Fog and Low Visibility on Northern Vietnam Roads: What Official Advice Says About Waiting

A forecaster at Vietnam’s national hydro-meteorological forecasting centre (NCHMF) said on 1 March 2026 that fog reduces visibility and can endanger traffic, especially on national highways. This page gathers what nine sources say about fog riding in northern Vietnam: where the pages place fog, what the traffic police and the road-traffic law ask, and what two overseas pages, from the UK and New Zealand, add. They give advice on slowing, lights and waiting. None sets a distance at which to turn back, so this page does not either.

Where the pages place fog in northern Vietnam

The Vietnam+ report quotes Nguyễn Văn Hưởng of NCHMF describing advection fog: cold air that had sat over the north-east weakens and moves east, bringing more moisture inland, while inversion layers at 500–1,500 m and calm surface wind supply the combined conditions. The page lists four fog types (advection, radiation, evaporation, frontal) and says fog needs high humidity, relatively low temperature and weak or calm wind. It also describes National Highway 4B in Lạng Sơn on the mornings of 9 and 10 January 2026, where fairly dense fog began about 6 km from the central wards. Other pages name these roads:

PLO reports that the traffic police department (Cục CSGT, Ministry of Public Security) says dense fog often appears on passes in Phú Thọ, including these four, at night and in the morning, limiting visibility and making the road slippery. For route planning on the Tam Đảo road, see Tam Dao from Hanoi by Motorbike: Mountain-Road Planning for Experienced Riders.

What the official forecast page showed

The NCHMF forecast page, read on 25 October 2026, lists forecasts for the night of 25 and the day of 26 October for Hà Nội, the north-west (Tây Bắc Bộ) and the north-east (Đông Bắc Bộ). The text for all three gives temperatures, cloud, night showers and light wind, and does not mention fog. Its visibility figures (“Tầm nhìn xa”) are for sea areas, such as above 10 km, falling to 4–10 km in rain. A “Thời tiết nguy hiểm” (dangerous weather) menu entry was not opened. For comparison, the Met Office says dense-fog warnings are issued when visibility is expected to fall below 200 metres and severe transport disruption occurs below 50 metres; these are UK figures. For rain rather than fog, see Hanoi Rainy-Season Riding: A Go-or-Postpone Decision Checklist.

What Vietnamese traffic police advise

Four pages relay police advice, dated from February 2023 to February 2026.

The 2023 page adds Cục CSGT figures: 3 serious fog accidents between 15 December 2022 and 8 February 2023, with 3 people killed and 3 injured. The Ministry’s Lào Cai page says a public hotline number was released for drivers with a breakdown or who need rescue.

What the road-traffic law says

Law 36/2024/QH15, read on vbpl.vn, has these provisions that bear on fog. Article 20(1) says front headlights must be on from 18:00 to 06:00 or when fog, smoke, dust, rain or bad weather limits visibility; it addresses “người lái xe”, defined in Article 2 as the operator of a motor vehicle, and Article 34 lists motorcycles and mopeds among motor vehicles. Article 12 asks anyone operating a road vehicle to keep a speed suited to conditions including weather, and to slow down or stop in listed cases, among them limited visibility, winding and mountain-pass roads, and mist (sương) or slippery surfaces. Article 14(6) says no overtaking on curves with limited visibility, near crests with limited visibility on two-way roads, or when weather or road conditions do not make overtaking safe. Article 18(4)(b) says no stopping or parking on a curve or near the top of a slope where the view is obscured.

Waiting, stopping and turning back

The Met Office says fog can drift rapidly and be patchy, and the Vietnam+ account of National Highway 4B above has fairly dense fog beginning about 6 km from the central wards. On waiting, the pages split like this:

For turnaround decisions on a hill route, see Ba Vi National Park by Motorbike: Gates, Climb and Turnaround Decisions.

Lights, visor and following distance in overseas guidance

The Met Office (for road users) and NZTA (for riders) both say to dip the headlight in fog: full beam reflects off the fog, a “white wall” effect in the Met Office’s words. The Vietnamese pages also say low beam. NZTA adds that a front fog light has a wide, low beam, white or yellow; a rear fog light, a high-intensity red, should only be used when visibility is very bad; and fog lights go off as conditions improve. It says to keep the helmet visor and the motorcycle mirrors clean when rain, snow or fog cut visibility and, in its advice for wet, frosty or icy roads, to use a 4-second following distance. The Met Office warns against hanging on the tail lights of the car in front, as they can give a false sense of security. See also Helmet Visor Scratches: Visibility Checks Before Accepting a Rental Helmet.

What the pages leave out

• A visibility distance, in metres, at which a rider should stop, wait or turn back. The Met Office figures of 200 m and 50 m are UK warning thresholds, not riding cutoffs.
• Any statement to turn back. The nearest are “avoid travel if possible”, “find shelter and wait” and “call for help”.
• Anything about rental bikes: what a shop provides, charges or requires, or whether a rented motorbike has a fog lamp. That is a question for the shop.
• Fog wording for the north on the NCHMF forecast page on the day read, and where a fog warning would be published.
• How long fog lasts on a given road or how fast it clears. The Vietnam+ page of 1 March 2026 says only that fog could still appear for many days to come in the north.
• Reasons for the 40 km/h figure, which the page words as “ideally”; the Ministry’s Lào Cai page gives no number.
• Guidance aimed at motorbike riders in Vietnam: the police pages address drivers in general, the Met Office page road users in general, and the Met Office and NZTA pages cover UK and New Zealand roads; one police page dates from 2023.
• Implementing rules: Article 12(4), which the page flags as replaced, refers speed and distance details to the Transport Minister, and none were read.

Sources checked

• vbpl.vn: Law 36/2024/QH15
• Met Office: advice for travelling in fog
• Ministry of Public Security: Sa Pa fog outreach
• PLO: police advice for passes in foggy season
• Vietnam+: fog warning for the north
• NZTA: riding in bad weather
• NCHMF: forecast page
• Bao Quang Ninh: driving in fog, 2023
• Lạng Sơn TV: police advice for wet roads and fog

Thuê xe máy Nguyễn Hà is open 09:00–21:00 daily at Ngõ 5 Nguyễn Văn Cừ, Bồ Đề, Long Biên, Hà Nội (near Gia Lâm bus station). Phone: 0334 699 969.