ABSTRACT
The primary objective of this paper is to explore the impact of horizontal alignment
characteristics on capacity and capacity loss at two successive elements, tangent and
succeeding horizontal curve. The horizontal alignment chara cteristics include lane
width, shoulder width, carriageway width, forward visibility, number of side access
points, curve radius, curve length, tangent length, deflection angle and superelevation.
Traffic volumes, speeds and densities are used to estimate capacity by extrapolating
free-flow observations. Vehicle speeds and flows on the two successive elements
were recorded for each five -minute intervals during the survey period, enabling the
capacities of the two elements to be estimated and capacity loss d etermined.
The effect of different types of vehicle within the traffic stream is normally
accommodated for by converting vehicles into passenger car units (PCU) using PCU
values.
Correlation and regression analyses are used to investigate the relationships between
horizontal alignment characteristics and capacity and capacity loss. Several models
are introduced to indicate these relationships and the best one was chosen for each
case (i.e. capacity at tangents, capacity at curves and capacity loss between t he two
successive elements).