# Fire and Police can control the traffic lights **URL:** \ **Category:** Factual Questions\ **Created:** [January 27, 2011, 6:23pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214 "2011-01-27T18:23:51Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [January 27, 2011, 6:23pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/1 "2011-01-27T18:23:51Z")
Here in MA, some of the traffic lights can be controlled by emergency vehicles. Today, a local traffic light behaved a bit unusual. I suspect (but can’t prove it) that somebody had one of these “things” and decided to “extend” the green in his direction for 10-15 seconds. Are these devices universal or are they programmed to only behave in certain jurisdictions? I’d love to have one. I’m sure we’d all love to have one. It would save us time and “tough noogies” to the other guy. I conclude, therefore, that the possession of such a device is illegal. How illegal? What safeguards are in place to inhibit people getting one of these devices for their own benefit? Is usage logged so that unusual activity would be noticed? If a fire truck uses such a device when responding to a fire, do they have to log it? etc. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [January 27, 2011, 6:57pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/2 "2011-01-27T18:57:26Z")
They are devices mounted on the top of police and fire trucks (although I believe some systems use the flashing lights). The ones I’ve seen in eastern Mass have a visible flashing light on the top of the streetlights that indicates when they have been activated. There’s no way someone could use these without attracting attention. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [January 27, 2011, 6:57pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/3 "2011-01-27T18:57:39Z")
It became a federal crime during the Bush administration: > **[Traffic Hackers Hit Red Light](https://www.wired.com/2005/08/traffic-hackers-hit-red-light/)** > > Traffic signals equipped with pre-emption systems bear a telltale infrared sensor mounted on top. View Slideshow If you've ever been stuck in traffic longing for a magic box that could turn all your red lights to green, beware: Acting on that fantasy... There are a variety of systems - some log usage, and some have authentication codes. Older systems may have neither. ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [January 27, 2011, 7:01pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/4 "2011-01-27T19:01:00Z")
> [@Telemark](#): > > They are devices mounted on the top of police and fire trucks (although I believe some systems use the flashing lights). The ones I’ve seen in eastern Mass have a visible flashing light on the top of the streetlights that indicates when they have been activated. There’s no way someone could use these without attracting attention. The traffic lights in the Chicago area which can be manipulated in this way have those flashing lights on the booms, as well. So, it’s obvious that _someone_ has triggered them. I probably see this happen once a month or so – the white lights on the traffic light booms start flashing, the lights suddenly change…but there’s no sign of an emergency vehicle. What’s not obvious, i don’t think, is **who’s** done it. My understanding (I’d be happy to be proven wrong) is that the “triggering device” itself isn’t terribly obvious. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [January 27, 2011, 7:09pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/5 "2011-01-27T19:09:08Z")
> [@kenobi\_65](#): > > … > What’s not obvious, i don’t think, is **who’s** done it. My understanding (I’d be happy to be proven wrong) is that the “triggering device” itself isn’t terribly obvious. Stay unhappy, I’m afraid. One of the manufacturers of the devices makes a big sales point over how small and non-obvious their units are, so they can be mounted on undercover units and motorcycles: [http://www.themirt.com/index.html](http://www.themirt.com/index.html) ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [January 27, 2011, 7:19pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/6 "2011-01-27T19:19:55Z")
I’ve got the opposite device in my car. Every traffic light I approach turns yellow at juuuust the right distance. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [January 27, 2011, 7:23pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/7 "2011-01-27T19:23:16Z")
I see the flashing lights activated all the time on the booms whenever emergency vehicles are approaching. It’s like a signal to drivers “attention! emergency vehicle approaching!” They must be somehow directionally activated (either by line of sight or GPS) since they always seem to know which lights in an intersection to leave green vs. red. ---
**Author:** ![YamatoTwinkie](https://avatars.discourse-cdn.com/v4/letter/y/cc9497/32.png) [@YamatoTwinkie](https://boards.straightdope.com/u/YamatoTwinkie)\ **Post date:** [January 27, 2011, 7:42pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/8 "2011-01-27T19:42:02Z")
> [@Hampshire](#): > > They must be somehow directionally activated (either by line of sight or GPS) since they always seem to know which lights in an intersection to leave green vs. red. I thought many/most of them just turn _all_ lights red. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [January 27, 2011, 8:25pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/9 "2011-01-27T20:25:36Z")
> [@YamatoTwinkie](#): > > I thought many/most of them just turn _all_ lights red. if all directions turned red then lanes would be blocked by stopped vehicles. you want the lanes in the direction of emergency travel go green and clear out. ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [January 27, 2011, 8:44pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/10 "2011-01-27T20:44:45Z")
> [@johnpost](#): > > if all directions turned red then lanes would be blocked by stopped vehicles. you want the lanes in the direction of emergency travel go green and clear out. Yup…at least around here, the devices seem to work by beginning the “green cycle” for the direction in which the controlling vehicle is traveling. ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [January 27, 2011, 8:48pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/11 "2011-01-27T20:48:00Z")
> [@Leaffan](#): > > I’ve got the opposite device in my car. Every traffic light I approach turns yellow at juuuust the right distance. I have a similar device. The difference is that mine can cause train crossing gates to descend. 😉 ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [January 27, 2011, 9:09pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/12 "2011-01-27T21:09:40Z")
Some cities (particularly ones that don’t have real rapid transit) give similar transponders to busses. I don’t know if it’s an instant green like for an ambulance, but when there’s a bus they switch around the signal timing to its favor. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [January 27, 2011, 9:25pm UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/13 "2011-01-27T21:25:44Z")
> [@GreasyJack](#): > > Some cities (particularly ones that don’t have real rapid transit) give similar transponders to busses. I don’t know if it’s an instant green like for an ambulance, but when there’s a bus they switch around the signal timing to its favor. The links I gave indicated that some of the devices have a couple of different modes of operation - emergency vehicles can flip red to green, while another mode allows public transit vehicles to extend the green so they don’t have to stop. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 28, 2011, 12:16am UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/14 "2011-01-28T00:16:33Z")
> [@](#): > > Stay unhappy, I’m afraid. One of the manufacturers of the devices makes a big sales point over how small and non-obvious their units are, so they can be mounted on undercover units and motorcycles: It wouldn’t have to be obvious to the general public, but you’d think there’d be some way for something on the light to keep track. ---
**Author:** ![Sactogranny](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@Sactogranny](https://boards.straightdope.com/u/Sactogranny)\ **Post date:** [January 28, 2011, 1:41am UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/15 "2011-01-28T01:41:29Z")
In Sacramento on at least one route the buses can also control the lights. NO one in my family believes it but on at least four occasions I have sat at the left-turn light through one or more cycles without getting a green arrow…followed quite soon by a bus turning left from the opposite side. Once the bus goes through the cycles go back to normal. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [January 28, 2011, 2:39am UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/16 "2011-01-28T02:39:56Z")
Interesting reason for the flashing indicator lights: In case multiple first responders are traveling toward an intersection at the same time, the solid light indicates in the direction of the vehicle that triggered the signal first. The indicator then flashes in the other three directions to warn the _other_ emergency vehicle(s) of the presence of the first vehicle and basically give right of way. It doesn’t take much imagination to picture two firetrucks colliding having each assumed the intersection was clear. ---
**Author:** ![moejoe](https://avatars.discourse-cdn.com/v4/letter/m/9de053/32.png) [@moejoe](https://boards.straightdope.com/u/moejoe)\ **Post date:** [January 28, 2011, 4:05am UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/17 "2011-01-28T04:05:24Z")
> [@GreasyJack](#): > > Some cities (particularly ones that don’t have real rapid transit) give similar transponders to busses. I don’t know if it’s an instant green like for an ambulance, but when there’s a bus they switch around the signal timing to its favor. Our express busses have them. They can’t make a light turn green but they can keep it green long enough to get through the intersection. ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [January 28, 2011, 6:38am UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/18 "2011-01-28T06:38:09Z")
> [@jnglmassiv](#): > > Interesting reason for the flashing indicator lights: > In case multiple first responders are traveling toward an intersection at the same time, the solid light indicates in the direction of the vehicle that triggered the signal first. The indicator then flashes in the other three directions to warn the _other_ emergency vehicle(s) of the presence of the first vehicle and basically give right of way. It doesn’t take much imagination to picture two firetrucks colliding having each assumed the intersection was clear. Like [this](http://www.youtube.com/watch?v=G3uoVOOlT2s)? ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [January 28, 2011, 7:35am UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/19 "2011-01-28T07:35:52Z")
> [@kenobi\_65](#): > > I have a similar device. The difference is that mine can cause train crossing gates to descend. 😉 I doubt this. I know that emergency vehicles can change traffic lights but see no reason for this. Am I being whooshed? ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [January 28, 2011, 7:53am UTC](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214/20 "2011-01-28T07:53:49Z")
> [@Dag\_Otto](#): > > I doubt this. I know that emergency vehicles can change traffic lights but see no reason for this. Am I being whooshed? Big time. [Next page](https://boards.straightdope.com/t/fire-and-police-can-control-the-traffic-lights/569214.md?page=2)