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Shared Use
Paths (Trails): Introduction
In the last decade of the 20th Century, shared use paths (often
called trails or bike paths) for bicyclists and walkers sprang
up in communities cross the nation. There are more than 11,000
miles of paths on former railroad corridors and thousands
more alongside canals, rivers, and highways and running through
parks and recreation areas.
Shared use paths provide many valuable benefits including
transportation links, recreation areas, habitat corridors,
economic development attractors and outdoor fitness centers.
They may range in length from a mile or two in a downtown,
to a regional commuter route of 15 miles or more, right up
to a cross-state or interstate path covering hundreds of miles,
and the level of use on a trial may vary from a few thousand
people a year to several million per year.
Regardless of the location, purpose, level of use, or mix
of users, there are certain design elements that are important
for the successful and safe operation of a shared use pathway.
Applying these design criteria need not create a sterile,
overbuilt "mini-highway", and there is still plenty of scope
for applying engineering judgement and common sense solutions
to issues that arise in the development of a shared use path.
There is also a wealth of information available on trail design
to help identify solutions and approaches to problems.
Important Principles of Shared Use Path Planning and Design
1. Shared use paths are an addition, and complimentary,
to the roadway network: they are not a substitute for providing
access to streets and highways. In the past, some communities
have treated the development of a shared use path as the only
thing they needed to do to "provide for bicyclists" and give
them somewhere to ride. However, even the most extensive trail
network cannot provide access to all the origins and destinations
in a community, and trail users have to be able to get to
and from the trail on the regular street network.
The 1999 edition of the AASHTO
Guide for the Development of Bicycle Facilities specifically
notes that, "shared use paths should not be used to preclude
on-road bicycle facilities but rather to supplement a system
of on-road bike lanes, wide outside lanes, paved shoulders
and bike routes."
2. Shared use paths function best when they are in
their own right of way. Paths along former railroad corridors
or canals work well because they are likely to have fewer
intersections with roadways, and may even be completely grade
separated from crossing roadways (i.e. they cross roadways
on railroad trestles or other bridges/structures). By contrast,
paths that have frequent intersections with roadways and/or
driveways usually require path users to stop or yield at every
crossing and every crossing creates potential conflicts with
turning traffic.
The Idaho Department of Transportation bicycle and pedestrian
planning manual provides a "suggested analysis of separated
multi-use pathways" that recommends against installing a multi-use
path when there are more than 8 crossings per mile, suggesting
an on-street facility be provided instead. The guidance also
recommends proceeding with extreme caution and perhaps switching
to on street bicycle lanes when there are between 5 and 8
crossings per mile, and with one to four crossings per mile
the manual encourages the designer to use special care to
treat potential conflicts.
National and state design manuals strongly caution against
developing shared use paths immediately adjacent to highways
and to designating sidewalks as shared use facilities for
a number of reasons. Indeed, the 1999 edition of the AASHTO
Guide for the Development of Bicycle Facilities recommends
against such facilities in at least three separate places,
and provides a list of nine reasons why. A similar list is
included in almost all state design manuals, for example the
New Jersey DOT's Bicycle Compatible Roadways and Bikeways.
The list includes:
(a) They require one direction of bicycle traffic
to ride against motor vehicle traffic, contrary to normal
Rules of the Road.
(b) When the bicycle path ends, bicyclists going against
traffic will tend to continue to travel on the wrong side
of the street. Likewise, bicyclists approaching a bicycle
path often travel on the wrong side of the street in getting
to the path. Wrong-way travel by bicyclists is a major cause
of bicycle/automobile accidents and should be discouraged
at every opportunity.
(c) At intersections, motorists entering or crossing the
roadway often will not notice bicyclists coming from their
right, as they are not expecting contra-flow vehicles. Even
bicyclists coming from the left often go unnoticed, especially
when sight distances are poor.
(d) When constructed in narrow roadway right of way, the
shoulder is often sacrificed, thereby decreasing safety
for motorists and bicyclists using the roadway.
(e) Many bicyclists will use the roadway instead of the
bicycle path because they have found the roadway to be safer,
more convenient, or better maintained. Bicyclists using
the roadway are often subjected to harassment by motorists
who feel that in all cases bicyclists should be on the path
instead.
(f) Bicyclists using the bicycle path generally are required
to stop or yield at all cross streets and driveways, while
bicyclists using the roadway usually have priority over
cross traffic, because they have the same right of way as
motorists.
(g) Stopped cross street motor vehicle traffic or vehicles
exiting side streets or drive-ways may block the path crossing.
(h) Because of the closeness of motor vehicles to opposing
bicycle traffic, barriers are often necessary to keep motor
vehicles out of bicycle paths and bicyclists out of traffic
lanes. These barriers can represent an obstruction to bicycles
and motorists, can complicate maintenance of the facility,
and can cause other problems as well.
(i) Cyclists using the path against the flow of traffic
often cannot see the signs posted for traffic using the
roadway without stopping and turning around.
For the above reasons, bicycle lanes, or shared roadways
should generally be used to accommodate bicycle traffic
along highway corridors rather than providing a bicycle
path immediately adjacent to the highway.
There may, however, be some circumstances where a shared
use path adjacent to a highway does make sense. Examples
include:
i) where there are infrequent crossings, such as a alongside
an interstate or across a long bridge
ii) where the crossings can be grade separated, for example
where the trail is built in conjunction with a major highway
project
iii) where the section of adjacent path or sidewalk is
relatively short and provides a critical connection between
two paths, and the sidewalk has few driveways and intersections.
When two-ways paths are located adjacent to a roadway, the
AASHTO Guide recommends wide separation between the two
to demonstrate to motorists and path users that the path
is an independent facility. When separation of more than
five feet cannot be achieved, a physical barrier at least
42 inches high between the path and the roadway is recommended.
3. Shared use paths are used by a wide variety of users
traveling in both directions. Design manuals from the 1970s
and 1980s suggested that paths could be designed for the exclusive
use of bicycles, and further that those paths might be used
in just one direction. The reality of paths of almost any
size is that they are used by a wide variety of users including
pedestrians, joggers, in-line skaters, fitness walkers, people
with dogs or strollers, and people travel in both directions
regardless of any traffic control devices that try to say
otherwise.
Consequently, design manuals now acknowledge that paths are
"shared use" facilities and that they must be designed to
accommodate bi-directional mixed use. The most obvious example
of this is that the AASHTO Guide now recommends a minimum
trail width of 10 feet (up from 8 feet) and encourages the
use of 12 feet or more where heavy or mixed uses are expected.
4. Shared use paths need to be connected to the transportation
system. Trails do not exist in a vaccuum; users need to be
able to get to and from the facility on the regular street
network and the transition between the two should be safe,
obvious and convenient. Similarly, connections between the
trail access points and local transit service can encourage
trail use and boost bus ridership.
Strategies for achieving this connection include:
signing access to the trail from the roadway network
signing the trail at cross streets and vice versa, so that
trail users know where they are and motorists recognize
that they are crossing a trail
providing on-street facilities such as striped bike lanes
on streets approaching the trail
locating bus stops close to trail access points (but not
so close that a stopped bus would obscure the trail or block
the trail crossing!)
5.. Intersections between shared use paths and roadways
are the greatest challenge. Great care has to be taken in
managing the operation of trail/roadway intersections to ensure
safety, convenience and comfort are balanced. Trail users
don't want to have to stop every few hundred yards at every
driveway and intersection, especially where crossing traffic
volumes are very small. Nor do designers want to set up dangerous
conflicts between motor vehicle traffic and trail users by
providing inadequate information and traffic control at intersections.
More information on intersection design is provided in the
"detailed designs" section.
6.. Shared use paths should be designed based on the
same engineering principles that are applied to highways.
This doesn't mean that trails should always be mini-highways
that flatten everything in their path — but it does mean
that principles such as providing adequate sight distances
and stopping distances cannot be ignored just because these
are "trails".
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