Transport for London has confirmed that work will shortly begin on segregated "cycle superhighways" in Central London, due for completion in 2016, augmenting the fragmented blotches of blue paint that currently claim to do the job on some of the capital's roads. There will be an East-West route from Tower Hill to Acton, and a North-South route from King's Cross to Elephant & Castle, the two interconnecting at the north end of Blackfriars Bridge. No doubt the new MP for Uxbridge will be the first to try them out, probably on the longer Acton to Tower Hill route, which will allow for a photo opportunity at Parliament Square followed by lunch in The City. We can only hope the name "Boris lanes" does not catch on.
Coincidentally, the free marketeers at the IEA have issued a proposal to convert various urban rail lines into busways, i.e. dedicated, single-lane roads for high-capacity buses. Leaving aside their ideological antipathy to railways as natural monopolies that the state cannot avoid managing, their case is perfectly rational viewed in terms of minimising cost and maximising carrying capacity, but it will disappear without much trace. The same cost-benefit rationale would indicate that segregated cycle lanes are the worst possible use of a scarce resource, but the odds are that the current plans will lead to more routes in future. So why is it that the political establishment in London is (broadly) keen on cycleways but not on busways?
Carrying capacity (the number of passengers who can pass a specific point in a given period) is essentially a factor of the speed and size of vehicles. Generally speaking, the faster a mode of transport, the lower the capacity because of increased stopping distances (the stopping distance increases by the square of the increase in speed). You can potentially offset this reduction if you increase vehicle size, subject to aerodynamic drag. It is difficult to do this for trains due to the constraints of existing infrastructure (low bridges and limits on platform extension in urban areas), so high-speed railways inevitably end up being premium services enjoyed by the few. Conversely, the high capacity of the Tube is largely down to the relatively slow speeds dictated by short runs between stations and Victorian engineering.
Buses are potentially higher capacity than trains because of better braking (rubber on tarmac is superior to steel on steel) and upper decks (assuming you avoid low bridges and trees). The problem is that they are in competition for road space with cars and lorries, though this is elsewhere an advantage in that they can flexibly serve low-use routes - e.g. minibuses in rural areas. Railways have the advantage of dedicated corridors in urban areas by which they can carry relatively large numbers quickly into and out of city centres. Without this, nobody would ever build a railway (of course, without railways, you can't easily build large cities). Aeroplanes are far cheaper over longer distances (you don't have to build sky), but their capacity is constrained by speed, distance from urban centres and limited runways, as well as externalities such as noise and air pollution.
A dedicated busway makes sense in terms of capacity, but it is also attractive (to a certain mindset) because it creates two classes of road: mass transit for the majority in parallel with mixed-use roads for a minority who can afford tolls (e.g. the congestion charge). As with most libertarian fantasies, this boils down to segregation. The problem with converting existing railways to busways is that the tracks used by commuter trains are also often used in part by inter-city trains. Where routes aren't mixed use, they've usually been incorporated into light-rail systems already (e.g. the Overground in London). Where busways have been implemented, they are usually new-builds in expanding cities where land values are relatively cheap (e.g. South America).
Arguably, a better approach for London would be to convert existing roads to dedicated busways (the logical extension of bus-lanes), but that would be inconvenient for car and van-drivers, which is why the IEA doesn't argue for it. This reluctance to offend drivers is matched by the popularity of trains with the middle-classes, which together limits the potential for the re-purposing of either roads or railways. This in turn explains why schemes that carve out road capacity for cycling can only succeed where they clearly benefit the influential upper middle classes, which is why a cycleway between The City and Acton (crossing Hyde Park and skirting Notting Hill) is being referred to admiringly by both the cycle lobby and the Evening Standard as "Crossrail for bikes". The shorter North-South route will cement the gentrification of Elephant & Castle.
Cycleways are low capacity. High-capacity platoon cycling, i.e. where everybody chugs along in a group at a common speed, was the norm before mass car-ownership but is now a distant memory, even in China. In an environment with vehicles travelling at different speeds, the fastest effectively dictates the carrying capacity because of the natural desire to maintain safe distances (the proposed TfL routes are two-way, i.e. you have to avoid on-coming traffic). Once you get racing bikes, mountain bikes and fixed-gear bikes on the roads - the result of wealth plus concerns over fitness and the environment - you reduce carrying capacity due to competition. This is not just testosterone, but the result of the plurality of bike capabilities, personal objectives (working up a sweat versus transport) and attitudes towards risk (exemplified in jumping lights, which will still be a problem with segregated routes that intersect with roads and pedestrian crossings).
Because of modern cycling manners, the per capita capacity demanded by cyclists will always be in excess of other modes of transport. This is a triumph of the individual over the collective, and thus an inefficient use of road space and transport spending. Cycling has become popular with politicians not just because it is seen an environmentally-friendly, with the added cultural bonus of an image that mixes the common touch, the fashionable and the slightly lairy, but because it is emblematic of constant striving and individual achievement. Like marathon running, it is an exemplary neoliberal mode of transport - i.e. elitist and antisocial (this is sidestepped by cyclists who habitually cast themselves as victims). Whereas segregation once meant denying access to others, now it means opting out. Arguably, it has done ever since the 1960s.
Cycle superhighways are part of the emerging urban transport environment in which segregation between different modes in city centres is not just a practical necessity but a means of status identification - i.e. a privilege. The further expansion of the segregated cycle network in London will depend on the reduction of existing road traffic, which may be achieved through a combination of autonomous vehicles (Uber increasingly looks like a stepping-stone) and more expensive tolls. Once, the chief difference between urban and suburban transport was underground. In the future, it will be overground. The city gates of old will be reintroduced, just further out.