2.4 Traffic Density and Speed
Observations indicated that travel speeds were lower during
rush hours and weekday speeds were also slower than weekend
speeds. During these periods of lower travel speeds, more
vehicles can be found on the streets with slow-moving traffic.
Theoretically speaking, when traffic is heavy and as density
increases, maneuverability becomes restricted and speed is
reduced. The observed congestion conditions at Yaowarat and
Din Daeng stations were also supported by the recorded travel
speeds at these locations. Their average travel speeds were found
to be slower than other locations (Figure 7). This thus proves for
the case of Bangkok that traffic speeds were very well correlated
to the number of vehicles.
Conclusion
Results of this study revealed that current air pollutant
concentrations in Bangkok street air are relatively dependable on:
emission conditions, traffic characteristics and atmospheric
dispersion conditions. In traffic analysis, the combined effects of
street topography and traffic flows established high impact on the
overall air pollutant concentration in Bangkok. High levels of air
pollution found at roadsides, such as bus station areas, are a cause
of concern for passengers waiting at these stops who will be
exposed to vehicular air pollution. In this study, the area of
greatest concern to health is the elevated level of PM10 in
Bangkok air. To protect the public from this pollution, preventive
measures are necessary to reduce the air pollutant emission rate
by improving traffic conditions. As data on atmospheric pollution
and conditions in Thailand are rather scarce, this study could
serve as a good support to better understanding of the
atmospheric environment in Bangkok. In addition, the presented
monitoring work can also serve as useful data for applicability to
other tropical cities.