In traffic signal timing, a demand-actuated traffic signal is one that remains red most of the time and turns green only when it detects a vehicle stopped in an approaching lane. A dead red is a demand-actuated traffic signal that is malfunctioning because it is failing to detect a smaller vehicle, especially a bicycle or motorcycle. Dead reds harm the environment by discouraging people from using a bicycle or motorcycle to commute to and from work.
There are two ways to fix a dead red: either detect all vehicles, or acknowledge that some vehicles will never be detected.
Many signal sets use an induction loop as a "metal detector". The detector pumps kilohertz radiation into a loop of wire embedded in the pavement, and proximity of the metal surface in a vehicle disrupts a magnetic field and decreases the loop's inductance. These can be set more or less sensitive depending on the size of vehicles that one wants to detect. Ideally, a loop would be sensitive enough to detect a bike but selective enough not to detect a tractor-trailer in an adjacent lane.
A 6 by 20 foot (1.8 by 6 m) rectangular loop is probably the worst for detecting bicycles. It's apparently intended to detect vehicles while rejecting adjacent lane noise, but it's not sensitive enough to pick up a bike. An octagonal loop 6 feet (1.8 m) in diameter is better; a bike with metal wheels can ordinarily trigger these by making a chord of the circle with its front and back wheels. There are even better patterns: a figure eight loop and a diagonal pattern. The figure eight loop is most sensitive in the middle, allowing the trigger threshold to be turned down to detect bikes without picking up adjacent-lane noise, and the diagonal pattern is more evenly sensitive all over.
Another way is to install a low-resolution camera that senses motion. These visually detect a small vehicle entering the lane and work even for carbon-fiber bicycles.
A third way, used commonly on streets with enough pedestrian traffic to have a sidewalk, is to install pedestrian call buttons. This way, a cyclist can at least leave the bike to request a green light.
The problem with methods of improving detection is that they all cost money to install and obstruct the flow of traffic while they are being installed. Installing them might frustrate motorists who encounter closed roads and taxpayers who notice an increase in their income tax, property tax, or fuel price. If there aren't enough bicyclists or motorcyclists to outvote inconvenienced motorists, there's no political justification for making a change. Cameras also have the disadvantage that they might be confused with "big brother" surveillance cameras or with the red-light cameras that commonly prompt allegations of conflict of interest on the part of law enforcement.
The other way is to acknowledge that not all vehicles will be detected.
One way is to make the signal not purely actuated by adding a "nudge phase", or an occasional green phase every few minutes even if no actuation occurs.
Another is to enact a "dead red law", as has been done in Missouri and some other states. Such a law creates a defense to running a red light if the intersection is clear and the driver reasonably believes that a signal is a dead red.
A third, and probably least desirable, way is to add signs directing bicyclists and motorcyclists to make a right turn on red followed by a U-turn.
The disadvantage of a nudge phase is that it may inconvenience motorists who wonder why they are stopped at a red when a lane with no vehicles is getting a green. Critics have called dead red laws a license to run red lights.
- Brent Hugh. "Dead Red for motorcycles & bicycles passes (again)". Missouri Bicycle and Pedestrian Federation. 2009-05-15. Accessed 2012-05-18.