can someone explain how the railroad crossing gates get activated… is it from sensors… or the dispater… or??? by a little tiny man that sits along the rails 
Over the years there have been many different schemes and ideas to accuate crossing gates, many of them in the early years of the railroad and not working! Before the advent of electrically actuated gate out in the country there would often be only a crossbuck whereas in towns there would be a centrally located crossing tower or shanty with a man stationed there to manually operate the gates by levers upon the approach of a train. The most currently used system uses the electical resistance from one rail through the train to the other rail to detect a train and through simple timing lower the gates. With the advent of today’s electronics sometimes optical sensors are used and the most modern systems actually measure a trains speed to lower the gates at the most opportune time for the motorist’s safety without holding them up too long.
Grade crossing signals and gates are usually activated by senors or switches installed on the rails at a short distance from the crossing. The distance can be governed by several factors, including the track speed through that particular area. At a gated signal, for example, this allows the gates to fully drop before a train enters the crossing.
As a presenter for Operation Lifesaver, I am often called upon to address grade crossing mechanics in my discussions about crossing safety.
Here are some important things to keep in mind:
There are more than 260,000 grade crossings in the U.S.
About 40 percent of them have automated signals, that is, your combinations of bells, lights and gates or other barrier devices. these are known as actively-protected crossings, because there is an active device helping provide protection.
Actively-protected crossings mainly have flashing red lights. A very few older grade crossings, mostly in the West, have what are know as “wig-wag” signals, where the warning device, suspended on a vertical arm, swings back and forth like a pendulum.
The other 60 percent are known as passively-protected crossings. These usually have just the traditional crossbuck sign, the x-shaped sign the says “Railroad Crossing”. At some locations, passively-protected crossings also have stop signs, just like at many road intersections. Incidentally, ALL public grade crossings have the crossbuck sign, whether they are active or passive.
There are also many “private” grade crossings where tracks cross driveways and other privately-owned roads. Crossbucks are not required at these crossings. Mostly, they have a small metal sign that identifies them as private crossings; some also have stop signs.
Train crews, by law, must whistle for EVERY crossing on their route, public and private, except where so-called “whistle bans” are in effect. The whistle (or air horn) signal that a train is approaching a crossing is:
well to add to the post here we dont haft to blow for all crossing. if it is a private crossing, with no whistle board then we dont blow. and when blowing we must do the 2 longs a short and the last long must be blown til the engine makes it thru the crossing.
Mccannt, I just wanted to let you know that I think that Operation Lifesaver is an awesome organization. I personally have seen people zig-zag through gates numerous times. Never was able to get the license. One of these idiots had a carload of kids. These clowns don’t have any idea of what a 19,000 ton coal train can do. And they don’t think what it does to the crews emotionally when we hit them. Thankfully I havn’t been involved in an auto/train accident. Hopefully I never will.
I agree, we dont blow for private crossings
either, unless there are whistle boards,jackflash