It has been predicted by DTO that between 1999 and 2016 a further 72.4% of
growth will take place.
The cause of these substantial increases can be seen when one examines the
main factors influencing traffic growth – population, number of cars per house-
hold and economic growth. Between 1991 and 1999, the population within the
area increased by just over 8%, and car ownership by 38.5%, with gross domes-
tic product increasing to 179% of its 1991 value. DTO have predicted that,
between 1999 and 2016, population will increase by 20% and car ownership by
40%, with gross domestic product increasing to 260% of its 1991 value (see Table
1.2).
The Transportation Planning Process 5Demand for travel 1991 1999 2016
Thousand person trips (morning peak hour) 172 283 488Table 1.1Increase in
travel demand within
Dublin City, 1991–20161991 1999 2016
Population (million) 1.35 1.46 1.75
Car ownership (per 1000 population) 247 342 480
% Growth in gross domestic product since 1991 — 79% 260%Table 1.2Factors influencing traffic growth within Dublin City, 1991–2016
The significant growth indicated in Table 1.2 is consistent with the past
recorded and future predicted traffic demand figures given in Table 1.1. High
levels of residential and employment growth will inevitably result in increased
traffic demand as more people link up to greater employment opportunities,
with the higher levels of prosperity being reflected in higher levels of car own-
ership. Increasing numbers of jobs, homes, shopping facilities and schools will
inevitably increase the demand for traffic movement both within and between
centres of population.
On the assumption that a road scheme is selected to cater for this increased
future demand, the design process requires that the traffic volumes for some year
in the future, termed the design year, can be estimated. (The design year is
generally taken as 10–15 years after the highway has commenced operation.)
The basic building block of this process is the current level of traffic using the
section of highway at present. Onto this figure must be added an estimate for
the normal traffic growth, i.e. that which is due to the year-on-year annual
increases in the number of vehicles using the highway between now and the
design year. Table 1.1 shows the increase in vehicle trips predicted within the
Dublin Region for the first 16 years of the new millennium. Onto these two con-
stituents of traffic volume must be added generated traffic – those extra trips
brought about directly from the construction of the new road. Computation of