Cycle facilities have been the subject of great debate from both engineering and ideological perspectives since the 1930s. This debate includes the use of the terms "facility" and "segregated facility".
See main article: Segregated cycle facilities: Official definitions and legislation.
While the names and definitions of the various cycle facility types vary from country to country, they generally can be categorised as: "on-road" or "off-road".
"On-road" facilities are typically termed "cycle lanes" (United Kingdom, et al.) or "bicycle lanes" (United States, et al.), and are portions of a roadway or shoulder designated for use by cyclists.
"Off-road" facilities may be an alternate route or right-of-way alongside a road. In the USA, off-road unsurfaced trails are commonly called "bike trails" or "mountain-bike trails", while surfaced trails that are separate from roadways and that meet more rigorous standards for width, grade and accessibility are commonly called "bike paths". In the UK and some other jurisdictions, the terms "cycle path" or "cycle track" are sometimes used as a blanket term for any such off-road facility.
This article observes the following conventions.
By the end of the 19th century, cycling was growing from a hobby to an established form of transport. Cyclists began to campaign to improve the existing, often poorly surfaced, roads and tracks, in the USA via groups such as the Good Roads Movement.  In the UK, the Cyclists' Touring Club distributed a treatise entitled Roads:Their construction and maintenance. In Germany concerns arose regarding conflicts between cyclists, horse traffic and pedestrians, leading to sections of routes being upgraded to provide smoother surfaces and separate portions for the different groups.
An example of an early segregated cycle facility was the nine-mile dedicated Cycle-Way built in 1897 to connect Pasadena, California to Los Angeles. Its right of way followed the stream bed of the Arroyo Seco and required 1,250,000 board feet (2,950 m3) of pine to construct. The roundtrip toll was 15¢ US and it was lit with electric lights along its entire length. The route did not succeed, and the right of way later became the route for the Arroyo Seco Parkway, an automobile freeway opened in 1940.
With the advent of the motor car, conflict arose between the increasingly powerful car lobby and bicycle users. By the 1920s and 1930s the German car lobbies initiated efforts to have cyclists removed from the roads so as to improve the convenience of motoring. In the UK, the cycling lobby was attempting to remove motor vehicles from the roads by calling for the building of special "motor roads" to accommodate them. This idea was opposed by the Motorists' Union, who feared that it would lead to motorists' losing the freedom to use public roads.
In Germany, the Nazi regime was committed to promoting the mass use of private motor cars and viewed the bicycle as an impediment to this goal. For the authorities the exclusion of cycle traffic from main routes was viewed as an important pre-requisite to the attainment of mass motorisation. Accordingly a mass programme of cycle track/cycle path construction was implemented. In addition, new laws were imposed to force cyclists to use segregated cycle paths. to which it is reported that German cyclists objected. The Nazis outlawed cyclists' organisations and seized their assets or subsumed them into the state-controlled Deutscher Radfahrer-Verband, a unit of the Nazi Sports Body. By 1936, the German motoring press was discussing the use of narrow cycle lanes marked on the carriageway, to facilitate overtaking and to frustrate cyclists in the "unpleasant" practice of cycling side-by-side.
In 1926 the CTC discussed an unsuccessful motion calling for cycle tracks to be built on each side of roads for "the exclusive use of cyclists", and that cyclists could be taxed, providing the revenue was used for the provision of such tracks. The first (and one of the very few) dedicated roadside optional cycle tracks was built, as an experiment for the Ministry of Transport, beside Western Avenue between Hanger Lane and Greenford Road in 1934. It was thought that "the prospect of cycling in comfort as well as safety would be appreciated by most cyclists themselves". However, the idea ran into trenchant opposition from cycling groups, with the CTC distributing pamphlets warning against the threat of cycle paths.  Local CTC branches organised mass meetings to reject the use of cycle tracks and any suggestion that cyclists should be forced to used such devices. In 1935, a packed general meeting of the CTC adopted a motion rejecting ministerial plans for cycle path construction. The CTC were listened to, and the use of cycle tracks largely fell out of favour in the UK.
Post-war German governments chose to continue the transportation objectives of their Nazi predecessors, and cyclists were viewed as an impediment to motorised traffic to be excluded and restricted whenever feasible. By the end of the 1960s Germany's transport policies had caused cycling to fall from 50% to 5% of trips. In the UK, little use of separate cycleway/cycle track systems took place except in the so-called "new towns" such as Stevenage and Harlow. From the end of the 1960s in Nordic countries, the Swedish SCAFT guidelines on urban planning were highly influential and argued that non-motorised traffic must be segregated from motorised traffic wherever possible. Under the influence of these guidelines cyclists and pedestrians were treated as a homogeneous group to be catered for using similar facilities. The guidelines strongly influenced cities such as Helsinki and Västerås to build large cycle path networks. By the late 1960s and 1970s, with the cyclists mainly gone, many German towns began removing cycle tracks so as to accommodate more car parking. Increasing traffic congestion and the 1970s oil shocks contributed to a resurgence in cycling in some countries. Outside of SCAFT-inspired developments in Nordic countries, the use of segregated cycle facilities was mainly confined to university towns with established populations of bicycle users.
In 1971, the California state government contracted with University of California, Los Angeles (UCLA) for the design of bikeways (bicycle paths, bicycle side-paths, bicycle lanes). UCLA largely copied Dutch bicycle facilities practice (primarily sidepaths) to create their bikeway designs, but the derived designs were not made public. The California Statewide Bicycle Committee (CSBC) was created. Initially composed of representatives of governmental and motoring organisations. When John Forester, a cyclist representative, became a member he concluded that its real motivation for moving cyclists aside was the convenience of motorists, although the stated reason was the safety of cyclists. Serious safety issues were identified with the proposed designs. The resulting cyclist opposition discredited the designs and prevented enactment of a mandatory side-path law. This forced the state to start over with new bikeway design standards in 1976. Those designs were subsequently adapted by the Association of American State Highway and Transportation Officials (AASHTO) to form the first edition of the AASHTO Guide for Bicycle Facilities, which is widely followed in the USA.
The 1980s saw the start of experimental cycle route projects in Danish towns such as Århus, Odense and Herning, and the beginning of a large programme of cycle facilities construction as part of a "bicycle masterplan" in the Netherlands. Following the "bicycle boom" of the early 1980s, German towns began revisiting the concept. The use of segregated cycle facilities is promoted by a large segment of the cycling community, for example lane and path cyclists, and also by many organisations associated with the environmental movement. The rise of the "Green" movement in the 1990s has been accompanied by requests for the construction of cycle networks in many countries. This has led to various high-profile cycle network projects, in Bogotá, Montreal, Dublin, Portland and many other cities.
The issue of the safety of segregated cycling facilities is one of controversial. Proponents tout segregation of cyclists as necessary to the provision of a safe cycling environment. In contrast, some research imply increases, some significant, in the rate and severity of car/bicycle collisions due to such segregation. Traffic reform advocate David Engwicht suggests that the added perception of risk in shared facilities increases safety.
Since the 1930s, the established cycling lobby in the UK and Ireland has taken a critical and measured view of the utility and value of segregating cyclists. In 1947, in response to official suggestions that cyclists should use cycle-tracks, the CTC adopted a motion expressing determined opposition to cycle paths alongside public roads. In 2007, official claims of safety for cycle tracks provoked a position paper from the umbrella body for UK cyclists' groups, stating "Cycle Campaign Network knows of no evidence that cycle facilities and in particular cycle lanes, generally lead to safer conditions for cycling".
In the 1970s the California Statewide Bicycle Committee arranged with Kenneth D. Cross for a study of car-bike collisions, expecting that this study would support their arguments on collision prevention. When presented to the Committee in Sacramento on 19 June 1974, Cross's study showed the opposite: only 0.5% of car-bike collisions had occurred between straight-ahead cyclists and overtaking straight-ahead motorists. Cross later had a contract with the National Highway Traffic Safety Administration (NHTSA) to produce an improved study (on a pseudo-random national sample), and the results were much the same. A 2006 report concludes that "bicycle safety data are difficult to analyse, mostly because bicycle trip data (and thus accident probability per trip) are hard to uncover" (see NCHRP Report 552, 2006, "Guidelines for Analysis of Investment in Bicycle Facilities", National Cooperative Highway Research Program, Transportation research Board of the National Academies, page F-1). The Netherlands and Denmark, which have the highest rates of cycle usage combined with the best records for safety, used to give their segregated cycle path networks primary importance in achieving these goals. However, the largest study undertaken into the safety of Danish cycle facilities has found that safety has decreased as a result. More recently, Shared Space redesigns of urban streets in those and other countries have achieved significant improvements in safety (as well as congestion and quality of life) by replacing segregated facilities with integrated space.
The source of the direct safety problem lies in the nature of the predominant car/bicycle collision types. The majority of collisions on urban roads occur at junctions and involve turning vehicles. Rear-end type collisions are only a major factor on arterial or interurban roads.       More width for cyclists to use on rural/arterial roads with few junctions might lower the net number of collisions, but the data does not help answer the question of whether separating cyclist from other users would make a significant difference one way or the other.
For urban roads with many junctions, accident analysis suggests that segregated cycling facilities are likely to produce a net increase in the number of collisions. These conclusions are supported by the experience of countries that have implemented segregated cycling facilities. In the United States, UK, Germany, Sweden, Denmark and Finland, it has been found that cycling on roadside urban cycle tracks/sidepaths results in up to 12-fold increases in the rate of car/bicycle collisions. At a 1990 European conference on cycling, the term Russian roulette was used to describe the use of roadside cycle paths.
In Helsinki, research has shown that cyclists are safer cycling on roads with traffic than when using the city's of cycle paths. The Berlin police and Senate conducted studies which led to a similar conclusion in the 1980s. In Berlin 10% of the roads have cycle paths, but these produce 75% of fatalities and serious injuries among cyclists. In the English town of Milton Keynes it has been shown that cyclists using the off-road Milton Keynes redway system have on a per-journey basis a significantly higher rate of fatal car-bicycle collisions than cyclists on ordinary roads. Cycle lanes and bike lanes are less dangerous than cycle paths in urban situations but even well-implemented examples have been associated with 10% increases in casualty rates.
Particular concern attaches to the use of cycle lanes in urban situations such as large roundabouts. For adults, the standard safe cycling advice for handling roundabouts is to try to maintain a prominent position while circulating. The use of cycle lanes runs counter to this advice and places cyclists outside the main "zone of observation" of entering motorists, who represent the overwhelming source of risk (50% of collisions). In 2002, cycle lanes were removed from a roundabout in the English town of Weymouth after 20 months because the casualty rate had increased significantly. German research has indicated that cyclists are safer negotiating roundabouts in traffic rather than on separate cycle lanes or cycle paths. A recent paper on German roundabout design practice states "Cycle lanes at the peripheral margin of the circle are not allowed since they are very dangerous to cyclists". See also cycle facilities at roundabouts.
In the UK at least, separate and shared-use (with pedestrians) cycle paths are not salted or gritted in icy conditions, making them dangerous or completely unrideable; those who are willing to continue cycling in such conditions are safer on the main road if that has been appropriately treated. Broken glass causing punctures is also a problem on cycle paths for two reasons: drinkers are more likely to drop bottles on paths than on the road, and any broken glass on a busy road is quickly crushed to harmlessly small powder and swept aside by passing vehicular traffic.
Direct rear impacts with cyclists are a more prominent collision type in arterial/rural road type situations. When they occur in such circumstances they are also associated with significantly increased risk of fatality. Data collated by the OECD indicates that rural locations account for 35% or more of cycling fatalities in Denmark, Finland, France, Great Britain, Japan, the Netherlands and Spain.
Cycling collision data recorded by police in the UK data indicates that at non-junction locations, where a cyclist was struck directly from behind there was an overall fatality rate of 17%. The rate of fatality increases with speed limit of the road:
The use of appropriately designed segregated space on arterial or interurban routes appears to be associated with reductions in overall risk. In Ireland, the provision of hard shoulders on interurban routes in the 1970s reportedly resulted in a 50% decrease in accidents. It is reported that the Danes have also found that separate cycle tracks lead to a reduction in rural collisions.
There is evidence that one of the main factors influencing the individual safety of cyclists is the base number of cyclists using the roads - see safety in numbers effect. Therefore it is arguable that if a segregated cycle facility attracts more people to cycle, this should contribute to an increase in safety. For instance, a study of the accident impacts of re-engineering bicycle crossings in the Swedish city of Gothenburg attributes collision rate reductions in part to significant increases in cyclist volumes at the treated sites. In addition it has been shown that in Western countries the health benefits of regular cycling significantly outweigh the risks due to traffic danger.   Therefore, notwithstanding a net increase in collisions, measures that promote cycling should produce an overall societal health benefit. Dutch analysts have argued as a statistical exercise that given that three times as many cyclists as car occupants are injured in collisions, and that cars harm about three times the number of other road users that bicycles do, in situations where casualties due to car traffic predominate increasing the number of cycling journeys and reducing the number of car journeys will reduce the total number of casualties However, given their historical purpose, a positive relationship between the use of segregated cycle facilities and increased cyclist numbers cannot be assumed.
The "safety in numbers" argument has also been used to explain the apparent success of cycle facilities in some cities. In most cases, the most prominent examples of "successful" cycle networks were implemented in towns that already had significant numbers of cyclists. It is argued that in such cases this existing large cycling population already exerts a strong "safety in numbers" effect, and it is this, rather than their diversion onto off-road tracks, that accounts for the better safety record. More people might start cycling if the perceived safety of doing so improved sufficiently. Segregated cycle facilities are one way to improve the perception of safety. There are other approaches, such as Shared Space, which improve actual safety in part by decreasing the difference between real and perceived safety. See the Utility cycling article for other examples of measures to improve both actual and perceived safety.
Various remedial measures have been developed in an attempt to solve the identified safety problems of segregated cycle facilities. In some environments these represent established engineering practice while in others they may have to be retroactively applied in response to complaints and safety concerns. Examples include the addition of a separate system of traffic signals for bicycle traffic. This can result in greater cost and complexity in implementation particularly if there are already separate traffic signal phases for pedestrians, motorised traffic and public transport.
Some treatments involve raising the cycle track onto a speed ramp type structure where it crosses side roads. In addition, various road markings have been developed in an attempt to remedy the issue of increased junction collisions. Examples of these include the use of special road markings, e.g. "sharks teeth" or "elephants footprints", and treatments using red, green or blue coloured tarmac. Cycle-facility sceptics counter these improvements often simply "restore" the level of safety that existed before the marking or construction of the segregated cycle facility.
Other approaches include efforts to "traffic calm" the bicycle traffic by introducing tight curves or bends to slow the cyclists down as they near a junction. Alternatively, traffic engineers may remove priority from the cyclists and require them to yield to turning traffic at every side road. In 2002, engineers proposing a sidepath scheme in the Irish university city of Galway stated that cyclists would be required to dismount and "become pedestrians" at every junction on the finished route.
One of the potential pitfalls for observers trying to interpret the operation of segregated cycle facilities is that the same legal assumptions do not apply in all environments. For instance, in contrast to most English speaking countries, some Northern European countries, including Germany, France, Denmark, Belgium and the Netherlands have defined liability legislation. Thus there is a legal assumption that motorists are automatically considered liable in law for any injuries that occur if they collide with a cyclist. This may hold regardless of any fault on the part of the cyclist and may significantly affect the behaviour of motorists when they encounter cyclists.  In some countries it is legal for cyclists to overtake motor-vehicles on the inside, and cyclists doing so may enjoy the protection of the law. In this case, the use of segregated cycle facilities conforms to existing traffic law. In other jurisdictions similar "undertaking" manoeuvres by cyclists are illegal. Such distinctions form the basis of the argument that segregated cycle facilities encourage behaviours that flout existing traffic law and in which cyclists enjoy no legal protection.  
This variation also applies to the operation of traffic signals and cyclist-specific traffic lights. For instance, in Germany and elsewhere at junctions with segregated facilities all the traffic in a given direction (motorists, pedestrians and cyclists) may get a green signal at the same time. Turning motor traffic is obliged to wait for cyclists and pedestrians to clear the junction before proceeding. In this situation all the transport modes get equal green time. In contrast, UK and Irish practice restricts pedestrians to a dedicated signal phase, separate from and usually much shorter than the green phase for motorists (e.g. 6-12 seconds, vs. signal cycle times of up to 120 seconds).  If cyclists were to be segregated and treated in a similar manner this would imply a significant reduction in green time for cycle traffic at every junction. In the English city of Cambridge the use of cyclist-specific traffic signals is reported to have resulted in increased delays for cyclists, leading some to ignore the cycle-facilities and stay on the road. A similar example occurred in a Parisian bikepath scheme in 1999. Cyclists faced twice the number of traffic signals as motorised traffic and were expected to wait over one minute to get seven seconds of green time. Conversely, in Copenhagen cyclist-specific traffic signals on a major arterial bike lane have been linked to provide "green waves" for rush hour cycle-traffic.
Other potential pitfalls in interpreting the operation of segregated cycle facilities are the issues of design vehicles and design users. The Netherlands is a flat country and Dutch town planning keeps cycling distances short. The typical Dutch town bike or "granny bike" has no gears or a three-speed hub gear and back pedal brakes. In countries with different geographies and cycling cultures bicycles tend to have 7-15 gears (not counting duplicates), and a reasonably fit adult commuter can expect to reach speeds of 30 km/h (20 mph) Sports cyclists can travel even faster: with tailwinds or downhill gradients, some cyclists may exceed 50 km/h (30 mph). While a Dutch sidepath system may work for Dutch cyclists, serious questions have been raised since at least the 1970s that other cyclists using faster bicycle types cannot use such a system safely at their higher normal cycling speeds. The Danish Roads Directorate acknowledges that the advent of faster bicycle types has not increased safety, since their cycle track system "functions best when cyclists travel at relatively low speeds"
In some cases designers may focus on a particular design user. The UK’s Sustrans guidelines for the National Cycle Network are based on recreational use with a design user who is an unaccompanied twelve-year-old. The Dublin Transportation Office has advertised their cycle facilities as being based on an unaccompanied ten-year-old design user. This raises the issue of what happens if different cyclist types find themselves forced onto such devices either by legal coercion or as a result of motorist aggression. This issue is captured in a 1996 review of the Sustrans approach from the Proceedings of the Institution of Civil Engineers.
The fast cycle commuter must not be driven off the highway onto a route that is designed for a 12-year-old or a novice on a leisure trip, because if that happens, the whole attempt to enlarge the use of the bicycle will have failed
Moving motor vehicles generate a "sweeping" effect that pushes debris such as grit and broken glass to the edge of the roadway. By excluding motor traffic, cycle lanes and cycle tracks become parts of the road that are no longer routinely "swept", thus collecting more broken glass and gravel. In addition, some off-road designs are simply not accessible to standard road sweeping equipment. One UK study estimated that cycle path users are seven times more likely to get punctures than are road cyclists. Both sides of the argument acknowledge that many cyclists will simply refuse to use poorly maintained facilities. Cycle facilities sceptics go further and argue that there is no point funding new cycle facilities unless there is a simultaneous commitment of increased funds to maintenance and sweeping afterwards. Similar problems arise in areas subject to high leaffall in autumn, or high snowfall in winter, any cycle facilities must be subject to regular clearing or else rapidly become unusable. Danish guidance specifies three different categories of cycle track. Category "A" tracks must be kept clear of snow 24 hours a day, category "B" tracks are swept or cleared daily, and category "C" receive less regular winter maintenance. In 2007 the city of Copenhagen spent DKK 9.9 million (US$1.72 million, €1.33 million) annually on maintaining its cycle track network. German federal law requires local authorities to declassify cycle tracks that do not conform to strict design and maintenance criteria.
There is well-established historical precedent for the use of cycle facilities as a means of promoting motoring at the expense of cyclists.  Despite this, some commentators, particularly those associated with the environmental and/or motoring lobbies, proclaim segregated cycle facilities as the "measure of choice" for restoring cyclist access to western cities. This is highly controversial and is a source of dispute, occasionally quite bitter - see also cycle path debate.
In contrast, in 1996 the CTC and the Institute of Highways and Transportation jointly produced a set of Cycle-Friendly Infrastructure guidelines that placed segregated cycling facilities at the bottom of the hierarchy of measures designed to promote cycling. Planners at the Directorate Infrastructure Traffic and Transport in Amsterdam place cyclists and motorists together on roads with speed limits at or below 30km/h, and segregate them through bicycle lanes at higher limits. This is in a context where most of the measures prioritised by Cycle-Friendly Infrastructure (HGV restrictions, area-wide traffic calming, speed limit enforcement etc) are already in place - see Utility cycling for more detail.
Between the late 1980s and early 1990s the Netherlands spent 1.5 billion guilders (US$945 million) on cycling infrastructure, yet cycling levels stayed practically the same. When the flagship Delft Bicycle Route project was evaluated, the results were
not very positive: bicycle use had not increased, neither had the road safety. A route network of bicycle facilities has, apparently, no added value for bicycle use or road safety.In the UK, a ten-year study of the effect of cycle facilities in eight towns and cities found no evidence that they had resulted in any diversion from other transport modes. A similar finding had been reported for Denmark in 1989, where it was found that there was no correlation between cycle facilities and increased cycling unless active traffic restraint measures were also present. In Denmark as a whole, the establishment of a huge cycling infrastructure has been accompanied by cycling levels that have stayed roughly stable (with minor fluctuations) since 1975. The construction of of "Strategic cycle network" in Dublin has been accompanied by a 15% fall in commuter cycling and 40% falls in cycling by second and third level students. In contrast, in the late 1970s and early 1980s cycling underwent robust growth in Germany, while in the UK and Ireland there was little or no investment in cycling infrastructure.
A key criticism made by the opponents of such schemes is that the focus is often on constructing "cycle facilities" rather than "facilitating cyclists". It is readily apparent that there are many cities that have extensive cycle networks and also high levels of cycling. However, the most prominent examples tend to be compact, often mediaeval, university cities. This common theme has been taken to suggest that other underlying factors are driving the levels of cycle use.
Some commentators argue that the "cause and effect" being seen is actually the reverse of that which is often claimed: that it is the presence of large numbers of cyclists that tends to precipitate the construction of segregated cycle facilities. For instance, bike planning in Davis, California was driven by the prior existence of a "dramatic volume" of cyclists in the 1960s. Possibly the best that can be said is that the safety of cycling and the number of cyclists results from a complex interaction of spatial planning, population density, legislative environment, and wider traffic/transportation management policies. The evidence suggests that segregated cycle facilities can play either a positive or negative role, secondary to other factors - see utility cycling.
Separate cycleways and bike trails are less controversial when used to promoting recreational cycling. In Northern European countries, cycling tourism represents a significant proportion of overall tourist activity. Extensive interurban cycleway networks can be found in countries such as Denmark, which has had a national system of cycle routes since 1993. These may use roads dedicated to exclusively cycle traffic or minor rural roads whose use is otherwise restricted to local motor traffic and agricultural machinery. The UK has recently implemented the National Cycle Network.
Where available these routes often make use of abandoned railway corridors - see picture right of Mosel Maar cycle route. A prominent example in the UK is the Bristol & Bath Railway Path, a off-road cycleway that is part of National Cycle Route 4. Other UK examples include The Ebury Way Cycle Path, The Alban Way, the Hillend Loch Railway Path and the Nicky Line. In 2003 the longest continuous cycleway in Europe was opened, along the Albacete-Valdeganga highway in Spain, a distance of . Bogota's Bike Paths Network or "Ciclo-Ruta" in Spanish, designed and built during the administration of Mayor Enrique Peñalosa attracts significant recreational use.
In terms of multi-use trails, a "shared trail" may refer to a shared trail corridor with or without segregation within the corridor. In this context, segregated cycle facilities are a subset of shared facilities. Segregation may be supported by physical separation.