Signalised Traffic System

1.0 INTRODUCTION

An intersection is a road junction where two or more roads either meet or cross at grade (they are at the same level). An intersection may be 3-way, such as a T junction or T intersection and fork, 4-way such as a crossroad, or 5-way or more.

Intersection performance as measured by delay is a function of many factors including signal timing plan, turning movement traffic demands, traffic stream composition, pedestrian volumes, intersection geometry, temporal variation in traffic demands, the headway distribution of each traffic stream, driver characteristics, weather and road surface conditions and visibility. Some of these factors are invariant for a given intersection operating under a defined signal control strategy such as geometry and signal timing plan while others vary such as weather, traffic demands.

Highway Capacity Manual (HCM 2000) is the most widely adopted method for analysis of signalized intersections. The HCM defines signalized intersection performance in terms of average vehicle delay (seconds per vehicle) and then maps this delay against predefined boundaries to define intersection performance in terms of six levels of service which are LOS A through LOS F. The HCM defines LOS (Level of Service) for signalised and unsignalised intersections as a function of the average vehicle control delay. LOS may be calculated per movement or per approach for any intersection configuration, but LOS for the intersection as a whole is only defined for signalised and all-way stop configurations.

LOS | Signalised Intersection | Unsignalised Intersection | A | ≤10 sec | ≤10 sec | B | 10-20 sec | 10-15 sec | C | 20-35 sec | 15-25 sec | D | 35-55 sec | 25-35 sec | E | 55-80 sec | 35-50 sec | F | ≥80 sec | ≥50 sec |
Table 1.1 Level Of Services

Signalised intersections with fully controlled cross-traffic light phases indicate