How to measure directness?
Directness can be measured in terms of detour factor: the length of the route (Lch) divided by the distance as the crow flies (Lo).
Detour factor = Lch/Lo
As one of the cycle highway goals is creating an attractive alternative to car trips, directness can also be considered in comparison to the car route (Lcar). Cycle highway should offer more direct connection than the route for cars:
Lch < Lcar
Why is it important?
A more direct route reduces time and effort necessary to get from A to B. Therefore cycling is more competitive and people are more likely to choose bicycle for daily journeys.
On network level, the benefits are not linear, but grow quadratically – routes that are 20% more direct mean cyclists can reach targets in area 44% bigger. Why? Area is proportional to the square of radius, so assuming one is willing to cycle e.g. 12 km one-way:
- If you have ideally direct routes to all your targets, you can reach targets in radius of 12 km and area of 452 km2;
- If the cycling routes require making 20% extra distance (detour factor 1.2), with the same effort and time budget you can reach targets in radius 10 km and area of 314 km2.
Of course, ideally direct routes are rare in the real world, but the same proportions hold for different numbers as well (e.g. detour factor 1.125 vs 1.350, 1.25 vs 1.5 etc.)
How is it related to other criteria?
As a side effect, direct route is usually cheaper to maintain: if the route is shorter, there are less signs to renew, less snow to clear in winter, less energy is needed to light the route etc. Directness can also contribute to route readability – a clear straightforward direction means you are able to quickly understand and follow the connection and are more able to orientate yourself.
Compromises might be made for example to increase the route connectivity (pass near another town, concentration of workplaces, important public transport hub), attractivity (f.i. through a more beautiful or less monotonous landscape) or to avoid steep slopes or conflicts with cars. Sometimes the most direct route would be extremely costly to construct (for example a bridge across a lake or a tunnel through the mountain).
How to make a direct route?
Directness is mostly decided during the phase of route planning, when different route options are investigated. Following another linear infrastructure (e.g. railroad, motorway, canal etc.) can result in a very direct route. However, it is often possible to provide shortcuts also at the design phase, e.g. by:
Best practice - planning
The cycle highway F1 between Antwerp and Mechelen follows the railroad line, including the high-speed line Amsterdam – Brussels. As the high-speed trains require extremely large curve radii, the line is very direct. Although the cycle highway makes a few extra turns and detours, it is still only 8% longer than the distance as the crow flies. It is also 13% shorter than the route by car.
Mistakes to avoid
- Kattenleger tunnel shortened the route of the RijnWaalpad cycle highway in the Netherlands by 250 m and eliminated the...
- Kattenleger tunnel location (map © OpenStreetMap contributors).
- Fixing the missed opportunities during the upgrade of the railroad line in 2002-2005: one of the tunnels under...
- The two tunnels will shorten the route by 800 m, eliminate 6 sharp turns in the route and the need to yield to traffic...
A recurring mistake is not integrating the key elements of the most direct route in other big investments (motorway, railroad, new settlement). Constructing a new cycling bridge or tunnel over or under existing infrastructure is more expensive and complicated than including in the original design.
- A section of the F325 cycle highway from Arnhem to Nijmegen follows the A325 motorway. In 2016, Kattenleger tunnel shortened the route by 250 m and eliminated the need of crossing a busy road.
- The F3 cycle highway from Leuven to Brussels follows the high-speed train line connecting Belgium with Germany, using the service roads built during the upgrade of the railroad line in 2002-2005, but as for today, in a few places cyclists have to make a detour. Two bicycle tunnels are currently under construction to fix the missed opportunities: shorten the route, eliminate sharp turns and the need to yield to traffic coming from the viaducts over the railroad.
Both cases are examples of good practice in terms of design for the current situation. But it would have been even better to include the necessary tunnels (or e.g. make a longer bridge over the motorway or railroad line to reserve space for cycle highway) when the motorway or railroad was constructed.