Tuesday, March 8, 2011

London Congestion

Looks like the focus is on congestion this week - London Assembly's transport committee has launched an investigation, reports Dave Hill. Freewheeler also has a good analysis here.

London has the most congested roads in Europe.

The reason is simple: TfL's approach is to try to maximise traffic flow, by maintaining all roads at their current capacity and refusing to entertain the idea that the current traffic situation is less than ideal.

You can't blame roadworks. As I've pointed out before, roadworks are an undesirable fact of life that arises from services such as gas, water, telecoms and electricity being located under roads. No one likes them but no-one's figured out a way to get rid of them.

Unfortunately, maximising network capacity doesn't make journeys faster. This is not speculation: it's science. Braess's paradox tells us that additional links on a network can make the average trip slower, and the Downs-Thompson paradox tells us that increasing road capacity can make congestion worse.

It's mainly private transport - meaning taxis and private cars - that determines the level of congestion in central London. If private transport were a closed system, that would not be a huge problem, but because buses use the same road network, the congestion affects bus journey times as well, reducing the incentive for people to switch from private to public transport. Furthermore, motor traffic initimidates cyclists off the road.

Commercial traffic also shares the same road network. Slow journey times and lack of predictability can increase costs on business significantly.

If you accept the position that congestion cannot be allowed to be self-limiting (in other words, congestion will get worse until sufficient numbers of people switch modes or quit travelling), it follows that there must be attempts to discourage road use. This could either be done through economic mechanisms such as road pricing, or it could be done through restrictions. The London Congestion Charge has had some effect, but Boris has abolished the Western Extension Zone, and there's a large amount of vehicles that are now exempt, including taxis and lower-emitting private cars.

If we assume that all journeys are necessary (which is certainly arguable), the key is to get people to switch from private motor transport, which is the least efficient use of roadspace, the most congesting and the most polluting, to other modes.

Clearly it makes sense to speed up bus journeys, because that will make the bus a more attractive option, increase the capacity of the bus network and reduce operating costs. However, speeding up bus journeys requires lower congestion on bus routes as a precondition. One approach would be to ban taxis from some bus lanes, another would be to restrict private motor traffic somehow to non-congesting levels.

Cycling is not currently an attractive option but as with buses, there are good reasons to make it attractive. It is an efficient use of roadspace, and as well as health, noise and atmospheric pollution benefits, cycles can use routes (such as quiet, narrow routes) that other traffic cannot effectively use. However, to increase cycling, you need to reduce the intimidation by motor vehicles, which effectively means placing restrictions on how and where motor vehicles can be driven.

Let's look at the Mayor's current policy responses:

Crossrail, the Tube upgrades, Thameslink and expansion in the capacity of suburban rail services
All good, but how much effect will they have on road congestion? To a large extent, people are choosing to drive because the rail network doesn't provide a good alternative.

ensuring the existing network is working as well as possible - ‘smoothing the traffic flow'
This is pretty much what TfL have been doing. Trouble is, if you improve flow, you attract more traffic, and you can end up with worse congestion.

Using SCOOT to intelligently re-sequence traffic lights in response to fluctuations in traffic demand...reviewing traffic signal timings...removing traffic lights.
Again, the risk here is you simply attract more traffic. The same bottlenecks, such as Trafalgar Square and the Thames bridges will still be there. Another risk is because you're bringing the system nearer saturation point, it  becomes much more sensitive to minor disruptions such as crashes.

reducing the level of disruption caused by roadworks
As I've pointed out, it's easy to talk about this but a lot harder to do something effective about it.

Maintaining and building new road assets
Not much space for new roads in London. And again, see above - adding capacity can simply make matters worse through induced demand.

reducing demand...improving information to people before they travel...helping people to choose more sustainable forms of transport, such as walking and cycling, through smarter travel programmes
It's unclear how much effect this will have without better infrastructure. People don't cycle principally because of traffic fears, and 'smarter travel' iniatives have not increased modal share beyond a very low level. There's been more success in persuading people to use public transport, but there remains the problem that existing congestion levels make buses unattractive, and public transport fares are among the highest in Europe.

You'd have to be an incorrigible optimist to conclude that these policy initiatives are going to make much difference to congestion, mainly because Boris is making no serious attempt to manage demand. The inevitable result will be that demand will be self-limiting. People who have the highest tolerance for delay will continue making their journeys, no matter whether they are important or not. People who have no choice but to use the roads will either be forced to change their schedule or simply put up with delays.

The Mayor and TfL need to accept that the whole paradigm of trying to provide for the amount of traffic that's on the roads already is a flawed one. The idea that all road journeys are of equal value and that the system will find an optimum equilibium is wrong. It's time to accept that the need to provide fast and predictable travel for the most number of people is not compatible with unrestricted access to roads by private cars. That's even without considering air quality, oil-dependency, health and quality of life.

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