Traffic trail photography tram Hong Kong

Traffic trails are simply a way of blurring moving traffic with a long exposure. This can be done both during the day and at night, but the effect is far more dramatic at night when car lights paint the scene as they move across the frame. If you’ve never tried it but want to give it a go, or if you have tried it before but without much luck, then this step by step tutorial will hopefully see you getting shots with the wow factor.

First of all, let’s look at what equipment you’ll need. Luckily, there isn’t anything particularly specialist or expensive, as it’s all about technique rather than the gear you use, although as with all areas of photography, the better your equipment, the more potential your photos will have.

Tripod - A good sturdy tripod is the most important thing, as it is essential to have the camera perfectly still during the exposure. Using a cheap flimsy tripod isn’t going to get the results you are after, so don’t try to save money when purchasing a tripod. It is also important to have a tripod which goes to a reasonable height (without having to raise the centre column) as it is likely you will be shooting from a bridge and will need to get the camera above a railing or barrier.

Camera -  The only important criteria is that you can control it fully manually, as an auto or semi-auto setting (such as Aperture Priority) isn’t going to achieve consistent results.

Lens - There is no particular lens specification for shooting traffic trails. You can shoot with any focal length and at many apertures, so just use what you already have.

Cable release - It is important to be able to take a photo without having to touch the camera, and a cable release will allow you to do this. If you don’t already have one then these are inexpensive pieces of equipment which plug into your camera. My preference is for one which can be physically plugged into your camera rather than a wireless one which in my experience will always fail to work just when you need to take the shot. You don’t need to buy branded cable releases as copy ones work just as well. Look on Ebay and you will find a whole range of third party cable releases costing a fraction of the price for the likes of Canon or Nikon. If you think you can just use the camera’s self timer as a substitute for a cable release, then you will struggle to get the timing of your shots perfect, as you will need to predict where the traffic will be in 2 or 10 seconds time, rather than being able to react to the exact moment when the conditions are at their best.

Traffic Trail Long Exposure photography
Here the photographer has a sturdy tripod which is tall enough to get over the barrier. She is using a cable release to eliminate any contact with the camera during the exposure. The timing is perfect, with a nice balance of ambient and artificial light, and the traffic trails are a nice length. Note that the scene would work well enough without the traffic trails.

Scene - Now that we are armed with the necessary equipment, we need to find a suitable scene and location. One thing to remember with traffic trails is that they are not a strong enough subject on their own. You need to find a scene which works well enough without traffic trails, and then include them for extra impact. You can certainly practice on any scene though, and once you are confident of your technique, you can then go looking for the ideal scene to capture your masterpiece. An obvious vantage point is from a footbridge over a busy road, as this allows the traffic to pass below you and also elevates your viewpoint to allow you to see more of the traffic than if you were standing at street level. Just be aware that many bridges vibrate with passing traffic, so try to position yourself above a bridge support, or time your exposure when there is nothing passing behind you on the bridge. However, you don’t need to be up high or on a bridge to get successful shots.

Traffic trails Hong Kong Photography
Taking traffic trail shots from street level can provide some great results. Note that the scene would work without traffic trails.

Timing - As mentioned before, blurring traffic can be done during the day, but if you do this you need to choose a reasonably short exposure time - long enough to blur the movement of passing traffic but short enough to keep the detail and form of the vehicles.

Hong Kong Photography
Blurring traffic during the day needs to retain the features of moving vehicles so that they are still recognisable as cars.

Most people will choose to shoot traffic trails at night, when vehicles have their lights on. In this situation you can opt for much longer exposure times, something we will look at in detail below. As with most night-time cityscapes, the optimum time for photography is at twilight, not once it has become totally dark. Ideally you want to have a subtle glow in the sky, as this will show any cloud detail present, or will add a nice blue tone to your image if no clouds are present (or indeed if the sky is totally overcast). Once the sky is totally black then the scene will be past its best and this is when you should be packing up and heading home. The mistake many photographers make is that this is when they usually turn up on scene. Having a totally black and featureless sky never looks good, so turn up at your chosen location just before sunset, set up, and wait for the perfect balance where the ambient light is low enough for the scene to take on a night time feel, but bright enough to still render detail in the sky and help to fill in any dark shadow areas such as unlit roof tops. The closer you are the equator, the shorter the window of opportunity. In the UK, there could be a 5 minute window as the ambient levels pass through the same exposure as the artificial light. Where I shot this example in Hong Kong, this time is reduced to less than 2 minutes. On the equator it could be a minute or less, so take your latitude into account when anticipating the best moment to take your night shot.

Hong Kong Night Photography
The left shot is taken too early when there is too much ambient light. The right hand shot shows a much better balance of ambient/artificial light.

Shanghai traffic trail night photography
The left hand shot is taken at the perfect time. Note you can still clearly see the unlit dome on top of the building on the left with the red advertising text. The right image is taken when the sky is too dark. Notice how the dome is no longer obvious.

Composition - As already mentioned, find a scene which works well without traffic trails and compose it as you would normally. Now factor in how the light trails are going to influence your scene and make any necessary adjustments to your composition. As a general rule, you want to try to have any traffic trails going diagonally, or in curves through your frame, as the lines will then act as leading lines to draw the viewer’s eye through the image. If you can make these lines find the corners of the frame, all the better.

Traffic Trail Photography
Try to make your traffic trails find the corners of the frame for added impact.

Technique - This is the most important part, so pay attention! Remember that you need to be in Manual Shooting Mode. Once you have found your viewpoint and decided on your composition you need to get the exposure correct. This is a little more complicated than usual, but not anything to worry about. Basically you are trying to get two lighting scenarios (ambient and artificial) to balance and expose together. The key to this is all about timing (see above). All artificial light, such as car headlights, tail lights, and street illumination will be at a constant brightness. It won’t get brighter or darker. The ambient light however will change drastically. Assuming we are on location at dusk (as opposed to dawn), then the ambient light will be falling in luminance. All we need to do is expose for the artificial light (which is easy, as it is constant), and then wait until the ambient light falls enough to look good on the same exposure. If we shoot too early then the ambient light will be too bright, but this isn’t a problem as we just need to wait a little longer for the problem to solve itself. If we shoot too late, then the ambient light will be too dark. This is a problem, because it isn’t going to get lighter again until the following day, so you’ve missed your chance.

Now here’s the clever part. We can alter the luminance of the traffic trails, as well as the length of them by changing the ratio of the exposure triangle (time/aperture/ISO). If we change the ISO or the Aperture, then we simply make the entire scene brighter or darker. If, however,  we change the exposure time, then as well as making the entire scene brighter or darker, it will also change the length of the traffic trails. The longer the camera’s shutter is open, the longer any traffic trails will appear.

Adjusting each one of the Exposure Triangle settings by itself doesn’t achieve much, but if we use them in combination it gives us a lot of creative control. For example, let’s say that we have the correct exposure for our scene, and the balance between the artificial light and the ambient light is looking good. Our traffic trails, however,  aren’t looking as long as we would like them to be. We can solve this problem very easily. Let’s assume that our correct exposure is ISO 100, f/8 at 1 second. At the moment, we are only capturing the movement of traffic for exactly 1 second. If we want to achieve longer traffic trails then there are a couple of things we can do. The first is to get all the traffic to drive much faster, but in most situations this is not practical. Our second option is to close down our aperture by 2 or 3 stops and increase our shutter speed by the same amount. This will have a neutral affect on the overall exposure of the image but will give us a longer exposure time to allow any moving traffic to pass further through our scene. For example, let’s change our aperture from f/8 to f/16 (a reduction of 2 stops). This alone will have the affect of darkening our entire scene by 2 stops which is not what we want. But if we also change our exposure time to 4 seconds (an increase of 2 stops), we get the image back to the correct exposure, but now we have 4 seconds of traffic movement being recorded rather than our original 1 second. We will also see another change in our image. The luminance of any moving light will be 2 stops darker than it was originally, but any ambient light or static artificial light will remain unchanged.

So we can use a combination of exposure time and aperture/ISO to influence the luminance of any moving lights, as well as how much movement we record. We can’t however influence the luminance of moving light without also influencing the amount of movement we record, unless we can also control the speed of the traffic. This can be possible if you are using just a single car and have a friend driving.

Venice Night Photography Accademia
These light trails aren’t long enough. Ideally they need to go further into the scene, but due to them being slow moving boats, and with increasing ambient light levels (dawn), this wasn’t possible. Notice how the scene is strong enough to work without the light trails.

Movement - The length of traffic trails is influenced by two factors.

1 - The speed of movement across the camera’s frame (note that this has nothing to do with the actual speed of the vehicle).
2 - The length of exposure.

We always have control over both of these factors, even if we cannot control the speed of the traffic. Let’s assume we have a car travelling across our frame from left to right at 30km/h, and this car is at a distance of 50 metres from the camera. Let’s also assume we have an exposure of 2 seconds at f/5.6 on ISO 100. If we shoot our scene with a 200mm lens, the chances are that the car will pass across the entire width of our frame during the exposure. If we now change to a 24mm focal length and shoot the same scene, the car will only cover a fraction of the width of the frame in the same time. So even though the car is moving at the same speed, it is moving across our frame at a much slower speed due to the reduction in focal length.

Let’s now assume that we need to use a 24mm lens in order to achieve the desired composition of our scene. However, we need the car to travel across the entire frame during our exposure. There are two things we can do to achieve this. The first has already been covered above - we simply reduce the aperture to f/16 (a reduction of 3 stops from f/5.6) and increase the exposure time by the same amount (in this case 2” to the power of 3 = 16”) and we now have plenty of time for the car to travel all the way across our frame. However, being at f/16 means that the car lights are now only 1/8th of their original luminance which may not be desirable. In this case we need to go to our second option - moving closer to the car. If we return to our original exposure of 2 seconds, f/5.6, ISO 100, but move forwards so that the car is now passing only a few metres in front of us, even though it is still going at 30km/h and even though we still have a focal length of 24mm, it will now pass across our frame fast enough to cover the entire width of the image within the 2 second exposure. Being at f/5.6 means we still have the desired luminance of the light trails, and using a 24mm lens means we hopefully still get the desired composition.

We could use a combination of both of these methods by changing our exposure to 8 seconds, f/11, ISO 100 and moving to within 25 metres of the car. This may still give enough luminance of the light trails and still provide our desired composition.

Another influence of how fast a moving subject passes across the frame of a camera is its direction of travel in relation to the sensor. If a car is driving directly towards the camera at 60km/h it will appear to be static on the frame. If it is moving diagonally then it will appear to be moving half the speed than if it were travelling at right angles to the frame.

So speed of movement across the frame is influenced by the following…

1 - Speed of object
2 - Focal length
3 - Distance of object
4 - Direction of movement in relation to sensor

Once you appreciate that traffic trails should only be used to add impact to an already strong scene, and that the ambient light has to balance the artificial light correctly, and once you understand how to control the balance of moving lights with static lights, along with how to influence any moving light’s speed, then you will be on the right path to creating some great traffic trail shots.

Final checklist

1 - Get a good sturdy tripod, camera which allows full Manual Mode, cable release.
2 - Locate a suitable scene which works well on its own, but will have more impact with traffic trails.
3 - Arrive in plenty of time to decide on best viewpoint and composition.
4 - Connect cable release.
5 - Set ISO to 100, aperture to around f/8, and then achieve correct exposure with Exp Time.
6 - Wait for ambient light to perfectly balance artificial light.
7 - Influence traffic trail length and luminance by altering Exp Time and balancing with Aperture/ISO
8 - Amaze your friends with your impressive images!

Urban night photography
For a bit of fun, you can try shooting light trails where the camera is moving instead of the lights. This was shot from a moving tram in Hong Kong, handheld at 2 seconds.

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