Table of Contents

5.2.2 Absorption Capacities

An important value for road traffic applications is the theoretical maximum rate at which minor traffic stream vehicles can cross or be absorbed into the major traffic stream in a gap acceptance situation. This maximum rate is known as the theoretical absorption capacity.

The formula for theoretical absorption capacity in gap acceptance situations with random arrivals in both the major and minor traffic streams is derived in Commentary 8.

This formula is as follows.

   \[C      =        \frac{q e^{-qT} }{1  -  e^{-qT_{0} } } \]5.4
 q and T=defined in Section 5.2.1 
 T0=the follow-up headway, in s/veh 
 C=the theoretical absorption capacity in veh/s (multiply by 3600 for veh/h). 

It is observed that the absorption capacity C is a theoretical upper limit, which may not be achieved in practice. It is common practice in traffic analysis to define a practical absorption capacity as

\[C_{p}      =     \alpha   . C\]5.5

where the factor \(\alpha \) is typically taken to be in the range 0.80 to 0.85.