Barrier features

The same barrier can have more than one of the characteristics listed below, and they may be different for different types of vehicles.

  • Containment: The barrier prevents a vehicle from, for example, going over a cliff, or straying into oncoming traffic. Examples: curbs, guardrails, Jersey barriers.
  • Deflection: The barrier guides a vehicle that has gone off course back into the intended direction of travel. Examples: Jersey barriers, guardrails.
  • Threat: The barrier is hazardous in itself, so drivers shy away from it. Example: boulders, rigid bollards.
  • Sham: The barrier appears to pose a threat of damage to a vehicle but in fact is designed to minimize or avoid damage. Example: flex posts.
  • Stop: The barrier is intended to stop a vehicle approaching it.
  • Energy-absorbing: The barrier is designed to lengthen the time and so decrease the severity of an impact — same idea as with air bags or helmets. Examples. crash cushions, deformable barrier walls.
  • Warning: The barrier generates an audible or visual warning. Examples: rumble strips, proximity alarms.
  • Virtual: The barrier is established using signs, signals or markings and the laws which pertain to them.

A barrier may be benign for dual-track motor vehicles, yet  overturn single-track vehicles. These can topple over a low guardrail or Jersey barrier. A sham barrier for dual-track vehicles such as a flex post can tangle with the pedal or leg of a bicyclist, becoming a threat barrier. Reflectorized pavement markers, which are little more than a virtual barrier for dual-track vehicles, can throw a bicyclist –see this video example.

These considerations are lost in the design of many bicycle facilities. Barriers that are hazardous to bicyclists are being used because they are normal traffic-engineering practice, sometimes only due to lack of knowledge but sometimes enforced through design standards.

On the other hand, a high railing with a handlebar rub strip can serve as an effective and safe deflection barrier for bicyclists, even though it may be too weak to contain a heavier dual-track vehicle.

In Orlando, Florida recently, I saw two other examples of misuse of barriers:

  • Flex posts used ahead of and behind a parallel parking space which had been reconfigured as a bicycle parking station. Motorists parking in the next spaces would expect a light, stopping impact if they moved too far forward or back at very low speed. The colloquial expression is “kissing bumpers.”  Lacking this warning, a motorist already had backed up into the flex posts and damaged one of the bike racks. Here, rigid bollards or a guardrail would be appropriate.
  • Raised reflectorized pavement markers are being used on bike lane lines, neglecting the fact that bicyclists must enter and leave the bike lane, and often do best to ride along its edge. Nationally recognized guidelines specifically prohibit the use of raised markers here, for that reason.

The most common misused barrier for bicyclists is probably the low railing, which will topple a bicycle over. That is seen in many different varieties, ranging from the conventional Jersey barrier or guardrail to low wooden curbs lining boardwalks, to hand-height railings alongside paths.

11 responses to “Barrier features

  1. For bike lanes, I really think only the flexible posts (delineators) are appropriate. A rigid bollard may be fine for a parking lot, but not where there might be bike traffic.

  2. I’d add another category: “baited trap”: any barrier which is safe for one type of vehicle but hazardous for another when the wrong expectations apply, or whose safety is reduced by weather, accumulation of trash, etc. The barrier looks innocuous but in fact poses a hazard. Examples: Slippery painted lines; mountable curbs.

  3. An anonymous report from Austin, Texas:
    This baited trap is now in the process of having the ‘more durable’ flexible pylons (the replacements for the ones knocked down by motorists beginning within days of their erection). At least we can see that, now that the second set has been installed, right-hook maneuvers of motorists are on the increase and the wet leaves are ever accumulating in the ‘protected’ space. The Green Lanes Project has ruined this commuting corridor and the Guadalupe corridor as well. Another story.

  4. ‘Also from Austin, the local program is really interested in cost per foot in “tripping” barriers, without taking very much consideration to safety. “Nathan Wilkes, a bikeway engineer in Austin, said he’s looking closely at various options for curb-style separation, including parking stops and other linear barriers no taller than six inches.

    ‘Parked cars work well at protecting bikes on long streets with few driveways, he said. But when there are more driveways, lines of sight become important.

    ‘”You end up pulling parking back from every single driveway, and then you end up with very little parking and very little barrier,” Wilkes said.

    ‘Posts have their own problems: a garbage truck can’t roll over them once a week to pick up the trash, for example.

    ‘Wilkes, like Amsden in Chicago and city engineer Dongho Chang in Seattle, said the main obstacle with curbs is cost.

    ‘Wilkes said he estimates that the simplest possible protected bike lane, a flexible bollard every 40 feet plus a painted buffer, would cost Austin $3 per lineal foot, or about $16,000 per mile of bike lane. Cast-in-place curbs, meanwhile, seem to cost about $50 per foot ($264,000 per mile). Precast curbs like on Austin’s Third Street: $90 per foot ($475,200).

    ‘Wilkes said he’s searching systematically for a cheap way to build bike-lane curbs.

    ‘”We’re looking for the highest quality from the cyclist perspective for the least cost and the least maintenance,” Wilkes said. “I feel like we’re still looking.”‘
    Looking in the wrong direction, it would seem. He could reduce the cost of the barriers by putting fewer in, couldn’t he?

    • More from Nathan Wilkes in this recent Green Lane Project bulletin: A compilation of $ per unit length of barriers to “protect” cyclists with a “perceived safety” rating.
      Note he stresses “perceived safety” rather than actual safety, since actual safety isn’t something that he has data to compare. “‘The cyclist’s perceived safety rating is based on my professional experience, basically following a rule that the more substantial the barrier, the more substantial the protection and thus perceived safety,’ Wilkes wrote.”
      Comments to the article are to be forwarded to Wilkes, it is claimed.

      • There is safety and there is lack of safety: there is no such thing as perceived safety. Giving that name to perception of safety, as inaccurate as the perception may be, lends it a credibility which it does not deserve.

        • You are right of course. “Perceived safety” as a goal for municipal traffic planners to achieve has gotten to be a real-enough “thing,” despite the plain incongruity between what actually helps cyclists be safe and what the oft-championed “60%” of non-riders who’d (or “say” they would) like to ride only if they felt safer wrongly think would make them safer. In a few places I’ve seen “safety” “explained” to us reality-based thinkers as being of 3 different “kinds” (actual, perceived, and social). E.g.: To talk of perceived safety in the same context as actual safety is an abuse of the language. The real question for those promoting cycling should be “how can we increase the prevalence of non-riders understanding how safe proper cycling is and how to properly cycle?” instead of “how can we exploit non-riders’ wrong-headed ideas so that we can get more butts on bikes?”

          • “Perceived safety” might better be called comfort. Increasing comfort is fine. I like to ride on quiet streets too. Creating a false sense of security is the problem.

  5. The Austin “more durable” pylons for “This baited trap” are replacements for the original pylons that were quickly knocked down by motorists before. Very soon after the new “more durable” replacements were put in, a half dozen were already knocked down or broken. “This baited trap” was put up in place of a sharable curb lane and the room to do that in one direction caused the city narrow the remaining lanes and to push bicycle traffic in the other direction all the way off the street onto a “shared use” sidewalk path.

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