Traffic, its impacts and public attitudes - Transport Policy and Planning in Great Britain - page 42

significance of this issue and into the related matter of personal security whilst walking
and using public transport (3.4).
With other types of impact there may be some monitoring of physical conditions
but the significance attached to them for policy purposes depends on the application of
more subjective norms - on the numbers of people affected and the context in which
the impacts are experienced. We explore these considerations in relation to noise, air
pollution and visual intrusion (3.5 to 3.7).
We then consider the related matters of fuel consumption and the emission of
carbon dioxide and other greenhouse gases (3.8). Finally we devote a single section to
reviewing evidence of public attitudes to traffic and transport viewed as a whole (3.9).
3.2 Traffic volume, composition and distribution
Even in relation to personal travel there is not a straightforward conversion of distance
by mode into traffic volume. There are three additional considerations we need to be
mindful of - population numbers, vehicle occupancy and multi-stage trips.
The trends in personal travel reported in the previous chapter were largely
expressed in terms of travel per person. The increases in total population (2.2) will
however mean that there is an increase in travel and hence traffic independent of any
increase in per-person movement, all other things being equal.
Trends in vehicle occupancy also affect the rate of conversion from travel into
traffic. Overall car occupancy rates have been declining although, as with several other
aspects of car use, long-term trends have slowed or ceased during the last decade. The
rate of single-car occupancy for example (60%) has not changed in this time. Average
car occupancy is now 1.58.
Occupancy rates vary between trip purposes so the changing proportions of distance
by purpose will impact upon traffic volumes. It is particularly important that in the case
of commuting and business trips (which are relatively long and concentrated during
weekday peak periods) car occupancy is low (1.2 persons per car). It is also important
that occupancy rates for day-trips and trips to holiday destinations (which are higher
than for other purposes) have been declining. As noted earlier, bus occupancy has
declined markedly over the long term. All these factors have the effect of increasing
the volume of traffic relative to overall distance travelled.
The results reported in the NTS derive from the coding of multi-stage trips (i.e.
trips involving the use of more than one mode) according to main mode by distance.
Hence the traffic associated with car or taxi stages to or from rail stations for example
is additional to that represented by the number or length of trips by these modes.
(Equally the overall volume of walking is under-represented in trip-based reporting,
because of its common role as an ancillary mode.)
In depicting the long-term trends in road traffic by mode it is necessary, as with
travel previously, to utilise two graphs (Figures 3.1 and 3.2). Because of the dominance
of car traffic Figure 3.1 distinguishes between car traffic and all other vehicle types
combined. Figure 3.2 shows the split between the non-car categories.
At first sight the graph for all traffic (Figure 3.1) appears to resemble that for all
travel shown in the previous chapter (Figure 2.5). However this is misleading because
of differences in their vertical scales. The volume of travel by mechanised modes is
3.7 times greater than it was at the beginning of the 1950s but the volume of traffic
is 7 times greater. This is due overwhelmingly to car traffic increasing nearly 16-fold.