Solving London's Street Pollution
First of all there should be no confusion between greenhouse gas problems (essentially the carbon argument) and health related air pollution (sulphur oxides, nitrogen oxides and small particles). They are completely separate issues and some technologies which reduce one either increase or make no difference to the other. Electric trams and trolleybuses of course totally eliminate the health related air pollution (power stations even if fossil fuelled are well filtered and not in city centres) and they reduce (or eliminate with renewable electricity production) greenhouse gas production. No other technologies can truthfully claim this.
Proposed 5 minute frequency Trolleybus network, central area, on NO² map
Whilst there is no absolute agreement as to what are 'safe' levels of the various air pollutants (even if any level is 'safe'), there are a number of standards: UK, EU, USA, UN etc. Whilst these may be slightly different, essentially everyone recognises that you will not get zero levels along roads in cities, however many filters, low sulphur fuels etc. you have. What you do need to achieve is to get levels along all roads and areas below levels which are accepted as being seriously hazardous to health. What this means is that less average overall pollution in the whole city is not necessarily better than more.
It is the maximum level along specific local corridors (city roads are always pollution corridors) that is important. If you have a side street where there is minimal other road traffic and one bus route that runs about every half an hour, then the air pollution is not likely to be of a high order or anywhere near the 'danger levels' even if the route is operated by the worst of older buses. On the other hand if you have a very busy road (such as the Marylebone Road in London , which is consistently the worst air pollution 'hot-spot') and you have heavy non-bus traffic together with a large number of very frequent motor bus routes, it could easily be the motor bus exhausts that take you over the limit even with the best possible filters, fuels, engine designs etc.
Where there are heavy concentrations of buses running frequently along busy corridors, you therefore need electric trolleybuses on all (or nearly all) the routes to bring down the air pollution to acceptable levels. If you succesfully get a very large number of people out of cars and into motor buses (of whatever sort), you may actually make air pollution (and thus health) worse, as the cars would be spread over a greater area using side streets, 'rat runs' etc., whilst the buses are concentrated on a few major roads. Whilst the side streets (already within acceptable levels) would get slightly better, the major roads may well now exceed the acceptable levels.
The introduction of less polluting motor vehicles and electric trolleybuses of course does not need to be mutually exclusive. The less polluting motor vehicles can replace older buses in the normal replacement cycle or alternatively earlier on more sensitive areas with the older vehicles then cascaded to the lesser used, less frequent services using less congested roads.
If planned properly a combination of measures (including less polluting motor buses) could significantly improve health by reducing levels in those areas where pollution is above or approaching dangerous levels. What you can not do is achieve this by having more (or even all) less polluting motor buses and thus simply lowering the average pollution per vehicle. I suggest in a large city like London you are never going to make the necessarily large change along the busiest corridors without a sizeable electric (trolleybus) network using those corridors, instead of the present motor buses. More modal change from cars to public transport makes this more vital not less.
link to 5 minute network
Related pages -
London low emission zone study
Download 'Calculations and references relating to health and environmental costs, in relation to Public Service Vehicles'
(88kb Word document)
Promoting quiet, clean urban transport using Overhead Electric, Zero Emission Trolleybuses -
email The Electric Tbus Group