CE 578 Highway Traffic Operations Freeway Merge and Diverge Segments

Objectives Scope and limitations of the methodology Outline of the methodology Critical ramp junction variables

Scope Ramp merge and diverge operations –evaluate operations (LOS A to E) –identify congestion (LOS F) –see freeway facilities chapter for analysis of congested conditions ramp roadway

Limitations HOV lanes Ramp metering Oversaturated conditions Speed effects of ramp characteristics Intelligent Transportation System services

Merge and Diverge Capacities Capacities –Upstream segment capacity for diverge area –Downstream segment capacity for diverge or merge area –Flow entering ramp influence area –Flow of ramp

Critical Variables Adjusted volume (for all movements VF, VR) –fp see Chapter 23 –fHV see Chapter 23 Ramp roadway capacity –Give ramp free-flow speed and number of ramp lanes  See Exhibit 25-3 Upstream traffic demand flow (VF)

Critical Variables (cont.) Proportion of traffic remaining in lanes 1 and 2 (P FM or P FD ) –Ramp demand (V R ) –Demand flow rate on adjacent downstream ramp (V D ) –Demand flow rate on adjacent upstream ramp (V U ) –Free-flow speed of ramp (S FR ) –Length of acceleration (L A ) –Distance to upstream ramp (L up ) –Distance to downstream ramp (L down ) Upstream traffic in lanes 1 and 2 –V 12 = P FM * V F

Capacity Checks