This article was published in 2015, in Newsletter 123.
Now that segregated cycle lanes are becoming more common, both in Cambridge and elsewhere in the UK, we have examples of different ways of including bikes on roads. This article will look at the advantages and disadvantages of bidirectional versus one-way cycle lanes on roads.
One-way cycle lanes with traffic
This is the classic cycle lane: it can be a painted strip, or a raised lane, or a kerb-segregated lane. One-way lanes go in the same direction as traffic, one on each side of the road. The Hills Road and Huntingdon Road cycleways are of this kind.
The advantage of this is that you are making the same kind of manoeuvres as people in cars, so broadly the road layout is designed to accommodate your journey. People leaving side roads are looking in your direction for traffic. If the cycleway stops, or you need to turn off, you can rejoin traffic travelling in the same direction.
Bidirectional cycle lanes
The bidirectional cycle lane has people on bikes going in two directions on one side of a road. The Cycle City Ambition plans for Trumpington Road include a short section of bidirectional cycleway, next to a one-way on-road hybrid lane.
The main advantage of a bidirectional cycle lane is it uses less space. You only need one buffer from traffic, rather than two (even if there is no physical buffer, the full width of a cycle lane often isn’t usable owing to proximity to traffic). If travel is tidal (e.g. heavy commuting flow in one direction at a time) the layout is more flexible: the busier direction can use some of space available to the opposite direction for overtaking or cycling two abreast, while still leaving space for someone to cycle in the non-dominant direction. In a conventional one-way layout, both lanes would need to be wide enough to accommodate overtaking at all times of day.
However, bidirectional cycle lanes can be dangerous if they cross busy side-roads. People leaving the side-roads are looking in the direction of conventional traffic, and can forget to check the other direction for people on bikes. Torrington Place in London is an example of an otherwise popular and successful segregated bidirectional cycle lane where collisions have resulted in new plans to change it to two one-way segregated lanes. However, where the side roads have low usage, or are for local access only, it can be acceptable as users will be used to the layout and the chance of problems is reduced. Alternatively, the crossings of side roads can be set back from the main road by at least one car length, so people exiting can make two separate manoeuvres: one to check both ways for people on bikes, cross when clear, and then another to join the main road. This requires more space at the junction, but can be useful for long-distance rural routes, where providing cycle lanes on both sides of the road is more expensive for fewer users.
- uses less space
- can be cheaper and less disruptive to build
- can be used to minimise crossing side-roads on opposite side e.g. along a riverfront or next to a railway line.
- junctions with the rest of road network need careful thought
- if there are side roads, can be more dangerous.
Bidirectional lanes work very well where there is no access on one side, for example along a river or a railway track. This can also help avoid crossing side-roads on the opposite side, reducing interactions with motor traffic. The proposed London Embankment Cycle Superhighway is a good example of this. In some circumstances the bidirectional track may be catering for a particular high-volume journey, such as the Trumpington Road cycleway, designed specifically to allow journeys between the Accordia development and the schools in the New Town area.
Another problem with bidirectional cycleways, especially in urban environments, is that they may not be going where you are. In some circumstances you would have to cross the road twice to use the cycle lane for only a short section. Coldham’s Lane bridge has this problem if you are trying to head south along the length of Coldham’s Lane, rather than turning into Cromwell Road. Even if you can use it for a greater length, you will need to turn at some point, and junctions with the main road network are often poorly thought-through. This is a particular problem if the cycle network is inconsistent and you have to rejoin traffic: half the time you will be on the wrong side of the road to continue your journey easily. You are making a manoeuvre that drivers don’t need to, and may not be looking for. This is not an insoluble problem, but does require good intersection design.
Generally speaking, bidirectional and one-way cycle lanes on roads are both useful but in different circumstances, and are not necessarily interchangeable proposals.