LRT Priority - Traffic Signal Systems Committee

Light Rail Signal PrioritySean SkehanCity of Los AngelesDepartment of TransportationLADOT

Metro Blue Line■ Opened in June 1990■ Five miles of street running■ Center median operationLADOT

Signal Network■ UTCS once-per-second control■ Semi-actuated coordinated operation■ Protected-only left turn phasing■ Separate signal indications for trainsLADOT

LRT Detection■ Two small loops placed between the tracks■ Advance detector just past upstream signal■ Release detector at limit lineLADOT

LRT Signal Indications■ Permissive indication shown only when anLRT is detected at the intersection■ LRT phases are operated concurrently withthrough traffic■ Dwell operation used in short-block areas tominimize slowing between intersectionsLADOT

LRT Priority Operation■ Early green - LRT phase is started earlierthan normal to minimize delays to stoppedor approaching trains■ Green extension - LRT phase is held pastnormal endpoint to help slower trains passthrough critical intersectionsLADOT

Early Green■ Used only for trains entering a group ofsimultaneous signals■ Helps get trains moving so they have thebest chance possible to pass through theentire group of signals■ Reduces stopped delay when trains areahead of the progression bandLADOT

Green Extension■ Used only for trains exiting a group ofsimultaneous signals■ Helps give slower trains a better chance atpassing through the entire group of signals■ Reduces unnecessary stops when trains arebehind the progression bandLADOT

Coordinated Priority Operation■ Vehicle phases are shortened or lengthenedas necessary to provided LRT priority■ No vehicle or pedestrian phases are skippedduring LRT priority■ Coordination is maintained by completingall phase adjustments within one cycleLADOT

Free Priority Operation■ Only Green Extension timing is providedduring LRT priority■ Compatible vehicle phases are called whenan approaching LRT is detected■ No vehicle or pedestrian phases are skippedduring LRT priorityLADOT

Normal Cycle35%45%Main StreetLeft TurnsCross Street20%LADOT

Green Extension Cycle30%55%Main StreetLeft TurnsCross Street15%LADOT

Normal Cycle35%45%Main StreetLeft TurnsCross Street20%LADOT

Early Green Cycle30%55%Main StreetLeft TurnsCross Street15%LADOT

Current Limitations■ Time taken from Cross Street and Left Turnphases during priority is not restored insubsequent cycles■ Any time used for LRT priority is alwaysadded to the Main Street phase■ Priority granted based on LRT detectionwithout any regard for traffic congestionLADOT

Proposed Enhancements■ Ability to assign LRT priority green time toany phase, not just the main street phase■ Optional second recovery cycle where thetime given during priority is restored tothose phases which lost time■ Priority enabled based on traffic congestionat key intersectionsLADOT

Questions?Comments!LADOT