How To Trigger Green Traffic Lights

Step 1

Understand how "demand-actuated" traffic signals work. These are traffic lights that will only turn green when a vehicle is sensed, usually to allow the vehicle to cross a street or make a left turn. At problematic traffic lights, look for a loop of wire buried in the pavement of the road near the stop line. This is called an "inductive-loop traffic detector" that works somewhat like a metal detector, sensing any ferrous metal (steel, iron, etc.). Sometimes these sensors are improperly designed or adjusted, so they don't pick up on the presence of a smaller vehicle. These sensors do not detect the weight of a vehicle, but rather sense how much it disturbs an electromagnetic field. Once tripped, the signal will begin the light switching process using pre-programmed rules (within 30 seconds, usually less). "Bigger" or more noticable vehicles do not cause the light to turn quicker - your vehicle either trips the switch to begin the process or not. There are ways to make yourself more noticeable to prevent waiting indefinitely.

Step 2

Observe the shape of the inductive loop and position your bicycle, scooter, or motorcycle accordingly. If you keep hitting a problematic traffic light on a daily basis, take the time to examine the area where you're stuck. Look for "sawcuts" or lines showing where the loop was inserted. There are three commonly seen shapes, and the way you position a two-wheeled vehicle over them can affect whether or not it gets detected. If you can't see the outline of the loop (such as if the road was repaved) try both techniques and see which one works.

Dipole loop - Put both wheels directly on one of the sawcuts at either the right or the left. If you're still not detected, lean slightly towards the center.
Quadrupole loop - Place both wheels on the center sawcut, which has two wires and is more sensitive. If the traffic light doesn't change, lean slightly towards one of the outer lines on either side.
Diagonal Quadrupole - Designed to sense two-wheeled vehicles more easily. If a two-wheeled vehicle isn't detected, the sensitivity of the loop might be too low in general.

Step 3

Attach neodymium magnets to the vehicle. While there is significant debate as to whether a magnet can be strong enough to alter the electromagnetic field which triggers the sensor, you may decide to give it a shot. You can buy a commercial magnet or make your own.

If you do make your own magnet trigger, be very careful when handling them as they're very strong. Wear eye protection when handling them because they're very brittle, and if they slam together or against any other surface, a piece of magnet can easily get into your eye. Protect the magnet before exposing it to the elements (e.g. put it in a chrome plated pill holder with a rubber ring). Never bring these magnets close to anyone with a pacemaker (the strong magnetic field can interfere with its operation), children (who can get their fingers pinched between two magnets, ingest one, or get a shard in their eye), floppy disks, credit cards, magnetic I.D. cards, cassette tapes, video tapes, televisions, VCRs, computer monitors, or any other electronic appliances.
Attach the magnet case to the bottom of the vehicle with epoxy paste or screws. Where you place it on a car will depend on what kind of loop you tend to come across. If you want to cover all the bases, place magnets along the center and the sides (in line with the wheels). If you used epoxy paste, let it dry and check that the magnet is secure regularly--you don't want this magnet flying off of your car at 70 miles per hour on the highway.
If you ride a two-wheeled vehicle, you can attach the magnet to your shoe with epoxy paste so that when you pull up to an intersection, you're able to spot the wire and put your shoe right over it with the magnet.

Alternate Methods

Push the crosswalk button. If the intersection has a crosswalk, you can leave your motorcycle/scooter/bike and push the pedestrians' crosswalk button to force the lights to cycle.
Report the traffic light. If none of the above methods work, it's likely that the sensor is poorly adjusted or broken. Either way, the problem needs to be addressed.
Press the starter button If you're on a motorcycle you can pull in the clutch, stop the engine, and press the engine starter button. The starter is powered by an electromagnetic motor, creating more magnetic energy and tripping the sensor.

Tips

Putting your motorcycle or scooter's sidestand down directly on the induction loop sometimes will work. (On some motorcycles, putting the stand down while the motor is running and the transmission is in gear will cause it to cut off as a safety feature.)
You can salvage very powerful magnets from old hard drives. Remove the cover and then the round platters. The magnets will be in the corner. Your screw driver will find them quickly. You will likely need a Torx driver to remove the special screws. Torx bits are available at most car parts and hardware stores. These magnets are bonded to a metal plate which you can use to attach the magnet to your vehicle.
Local laws may permit you to cross an intersection after stopping if the traffic sensor does not recognize your presence. Check with your local authorities.
Moving the vehicle back and forth and/or restarting an electric or motorcycle motor may affect the magnetic field enough to trigger the light.
Some traffic signals use video camera detectors instead. If you're on a two-wheeled vehicle, you can try turning to the side to increase your visible surface area. If this doesn't work or a car isn't being detected, report it to the appropriate department.
A number of communities in the United States, including Bakersfield, California; Santa Cruz, California; Chico, California; and Santa Clara County, California, have adopted policies to design and adjust all traffic signal sensors to detect bicycles.
There are electromagnets that you can buy to attach to the underside of motorcycles that were designed specifically to help trigger the sensors.
Make sure that the signal is on a detection system. Not all traffic signals are actuated by detectors, as the majority are on a timing system.
If you have a green light, don't dawdle! It only takes about three seconds for a signal actuator to decide there's no more traffic waiting to get through the intersection from your direction. If you are slow to move, the actuator will flip the switch and you'll be staring at a red light again in no time. And THAT won't make anyone behind you very happy.

Warnings

Not all cities have "demand-actuated" traffic signals. Do not expect this to work at all times.
Approaching emergency vehicles (primarily Fire Department vehicles and ambulances) can override the normal pattern of traffic signals in some circumstances. Both the emergency vehicle and the traffic signal must be equipped with the appropriate devices, and only some cities and certain intersections have such devices installed. One of the most common is the "Opticom" system, basically recognized as a very fast-flashing white strobe light mounted at or near the top of the emergency vehicle (not the "wig-wag" flashing high-beam headlights). A small receiving unit mounted on the traffic signal pole receives the "strobe code" and turns traffic lights green for the approaching emergency vehicle and red in all other directions. Such systems have been shown to reduce traffic accidents and injuries/fatalities involving emergency vehicles while improving response times to life-threatening emergencies. Emergency vehicles can only take control of intersection traffic lights if they are traveling in an emergency response mode - with all emergency lights activated and siren sounding. Once the emergency vehicle travels through the intersection, the traffic signal returns to it's normal pattern.

Things You'll Need

Neodymium magnets or a broken/unused hard disk (which contains neodymium magnets), with pulling force of 6lbs each.
Roll of heavy duty exterior mounting tape.
Protective covering for the magnet(s).

Via wikihow