A typical transport planning process defines the minimum level-of-service considered
acceptable (typically LOS C or D). Roads that exceed this are considered to fail and so
deserve expansion or other interventions. This approach is criticized on these grounds:
It focuses primarily on motor vehicle travel conditions. It assumes that transportation
generally consists of automobile travel, often giving little consideration to travel conditions
experienced by other modes. As a result, it tends to result in automobile dependency,
reducing modal diversity.
It defines transportation problems primarily as traffic congestion, ignoring other types of
problems such as inadequate mobility for non-drivers, the cost burden of vehicle ownership
to consumers and parking costs to businesses, accident risk, and undesirable social and
environmental impacts.
It ignores the tendency of traffic congestion to maintain equilibrium (as congestion increases,
traffic demand on a corridor stops growing), and the impacts of generated traffic (additional
peak-period vehicle travel that results from expanded congested roadways) and induced
travel (total increases in vehicle travel that result from expanded congested roadways). As a
result, it exaggerates the degree of future traffic congestion problems, the congestion
reduction benefits of expanding roads, and the increased external costs that can result from
expanding congested roadways.
It can create a self-fulfilling prophecy by directing resources primarily toward roadway
expansion at the expense of other modes (widening roads and increasing traffic speeds and
volumes tends to degrade walking and cycling conditions, and often leaves little money or
road space for improving other modes).
Short trips (within TAZs), travel by children, off-peak travel and recreational travel are often
ignored or undercounted in travel surveys and other statistics, resulting in walking and
cycling being undervalued in planning.
In recent years transportation planning has become more multi-modal and comprehensive,
considering a wider range of options and impacts. Transport planners have started to
apply Level-of-Service ratings to walking, cycling and public transit, and to consider
demand management strategies as alternatives to roadway capacity expansion.