Right-Turn Traffic Volume Reduction in Traffic Signal Warrant Analysis: A Delay Perspective

Center for Advanced Transportation Education and ResearchUniversity of Nevada, Reno

Presenter: Cui ZhouPresenter: Cui ZhouUniversity of Nevada, RenoUniversity of Nevada, Reno

Center for Advanced Transportation Education and ResearchCenter for Advanced Transportation Education and ResearchMarch 27, 2014March 27, 2014

Research Project for Nevada Department of TransportationResearch Project for Nevada Department of Transportation

Right-Turn Traffic Volume Reduction in Right-Turn Traffic Volume Reduction in Traffic Signal Warrant Analysis: A Delay PerspectiveTraffic Signal Warrant Analysis: A Delay Perspective

Presentation OverviewPresentation Overview

IntroductionIntroduction Previous ResearchPrevious Research ITE Community DiscussionITE Community Discussion Problems in Existing MethodsProblems in Existing Methods Proposed MethodologyProposed Methodology Case StudyCase Study Summary and ConclusionsSummary and Conclusions

Importance of Traffic Signal WarrantsImportance of Traffic Signal Warrants• What’s traffic signal warrants?What’s traffic signal warrants?Standard: An engineering study of traffic conditions, pedestrian Standard: An engineering study of traffic conditions, pedestrian

characteristics, and physical characteristics of the location shall be characteristics, and physical characteristics of the location shall be performed to determine whether installation of a traffic control performed to determine whether installation of a traffic control signal is justified at a particular location.signal is justified at a particular location.

IntroductionIntroduction

characteristics, and physical characteristics of the location shall be characteristics, and physical characteristics of the location shall be performed to determine whether installation of a traffic control signal is performed to determine whether installation of a traffic control signal is justified at a particular location.justified at a particular location.

• Consequences of an unwarranted signalConsequences of an unwarranted signal• Rear-end collisionsRear-end collisions• Excessive delay and congestionExcessive delay and congestion• Disobedience of signalsDisobedience of signals

characteristics, and physical characteristics of the location shall be characteristics, and physical characteristics of the location shall be performed to determine whether installation of a traffic control signal is performed to determine whether installation of a traffic control signal is justified at a particular location.justified at a particular location.

• Consequences of an unwarranted signalConsequences of an unwarranted signal• Rear-end collisionsRear-end collisions• Excessive delay and congestionExcessive delay and congestion• Disobedience of signalsDisobedience of signals

In short, traffic signals should be only installed when they will alleviate more problems than they induce.

Right-turn Traffic in Traffic Signal WarrantsRight-turn Traffic in Traffic Signal Warrants

MUTCD and MTSD have clearly stated that some portion of the right-turn traffic should be reduced from the minor street traffic count.

Previous ResearchPrevious Research

Right-turn adjustments are usually based on engineering judgment (EJ), field observation (FO), or an accepted right-turn

adjustment methodology (AM).

Previous ResearchPrevious Research

Right-turn adjustments are usually based on engineering judgment (EJ), field observation (FO), or an accepted right-turn adjustment methodology

ITE Community DiscussionITE Community Discussion

Our topic was posted in the ITE community discussion section in October 2013 and eight responses were received in this survey

Most of them are based on engineering judgments

Problems In Existing MethodsProblems In Existing Methods

Pagones Theorem and NCHRP methods are relatively sound

Problem In Existing MethodsProblem In Existing Methods

Pagones Theorem and NCHRP method are relatively sound • The intersection’s LOS after reduction is often one alphabet better • Pagones Theorem fails to take into account the uneven volume

distribution • The NCHRP method works out the reduction based on the

conflicting major-road. It doesn’t give any thought to the through and left turn traffic

Problem In Existing MethodsProblem In Existing Methods

The approach is based on delay equivalence• Find the delay equivalent relationship between right-turn

and through traffic

MethodologyMethodology

and through traffic

The estimation of control delay is implemented in VBA programming in EXCEL according to HCM 2010

An isolated intersection is studied

Directional ratio=WB Volume: EB Volume

An isolated intersection is studied

Five minor-street lane conditions are discussed

Different traffic volume scenarios are applied (12,096 cases in total)

Condition 1Condition 1

Different traffic volume scenarios are applied (12,096 cases in total)

One Study Situation

20% LT20% LT

Different traffic volumes scenarios are applied (12,096 cases in total)

The reduction factor could be calculated:

The reduction factor graph in one specific study situation where the mainline volume is 500 vph with 1:1 directional ratio

The reduction factor graph in one specific study situation where the mainline volumes are 500 vph with 1:1 directional ratio

Reduction Factor Table Reduction Factor Table

Using the same traffic volume scenarios, almost the same reduction factors are obtained

From here, we could also see that the assumed left-turn percentage doesn’t significantly affect the equivalent results

20 left turns and zero through traffic are assumed before reduction. The right-turn movement volume is from 50 vph to 510 vph with 20 vph increment

The adjusted minor street volume is the maximum of adjusted right-turn and through & left-turn traffic ( critical volume)

Reduction Factor Table Reduction Factor Table

Minor street left-turn and through volume is from 40 vph to 700 vph with 20 vph increment

Reduction factor graph when the mainline volume is 500 vph.

Minor street left-turn and through volume is from 40 vph to 700 vph with 20 vph increment

Reduction factor graph when the mainline volume is 500 vph.

Reduction Factor Table

Because there is exclusive left-turn lane, left-turn traffic is not considered in this condition.

Reduction Factor Table

26 intersections’ turning volumes provided by NDOT

According to 8 hour warrant in MUTCD, divide these cases into three categories:• warrant meets without right turning (7 cases) ;• warrant doesn’t meet with all turning movement (12

cases); • warrant meets when considering all turning movement

(7 cases)

Case StudyCase Study

26 intersections’ turning volumes provided by NDOT

According to 8 hour warrant in MUTCD, divide these cases into three categories:• warrant meets without right turning (7 cases) ;• warrant doesn’t meet with all turning movement (12

cases); • warrant meets when considering all turning movement

(7 cases)

Case StudyCase Study

Case Study: Lamoille Hwy and Spring Creek Pkwy

Lamoille Hwy

Spring Creek Pkwy

Case Study: US395 and Airport Rd

US395 Airport Rd

Unwarranted traffic signals are detrimental

Summary and ConclusionsSummary and Conclusions

Unwarranted traffic signals are detrimental Engineers agree on reducing right-turn volumes, but

there is no mature guidance

there is no mature guidance This paper proposed a new guideline which is based

on the equivalent relation when right turns and through traffic achieve the same delay

Five conditions are divided, and further 63 study situations are provided in each condition

Case studies were conducted. The proposed guideline can easily help engineers make sound decisions for the adjustment of right turns

Thank you for listening!Thank you for listening!

Right-Turn Traffic Volume Reduction in Traffic Signal Warrant Analysis: A Delay Perspective

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