Bicycle Network Victoria: Good Design Guides

What’s the problem?

Riders and other path users tend to cut corners if they can and can reenter on the wrong side of the path or into the path or other path users.

What are the risks?

The major risks from paths with tight corners and curves are:

• collisions or close calls between bicycle riders and other path users as they cross to the inside of the corner;
• riders overshooting the curve and crashing;
• riders cutting the inside of the curve and colliding with an obstacle;
• a reduction in safety if other aspects of the path design are also compromised. For instance a sharp curve in the path combined with steep slope, off camber surface or poor clearance to obstacles can result in a crash.

What is the solution?

Don't unnecessarily introduce curves to path - keep them as straight as possible. Avoid the use of sharp corners or bends with a radius of less than 15m. Do not use them to attempt to slow bicycle traffic as they introduce complexity especially on the approach to intersections and often reduce safety. A minimum radius of at least 30m is preferred.

If a path must pass around existing obstacles, make the curves gentle and avoid sharp corners from side to side. The guidelines give the following example (figure 5.2):

A corner or curve in the path is one compromise in the path design that may decrease its safety. Therefore, care must be taken with other aspect of the path design to avoid further reductions in safety. Of particular concern are sight lines, camber (superelevation), path surface and the slope of the path. For instance, if the path must curve, then make sure the surface is not slippery or off camber and that people can see each other and any potential hazard.

What do the guidelines say?

The Austroads guide to Road Design Part 6A deals with corners and curves under section 7.3- horizontal curvature (see full wording at right). The guide give tables to guide minimum curve radii for differing design speeds and superelevations (cambers).
“Where a path location or alignment is not constrained by topography or other physical features, a generous alignment consisting of straights and large radius curves is desirable. Such an alignment will provide good sight lines and a pleasant riding experience for cyclists.

"the fact that a path is provided primarily for recreational use does not remove the need for a good alignment; nor should it encourage designers to provide tight curves to achieve what they consider to be a visually pleasing alignment.

"tight curves should not be provided to improve visual amenity because:
• pedestrians and cyclists are likely to cut across the verge on the inside of the curve leading to unsightly bare patches, possible erosion and safety issues
• there will be a subsequent requirement to treat the area on the inside of the curves at additional cost in order to constrain cyclists and pedestrians to travel along the inadequate alignment."

The guide provides a table which recommends minimum radii of curvature. For a design speed of 30km/h the miniumum radius is 25m though a minimum radii of 30m is generally preferred as tight curves bring safety concerns:

"Where practicable designers should not design for the minimum radius as tight curves can result in sight distance restrictions, a poor level of service and some cyclists choosing an informal alternative path to avoid restriction. Exceptions include locations where alignment is severely constrained (e.g. steeply sloping land) and smaller radii cannot be avoided. However, isolated tight bends that do not have preparatory approach geometry should be avoided as at night, in an unlit environment, curve warning signage may not be visible with bike lights.
It is acknowledged that a curvilinear alignment is often preferred to achieve a visually pleasing path and environs. However, minimum radius or sharp curves should not be used to achieve landscaping objectives to the detriment of the level of service and social safety for cyclists on any path that has a commuter, major recreational or utility function."

What does Bicycle Network Victoria say about the guidelines?

The guidelines provide good quantitative guidance on the minimum radii of curves for differing design speeds (in Table 7.1) and cambers (superelevations – in Table 7.2, both tables are reproduced below). They are also clear on the importance of maintaining clear sight lines across the inside of curves and give quantitative advice in Figure 7.7 (below)). The new guide is an improvement on the old Part 14 guidelines which seemed to endorse tight corners on approaches to intersections without making it clear that this may not be the preferred design approach (for instance figure 6-29 from Part 14 below, showing probable shortcutting of corners).

Any examples, good and bad?

Bridge on the Drouin to Warragul Trail, Baw Baw Shire. The bridges have been offset from the trail alignment introducing a significant hazard to an otherwise pleasant path. Any cyclist who overshoots the corner may end up falling into the creek and risking head or neck injuries or hitting the pole at the edge of the path. The path should align with the bridge. The offsets were fixed (see pic at top of page), rather inelegantly and less than ideally, in Feb 2010.
Mullum Mullum creek trail at Oliver St, Ringwood (Melways map ref. 49, J6). Here the double curve of the path occurs on both sides of the road is designed to slow path traffic at the approach to the minor road crossing. However, most path users cut across the corners and are therefore crossing the road at the driveway and not where motorists might be expecting them. A simpler and safer solution would be to continue the path directly across the road and mark the crossing clearly for both road and path users. At least sight lines have been kept clear.
Sandridge Trail at Ingles St, Port Melbourne (Melways map ref. 2J, G1). A tight corner with fences has been introduced at the road crossing which introduces a hazard as cyclists negotiate the corner and the fence obstacles alongside the path as well as pass other path users. Also, in busy times the cyclists waiting to cross can block the exit of those trying to exit the crossing. The handrail at the entrance also reduces the usable path width. To negotiate the corner, cyclists cross to the wrong side of the path. A more direct approach to the road would be simpler and safer.
Footscray Rd path at Waterfront Way intersection (Melways map ref. 2E, D2). A tight corner at the approach to the intersection is often cut across. Cyclists are expected to cross the slip lane at the zebra crossing but most cut across to take the shortest route across the lights. In the background cyclists struggle to pass each other on the tight corner and their attention is diverted from scanning for oncoming traffic in the slip lane and at the intersection.
Gregory Rd path, Ballarat. The path was planned to divert around the electricity pole with a sharp bend. The council has since redirected the path to align more directly to the right of the pole.
Capital City Trail at Hardy Gallagher Reserve Before - cyclists were cutting the corner and a "goat track" had formed.	Capital City Trail at Hardy Gallagher Reserve After - The new section improved the directness and safety of the path.

From p70 Austroad Guidelines

From p40 Austroad Guide to Road Design Part 6A: Pedestrian and Cyclist Paths
 

Source: Californian Dept. of Transportation (2006)

From p40 Austroad Guide to Road Design Part 6A: Pedestrian and Cyclist Paths