The bridge is frozen but the road before it is dry: where ice appears first

An ordinary winter drive across Riga. Dry asphalt, the car tracking straight. You drive onto a bridge — and halfway across the span the steering goes light and the car drifts a little sideways. A hundred metres later, back on the embankment, everything is normal again.

The weather did not change in those seconds. The place did. Ice does not settle on a road as an even carpet; it arrives in patches, and those patches repeat in the same types of place. What black ice is and how to behave on a slippery surface is covered in the general winter article. This one answers a different question: where it will appear first, and why exactly there.

One set of weather, several different roads

The thermometer in your car reads the air temperature. What holds you up, though, is not the air but the road surface, and that has a temperature of its own. The temperature of the road surface differs from the air temperature: the gap can be several degrees, and the surface does not warm up as quickly as the air does. So, as Latvijas Valsts ceļi (LVC), the state company responsible for Latvia's national roads, warns, icing is possible even while your thermometer shows a figure above zero.

How seriously the road service takes this shows in how it works. Duty staff decide on preventive salting as soon as the air temperature is around zero: the salt goes onto a surface that has not iced over yet, getting ahead of the ice. In other words, zero in the air is, for the people who maintain the roads, a working situation rather than mild weather.

A bridge has no ground beneath it

An ordinary road sits on soil, and that soil is a large reservoir of heat which gives its warmth up slowly. A bridge has no such cushion: its deck is washed by air on every side and has no thermal insulation from the ground below — that is how the engineers who design heated bridge decks describe it. Overnight a bridge cools faster than its own approaches and goes below zero first.

Hence the LVC advice that comes back season after season: icing is particularly likely on bridges and flyovers. For Riga that is not an abstraction — the bridges over the Daugava, the flyovers at the big junctions, the overpasses above the railway. Those are the few hundred metres where the road can be a different surface from the street before and after it.

Shade, dips and the water's edge

The second type of place is wherever the sun does not do its work. During the day open asphalt dries out while shaded asphalt stays wet and freezes by evening. LVC names exactly the same addresses: icing forms sooner and most often on bridges and on roads that are shaded or run through dips where cold air collects.

Worth holding in your head as distinct types:

• Shade thrown by tall buildings on narrow streets — a strip the winter sun never reaches at all.
• Avenues and stretches along parks — the canopies hold shade and damp even with no leaves on them.
• Dips and hollows — cold air is heavier, drains downhill and pools in the low points of the terrain.
• Stretches near water — LVC separately mentions roads close to the sea, a lake or a river, and wooded country: there is more moisture there, and moisture has something to turn into.

A clear, still night is its own mechanism. Surfaces radiate their heat to the open sky and cool further than the air does, while cloud works like a blanket and slows that cooling down. The Met Office describes the everyday consequence everyone recognises: frost on the windscreen while the car thermometer reads above zero. Exactly the same thing is happening to the road.

Bus stops, junctions and the run-up to traffic lights

The third type of place is not created by physics alone — the wheels help. At a bus stop, in front of a traffic light and at a junction, cars brake and accelerate. Thin snow there gets compacted, melts a little from the friction and freezes again; frost crystals crushed under a wheel melt slightly and set as smooth ice — a mechanism described by the same Met Office. The result is a polished film that looks like wet asphalt.

The awkward part is that these — junctions, bus stops, the run-up to traffic lights — are exactly the places where you have to brake.

Courtyards and side streets the gritter reaches later

Preventive treatment does not go everywhere: LVC applies it to roads in the highest maintenance class, the ones carrying the heaviest traffic. A courtyard, an internal block road, a short ramp down to the garages are not on that list. Which makes pulling out of a courtyard in winter a hazardous place-type of its own: five metres of slope, a gate, a pavement and a crossing flow of traffic, with something nobody has cleared under your wheels.

The danger is not the ice, it is the moment you drive onto it

LVC puts it in a single phrase: roads ice over rapidly and unevenly. Unevenly is the key word. If the whole road were equally slippery, a driver would drive accordingly. The danger is created by the seam: for forty seconds the car behaves normally, the driver has time to get used to that — and at the boundary between surfaces the habit stops working.

Aquaplaning follows a similar logic but is a different phenomenon: there it is water between tyre and asphalt rather than ice, and it has an article of its own. Ice does not even give you the second that water gives you.

What to do on a suspicious stretch

• Make the decision before the place, not on it. You shed speed on the approach to the bridge, not in the middle of the span.
• Nothing abrupt on the bridge itself. No braking, no lane changes, steering straight, throttle steady.
• Test the grip early. LVC advises exactly that: once you are out on the road, brake gently at a safe speed and in a safe place, and find out whether the car slides.
• Following distance is the one tool that always works. The road traffic rules require a speed that suits road and weather conditions (Rule 99) and, on a hazard, reducing it up to a full stop (Rule 100).
• Clean glass and lights. You cannot steer around a patch you cannot see; the ten-minute check of the car before the dark season is covered separately.

On winter tyres, briefly: they are seasonally mandatory — a conversation of its own; good rubber widens your margin, but it does not cancel the map.

Nobody hands you that map ready-made. A driver assembles it personally, out of the bridges, shaded strips and junctions on their own daily route. In a lesson we drive such a route together and talk through every place out loud; you can book online.

A winter road does not become slippery all at once. It becomes uneven — and the only question is whether you notice where.