Tag Archives: double left turn lane

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.

Advertisements

Leave a comment

Filed under Bicycling, Transportation

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.

Leave a comment

Filed under Bicycling, Sprawl, Suburbia, Transportation