When the City of Dallas developed its Bicycle Transportation Plan (working with local cycling organizations), they took a “clean-slate” design approach. There are basically three bicycle facility designs: Street separated trails, on-street bike routes (shared lane), and on-street bike lanes (segregated facility). Each has its preferred application scenario.
From a traffic engineering perspective, a Bike Lane is classified as a “bicycle control device”, whose job is to channel EXISTING bicyclists out of the way of motor vehicles. The popular notion is the opposite, that bike lanes are designed to attract cyclists, but that is not how they function or why they were designed. To install bike lanes that function, you need a minimum of two pre-existent conditions: high volume of cyclists in a concentrated area (i.e., a large college campus and surrounding area), and sufficient road width to accommodate a lane.
Most urban thoroughfares and collectors in Texas have 11’ vehicle travel lanes (a foot narrower than the current recommended practice). The recent TxDOT/UT Austin study on bike lanes is premised on 12’ travel lanes and 3' bike lanes (two feet narrower than the minimum recommended width). Here’s how their before and after study looked for a divided thoroughfare: without bike lanes 12-12-12----12-12-12, with bike lanes, 3-11-11-11----11-11-11-3.
On a typical Dallas (or San Antonio, Houston, Austin, Ft Worth) urban thoroughfare, the cross-section looks like this: 11-11-11----11-11-11. Attempting to install bike lanes on such a street results in vehicle travel lanes that are only 9.5 feet wide (3-9.5-9.5-9.5----9.5-9.5-9.5-3), taking stripe width and curb offset into consideration, or almost 20% narrower than current recommendations. This creates traffic conflicts that can lead to not just property damage, but can even endanger lives (especially the lives of cyclists as cars are “pushed” into the available space). Further complicating the bike lane installation is the reality that most Dallas thoroughfares have a curb and gutter construction that makes the out foot of the lane dangerous for cyclists due to the frequent paving gaps between the asphalt road-bed and the gutter-curb, reducing the 3’ lane to an effective width of two feet.
To install bike lanes of the recommended 5’ width, the street cross-section now looks like this, 5-14-14----14-14-5, dropping a full lane of traffic in each direction. When you consider that people tend to ask for bike lanes on streets that are already overcrowded, you can see how the problems are exacerbated by the attempts at alleviation.
I haven’t even mentioned the problem with banning all on-street parking on streets with bike lanes and the resulting backlash from homeowners and businesses.
So rather than install a few miles of bike lanes, what Dallas did was create a 400 center-line mile signed bicycle route system on local, low volume streets that parallel thoroughfares. Where a thoroughfare (or bridge) is required, the City committed to build wide-outside-lanes to create extra room for cyclists and motor vehicles to share the road. On new road construction (and reconstruction when right of way is available), depending upon posted speeds, the roadway will look like this; 14-11-11----11-11-14, or 15-11-11----11-11-15.
So, long answer, instead of striping 50 lane-miles of bike lanes (.05% of the City's streets), the City signed 800 lane-miles of bike routes (10% of the City's streets), resulting in a far more comprehensive bike plan than a simple bike lane system that improved real conditions for cyclists without degrading conditions for the dominate motorist traffic. Mind you, this approach works best in a city with a complex street grid system dating to the late 19th and early 20th centuries. Suburbs have a more difficult task.
(Updated July 9, 2008)
2 comments:
I am a bicyclist in the Houston area. The bike lanes in Houston are not maintained very well. What good is it to have a 3 ft. lane on the street with all of the road trash washed there and pot holes? It appears once the bike lane marker line is painted it is never re-marked again. I think they used water color paint to mark the lanes.
Rick, you touch upon bike-lane problems I didn't mention (not wanting to fall into rant mode). Wide-outside-lanes are preferred by many cycling advocates because the sweeping motion of the occasional car/truck keeps the road edge much cleaner. Cities that rely on bike-lanes don't use sand and gravel during the winter as Texas cities do (not sure about Houston). I've seen abandoned furniture and TV sets sitting bike lanes. With the common curb/gutter construction of most urban streets, there is a potentially dangerous seam 1' from the curb where the concrete ends and the asphalt begins. In practice, this narrows the street 1', and yet the bike lanes seldom account for that.
In Houston, they do use water-based paint. Houston is an air-quality non-attainment zone, and so the EPA mandates non-volatile paint. Thermoplastic could be used (like they use for "serious" traffic marking), but it costs too much (they say).
I watched with interest the development of the Houston Bike Plan. Bike-Fed and TxDOT (with Wilbur-Smith's willing/unwilling assistance) essentially conspired to force a model upon Houston that was inappropriate for the city... but it worked in Madison, Wisconsin!
See "Cycling Inferiority Complex" to better understand TxDOT and Bike-Fed's thought process.
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