Diamond-shaped traffic signs: who they instruct

A diamond-shaped traffic sign is not aimed at you, unless you drive a tram. In Great Britain, every diamond-shaped sign gives instructions to tram drivers only, and to nobody else. That single fact answers most of the confusion around these signs: car drivers, lorry drivers, bus drivers, cyclists and pedestrians are not the audience for a diamond sign, but they still need to understand what it means, because a tram following its diamond-signed instructions may move when other traffic must wait. This page explains what the diamond shape means, what diamond signs look like, and what to do when you meet one.

The short answer: tram drivers only

The Department for Transport's Know Your Traffic Signs booklet is explicit: all diamond-shaped signs are for tram drivers only. The Highway Code says the same thing in its tramways section, where it states that diamond-shaped signs and white light signals give instructions to tram drivers only. So when a diamond sign tells a tram driver to stop, to proceed, or to keep within a speed limit, that instruction binds the tram driver and does not bind anyone else on the road. It is not a general instruction that happens to be diamond-shaped; the shape itself is the marker that the sign belongs to the tram system. If you are driving a car and you see a diamond sign, it is not telling you to do anything, but it is telling you something about what the tram near you may do next.

What diamond signs look like

The clearest example is the speed limit sign for tram drivers, shown in kilometres per hour inside a diamond. A tram running along a street shared with other traffic may have a different speed limit from the cars beside it, and the diamond shape is what keeps the two limits apart: the circular speed limit sign on the same street applies to other vehicles, while the diamond applies to the tram. Diamond signs also sit alongside the white light signals used by trams, which give tram drivers their own stop and proceed instructions that may not match the traffic lights facing other drivers. The point of giving trams their own shapes and signals is separation. A tram cannot steer around an obstacle, so its movements have to be predictable, and a shape that no other sign uses makes a tram instruction impossible to confuse with an instruction to anyone else.

Why trams need their own signs

Trams can run on roads used by other vehicles and pedestrians, and the part of the road used by trams, known as the swept path, may have a different colour or textured surface, or may be edged with special road markings. The official guidance is blunt about the consequence: trams cannot move out of the way of other road users, so other road users must keep the swept path clear. That is why tram instructions live in their own visual language. A car driver who mistakes a diamond speed limit for their own limit, or who follows a tram signal meant for the tram, risks moving into the path of a vehicle that cannot swerve. The diamond shape exists so that does not happen: one glance tells every road user whether the sign is theirs or the tram's.

What it means for everyone else

Not being the audience for a diamond sign does not mean ignoring trams. Drivers of other vehicles must give way to trams at level crossings without barriers, gates or road traffic light signals, where sometimes just a give way sign and a tram plate are used. Tram drivers usually have their own traffic signals and may be permitted to move when you are not, so you should always give way to trams, and never try to race or overtake one, or pass on the inside, unless it is at a tram stop or stopped by tram signals and there is a designated tram lane for you to pass. You must not enter a road, lane or other route reserved for trams, and you should take extra care where the track crosses from one side of the road to the other and where the road narrows and the tracks come close to the kerb. In short, the diamond sign tells the tram driver what to do, and your job is to anticipate the tram doing it.

Worth knowing even though you will never obey one

If you are learning to drive, diamond signs are worth knowing precisely because they are the exception that proves the shape system. Most road signs follow a pattern you can read at a glance: circles give orders, triangles warn, rectangles inform. Diamonds break that pattern on purpose, and the break is the message. When you see a diamond, you know instantly that the instruction belongs to a tram, which tells you a tram is operating nearby and that its driver is working to instructions you cannot see on your own signs. Look for the rails, the swept path and the tram signals, give the tram room, and let it move first. For the signs that do give orders to ordinary drivers, including the one sign that breaks the circle rule, see our what shape is a stop sign page and our traffic sign shapes that give orders page.