Yellow change and red clearance intervals direct the safe transfer of right-of-way at signalized intersections. The generally accepted purpose of the yellow change interval is to warn users that the green interval is being terminated and that a red signal indication will be displayed immediately thereafter. The red clearance interval, used in many jurisdictions, provides additional time before conflicting phases display a green interval. Dating back to 1941, the Institute of Transportation Engineers has published guidelines and reference material to support the establishment of the duration of change and clearance intervals. In 1960, Gazis, Herman and Maradudin published a paper in which they define a dilemma zone as a situation where a driver at the onset of the yellow interval is faced with the predicament of being too close to the intersection to stop safely and comfortably, and too far away to pass through the intersection before the red signal commences. This research laid the groundwork for the development of what is commonly now referred to as the kinematic equation, first published in the 1982, ITE Manual of Traffic Signal Design. In 1985, ITE attempted unsuccessfully to gain approval for the publication of A Proposed Recommended Practice for Determining Change Intervals. The recommended practice listed several constraints and three versions of the equation that should be applied based on those constraints. Several factors likely contributed to the lack of approval for publication, key among them are the differences in laws regarding restrictive and permissive yellows specified in State Vehicle Codes (Mohammed et al., 2018); differences in the determination of approach speeds, deceleration rates, changes in perception reaction time and different approaches for the geometric analysis of intersections. Significant research findings have contributed to better understanding of the factors that influence the appropriate duration of yellow change and red clearance intervals. NCHRP Report 731, Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections was published in 2012. The objective of the research as stated in the document was “to develop a comprehensive and uniform set of recommended guidelines for determining safe and operationally efficient yellow change and red clearance intervals at signalized intersections. The author’s opinion was that the kinematic equation, using separate statements for the yellow change and all red intervals is the preferred method for calculating the yellow change and red clearance interval duration . A key recommendation in NCHRP 731 “states with “restrictive” yellow laws to consider changing their vehicle code to follow the “permissive” yellow law to promote national uniformity and alignment with driver expectations.” This statement is controversial amongst some that believe that enforcement would become more difficult using the permissive yellow law. In March 2020, ITE published Guidelines for Determining Traffic Signal Change and Clearance Intervals, A Recommended Practice of the Institute of Transportation Engineers. The practice proposed recommends the use of an extended kinematic equation. A stated intent of the extended kinematic equation is to address the oversimplification of driver behavior in the context of turning movements. For through movements, the assumption is that entry and approach speeds remain relatively constant, reducing the extended kinematic equation to its standard form. These differences in approach and entry speed for turning movements result in calculated values that are in excess of general accepted limits for yellow intervals and thus a multitude of practitioners have raised concerns. The Guidance also results in differential durations of yellow change intervals on a single intersection approach depending on phasing and protected or permitted turns. Depending on phasing, this would present human factors challenges to approaching ro

The goal of the Traffic Signal Change and Clearance Interval Pooled Fund Study is to ensure the application of traffic signal change and clearance intervals maximize the safe transfer or right of way at signalized intersections. The objective of the Pooled Fund Study is to provide a forum for participants and interested observers to collaboratively identify and pursue research needs that extend existing knowledge about the interaction between human factors and traffic signal change intervals and clearance intervals. The research findings of the pooled fund study will clarify existing assumptions and provide supplemental procedures, and methodology to appropriately and consistently apply current and recommended practices for the computation of traffic signal change and clearance intervals.

1. Evaluate the influence of yellow change and red clearance interval duration on driver behavior by movement type (left turn, through, right turn), approach speed (<30 mph, 30-40 mph, >40 mph) and context (downtown settings, suburban conditions, etc) including: • The sensitivity of yellow change and red clearance interval durations on driver compliance rates and red-light running. • Safety benefits, crash impact, fatality, and injuries. • Change intervals greater than 5 seconds. 2. Evaluate signalized intersections with longer change and clearance intervals • Observe and document human behavior over multiple years of increasing yellow times. • Assess human factors to identify contexts and conditions that may require longer change intervals. 3. Evaluate perception-reaction time, for alerted drivers for left and right turn movements. Factors considered should include: • Age groups • Vehicle type • Intersection Geometry • Influence of countdown pedestrian signal indications • Traffic demand • Presence of non-motorized modes 4. Approach and passage speed variations associated with different left-turn lane characteristics. 5. Entry delay to account for the delay of drivers and pedestrians entering the intersection on the next signal phase (variation by context). 6. Comprehension of restrictive and permissive yellow change laws and the impact of these laws on safety. 7. Interaction with, and impacts on non-motorized modes of pedestrian and bicycle movements. Potential Data Sources: Driver Behavior / Vehicle dynamics o Naturalistic Driving Data Study speed data including vehicle, driver and environment inputs o Connected Vehicle Data o Video automated data reduction results o On-Board Diagnostic (OBD) data sets ? Hard braking data o Probe data o Red-Light Running System data sets • Signal Timing and Interval Duration o Automated Traffic Signal Performance Measures Data Sets o Signal Phasing and Timing (SPaT) Data o Traffic signal system detection data sets Context Considered: NCHRP 731 context parameters should be reviewed and applied appropriately to ensure representative application of research outcomes across a variety of context, for example: • Posted Speed: Low < 30 mph; Mid 35-40-45 mph; High > 50 mph • Area: Urban/Suburban/Rural • Street size: Small – 2-3 lanes, 4-5 lanes, 6+ lanes • Turn Lanes: 1, 2, 3 (u-turn = yes/no) • Cross Street Size: Small: < 50 feet; Mid: 51-99 feet; Large: > 100 feet • Angle of cross street: 90 degrees, shallower, sharper • Grade: -6% to +6% by 1% • Access (driveway influence in intersection approach): yes/no • Vehicle Movement: left, through, right • Adjacent Signal: < 0.5 mile, > 0.5 mile • Signal Cycle Length: <90 sec, 90-120 sec, 120-180 sec, 180+ sec • Yellow Interval: < 4sec, 4.1-4.5, 4.6-5, 5.1+ • Red Interval: 0 sec, <1 sec, 1.1-2 sec, 2.1-3 sec, 3+ sec • Signal Phasing: Permissive, Protected, P/P lead, P/P lag • Automated Enforcement: Yes (at intersection), In community, None • Vehicles: passenger car, motorcycle, bus, RV, truck (SU), truck (tractor/trailer), truck (multi-unit) • Driver Demographics • Driver Familiarity (commute vs recreational/event) • Weather: dry, wet, ice/storm

Required Funding $920K Desired Participation* FHWA = $200,000 11 States = $660,000 over 3 years ($20,000/year per State DOT) 5 Local Agencies = $60,000 over 3 years ($4,000/year Per Local Agency) State and Local Agency participants are allowed one voting representative to attend semi-annual meetings. Agencies may have an additional non-voting person(s) participate in the semi-annual meetings at an additional $4,000 per person per year. Agencies may contribute additional funds, beyond the base contribution, for other specific research, training, and implementation activities that meet their needs. The intent of the funding and participation structure is to begin the research effort immediately and continue subject to availability of funds each subsequent year. *NOTE: The number of state and local participants and funding amounts are for planning purposes and may vary.