I use the Logic Rail GCP-IR Grade Crossing Pro IR withe the additional bell module. These use IR directional detection. It is powered by a separate 12VDC power supply. You can also add the module for gates, I have these but have not yet installed the crossing with the gates. These work very good, I have them hooked up to Walters crossing lights.

Features

Prototypical control of grade crossing signals (LED or bulbs) and gates.
"TrueLamp" feature gives realistic flashing lamp persistence; the lamps (LED or bulbs) appear to fade out rather than simply turn on and off.
Uses 4 Infrared (IR) Sensors (included) for proper bi-directional behavior; Infrared makes this unit suitable for operation under any ambient lighting condition.
Adjustable gate motor speed.
Cascade multiple GCP units for multi-track crossing arrangements. NOTE: Although it may be tempting to simply add additional photocells to handle a multi-track crossing, this will not yield correct behavior! The GCP would not be able to properly sense the direction of travel on different tracks!
Can also be triggered by other electronic circuits; trigger output can also be used to turn on a bell circuit.
It is also possible to use current-sensing detectors rather than IR sensors.
Works with all scales; signals and gates not included (use with products made by Tomar, Oregon Rail Supply, Walthers, NJ International, etc).
Powered from 7-9VAC or 9-12VDC; current draw is ~390mA with dual LED signals.
Solid State Design
1 year limited warranty

Thanks. Will check them on the web. Sounds what I'm looking for.

I ment to say you can add the bell module, the unit itself controls gates

This is the wiring that I have set up for our Walthers Crossing.  It is manually controlled but you could set up blocks either side that output to a I/O sensor to turn the power to this setup.

http://model-railroad-hobbyist.com/node/17396

It's a pretty easy to setup and works quite well.

Jas...

...lit with bulbs or LEDs is the first question?

The second question is which wire is which? As there are three wires you will have a common and 2 "active" wires.

To figure out which wire is which first look at the colours if there are  only 2 colours such as 2 red and 1 black then more than likely the single wire is the common. If all wires are the same colour or 3 different then it is a bit more problematical.

If you have bulbs then they will probably be 12V. I would use a 9V battery to test them. If you only have 2 colours then I would connect the single colour to one polarity and try the other 2 wires individually to the second polarity. If the 2 lamps light up with the same brilliance then you have figured it out. If you both lamps come on dimly when only 2 wires are connected you have too as the unconnected wire is the common.

If all the wires are the same colour or all different colours then just start by guessing which 2 to use. again if both lamps come on dimly then the third wire is the common.

If the crossbucks use leds then it is a bit more complex because they are polarity sensitive. I would use a 1.5V battery and connect 2 wires as per above and if no lights light up then reverse the polarity. If it still doesn't light try a different pair of wires. There are three ways that LEDs could be wired. Most likely it will be common anode, the third type below. The Logic Rail CCT mentioned by Bob is for common anode.

I now have several things to test and then select whether I want to have them operate with the approaching train; always "on;" or operate with a small slide switch for "effect." You guys, as always, are why I love this site so much.