densities, by contrast, almost always compels a community to build monster roads and intersections.huge turn radius for road

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About Traffic Congestion and Bicyclists at Intersections

By Dom Nozzi

October 15, 2014

Congestion

I serve as a member of Boulder, Colorado’s Transportation Advisory Board (TAB). In the fall of 2014, I suggested that TAB take a position opposing the City transportation objective that seeks to limit increases in traffic congestion (an objective that I think is undesirable for several reasons – see below).

The Chair of the Board at the time questioned my judgment by saying it was inappropriate for TAB to revise or remove the congestion objective without getting input from citizens or businesses. The City had engaged in a multi-year process of gathering comments from citizens, and there was no call for revising or removing the congestion objective, I was told.

I responded by saying that citizen comments are not always the basis for crafting a new objective for the City’s Transportation Master Plan (TMP), revising an objective, or removing an objective. For example, it was probably not citizens who called for an objective seeking a “reduction in VMT to 7.3 miles per capita and non-resident one-way commute VMT to 11.4 miles per capita.” Or “80 percent of all residents living in complete neighborhoods.” Or “reduce SOV travel to 20 percent of all trips.”

Instead, the task of Council, staff, and advisory boards is to use their knowledge of professional research tempered with citizen desires or comments to craft objectives that will achieve overall quality of life desires of citizens.

I pointed out that the congestion objective flies in the face of several objectives of Council, citizens, and professional research because it results in the following:

  • Increased GHG car emissions and gas consumption (citizens have often stated that they would like a reduction in GHG emissions and gas consumption)
  • Increased SOV travel
  • Increased regional (in-commute) car trips to Boulder
  • Increased levels of dispersed sprawl (citizens have often stated that they would like a reduction in sprawl)
  • Reduced amounts of bicycling, walking and transit (citizens have often stated that they would like an increased number of trips by bicycling, walking and transit by Boulder residents)
  • Increased speeding (citizens have often stated that they would like a reduction in speeding)
  • Promotion of Big Box retail, and a reduction in locally-owned small businesses (citizens have often stated that they would like a reduction in Big Box and protection of small, locally-owned businesses)
  • Harm to residences and local businesses due to big, high-speed roads and the nuisance and danger of high-speed, high-volume car traffic (citizens and business owners have often stated that they would like an improvement in conditions for residences and local businesses)
  • Increased social isolation (reduction in social capital) (citizens in Boulder have often stated that they would like more neighborliness and sociability)
  • Road narrowing is strongly discouraged (citizens in Boulder have often expressed a desire for road narrowing. One example was at the Walk/Bike Summit, where many called for road narrowing.)

Given the above, revising or removing the congestion objective, I noted, strongly supports expressed citizen and business owner desires, and it is therefore appropriate for staff, Council, or advisory boards to call for such a change.

Bicyclists Using Intersections

The chair also stated, in response to staff proposals that a second left-turn lane be added at intersections, that bicyclists would prefer less congested intersections because like motorists, they want to be able to make left turns or proceed forward without missing green lights at intersections.IMG_2987

I responded by pointing out that as a lifelong bicycle commuter and academic researcher regarding bicycle travel, I can unequivocally state that low-speed two- or three-lane roads are far safer and more comfortable for bicyclists than roads widened to several through lanes or multiple turn lanes. An enormous number of bicyclists would feel extremely uncomfortable on big, multi-lane roads or at huge, multi-turn lane intersections, and would therefore never consider using such roads or intersections on a bike.

Nearly all bicyclists pass a waiting line of motorists and queue up at the front of the waiting line when waiting for a signal light to change (partly for safety reasons). Therefore, a long line of waiting cars typically does not force bicyclists to miss signal lights.

Free-flowing car traffic (briefly) created by widening a road or intersection induces a very large “speed differential” between cars and bicyclists. High speed cars are extremely uncomfortable and unsafe for bicyclists. Therefore, an intersection enlarged to two left-turn lanes (to reduce congestion) is extremely undesirable to bicyclists.

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Gigantism Versus a “Small Town Feel” in Boulder Colorado

By Dom Nozzi

August 5, 2013

A great many citizens Boulder, Colorado admirably seek to retain or restore a “small town feel” (or “ambiance”) in our community. The most significant transportation action (or, arguably, ANY action) a community can take to obliterate that “small town feel” and instead create a feeling of placeless sprawl or “big city feel” is to build oversized roads, intersections, and parking lots.

Tragically, this is precisely what Boulder has done too many times in its frequent (and highly counterproductive) efforts to “reduce congestion” or “promote free-flowing car traffic.” Boulder has oversized a great many of its roads and intersections (and required developers to build too many oversized parking lots), which powerfully admin-ajax (3)induces excessive car trips, regional sprawl, local government financial woes, a large increase in traffic injuries and deaths, a large impediment to bicycle, walking, and transit trips, and much higher levels of fuel consumption and air emissions (despite the conventional wisdom).

The end result of this ruinous pursuit of free-flowing car traffic is a loss of that “small town feel” – that “human scale” – that so many in Boulder seek to protect and retain.

The much more progressive way to address traffic congestion is not to reduce it (which is nearly impossible given the HUGE space-hogging nature of cars, and given a healthy city), but to create ALTERNATIVES to congestion so those unwilling or unable to tolerate it can avoid it (via alternative routes, traveling at non-rush hour times, driving on routes optimized by pricing, or traveling by bicycling, walking, or transit).

The provision of “bus queue lanes” or “protected bicycle tracks” should not be at the expense of removing on-street parking or by widening a road. Instead, such facilities should only be installed by replacing existing car travel lanes.

In sum, the primary task of the urban designer is to control size. By not controlling size – in this case, the size of transportation facilities – the resulting gigantism

MINOLTA DIGITAL CAMERA

MINOLTA DIGITAL CAMERA

obliterates that small town feel that so many of us love.

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What’s with the Double Standard on Right-Sizing a Road?

By Dom Nozzi

Over the past several weeks, there has been an avalanche of letters attacking the City proposal to right-size Folsom. Hundreds of opponents filled the Council auditorium to denounce the idea at multiple meetings. The complaints have been repetitive: There are no metrics telling us whether the projects have succeeded or not! Not enough involvement by stakeholders such as businesses and neighborhoods! Not enough public involvement! No studies showing whether they will work! It will cause terrible congestion and air pollution! No before and after studies! Pro-bike bias! Waste of a huge Folsom-N.-rendering_web-400x267amount of money!

First of all, citizens should know that City staff has done many studies and public meetings that are alleged to be lacking. Far more than most other transportation projects conducted in the past.

Second and much more importantly, I am utterly shocked by the double standard here. I have been working professionally and academically in transportation for over 30 years, and I have never seen this level of enraged opposition, calls for studies, and requests for more public input. One would think that the City was proposing to bring about the end of the world.

The double standard is that I don’t recall ANY opposition when the City has proposed to install a second left-turn lane at an intersection (which has been done several times in Boulder), among many other pro-car projects. No calls for studies. No demands that stakeholders be involved. No metrics telling us if the double-left had the intended benefits a year later. No before and after studies. No cries that it will increase air pollution or car dependence. No demands that the double-left turn be tested first before it is made permanent. No whining that the double-left turn is a big waste of money (for the record, double-left turns cost a lot more money, generally, than right-sizing).

Few people, if any, attend meetings to oppose such an enormous expansion of an intersection.

I would think that the outcry from a proposed double-left would be furious. After all, double-left turns increase air pollution, car trips, local taxes, regional car trips, car crashes, speeding, inattentiveness, injuries and deaths. They reduce walking trips, biking trips, and transit trips (because the intersection is now much more dangerous to walk through or bicycle through). They are toxic to businesses and homes near the intersection.

double left turn lane intersection boulderBy striking contrast, national studies show that right-sizing reduces air pollution, speeding, inattentiveness, car trips, car crashes, injuries and deaths. They increase walking trips, biking trips, and transit trips. They improve the health of retail and residences (I understand that many businesses in Seattle now ask that their street be right-sized after they have seen their competitors benefit after their streets were right-sized).

Yet in Boulder, we see furious opposition to right-sizing and hardly any objection to a proposed double-left turn. And by the way, unlike right-sizing, double-left turns are NEVER tested first to see if they will work. They are just “rammed down our throats,” as many right-sizing opponents oddly tell us about right-sizing.

Making a road change that eases bicycling and walking is met with fury. Making a road change that eases driving (and discourages bicycling and walking) is met with silence.

Given this, one would think that there is a very pro-CAR bias in Boulder. One also has to ask: Who needs enemies when we have ourselves?

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The Folly of Double-Left Turn Lanes

There is a troubling, counterproductive “solution” that continues to be employed for addressing congested intersections – even in communities that are otherwise progressively promoting transportation choice. The “solution” is to add a second left turn lane to an existing left-turn lane when there is a perception that the number of motorists waiting in the single left-turn lane has grown too large.

Conventional traffic engineering claims that creating a double-left turn lane at an intersection is an double left turn lane intersection boulder“improvement” that will reduce greenhouse gas emissions by reducing congestion. And that a double left turn does not conflict with the transportation plan objective of promoting pedestrian trips.

On the contrary, I believe that double-left turn lanes will INCREASE emissions and will REDUCE pedestrian trips.

Double left-turn lanes cause serious problems for scale and safety for bicyclists and pedestrians, but have been shown to be counterproductive even if we are just looking at car capacity at an intersection. Adding a second left turn lane suffers significantly from diminishing returns. That a double-left turn does NOT double the left turn capacity – largely because by significantly increasing the crosswalk distance, the walk cycle must be so long that intersection capacity/efficiency (for cars) is dramatically reduced.

Cities across the nation are facing severe transportation funding shortfalls, yet at the same time, they are often building expensive and counterproductive double-left turn lanes.

Why? Probably because of the absurdity that transportation capital improvement dollars are in a separate silo than maintenance dollars, and that the former dollars are mostly paid by federal and state grants.  Of course, double-left turn lanes also destroy human scale and obliterates the ability to create a sense of place, but those are much more difficult arguments to make.

A colleague of mine adds that double-left turn lanes are an abomination. He adds that “they are a sign of failure: failure to provide enough street connectivity, so that when drivers do come to an intersection, it is gigantic, so it can accommodate all the left turns that had not been allowed prior to that point. Many trips on extra wide arterials are very short, and involve three left turns: one left turn onto the arterial and one left turn off the arterial: there trips could and should be made on connected local streets.”

How can a city claim it is short on transportation funding when it is building such counterproductive facilities? Double-left turn lanes…

  • Increase per capita car travel and reduce bike/pedestrian/transit trips.
  • Increase GHG emissions and fuel consumption.
  • Induce new car trips that were formerly discouraged (via the “triple convergence”).
  • Promote sprawling, dispersed development.
  • Discourage residential and smaller, locally-owned retail.

Cities need to draw a line in the sand: Place a moratorium on intersection double-left turn lanes and eventually removal of such configurations. Double-lefts are too big for the human habitat. They create a car-only atmosphere.

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Forcing Wal-Mart to Increase the Size of Roads or Intersections

By Dom Nozzi

A common strategy for “mitigating” (“reducing,” for those of us who speak Plain English) the negative traffic impacts of a proposed Big Box retailer such as Wal-Mart is to require the retailer to pay to widen roads or intersections that serve the store. Doing so is thought to do two things. First, it is thought that such “improvements” will allow the community to avoid traffic congestion caused by the giant retailer. Second, there is a dream that doing so will stop the retailer because the company will not be able to afford to “improve” the road/intersection.

A quick aside: Calling a road or intersection widening an “improvement” is inappropriate. While there might be a brief improvement for motorists, such widening is a degradation for bicyclists, pedestrians, and transit users.

Is it a good idea to require a proposed Big Box retailer to pay for a bigger road or intersection? In my view, doing so is the worst possible thing that can be done for a proposed retailer. “Easing traffic flow” is precisely what a huge retailer wants and needs, since they are striving to serve a regional population of consumers. They are striving to make things as convenient as possible for as many motorists as possible. Therefore, anything which “eases” traffic flow is an enemy of nearby neighborhoods, the community, and overall quality of life (largely because it would induce huge volumes of new car trips from all over the region – car trips that would have never occurred had the road or intersection not been enlarged).

Especially in town centers, streets must be designed for modest, low-speed car travel. Traffic calming, on-street parking, landscaped bulb-outs and landscaped medians can be very useful. A connected street network is essential, as it slows car speeds and provides travel route choices.

Effective, quality low-speed design obligates motorists to pay attention when they drive. To be careful when they drive. Using the conventional, free-flowing design model, motorists are encouraged to drive too fast, too recklessly, too inattentively. While driving in such “forgiving” places, motorists are enabled to put on make-up. Talk on the cell phone. Eat a sandwich.

Why? Because the street design allows the motorists to pay less attention. The result is dangerous, inattentive, high-speed car traffic.

Oversized streets or intersections make an area totally unwalkable. Quite unsafe, particularly for seniors and children. It becomes much more of a car-only place. It becomes, ultimately, an Anywhere USA indistinguishable from any other strip commercial area in the nation.strip2

Essentially, the street design vision of a community – particularly its town center — should be to create a “Drive To” place that is walkable and safe, rather than a “Drive Through” place that enables large-volume, high speed traffic. Only big retailers want (and need) the latter.

As for the thought that big retailers will be stopped if expensive road and intersection widening is required, don’t fool yourself. Big retailers have big pockets. Typically, even relatively expensive road and intersection modifications are pocket change for the big retailer looking to cash in on a prime market.

 

 

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