I have a Vauxhall diesel automatic with electronic handbrake.
Which of the following is the best procedure at a red light?
(For best, please consider both driver safety and mechanical wear)
tl; dr - Number 1.
Your Vauxhall is designed with an automatic transmission. The transmission has what's called a torque converter which couples the engine to the transmission. The torque converter has a stall speed. This means it will not throw power/torque at the transmission until the engine gets to a certain speed. Once it reaches the stall speed, power and torque will then start being applied. Stall speed will always be above idle speed. You can therefor leave it in drive while sitting at a red light without worry of damaging any internal parts or causing any extra wear in the transmission, engine, or drive train (as long as you let it idle).
You have to have some sort of braking mechanism for your vehicle. Whether that's the handbrake or the regular brakes, that's what's in question. In this case, you should leave your hand brake alone and use the foot brake. There are a couple of reasons for this. First, this is what the foot brake was designed to do. It was designed to convert your forward momentum into heat through friction to stop the vehicle when needed. Secondly, it's there to hold the vehicle still temporarily while you are waiting to go again, whether it's a stoplight, stop sign, or little kids crossing at a cross walk. Your hand brake was designed to keep the vehicle still for extended periods of time and to assist the parking mechanism within the transmission so there isn't as much pressure on it when engaged (especially on hills and such). It is not designed to be taken on/off at every stop light.
In any case other than number one, you are creating undue wear on mechanical parts for no reason. For the transmission, you'll be wearing out linkage mechanisms faster, as well as internal parts in the valve body (the part which directs the fluid flow within the transmission - the brains of the transmission). For the hand brake, you'll be creating wear on the braking mechanism, the parts which actuates the brake, and the brakes themselves.
Anyway you look at it, your best option is to allow the vehicle to work as designed. Just leave it in gear and apply the foot brake and your vehicle will be fine without causing undue wear and tear on it.
EDIT Removed a certain point about the need for parked vehicles to use warning lights/brake lights as this point was admittedly not relevant to the answer, neither was it insightful.
In remark to answers by @paulster and nick c. I guess there's no accepted convention here wrt using the handbrake at Signals. The brake lights serve their most important feature in indicating that a car is decelerating. This serves as a very essential reactionary aid. This is to do with how our brain figures out the apparent change in the relative distances. It uses perspective and apparent magnification. Both of these are slower than a trained response to the brake lights. Having an immediate visual aid significantly improves reaction and let's the trailing cars know of the drivers "intention" as soon as he touches the brake pedals.
At a signal however, the benefit from a safety point of view becomes a little subjective, and I'm not sure which side to take.
At long stops at a signal, I personally tend to engage the Handbrakes to prevent any kind of lapse on my part, where in I might get lazy and not hold down the brakes (on horizontal surfaces). I think it's well understood why that could potentially be dangerous , eg- car bumps you from behind.
Addition
Between leaving it in neutral or drive, I see no major advantage or disadvantage between the two.
From a safety point of view I can throw two points which maybe trivial-
Leaving it in drive allows one to quickly accelerate should such a requirement arise.
If the driver takes this time at the signal to move about and fetch something within the car, it maybe safer to engage neutral and the handbrakes.
I personally know of a particular case (with a manual transmission) wherein the driver was holding down the clutch with the car in gear at a pedestrian crossing. The drivers foot ended up slipping of the clutch and ended up causing an accident. Anecdotal, and maybe irrelevant in case of an automatic.
I can't recommend any option conclusively, and personally may subjectively choose between the 2 -
1. Handbrake + Neutral (long stops)
2. Drive + Foot on brake (stop and go situations)
I'm going to have to disagree with Paul here - the correct answer is #2. You should always apply the handbrake when stationary for more than a few moments, and release the footbrake. If you keep your foot on the brake pedal, you keep your brake lights on, and so you dazzle the driver behind you - it is a simple matter of common courtesy.
