Raising the Bridge...Automation with Arduino: Pin Count

You could have an isolated track section that runs under the bridge, which only has power applied when the 'bridge raised' limit switch is triggered. That will help prevent the tug from ramming the bridge when the bridge is in the lowered position.

You might need a Mega2560 at this rate for the increased IO.

For each bus stop location you will likely need a sensor to detect the bus and then an actuator to stop the bus. Although with only one bus you could tie all the stop actuators together onto one output.

So how does the 'current plan' prevent the ramp / bridge from raising when there is a bus on it ? The stop servo will only stop the bus if it reaches it after the tug has tripped the sensor. If the bus passes the stop servo just before the tug trips the sensor it will be entering the bridge as it starts to raise.

The gate at the far end will be closed as well so if the bus makes it across the bridge, it will then likely hit the gate. It will then stop once it reaches the stop servo on the far side of the gate.

Adding a delay before closing the gate and lifting the bridge will allow the bus to get across but it will still stop at the stop servo on exiting the bridge, so the closing gate could hit the back end of the bus.

I think that scenario is what additional magnet is for:

There is a bus stop option as part of the official kit. 

https://www.faller.de/en/car-system/road-construction-accessories/887/laser-street-bus-stop-set?c=39

Which uses a diverter motor that changes the wire path from straight ahead into a bus stop siding. So looks like buses fitted with magnets can trigger the diverter when approaching the bus stop whilst other vehicles continue straight on. Bus goes into the siding where it hits a stop servo.

More extensive automation than in the current plan.

I curious about the magnetic suggestion. I am currently looking for a way to detect the bus as it travels the loop. The goal is to have the bus randomly stop at bus stops.  Maybe a hall effect sensor embedded in the roadway can tell me where the bus is at.

If you are on the north american side of the pond I could sure use the extra pair of technical hands.

The kit electronics are expensive. The hobby is not cheap and looking at fancy stuff doesn't make it cheaper:) I enjoy coming up with inexpensive solutions. I have a hall effect sensor in the spares box to give this a try. Keep the ideas coming!

It looks like the Faller system has the option for an additional magnet.

As it is offset from centre then this could be used to detect direction of travel on a single track with end loops system and you could then count vehicles on and off the bridge.

You would need two reed switches at either end of the bridge (time to dig up the road) and some more Arduino inputs.

With a single gate either end you probably want some traffic lights as well The traffic light indicates for the traffic approaching the bridge to stop, whereas the lowered gates indicate the bridge is clear of traffic and is ready to raise. 

You can then have an up/down counter driven by the reed switches to track vehicles on the bridge, and only lower the gates if it is at zero. 

Placement of those reed switches will depend on the design of the roadway as if it is single track then the stop servo needs to only stop vehicles from entering the bridge and not vehicles exiting the bridge. It might be useful to know if there is a vehicle stopped, in which case the reed switches in the road and in the vehicle need to be activated at the same time, but this may depend on the positions of the additional magnet on vehicles of differing lengths.

Also depends on the number of vehicles in use at any one time as well, although the stop servo suggests that only one vehicle is ever expected to be waiting at the bridge at any one time, otherwise another vehicle would drive into the back of the one waiting.