Memorandum submitted by David Starkie
1. The Committee has invited evidence in
relation to the above Inquiry and is particularly interested in
a number of specific issues. This memorandum is focused on its
strategic issues and, in particular, on bullet points 4 and 5
listed in the press release.
2. The dominant source of transport emissions
is road traffic and, because of this, attention has focused on
changing the fuel mix of vehicles and reducing their average fuel
consumption as a result of developments in vehicle technology.
The Department for Transport's low carbon vehicle strategy is
such an example. What is overlooked is the important relationship
between vehicle speed and fuel consumption and hence between speeds
and emissions of carbon. The proposition in this memorandum is
that limiting or eliminating excessive traffic speeds, and especially
by achieving compliance with national speed limits, would make
a major contribution to meeting the Kyoto targets on carbon emissions.
3. The reason why compliance with speed
limits, and particularly with the maximum limit of 70mph, would
make a major contribution to reducing carbon emissions is two-fold.
4. First, fuel consumption, and hence greenhouse
gas emission, of vehicles is basically u-shaped with respect to
speed. The economical speed for most vehicles is between 50 and
60 mph. Increasing speed beyond this level increases fuel consumption
at a progressively faster rate, so that a vehicle travelling at,
say, 90 mph is emitting far more pollutants than a vehicle travelling
at 70 mph.
5. Second, speeding on Britain's roads is
endemic, especially on motorways and trunk roads, which account
for about one-third of total vehicle miles. The table below illustrates
this situation with respect to driving speeds on motorways and
dual carriageways over the 10 year period 1994-2004. I have compiled
the table by adapting figures in the Department for Transport's
annual publication Vehicle speeds in Great Britain. These figures
are based on survey sites where the traffic is likely to be free
flowing but slower recorded speeds during the morning and evening
peak periods suggest that this is not always the case. Consequently,
the survey data probably under-estimates free flow speeds.
6. From the table it can be seen that car
speeds have been steadily increasing over the period such that
by 2004 the average speed of cars on motorways exceeded the national
speed limit and on dual carriageways was almost identical to the
national speed limit. On motorways well over half of cars were
exceeding the speed limit, whilst on dual carriageways almost
one half exceeded the limit. Importantly, a large number of cars
(and light goods vehicles) exceeded the limit by more than ten
miles per hour. This proportion has also grown over time with
the result that on motorways nearly one in five cars exceeds eighty
miles per hour and thus emits disproportionately large quantities
CAR (LIGHT GOODS)
SPEEDS ON MOTORWAYS AND DUAL CARRIAGEWAYS
|Year||Average speed (mph)
||Speed limit (mph)
||Per cent over limit
||More than 10mph over limit
Source: Adapted from Vehicle Speeds in Great Britain
1994 and 2004 editions.
Statistics for light goods vehicles shown in parenthesis.
7. Increased enforcement of existing limits using traditional
policing methods is not an option, if only because the police
give speed enforcement low priority and are not willing to commit
more resources to the task, given what they perceive as the high
opportunity costs of doing so.
8. In urban areas greater use is being made of technology,
particularly speed cameras, to deter speeding. It is doubtful,
however, that the approach of using vehicle recognition technology
would have much success in reducing speeds on motorways and trunk
roads unless the commitment of resources was very considerable.
This is because exceeding the 70mph limit is so wide-spread that
changing behaviour will be very difficult without a very large
number of prosecutions (which would probably be unacceptable politically).
The circumstances might suggest that the maximum speed limit should
be increased and coupled with stronger enforcement, but it is
not at all clear that this would eliminate a tail of vehicles
exceeding a revised limit. It is most likely to lead to an overall
increase in emissions (and accident rates).
9. Another approach is to extend the application of speed-limiters
to vehicles. Mechanical speed-limiters have been fitted to all
new heavy goods vehicles (with a maximum weight in excess of 7.5
tonnes) since 1992 and since that date most buses and coaches
have been fitted. This has led to a significant drop in the number
of such vehicles exceeding the motorway speed limit with a consequential
saving in emissions. The technology has developed since the early
1990's so that electronic devices are now probably cheaper and
more effective (the technology is similar to that incorporated
in vehicle cruise control).
10. There are a number of options for extending the application
of speed limiters, which present themselves. The generic options
to incorporate speed limiters in newly registered
vehicles after a specific date; and
to retrofit tranches of the existing national
stock of vehicles (not already speed-limited), in accordance
with a roll-out programme.
11. Because parts of the existing stock of vehicles (HGVs
and buses and coaches) are already fitted with speed limiters,
there are also options in terms of which other classes of vehicle
might be (electronically) speed limited. My order of preference
would be as follows:
Medium weight goods vehicles: under current regulations
large commercial vehicles of up to 7.5 tonnes are not fitted with
speed limiters and are also free to use the third lane on motorways.
Because of the vehicle mass involved, high-speeds by these vehicles
are associated with particularly high fuel consumption.
Taxis and mini cabs: these are essentially a form
of public transport and are increasingly used for long-distance
journeys, particularly to airports. (I also have personal experience
of an unpleasant journey in a taxi at over 90 mph between Gatwick
Light goods vehicles (including the white van
Company cars: surveys have shown that company
motorists admit to speeding more than any other group of drivers
and have more points on their licences (see RAC Report on Motoring,
12. There are most likely to be objections to such a
proposal from those of a libertarian disposition. However, it
is difficult to present a civil liberties argument in relation
to most company cars and vans that are driven on behalf of third
parties. The incorporation of all but the last category of vehicle
in the above list would also address, to some extent, the issue
of employer liability and manslaughter. It would allow the employer
to claim that s/he had taken reasonable steps to ensure vehicles
were driven at the maximum legally permitted speed limit.
13. In addition to the important emission benefits that
the proposal would introduce, it would also have considerable
benefits in relation to road safety.
14. There are also likely to be benefits in relation
to road capacity. Removing the tail of vehicles exceeding the
limit is also likely to lead to smoother flows of traffic because
vehicle speeds will be more convergent; (this is what variable
speed limits on the M25 for example try to achieve). It is possible
that a reduction in accidents that could be expected to accompany
the elimination of excessive speeds, and that would otherwise
have interrupted the traffic flow, might be sufficient to offset
the reduction in maximum speeds; average journey times might be
affected little if at all by the speed constraint.
15. In conclusion, I am of the view that extending electronic/mechanical
speed limiters to more groups of vehicles would make a major contribution
to reducing emissions from road vehicles. This is because of the
disproportionate use of fuel as vehicle speeds increase progressively
beyond 50/60 mph, the very high proportion of vehicles exceeding
national speed limits on motorways and trunk roads, and the fact
that these road categories account for about one third of all
vehicle miles. Precise estimates would require technical study
but I would hazard a guess that if all vehicles were to comply
with the 70mph national speed limit, this alone would reduce total
road vehicle emissions by 5 to 10%. The object of doing so should
form part of the national strategy for achieving the carbon reduction