Bicycle Network: Good Design Guides

April 2012 - Thank you to Gold Coast City Council for their contributions on drainage grates - see below.

What’s the problem?

Bicycle wheels are easily deflected by relatively small defects in the travel surface. Also, since most bikes have no suspension, riders are sensitive to undulations, bumps and rough surfaces, which can get quite uncomfortable before getting hazardous. Bike riders have a relatively high centre of gravity so slippery surfaces can result in bad crashes and injuries when they fall.

The path at right had an existing crack that has opened up since it was last repaired. The resulting gap is about 25mm wide - enough to catch many bike tyres, stop them and catapult the rider over the handlebars. The crack would be hard to see at night. Paths need to be designed and properly maintained to avoid such hazards.

What are the risks?

If the surface is too rough or bumpy, riders could:

• Loose control of their bike and crash
• Be forced to ride elsewhere that is less safe (but more comfortable). On roads riders sometimes avoid rough shoulders and ride inside the lane. This increases the risk of being hit from behind by a motor vehicle.

If the surface has loose material and/or is slippery, riders could:

• Crash when their wheels lose traction, especially when rounding corners
• Not be able to stop in time to avoid crashing into another path user or obstacle
• Slide or ride off the edge of the path and crash onto the ground or into an obstacle

If steps, grooves or other hazards are present, riders could

• Get their front wheel caught or “railroaded” in a groove or alongside a step parallel to the direction of travel. The resulting crash from the front wheel being deflected often involves the rider falling forwards over the front of the bike and risking potentially serious head, neck or spinal injuries
• Loose control of their bike over a step and crash
• Hit the hazard with their wheel and have it slide or deflect causing them to crash. A crash is most likely if the front wheel is unexpectedly deflected or stopped. 

What is the solution?

Provide a smooth and grippy (non-slip) surface for cycling. Maintain existing surfaces so they are free of loose materials. When building surfaces, make sure they match up with existing surfaces at their interface so there are not steps or dangerous grooves.

Any particular problems?

Of particular concern are

• drainage grates where a bicycle wheel may get caught in the grooves in the grate themselves or the gap left on the edge of the grate. There are special grates designed with a metal grid mesh that leaves no long gaps that might catch bicycle wheels
• road gutters. Sometimes the edge of the road pavement at the drainage gutter “tray” leaves a step that can deflect a bicycle wheel
• edge of bike paths. Sometimes a bicycle path or shared path is built and the soil level beside the path is not reinstated to the level of the path. This leaves a short drop off, or step, that can deflect a bicycle wheel, particularly if a rider tries to ride back onto the path after riding off
• loose material accumulating on path on in a lane. An otherwise smooth surface then becomes hazardous. Regular maintenance is critical as is a good design that minimizes accumulation of debris. Motor vehicle tyres often remove small items from car lanes (glass, gravel, etc) and keep them clear while the same debris is deposited in bike lanes or verges making them unrideable.

What do the guidelines say? 

The Austroads Guides are clear on the importance of smooth surface for the comfort and safety of cycling.
Surface Quality
“Surface quality and trip length are of equal importance, and both are twice as important to cyclists as traffic volumes and the availability of bicycle facilities, in cyclists’ route choice (Bovy and Bradley, 1985).
“Many bicycles have narrow tyres inflated to high pressures to reduce drag and have no suspension system. A smooth (albeit skid resistant) surface is therefore desirable for bicycles to be used effectively, comfortably and safely. Surfaces used for cycling should desirably be smoother than those acceptable for motor vehicles and persons responsible for path construction and maintenance should be made aware of this requirement.”

New surface tolerances
New surfaces should be as smooth as possible and made to match up as closely as possible to existing surfaces:

“The new pavement surface of a bicycle lane or bicycle path should be shaped to match existing features such as pit covers, edgings or driveways, to within 5 mm. It is desirable that the finished surface of a new bicycle lane or path not:
• deviate from a 3 m straight edge by more than 5 mm at any point
• have a rate of change in deviation in excess of 1 mm in 240mm.”

Steps and grooves in existing surfaces
Steps and grooves can deflect bicycle wheels and cause serious crashes. Cyclists are particularly susceptible to defects parallel to the direction of travel that can deflect a bicycle wheel and cause a serious crash. The guide provides maximum heights and widths for steps and grooves parallel and perpendicular to the direction of bicycle travel.
Parallel to the direction of travel, grooves must be no wider than 12mm and steps no higher than 10mm. Perpendicular to the direction of travel steps should not be higher than 20mm and preferably no higher than 10mm. See table and notes below.

Aggregate Size
The guide in Appendix B4 provides aggregate sizes relating to bituminous surfaces:
“The aggregates used for asphalt should not exceed 10mm nominal size. In the case of sprayed seals, the aggregate size should not exceed 7mm. Larger aggregates result in an unacceptably rough surface.” 

The surface tolerance section of the guide notes that sprayed sealed surfaces with stone sizes of 14mm or more are uncomfortable for cyclists (see below)

Non-slip surfaces

The guide is silent on what constitutes a non-slip surface. See below

What do we say about the guidelines?

The Austroads guide provides good guidance to the importance of a smooth surface for cycling.
The guide, however is not as clear as it could be on: 

Aggregate Size
The acceptable gravel size for use in spray seals and other surfaces. Under surface tolerances it states that “due to the high pressure in many bicycle tyres it is desirable that sprayed sealed surfaces have a stone size less than 14mm in order to provide a comfortable ride for cyclists “, while in Appendix B4 under bituminous surfaces it states “The aggregates used for asphalt should not exceed 10mm nominal size. In the case of sprayed seals, the aggregate size should not exceed 7mm. Larger aggregates result in an unacceptably rough surface.”  The preferred aggregate size should be taken as 7mm or less. 

Acceptable step heights on new and existing surfaces
The guide only gives “desirable” max. heights for new and existing surfaces with no clear guidance on what is acceptable or not.
For new surfaces the maximum step height would appear to be 5mm.
“The new pavement surface of a bicycle lane or bicycle path should be shaped to match existing features such as pit covers, edgings or driveways, to within 5 mm” and that “it is desirable that ... the finished surface of a new bicycle lane or path not deviate from a 3 m straight edge by more than 5 mm at any point”

For existing surfaces the maximum step appears to be 10mm parallel to travel and 20mm perpendicular to travel though footnotes state “It is suggested that a height of 20mm, as suggested by the Californian Department of Transport (2006), may be excessive for many modern bicycle that have narrow high-pressure tyres. This value should be considered as a maximum intervention level for an existing facility rather than a design or construction tolerance. It is suggested that individual jurisdictions should consider a lower intervention level (e.g. 10mm for perpendicular to direction of travel) depending on local circumstances and the importance of the path within the bicycle path network. Designs and specifications should require smooth flat surfaces.”

We say that you should make the surface as smooth as possible. There should be no step greater than 10mm and it is desirable to keep all steps below 5mm in height.

In the commentary (section 9) of the guide (page 112) the guide states that expansion/ contraction joints or joints in pavers should be no wider than 13mm “in order to provide a safer facility for cyclists and pedestrians”. 

Non- Slip Surfaces

The guide is silent on what constitutes a non-slip surface. Taking the standards for pedestrian surfaces; rider experiences and recommendations from a VicRoads report we would say that, for sealed surfaces, non-slip equates to a mean Wet Pendulum Test value (BPN) of 60 or more. Under the Australian standard for slip resistance for pedestrian surfaces (AS 4586:2004, AS 4663:2004 and Handbook 197:1999 this coefficient of friction level is rated as class V slip resistance which is the recommended slip resistance class for ramps in outdoor areas for pedestrians (see Table 3).

The Wet Pendulum Test gives a measure of coefficient of friction for the surface using a standard testing procedure. A report by VicRoads on a performance criteria for bicycle paths recommended the above friction level and class and they are borne out by rider experiences. See Building Better Paths That Attract Riders. The recommended slip resistance for flat outdoor pedestrian areas (Class W materials with a BPN mean value of 45-54) may not provide enough grip for bicycle tyres under all circumstances - for instance the surface may not be grippy enough to prevent a rider falling while braking to avoid a dog or other hazard on the path. Materials tested as Class W slip resistance have been reported as slippery to bike riders especially when wet. Hence, new sealed surfaces for cycling should provide class V slip resistance with a mean BPN of 60 or more.

Examples, good and bad.

Drainage grates are a particular hazard Peel St, North Melbourne. At left - the grate gaps are less than 10mm wide and orientated perpendicular to the direction of travel shown in the photo. But the gaps alongside the grate are wider than 10mm and could catch narrow bike tyres and cause a crash. At right - the gap alongside a grate in Collins St in the CBD has been fixed with asphalt to no gap remains.
A drainage grate almost done well Racecourse Rd, Flemington. The bike lanes were designed against the kerb and the designers realised that the existing drainage gates would be a hazard. They inset the grates into the footpath, used a cross hatch grid to eliminate long grooves and made sure the grate matched up to existing surfaces. Unfortunately setting back the lintel of the pit creates a tripping hazard for pedestrians or bike riders on the footpath (if legal) and, to a lesser extent, bike riders on the road. In this case the kerb line should be continue in a straight line which might require a movable cover to allow access to the grate for maintenance.  On the way to being a good job. We'd previously assessed this as "good" but Gold Coast City Council pointed out the tripping hazard - April 2012
Examples below courtesy of Gold Coast City Council - they have developed a rating system to assess and prioritise replacement of grates - click here for copy.
Poor grates may force riders out into the path of motor vehicles.		The gap in grates parallel to the direction of travel must be less than 12mm wide to prevent tyres falling into them or tracking along them.
Old style "bear trap" grates are particularly hazardous to bike riders		The horizontal bars on this grate prevent bike tyres sinking into the gaps but a bike tyre will still tend to track along the slats parallel to travel.
Bicycle friendly cast iron grate with grooves perpendicular to travel direction.		Cast iron grate with narrow grooves parallel to travel direction - the gaps are less than 12mm so are not a hazard to bikes.
Pre-cast concrete grates are ok for bike riders as long as they remain in good condition.		"Lip-in-line" grate correctly installed so as not to pose a hazard to bike riders. Note the smooth finish between grate, concrete and ashpalt. Recommended where there is a footpath behind - see Racecourse Rd example above.
Bluestone Bluestone is a traditional pavement material in Melbourne. Many laneways are bluestone and many older roads have bluestone kerbing. Unfortunately, bluestone pavement is rough and uncomfortable for cyclists. Usually the gaps and grooves are close to the safe limit of 12mm. They can be hazardous for cycling, especially in the wet as they have a smooth surface. In this photo the lip at the driveway entrance is greater than 10mm and could cause a crash as a cyclist tries to cross it at an acute angle.
Bluestone kerbing Northern end of Swanston St, Melbourne.  The lane is at the end of a long stretch of bike lane (Melbourne's most popular bike route). Bike riders wanting to travel further north may find themselves in this lane and forced out into the middle of the lane amongst busy and fast moving motor vehicles which tend to travel in the left side of the lane while merging and taking the left hand bend. An alternative should be provided for bike riders either as off -road path (the current footpath is not a shared path) or the kerb repaved and marked to make it safe for cycling.
Cracks Cracks in the riding surface can trap bike tyres - this could result in the rider being thrown over the front of the bike. Paths and roads need to be designed and maintained to provide a safe surface.
Grooves and steps Laying of new road surfaces can leave steps parallel to the direction that are hazardous to cyclists (and motorcyclists). Steps or ridges parallel to the direction of travel can divert wheels and cause crashes. They must be avoided and be kept below 10mm.
Raised Road Pavement Markers and Tactile Ground Surface Indicators Raised road pavement markers (or cat's eyes) are used to mark road hazards or features, or in the case of blue RRPMs, the location of fire hydrants. Their height and profile make them a potential hazard for bike riders especially when wet. Care needs to be taken to locate them away from the desire line of bike riders. The relevant Australian Standard indicates they should be placed close to the centre line of the road where they should not normally pose a hazard to bike riders. But bike riders have come to grief when encountering "blue meanies" away from their normal location.   Tactile ground surface indicators (TGSIs) are used to assist visually impaired people negotiate their way around spaces. They are sometimes located on shared paths particularly at road crossings. Riders have reported slipping on these dimples and striped treatments when braking and/or changing direction. This is exacerbated in the wet. The slip testing regime for TGSIs is a "wet ramp" test that uses a standardised shoe sole profile. The test does not replicate the small contact patch and usage characteristics of bike tyres.  See above on non-slip surfaces. We are gathering evidence on the potential hazards posed by RRPMs and TGSIs and how to improve their design, location and usage. Other road pavement markers can also present an unexpected hazard to bike riders. Here on-street car parking sensors, though they help regulate parking usage, lie in the path of a bike rider when there is no parked vehicle. They are higher than a 12mm step and have slippery, curved sides.  A bike rider hitting these would likely crash. Sensors should be imbedded into the pavement to avoid this.
Gravel paths Main Yarra Trail, Ivanhoe East. Shared paths and trails may initially be constructed as gravel paths, especially in outer suburbs where trail usage may be very low initially. But gravel paths have their disadvantages. They are slippery and bike riders can find it hard to stop or change direction. As path usage increases and riders may have to stop or swerve to avoid other users more often and risk crashing. Gravel paths tend to develop low points along the travel alignment (see pic). Water ponds in these hollows and over time alternative paths will develop around the wet and/or muddy ground.  Gravel paths also tend to erode and leave dangerous ruts and grooves that can cause crashes.

a: A narrow slot in the surface that could catch a bicycle wheel, such as a gap between two concrete slabs.

b: A ridge in the pavement, such as that which might exist between the pavement and a concrete gutter or manhole cover; or that might exist between two pavement blankets when the top level does not extend to the edge of the roadway.

Note: It is suggested that a height of 20mm, as suggested by the Californian Department of Transport (2006), may be excessive for many modern bicycles that have narrow high-pressure tyres. This value should be considered as a maximum intervention level for an existing facility rather than a design or construction tolerance. It is suggested that individual jurisdictions should consider a lower intervention level (e.g. 10mm for perpendicular to direction of travel) depending on local circumstances and the importance of the path within the bicycle path network. Designs and specifications should require smooth, flat surfaces.

Source: Californian Department of Transport (2006)