Tuesday, July 30, 2013

Alexandria VA Creates Dangerous Door-Zone Bike Lanes

The City of Alexandria, Virginia has just resurfaced Quantrell Avenue, a short neighborhood street in the city's far west end, and is in the process of striping the roadway to create treacherous, substandard, and completely unnecessary door-zone bike lanes.



Quantrell Avenue runs through a relatively high-density residential neighborhood for only one or two blocks--between the stub end of Lincolnia Road (where it's also fed by a one-way local exit ramp from I-395) and N Beauregard St (a four-lane arterial with a wide landscaped median that provides a vital east-west bicycling alternative to I-395).  I haven't checked how Quantrell Ave is functionally classified by the City, but it primarily provides access to the mutlifamily dwellings lining Quantrell Ave and two neighboring streets (N Armistead St and the stub end of Lincolnia Rd) while also serving as a parking facility for the many vehicles of local residents that cannot be accommodated in the adjacent residential parking lots.

Quantrell Ave is served by both Metro and DASH buses, but every bus stop is used for on-street car parking, forcing the buses to stop in the travel lanes and block all other same-direction traffic.  While the traffic volume on Quantrell Ave is fairly high, due to the adjacent residential density, the street has a 25 MPH posted speed limit, and average vehicle speeds are much lower than that, due to the narrow roadway and limited sight distances, the many vehicles entering and exiting parking spaces and parking lots, stopped buses, the stop signs at Lincolnia Rd and at N Armistead St, and the traffic light at the intersection with N Beauregard St.

The Quantrell Ave roadway is just over 42 feet wide from curb face to curb face.  As seen in this 
Google Maps street view, the street accommodates parallel on-street parking at the curbs and one travel lane in each direction.


After the recent resurfacing, Quantrell Ave was striped last week with the left bike lane stripe a mere 12 feet from the curb face, providing a 5-foot wide bike lane space adjacent to a 7-foot wide (substandard) parking lane.  While these dimensions may still be the minimum sanctioned by the AASHTO Guide to the Development of Bicycle Facilities, this space is seriously inadequate wherever parking density and turnover is high, as along Quantrell Ave.

Note the red yard stick on the pavement in the photos.  These photos were taken on July 28 prior to the installation of any bike lane symbols.  On July 29, directional arrows to guide bicyclists were installed in the bike lane space.  The bike lane symbols will probably be installed very soon, if not today (July 30).

As documented by John S Allen here, the door zone of most motor vehicles found parked on U.S. streets ranges from 110 to 120 inches from the curb face, with the door zones of some vehicles even wider. With the combined 144 inches of bike lane and parking lane space on Quantrell Ave, bicyclists must keep their tire track no more than approximately 12 inches to the right of the left bike lane stripe for the right edge of their handbar to barely clear the majority of opened car doors.  Riding this close to car doors, however, leaves no safety margin for either the bicyclist being startled by a suddenly opened car door or for the bicyclist's natural wobble, not to mention any momentary inattention by the bicyclist.

On Quantrell Ave, however, this unsafe situation is compounded by the striping of very narrow 9-foot travel lanes, the minimum width allowed by the AAHSTO Green Book.  (Indeed, if the two travel lanes were any wider than 9 feet, the new "minimal width" bike lane and parking lane combination would be precluded by all accepted bike lane guidance.)  Consequently, if a bicyclist is suddenly startled by an opening car door, s/he could readily be struck by an overtaking vehicle in the adjacent travel lane.

To avoid the very real threat of a "dooring" collision, bicyclists should always track at least five feet from parked motor vehicles, placing their right handlebar at least four feet away.  To do this on Quantrell, bicyclists must either straddle the left bike lane stripe, risking a side-swipe collision with motor vehicles overtaking them in the narrow 9-foot travel lane, or ride entirely within the travel lane, ignoring the bike lane  completely and risking the wrath of motorists who are upset that the bicyclist is not in his or her "proper" place.

The new bike lanes on Quantrell Ave have no utility or useful purpose.  The typical motor vehicle here is not traveling much faster than most bicyclists and is often slowing or stopping for parking, turning, or entering vehicles; for stopped buses and crossing pedestrians; and for the traffic signal at N Beauregard St.  No connecting bike lanes exist or are safely feasible on the two connected neighborhood streets (namely, N Armistead St and the stub end of Lincolnia Road), and the City has no current plans to install bike lanes on N Beauregard St, a vital four-lane arterial for bicycling with a wide landscaped median and a 35 MPH posted speed limit and where bike lanes, at least in the uphill direction, are both warranted and relatively feasible.

The best solution to accommodate bicycling on Quantrell Ave is both simple and practically free:  Rather than install bike lane markings in the door zone, install shared-lane markings (aka sharrows) centered in the recently narrowed 9-foot travel lanes, to direct bicyclists to use the roadway as lawful drivers and completely clear of the door-zone hazard.  This solution would significantly benefit pedestrians and bus riders by helping to calm traffic.  It would also reduce the risk of car-bike crashes at intersections and driveways, by improving the visibility and vantage of bicyclists on the roadway at those crucial locations.  The risk of roadway crashes between bicyclists and pedestrians would also be reduced, both near and between intersections.

One simple change to reduce motorist speeds and improve safely for everyone on Quantrell Ave would be to install a stop sign for the traffic that enters Quantrell from the I-395 exit ramp.  Currently, this traffic is given the right of way over both traffic entering Quantrell by turning left from Lincolnia Rd and traffic turning right from southbound Quantrell onto Lincolnia.   An alternative, but more expensive, solution would be to install a small roundabout at this intersection and require all entering traffic to yield to the traffic that is already in the roundabout.

A decade ago, before the advent of shared-lane markings, such door-zone bike lane installations were often (wrongly) excused as an earnest, if misguided, attempt to accommodate traffic-averse bicyclists.  With the widespread use of sharrows, however, the Quantrell Ave bike lanes can be seen for what they truly are; namely, traffic-engineering malpractice.

The City of Alexandria should promptly fix this treacherous facility before bicyclists are seriously injured by it.

2 comments:

  1. Hmmm... I realize that bike lanes that are half in the "door zone" are not perfect, but I enjoy riding the bike lane sections of Commonwealth Ave much more than I do the sharrowed sections of that street.

    In these lanes, I ride outside the door zone and do notice that some others ride in the door zone. By contrast, on a sharrowed traffic lane with parking, I ride outside the door zone and do notice that some others ride in the door zone.

    OK, maybe I'm kidding about the contrast. My point is that, in practice, staying outside the door zone has more to do with education than with lane design. My other point, as always, is that the best lane design is the one that gets the most riders.

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  2. First of all, Jonathan, the Quantrell Ave bike lanes are not "half in the door zone"; they are at least 80% within the door zone. The only way to use these bike lanes and generally avoid the door zone is to ride with one's wheels only a few inches to the right of the left bike lane stripe. Not only does such a lateral position require riding more slowly than otherwise--with constant vigilance to avoid getting doored-- it also risks a side-swipe crash from a close pass by an overtaking vehicle in the travel lane. Thus, the Quantrell Ave bike lanes are neither "comfortable" nor safe.

    Second, the Quantrell Ave bike lanes are, in general, somewhat worse than the ones along Commonwealth Ave. The parking density and turnover along Quantrell Ave is greater than what is typically encountered along Commonwealth Ave, and the combined width of the bike lane plus parking lane along Commonwealth Ave is generally about one-foot wider. I will soon post some photos that illustrate these differences, and I will return to Commonwealth Ave to take actual measurements.

    Third, since the City of Alexandria has improperly placed the sharrows along Commonwealth Ave (and several other streets) inside the door zone, your observation that other bicyclists ride within the door zone along the sharrowed sections of Commonwealth Ave is meaningless.

    Fourth, it is unethical for you to advocate for door-zone bike lanes to attract novice bike riders, when you clearly recognize that such facilities are hazardous and you personally avoid using such bike lanes as they are designed.

    Fifth, I have not advocated removing or changing *any* of the lane striping along Quantrell Ave. I merely recommended that sharrows be installed in the center of the narrowed travel lanes, rather than install bike-lane symbols within the door-zones of parked vehicles. With my proposal, the door zones would still be equally available for traffic-averse bike riders to "enjoy", but the City of Alexandria would not be encouraging patently unsafe door-zone bicycling and opening itself to lawsuits by seriously injured bike riders for irresponsibly promoting this dangerous practice.

    Sixth, ignoring your unconscionable statement that "the best lane design is [always] the one that gets the most riders", nobody, to my knowledge, has ever clearly demonstrated that a street with door-zone bike lanes will attract more riders than a street with identical lane striping but with sharrows centered in the narrowed travel lane rather than bicycle symbols in the door zone.

    Seventh, this is not about being for or against bike lanes per se or about opposing comfortable bicycle facilities that attract new riders (although bike lanes on low-speed urban streets are often problematic and unsafe due to the many operational difficulties they create). Rather, it's simple math. Agency staff and bikeways advocates must recognize that there are minimum widths required to safely sandwich a bike lane between a parking lane for motor vehicles and a travel lane for autos, buses, and trucks. Where parking density and turnover is low, such as in large-lot single-family-home neighborhoods with ample off-street parking, the minimum acceptable width can be slightly less than on streets like Quantrell Ave with high-density curbside parking and frequent bus transit and school bus service.

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