Mastering Cycle Infrastructure Design - PART 1

Cycle track design, in general terms, is a design where a Highway Engineer needs to satisfy the following five main requirements: safety, coherence, directness, comfort and attractiveness. I will touch briefly on each requirement.

Safety

Cycle track design needs to be safe for people of all ages and abilities. Furthermore, proposed cycle track facilities need to be perceived as safest as possible. Cyclists need to feel safe using them.

Coherence

Proposed cycle tracks need to be connected and very easy to get around with. Changes in transitions (for example, from mixed street to the actual cycle track) need to be logical and intuitive.

Directness

Proposed cycle tracks should connect origins and destinations using the shortest route possible.

Comfort

Proposed cycle tracks need to be comfortable to use. This means that Highway Engineers should pay close attention to cycle track width, gradients, surfacing, etc.

Attractiveness

Cyclists ideally should experience a pleasant environment while driving along the route. Cycling through urban environments (enriched with suds), parks and waterfront locations is one of the most attractive cycling experiences.

One tip: Highway Engineers should use horizontal buffers between the cycle track and carriageway to improve the attractiveness of the route, wherever possible.

Cycle Track Horizontal design

There are several important geometric requirements of a cycle track to consider when tacking horizontal design:

• Design speed
• Sight distance (dynamic and stopping sight distance)
• Visibility splays
• The proposed width of a cycle facility
• The overall picture and site constraints

Design speed

Design speed is a speed that determines the horizontal and vertical requirements for cycle tracks. The image below shows the comparisons between design speed applied in the UK and Ireland.

Highway Engineers can freely apply a standard design speed of 30 km/h whether working on the project in the UK or Ireland.

If the long profile gradient is steeper than 3 %, then Designers should design their cycle track facilities with a design speed of at least 40 km/h.

Sight distance

When discussing sight distance, we need to distinguish dynamic distance clearly from stopping sight distance.

CDM defines dynamic sight distance as the advance distance a person cycling requires to see ahead so that they can make safe and comfortable progress on their journey.

CDM (Ireland) suggests the desirable minimum value of 65 m for dynamic sight distance (30 km/h design speed) while Cycling by Design (Transport of Scotland) suggests 67 m for a min DSD.

It should be noted that dynamic sight distance should be measured from an eye height range of 0.8 m to 2.2 m to a target height range of 0.8 m to 2.2 m.

On the other hand, stopping sight distance is the distance required for a rider to perceive, react and stop safely. The minimum values for different design speeds in the UK and Ireland are shown in the image below.

As you can see, the minimum stopping distance for 30 km/h design speed is not the same in Ireland and the UK. Cycle Design Manual (Ireland) demands more SSD for 30 km/h design speed.

Visibility splays

Let's revisit the basics. Visibility splays are composed of two elements: the X (setback) distance and the Y distance, as shown in the image below.

The X distance is the distance along the cycle track from which visibility is measured. It is measured along the centre of the track from the nearside edge of the intersecting route. If the intersected route is a road, then the X distance needs to be measured from the nearside edge of the paved surface.

On the other hand, the Y distance is the distance an exiting cyclist can see to the left and right along the route.

So, what are the recommended X distances at crossings? Let's take a look at the image below for values in the UK and Ireland.

We can see that in the UK, the absolute minimum X-distance is 2.4 m, which is 0.4 m higher than the requirement in Ireland.

The desirable minimum 'Y' distances at uncontrolled and controlled crossings correspond to SSD for vehicle traffic on the main road based on DMURS or Manual for Streets 2.

If we have a situation where cycle tracks intersect two adjacent facilities, then the visibility splay needs to be measured at two interaction points, just like in the image below.

For example, if the design speed of the cycle track with priority is standard 30 km/h, then the Y distance needs to be 35 m.

The proposed width of a cycle facility

The width of a proposed cycle facility will depend on the type of the cycle track and the direction of the travel peak hour cycle flow. CDM further breaks down the width carefully into four distinctive elements: A, B, C, and D.

A - Inside clearance (for example, to pedestrians and footpaths).

B - Central width (space for cycling).

C - Outside clearance (the space required to the right of cyclists).

D - Buffer, a horizontal separation between the cycle facility and the traffic.

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To learn more about the specific minimum values of these width elements, please download the Cycle Design Manual as your guide.

Both CID (Cycle Infrastructure Design) and CDM introduce two relevant terms: desirable minimum width and absolute minimum width. The absolute minimum width for a one-way cycle track is 1.5 m in the UK and Ireland.

I discuss more about it in detail in our free LinkedIn group Highway & Drainage Engineering Design in C3D & InfoDrainage Tips & Tricks.

The overall picture and site constraints

When discussing and later designing a cycle track horizontal layout, the entire site picture and its constraints need to be considered.

?Here are a couple of points to have in mind when catering to site constraints:

• In order to incorporate the one-way cycle track (1.5 m absolute min) into an existing road network, you need a min of 9 m of carriageway space. This breaks down as follows - 3 m lane widths + 1.5 one-way cycle width x 2.
• The horizontal buffer between the two-way cycle track and the carriageway is always needed, no matter the speed limit!
• The Highway Engineer should carefully choose the type of cycle track to incorporate and the ultimate connecting link and purpose.
• The Cyclists' safety should never be compromised in order to "squeeze" in the proposed cycle track.
• The cycle drainage design should be thought of at the same time as the cycle track design.

The Horizontal alignment design - the final piece

In order to design a safe and comfortable cycle track for cyclists, Highway Engineers need to consider adequate horizontal radii. In other words, Highway Engineers need to design an adequate horizontal alignment - the backbone of every cycle horizontal layout design.

No matter whether you are designing a cycle track in the UK or Ireland, the desirable minimum horizontal radii are the same for the chosen design speed, as shown in the image below.

It's important to note that in certain circumstances, like the approach to junctions, tighter horizontal radii may be introduced as a speed-reducing safety measure. CDM suggests the desirable minimum radius between 6-8 m and an absolute minimum radius of 4 m.

Here are some practical tips for Highway Engineers designing cycle track horizontal alignments:

• ?Visibility should never be compromised, and walls, fences or trees should never be located on the inside of cycle track bends.
• A cycle horizontal alignment should always consist of only straights and simple curves (usually circular and no transitions).
• At speed-reducing curves, adequate signage and line markings are needed.

Conclusion

In conclusion, the cycle track design is a process of satisfying five main requirements (safety, coherence, directness, comfort and attractiveness), carefully choosing the right type of cycle track for a given site constraint and following the country's standards to produce an optimal design.

Attention to every detail in the design process is crucial.

Lastly, if you want to learn more about how to design a cycle track in CIVIL3D, I am holding a two-day training course this August 29th & 30th called Designing a standard cycle track in CIVIL3D.

In the next edition of Engineering Design by PERVAN I will discuss how to master cycle track vertical design.