Shared Use Paths
| Design Details
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
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
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
(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
(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
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
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
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
access to the trail from the roadway network
the trail at cross streets and vice versa, so that trail users
know where they are and motorists recognize that they are crossing
on-street facilities such as striped bike lanes on streets approaching
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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