Trail density (how much is enough?)-
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  1. #1
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    Oct 2005

    Trail density (how much is enough?)

    Yesterday I was at the inaugural meeting of the cycling-subcommitte of the local stewardship committee. A question was asked about the density of trails. Sort of a when do you have enough trails, and when is there too much. In particular this individual was concerned about ecological and environmental concerns. I.e. certain plants & animals need a certain amount of space around them. But we also discussed this in terms of traffic, conflict, experience etc.

    I was wondering what thoughts any of you had on this. In particular are there any studies you know of in this vien?
    Jason Murray
    Rep for Ontario, IMBA Canada
    Visit the IMBA Canada site to keep current on all things IMBA in Canada.

  2. #2
    featherweight clydesdale
    Reputation: Fattirewilly's Avatar
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    Dec 2001
    Good topic.

    I've been thinking about this as we plan a new trail network. I don't have much as far as environmental thoughts, but I'd give some density examples.

    I recently rode a VA state park system (Poca. near Richmond) with about 10 miles on 100 acres. Usually this density gives me a feeling that the trails are just jammed in there just to get more miles in. In this park, they carefully studied the topo and hid one trail just over the ridge from the next. The trails made me feel like I was actually going somewhere. We came upon several wild critters, but the park is much bigger than the area allocated for bikes. Pocahantas is a fee use park. Hikers/trail runners are enjoying the mt bike built trails, and the park is counting the increased $$ at the gate.

    Here in Charlottesville, Walnut Creek Park (480 acres with 45 acre lake, parking, field, roads) has approximately 380 wooded acres with about 16 miles of trails. This density allows plenty of room for reroutes, and noticed several underdeveloped areas where an addition 1/2 mile can be added here and there. I don't think there's any shortage of deer or other critters here. The park is closed at night, so they have free roam of the place at night.

    I think in an urban setting, you need at least a 6 to 10 mile loop to avoid user conflicts. Pocahantas is supposed to be ridden one direction only, but they never alternate the direction. Blankets Creek, outside Atlanta, is alternates directions on different days of the week, and works well. Walnut Creek doesn't get the traffic to require one direction use.

  3. #3
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    Feb 2004
    As far as a trail system's impact on wildlife, here's a good study with some guidlines on the subject:

  4. #4
    since 4/10/2009
    Reputation: Harold's Avatar
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    Dec 2003
    I don't have any absolutes, but I can put a relative comparison on the table for you.

    I would have to say that it depends largely on vegetation type, vegetation density, and topography. Moist climates with lots of dense vegetation and good topography can really pack the trails in tight. Reduce rainfall, vegetation density, or topography and you need to reduce the density of trails.

    Places with fast-growing vegetation can handle high trail density. Places with slow-growing vegetation need less trail density.

    In places with dense vegetation, the wildlife WILL use the trail corridor regularly, so be aware. I have seen trails in the midwest with such dense vegetation that the deer use the trails heavily. In the late winter/early spring when it's rainy and the soil is thawing (therefore most bikers stay off), the deer traffic really chews up the trails. If particularly sensitive wildlife are in the area and likely to use the trails, the trails should be given some sort of time-out (no riding past dusk or possible seasonal closures during mating/laying/calving/birthing seasons depending on species) so the bikes don't seriously impact the wildlife.

    Part of it also depends on how the trails will be used in the given park. If the trails are being built with bikers in mind for the most part, then the density can be a little higher. If the land manager intends for the trails to have significant foot or horse traffic, then you'll need to reduce the trail density.

    My personal preference (as well as the preference of many people I've ridden with) is that when riding on a trail, I like to feel like the trail is pretty remote. I don't want to be able to see other trail users close to me on a different trail. It makes the woods seem more crowded that way. I especially don't like to be able to actually see other trails. It's one thing if the trail follows the topography and you can see the trail and other users on the other side of the ravine, or if the trail has long sight lines and you can see people in front of you. That's fine. What I'm talking about is when the trails are packed so tightly into a flat piece of land that you can see another trail just feet or yards away from the one you're on, or trails where you see other users on trails that are close enough that you can identify facial features, the bikes they're on, or can hear their conversations.

    That's not to say that trails can't be packed in within feet or yards of each other. You just need vegetation and/or topography between them to act as visual and sound barriers. That way, you FEEL like the trail is remote and lightly traveled, but that feeling is an illusion perpetuated by good trail design.

  5. #5
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    Aug 2003

    No studies, but...

    ... I wrestled with this question recently. My conclusions were similar to NateHawk's. I tried to lay out the trails so that where possible the trail was not visible from segment to segment. Or if it is, there is enough separation between the parts so that people are not tempted to short cut between them.


  6. #6
    Log off and go ride!
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    Jul 2003
    When I worked for the Forest Service I was on a team that did just that type of analysis for roads. We were primarily interested in soil and watershed effects, but impacts on T&E plants and wildlife were also considered.

    There are many variables. Stream type, soil type and slope were the biggies, but many other factors played in. Distance from canyon bottom stream and elevation (A trail close to the water edge is a bigger impact than one along a ridgetop. Elevation is used to determine Winter precip was rain, snow, or a mixture). Whether the road was native surface or was paved or aggregate, even type and amount of traffic, and road condition.

    At the end we had a HUGE database and GIS file with dozens of attributes for each road segment. Analysis boiled it all down to determining equivalency density by subwatershed and from that determined priorites for spending on mitigation measures. The stream subbasin with the most total miles of road miles per square mile was not necessarily the highest priority, if those roads were not causing any significant resource impacts. As I recall the #1 for rehab work was close to bottom of the list by total miles.

    The team intentionally did not consider trails, over my protestations.

    The same analysis could easily be done for a trail system. The local rule of thumb is a mile of forest road equals 2.5 acres of disturbance and a mile of trail is 0.3 acres, but trails produce about twice the sedimentation per square unit of surface than roads all other factors equal. These values may vary in different parts of the country.

    So you cannot just use total miles of trail, although some anti-bike groups will try to do that. A local analysis could possibly be done as part of university student work. We used local university students frequently (class projects, grad papers, masters thesis, etc) to do some of the basic data gathering and number crunching.

  7. #7
    since 4/10/2009
    Reputation: Harold's Avatar
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    Dec 2003
    Quote Originally Posted by dave54
    The local rule of thumb is a mile of forest road equals 2.5 acres of disturbance and a mile of trail is 0.3 acres, but trails produce about twice the sedimentation per square unit of surface than roads all other factors equal. These values may vary in different parts of the country.
    How was the sedimentation comparison reached? What was the local environment (with vegetation types and soil types?), and what sorts of roads were compared (percent paved/aggregate/native surface)? This is an interesting approach to the issue. Also, how was the disturbance value of a trail reached? Was an average width measured, or was it assumed? What was the value? Certainly, the sedimentation created by a trail is influenced far more by the original design of said trail than the road (especially a paved one), so a fall-line trail will produce far more sedimentation than a well constructed contour trail. It would definitely be wise to attempt to quantify the slope of the trail when determining its impact in order to make a fair analysis.

    Relating this line of questioning back to the topic of density, if a baseline of acceptable sedimentation was decided upon, and through analysis of the impact of the trails an estimate of the actual sedimentation was determined, it would be quite simple to determine the acceptable trail density. That said, such a study (sedimentation on a variety of trails) would be hugely labor intensive and probably far too much so for a non-profit org to undergo. Now if you could find a grad student or someone looking for postdoc work with funding to hire undergrads, you'd be in business.

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