Department of Correlation

Sometimes I honestly don’t understand traffic safety engineering. A random bit from something I was reading:

Motor vehicles and pedestrians can coexist on local residential streets on which both motor vehicle speeds and traffic volumes are low and on-street parking is either prohibited or limited. However, even on these streets the provision of sidewalks can be beneficial in encouraging walking, facilitating social interaction and creating play areas.

Am I wrong or does the first sentence miss the obvious inverse correlation between the presence of parked cars on a street and vehicle speeds on that street? (not to mention parked cars serving as a buffer from wayward cars in traffic).

This entry was posted on Thursday, April 7th, 2011 at 11:37 am and is filed under Pedestrians, Risk, Roads. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

13 Responses to “Department of Correlation”

  1. Dave Says:

    Hmm… perhaps it’s assuming that if the speeds and volume are sufficiently low, the presense or lack of on street parking makes no significant difference in pedestrian safety or volume. Maybe it’s not missing it, so much as just assuming drivers will obey a 20mph sign.

    I could be a bit too generous here, though.

  2. Omri Says:

    There’s (road and sidewalk), (road, sidewalk, and parking), and then there’s shared space.

  3. Harold Says:

    I can think of suburban areas here in the Bay Area where the first sentence is an accurate description. Better might be “In certain instances, motor vehicles and pedestrians…” I think you’re taking the sentence as an all-encompassing statement about all “local residential streets.”

  4. Andy Says:

    It’s the new “vehicular pedestrian” movement. I can’t believe you didn’t know about that!

  5. Eileen Says:

    It’s an odd read without full context, but perhaps they are really saying, “Where a street does not have sidewalks, motor vehicles and pedestrians may be able to share the street if speed and traffic volume are low and if parking is limited. But, really, it would be better to have sidewalks if you really want to encourage people to be out there walking, interacting and playing.”

    If peds and drivers have to share a narrow street, then parked cars can make if more difficult. One of my pet peeves is local regulations that say peds have to use the sidewalk and, if there is no sidewalk, we have to walk in the street close to the edge…which, in most cases, is not accessible because that’s where the cars are parked…so we end up having to walk in the middle of a street that is not that wide to begin with, while drivers pass us within a few inches.

  6. Josh R Says:

    I agree with Eileen’s assessment, the first sentence is assuming no sidewalk and thus cars & peds having to share the space.

  7. Kim Says:

    @Andy Have you not come across vehicular pedestrian before?

  8. davep Says:

    “even on these streets the provision of sidewalks”

    He’s talking about streets without sidewalk (in the first sentence). In such a case, on-street parking would seem to mean the pedestrians would be walking in the traffic lanes to the left of the parked cars.

    He’s also saying “where vehicle speeds are low” as an attribute independent from the lack of on-street parking. The parked cars are not required to slow traffic down because the traffic is already slow. That is, the “inverse correlation” isn’t happening on the types of streets he is talking about.

    I lived on such a residential street growing up.

  9. Stacie Says:

    The way I understand it is that local residential streets could be a road way for both pedestrians and vehicles as long as vehicles traverse at low speed and parking at road sides are limited or not allowed at all. However, I can’t imagine the sidewalk serving as play areas. It’s still very dangerous for wayward traffic and besides, it will obstruct pedestrians walking through.

  10. Barbara Phillips Long Says:

    The sentence just seems to be badly written to me. The way I read it, the two sentences say sidewalks are good for a neighborhood even if there isn’t much traffic on the road and pedestrians think the road is safe, since there aren’t high speed traffic and narrow spots where vehicles park.

    All too often, traffic safety engineering ignores the fact that people do what they want. To improve safety, I think all residential streets should have sidewalks.

    People want to have parking on the street available when they have guests.

    In my experience, people use sidewalks for recreation, walking their dogs, letting children bike on sidewalks, using the sidewalk as a place to play hopscotch or jump rope so children aren’t in the driveway, and sometimes using the sidewalk as a boundary for the accepted play area.

    People posting here seem to have a strong bias toward worrying about the risk of wayward traffic. Some people living in residential areas seem to have a strong bias toward ignoring that risk — even though the street has sidewalks, they walk in the street or allow children to play basketball or hockey in the street, even when the homes have paved driveways.

    Do parents think it is more dangerous for a child to be at a small park a block or two away playing basketball or in the street at the home playing basketball?

    Is the risk of wayward traffic is reduced by curbs?

    Would a low shrubbery barrier between sidewalk and curb provide protection against wayward traffic without damaging sidewalks and pavement the way trees and their roots might? Would the cost of maintaining such a barrier exceed the risk of wayward traffic?

  11. JJM P.E. Says:

    I bet the author is concerned about pedestrians walking out from between parked cars and getting hit.

  12. Blackdog Says:

    The benefits of on-street parking as a “buffer” and to slow traffic are common tenets of new urbanism so it isn’t surprising that Tom would be confused that traffic safety engineers would tout a street without on-street parking as a good place for pedestrians.

    New urbanists have made this claim so many times now that it has just become accepted that it must be correct. Yet, there is no scientific evidence to support it. In reality, a safety benefit is only touted to convince people that the new urbanist way is a better way.

    The fact remains that the biggest cause of serious pedestrian crashes in neighborhoods is the “dart out” where a pedestrian (usually a child) runs out in front of an oncoming vehicle. It is the classic child chasing a ball into the street scenario. On-street parking exacerbates this problem by limiting sight distance and thereby the time a motorist has to react. Without parking, tragedies are much more easily avoided as motorists can see the entire scenario unfolding well in advance and can take appropriate steps to avoid it.

    Although it may not appeal to new urbanist’s sensibilities, modern suburban neighborhoods with three car garages and little on-street parking may actually be a better model for pedestrian safety than the narrow street lined from end to end with parked cars.

  13. Wali Says:

    That is called Woonerf . According to Wikipedia “A woonerf (Dutch plural: woonerven) in the Netherlands and Flanders is a street where pedestrians and cyclists have legal priority over motorists. The techniques of shared spaces, traffic calming, and low speed limits are intended to improve pedestrian, bicycle, and automobile safety.”

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