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4. Performance of the transport networks
Table 4.9
Average traffic speeds (kilometres per hour) by functional sector of
London. Working weekdays, by time period. TfL’s ‘network of interest’.
2008/09 vs. 2014/15.
Area and
time period
2008/09
average
speed (18
month
period)
2014/15
average
speed (18
month
period)
% change
Central AM
peak
Central
inter-peak
Central PM
peak
Inner AM
peak
Inner interpeak
Inner PM
peak
Outer AM
peak
Outer interpeak
Outer PM
peak
14.7 14.1 -4%
13.5 12.6 -7%
14.4 13.1 -9%
20.0 18.7 -6%
21.1 20.3 -4%
18.4 16.9 -8%
31.5 29.4 -6%
34.5 33.9 -2%
29.9 27.4 -8%
Source: TfL Surface Transport, Outcomes Delivery, based on data from Trafficmaster.
Vehicle delay (congestion)
Figure 4.6 shows the trend for congestion (delay), corresponding directly to the
average speed data in figure 4.5 above. Trafficmaster delay values are calculated
against a variable ‘uncongested’ night-time speed, which is that actually measured
on a day-by-day basis, rather than a fixed nominal ‘night-time’ speed, as was the
case with previous moving car observer data. Furthermore, Trafficmaster
‘uncongested’ speeds relate to the period from 22:00 to 06:00 – a period that, in
many parts of London, sees substantial volumes of traffic. Previous indicators
based on moving car observer data used a faster night-time speed.
As well as the expected seasonal and geographical patterns shared with the speed
data, figure 4.6 shows large differences in the degree of variability of traffic
congestion by both area and time period. So, inter-peak congestion in outer London
has historically remained remarkably stable from month-to-month at about 0.5
minutes per kilometre, whereas morning peak congestion here may vary by up to
100 per cent from month-to-month. In inner London the degree of variation in
peak-period congestion is also roughly twice that of inter-peak congestion. In
central London the pattern is reversed – inter-peak congestion being the most
variable and this coinciding with the period of highest traffic demand on the
network. This pattern is characteristic of networks where traffic demand routinely
approaches the carrying capacity of the network. Congestion, as a measure of
89 Travel in London, Report 8