Red-Phase Countdown Timers at Signalized Intersections: A Systematic Review of Start-Up Efficiency and Premature Movement

Abstract

Countdown timers at signalized intersections provide drivers with advance information about phase changes and may improve queue discharge, but previous studies have reported heterogeneous operational and behavioral effects. This systematic review synthesized field, controlled-road, and human driving-simulator studies comparing visible red-phase countdown information with conventional signals without countdown displays for vehicle movement initiation, start-up delay, discharge headways, queue propagation, start-up lost time, and premature starts. Scopus and Web of Science were searched for studies published from 2000 to 8 September 2026, and study selection followed PRISMA 2020. Fifteen studies comprising 17 empirical components were included. Data were extracted using a structured framework, methodological quality was appraised with the revised 2024 JBI tool for quasi-experimental studies, and findings were synthesized narratively because each harmonized outcome family contained only two independent reports and dependent estimates precluded valid pooling. Countdown information was generally associated with shorter movement-initiation time, start-up delay, start-up lost time, and, in several settings, discharge headways, with favorable patterns extending beyond the lead vehicle. However, countdown displays were also associated with more frequent anticipatory or premature movement before green. Overall, red-phase countdown timers were associated with improved start-up efficiency but also with a behavioral trade-off whose expression depended on display design, traffic context, enforcement, and driver adaptation. These findings support evaluating countdown displays as human-centric traffic-control interventions in which operational performance should be considered jointly with anticipatory behavior and regulatory compliance. The review was not prospectively registered. Funding was provided by Universidad Técnica Particular de Loja (grant POA VIN-56).