Truck-aware routing: why car navigation sends lorries under low bridges

The phone on the dashboard is very good at one thing: getting a car from A to B. It knows the road network, it knows the traffic, and it is usually right about the arrival time. What it does not know is that the vehicle behind the windscreen is 4.2 metres tall, grosses 58 tonnes across seven axles, and is carrying two pallets of packaged petrol.

That is not a small gap. It is the difference between a route and a legal route.

The number that makes this concrete

Network Rail recorded 1,666 bridge strikes on the British rail network between 1 April 2024 and 31 March 2025 — which the operator describes as one strike every five hours. Britain publishes the figure; most countries do not, so treat it as the best-documented example of a problem that is not unique to Britain. Each strike means an examination, a possible closure, and a railway that stops until an engineer says it can start again.

Almost none of those drivers decided to hit a bridge. They were following a route that was never told what they were driving.

Height is not one number

Directive 96/53/EC sets the maximum authorised height for heavy vehicles in international traffic at 4 metres, with width at 2.55 m (2.60 m for temperature-controlled bodies). That is a ceiling on the vehicle. It says nothing about what the road can accommodate.

Sweden has no legislated maximum vehicle height at all. The network is built for roughly 4.5 m of clearance, and anything lower is signposted with the restricted-vehicle-height sign; clearances above 4.5 m are not signed, because there is nothing to warn about. So the road does tell you — provided the sign is there, provided it is accurate, and provided the driver reads it in time at 04:30 in November.

And the vehicle’s height moves. Swap the trailer and it changes. Put a container on a skeletal instead of a curtainsider and it changes. Load a machine that stands 30 cm proud of the deck and it changes for that run only. A height written on a sticker in the cab is a snapshot. A height held on the trailer record, picked up when that trailer is coupled to that run, is a routing input.

Weight is two numbers, and one of them is per axle

A road does not care what the whole combination weighs so much as what each axle presses into it. Both matter, and they are governed separately: EU rules allow 40 tonnes in general international traffic and 44 tonnes for intermodal transport, while axle loads are limited independently.

National road classification then narrows it again. Sweden grades roads by bearing capacity class: BK1 at 64 tonnes, BK2 at 51.4 tonnes, BK3 at 37.5 tonnes and BK4 at 74 tonnes gross — and within each class the permitted gross weight still depends on the distance between axles, so the class alone is not the answer. By default a public road is BK1 and other non-private roads are BK2, which means the trunk road your 64-tonne combination is legal on can hand you over to two kilometres of municipal road where it is not.

A consumer routing engine has no field for any of this. It will give you the shortest way to the door.

Dangerous goods are a routing constraint, not a placard

ADR assigns every substance a tunnel restriction code in column 15 of Table A, chapter 3.2 — a code naming the tunnel categories through which that substance may not be carried, from category A (no restriction) to category E (effectively prohibited). A two-part code such as D/E applies the first part to carriage in tanks and the second to all other carriage, so the same product routes differently depending on how it is packed.

That is not something a driver can reasonably hold in their head across a mixed load and an unfamiliar country. It is a lookup, and lookups belong to software. It also interacts with load building: consolidating a second booking onto the same vehicle can change which tunnels that vehicle may use, which means the routing question is reopened every time the load changes.

Turning geometry, and the last 500 metres

Routing engines with truck profiles avoid low bridges and weight-restricted roads reasonably well. Far fewer will tell you whether a 16.5 m articulated vehicle can actually make the turn into the yard, whether the street permits the reversing manoeuvre that turn implies, or whether the delivery point has a loading bay or a kerb and a tail lift.

This is where the map runs out. No routing engine replaces the line on the customer record that says approach from the north; the south entrance has a 3.4 m canopy. The useful improvement is not a better map — it is making that note reachable when it matters, on the driver’s stop list rather than in a folder in the office.

Why this is a data problem before it is a driver problem

Truck-aware routing is only as truthful as the vehicle profile it is handed, and profiles fail in three ordinary ways:

1. Never captured. The vehicle was created in a hurry with the dimension fields blank, and the routing engine quietly fell back to a default that behaves like a van.
2. Stale. The trailer was replaced, the body was changed, a tail lift was fitted. Nobody updated the record, because updating the record is nobody’s job.
3. Right, but load-blind. The vehicle is 4.0 m empty and 4.35 m with this particular load on it, and only the vehicle figure was ever used.

The habit that fixes all three is unglamorous: treat height, length, width, axle configuration and permitted gross weight as fields on the vehicle and trailer records, with an owner, reviewed on the same rhythm as inspection and tachograph dates. If your daily vehicle checks already get done, you have the rhythm — this is one more line on it.

The trade-offs, stated plainly

• A compliant route is often a longer route. Avoiding a restriction can add fifteen minutes and a few kilometres. If the planner is measured on distance alone, the safe route looks like waste, so measure something else.
• Map data lags the road. Roadworks, temporary weight restrictions, a newly posted bridge. Truck routing reduces exposure; it does not remove the need to read signs. Where the app and the sign disagree, the sign is law.
• Drivers will deviate, and should be able to say so. A system that treats every deviation as an exception to be explained teaches drivers to stop reporting them, and you lose the one feedback channel that improves the data. We wrote more about that gap in route planning versus reality.
• Truck-attributed map data costs more than consumer map data. That is one honest reason it is missing from free tools, and a reason to ask any vendor which map source sits underneath their planning screen.

A short check before you trust a route

1. Which map and routing provider is underneath, and does it carry truck attributes at all?
2. Where are height, weight, axle configuration and ADR class stored — on the vehicle, on the trailer, on the booking, or nowhere?
3. What happens when one of those fields is blank: a refusal, a warning, or a silent default?
4. Can a driver see the stop-specific constraints without ringing the office?
5. When the load changes, is the route re-checked, or is the first answer kept?

Where navichain sits

navichain plans on maps and routing from HERE, costs tolls across more than 20 country regimes before you quote, and keeps vehicle and trailer specifications with their documents and compliance dates on the records planners pick from. ADR classification, segregation and certification are part of the load check rather than a separate step, and the driver app shows dangerous-goods particulars scoped to the stop the driver is standing at. All of it is on every plan, from 995 kr a month, driver app included — see the platform page and pricing. The caveat is the one above, and it applies to us as much as to anyone: none of this is better than the specifications somebody took the time to enter.