Roundabout Entry Capacity (Basic Linear Model)

Simple linear entry capacity model: Csingle = a + b·Qc, with degree of saturation x and reserve capacity.

1. Entry & traffic data

Demand on the entry being checked (equivalent pcu/h).
Circulating flow on the roundabout that conflicts with this entry (pcu/h).
Number of lanes on this entry arm.

2. Capacity model coefficients

Generic linear model (per lane): Csingle = a + b · Qc. Use coefficients from your design standard or calibration.
Capacity at zero conflicting flow (per lane).
Typically negative. Example: −0.7 to −0.8 (pcu/h reduction per 1 pcu/h of Qc).

Single‑lane capacity: Csingle = max(0, a + b · Qc).
Total entry capacity: Ctotal = Csingle · Ne.
Degree of saturation: x = qe / Ctotal.