Glossary

This page is meant to define and clarify the meanings of traffic control terms and lingo. Expand.......

Words and Meanings

Signal Phasing Terms

Leading / Lagging Arrow

When a dedicated turn arrow is offered at a signal-controlled intersection, its operation will often be defined as either 'Leading' or 'Lagging'. Leading arrows happen at the beginning of the through green cycle, and generally end with a yellow arrow before the through green is finished. Lagging arrows often happen towards the end of the through green cycle, and usually have their yellow arrows tied with the through yellow, or simply rely on the through yellow entirely.

Signals that work together at either end of a bridge or overpass often feature lagging arrows to help clear out the short span of road between the two intersections, to help prevent cars from getting stuck in line while trying to turn.

Flashing Yellow Arrow

Many intersections contain doghouse signals to allow protected left turns. With leading left arrows, there's no harm. However, with lagging left arrows, the yellow trap becomes apparent. Pretend for a moment, you're approaching an intersection. There's 2 single section through signals, and a left turn doghouse over the left turn lane. There's already a car across from you waiting for a chance to make a left. All signals turn yellow, what do you think? You think the cycle is ending, so to prevent being stuck for longer than you need to, you try to beat the red and you make the left. Here's the problem: That yellow your side received isn't what the other side received. Your side got that yellow because the doghouses at that intersection are lagging, not leading. The car across from you waiting to turn triggered your side's cycle to end early, while the other side's through traffic still has green, right as you're cutting across the road. Bam! To fix this, engineers designed the Flashing Yellow Arrow, a signal configuration designed to prevent and eliminate yellow traps. Instead of leading drivers to make their own left turn judgments, it provides a flashing yellow arrow to signify left turns might not be safe, and the driver should yield when making left turns. An educational video further explaining Flashing Yellow Arrows can be viewed here.

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Terms of Physical Signal Features

Doghouse Signal

When MUTCD started requiring green arrows to be terminated with yellow arrows, many jurisdictions didn't have the clearance required for 5 signal sections to be hung in a stack over traffic. To overcome this issue, the doghouse configuration came to be. This consists of a red section placed center above 2 stacks, one of through traffic's yellow and green, and the other stack being the green and yellow arrows. This creates a doghouse shape if one were to loosely trace the configuration. Some newer doghouses consist of standard 3-section signals with 2-section arrow signals on the sides, and although this doesn't create the same doghouse shape, it's still classified as the same.

"Doghouse"

All sections are 12"

"Cheap Doghouse"

The R, Y, & G sections are 8"; the Arrows are 12"

"Pinhead Doghouse"

The Red is 8"; all other sections are 12"

WAIT-WALK Pedestrian Signal

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Franken-Signal

When a traffic signal (whether in public or not) is composed of sections or parts from multiple manufacturers or models from the same manufacturer that aren't designed to normally go together, this signal is unofficially called a Franken-Signal, in reference to Frankenstein's Monster. Due to newer signal models being composed of individual indication sections, contractors sometimes do this in the field to help use up old sections laying around and to save money. The term Franken-Signal generally only applies to the housings; lenses are often more difficult to spot as incorrect from ground level and often don't make enough of a difference to be discernible.