How to plan the route of oversized transport — bridges, tunnels, infrastructure

Why is route planning a separate discipline?

Any standard cargo driver can simply turn on GPS navigation and go. Code this is not possible with oversized transport. No commercial navigation system knows that the load is 5.2 m wide, that the semi-trailer in extended configuration is 42 m, or that the total mass is 180 t. It cannot warn about a bridge that carries 60 t, a tunnel that has a clear height of 4.1 m, or a low-voltage line that crosses the road at 4.3 m above the ground.

Route planning for extraordinary transport is expert analysis of infrastructure which must be completed before applying for a permit — because the route must be approved by the competent authorities, and any change to the route during transport requires a new permit.

Step 1 — Exact dimensions of the entire transport kit

Route planning starts with precise measurements — and not just the cargo, but the entire transport set. A 10 cm error in height can mean that the transport cannot pass through the tunnel that was planned on the route.

What is being measured?

• Total length — from the front bumper of the tractor to the rear end of the load or trailer, including the front and rear overhangs
• Total width — on the widest part of the load or trailer, including any protruding side parts
• Total height from the ground — is measured with the load loaded on the trailer, at normal tire pressure
• Mass — total mass of the set (tractor + trailer + load) and distribution by axle groups
• Back overhang — particularly important because it affects the turning radius and the passage through roundabouts
• Overhang forward — affects passage through narrow passages and tunnels with a restriction at the entrance

Step 2 — Check bridges

The bridges are the most critical infrastructure element in planning the route of oversized transport. Every bridge has two key characteristics that must be checked:

Bridge load capacity (ton limit)

Each bridge is designed for a certain maximum load. This load is not only the total mass of the vehicle — the distribution of the mass by axle groups and the distance between the axles are also important. A bridge carrying 60 t can pass a combination with the same total mass if the axles are sufficiently spaced, but reject another combination with better spacing but shorter spacing.

For heavy transports (above 60–80 t, depending on the country), the competent authorities carry out a special bridge load capacity analysis for each bridge on the planned route. This can significantly extend the time to obtain a permit — in Latvia for loads over 60 t the time can be up to 30 working days precisely because of this analysis.

Clearance under the bridge

Many older bridges, overpasses and passages have a clear height less than the standard 4 m. Particularly problematic are:

• Railway tracks crossing roads (often 4.2–4.5 m clear height, but sometimes less)
• Old city overpasses in urban areas
• It passes under the highway viaduct
• Industrial corridors with low-hanging installations

The clearance height is indicated on traffic signs, but for oversized transports these values must be physically verify or check the bridge's technical documentation — as the signs may be outdated or incorrect.

Where is the bridge inspection performed?

In Western European countries, road infrastructure managers (ANAS in Italy, RWS in the Netherlands, Bundesanstalt in Germany) maintain databases of bridge capacities. In Southeast Europe and countries outside the EU, these bases are less accessible, which requires direct communication with local authorities or physical verification in the field.

Step 3 — Tunnels and flyovers

Tunnels are similar in character to bridges, but with additional dimensions that need to be checked — not only height, but also aisle width, especially in older tunnels that are designed for narrow gauges.

Critical tunnels on European routes

For many tunnels, especially in the Alpine belt, it is necessary to announce the passage in advance and obtain special approval for oversized cargo — even if a permit for transit through the country has already been obtained.

Step 4 — Overhead lines and infrastructure

High loads — transformers, silos, tanks, cranes — can have a height of 5–6 m, and sometimes more. On such routes, the critical obstacle is not the bridges but overhead power lines, telecommunication cables and signaling.

Categories of overhead obstacles

• High-voltage power lines — a safety distance of 1 m below the power line is not sufficient; for loads above 4.5 m high, check and contact the network operator
• Low-voltage distribution network — most often hangs at a height of 4–5 m above the road; especially problematic in rural areas and villages
• Telecommunications cables — often hang lower than power lines and may be unmarked
• Traffic signals — traffic lights, road signs and information boards are sometimes mounted at a height of 4.2–4.5 m
• Railway infrastructure bridges — contact network (catenary network) of high electrical tension

For extremely high loads (above 5 m) passage through certain sections is required temporary lowering or raising of lines in coordination with network operators — which is planned weeks in advance and can be one of the most expensive elements of the entire transport.

Step 5 — Road classification and pavement capacity

Not all roads have the same load capacity. Belgium explicitly categorizes roads into load classes (e.g. 90 t class roads), and this directly affects the type of permit that can be obtained. The same is true for other countries — motorways generally have a higher load capacity category than local roads.

What to look out for

• Highways vs. national roads vs. local roads — heavy loads (above 60–80 t) can often only use the motorway network
• Protected zones — historic city centers, tourist areas and protected zones may be closed to oversized loads
• Seasonal carrying capacity coefficients — in the spring, while the ground is thawing (especially in the Baltic countries and Scandinavia), the carrying capacity of the roads is temporarily reduced and there are special weight restrictions
• Private roads and industrial zones — the last kilometers to the delivery point are often on local roads with a lower capacity

Spring — special attention

In the Scandinavian and Baltic countries, the period of ground thawing in spring (usually March–April) brings seasonal reductions in permissible mass on certain roads. Loads that are permitted in winter conditions may be temporarily prohibited until the ground stabilizes.

Step 6 — Passage through urban zones

Passing through cities and urban areas is one of the most demanding parts of route planning. Narrow street gauge, roundabouts, parking infrastructure and traffic density create a series of restrictions that must be verified.

Key factors in urban areas

• Minimum turning radius — long loads (above 30 m in total) have a large turning radius; every bend in the route must be checked
• Roundabouts — particularly problematic for long combinations; free passage with overhang must be checked
• Parking infrastructure and bollards — temporary obstacles that can block the passage
• Tram lines — especially in older cities with older infrastructure
• Night time slots — in Greece, oversized transport through urban areas is possible only at night, the same is true for certain cities in Ireland

For extremely heavy or long loads that have to pass through the city, it is sometimes the only option temporary traffic blockage in coordination with the local police — which is planned and announced days in advance.

Step 7 — The permission defines the route, not the other way around

It is important to understand the logic: in most European countries, with one-time permits the route is specified in the permit. This means that the route must be proposed when submitting the request, and the competent office approves, modifies or rejects it.

Any change to the approved route — even a detour due to roadworks — technically requires a permit amendment or a new permit. In practice, for minor deviations, communication with the relevant office may be sufficient, but this depends on the country and the situation.

Permanent permissions — different logic

Permanent permits (which exist in Belgium, Germany, the Netherlands and others) do not specify the route — they approve specific dimensions for a specific road network. The driver can choose a route within the approved road network. This gives much greater operational flexibility, but requires the driver to check the infrastructure elements himself on each specific trip.

Common mistakes when planning a route

1. Measuring height without load

The most common and most expensive mistake. The height of an empty trailer without a load can be 30 cm lower than the height with a loaded load. The permit is issued for height without load — but the actual passage requires height with load.

2. Ignoring the last few kilometers

The route to the local industrial park or construction site passes through local roads that have not been tested. It is in those last few kilometers that the problems lie — low gates, narrow streets, poor load-bearing capacity of the private road at the delivery location.

3. Assuming the GPS route is correct

Commercial navigation systems do not have data on the carrying capacity of bridges, the clear height of tunnels or the type of road. Even specialized software for heavy vehicles may have outdated data for South East Europe and non-EU countries.

4. Unverified objects on the route that are not always on the map

Seasonal canopies at markets, temporary cables for events and decorations, construction sites with wire fences — all these can block the passage of high loads and are not recorded anywhere.

5. Ignoring traffic rush hours

Passage through cities and critical points must be planned outside the morning and afternoon rush hours — not only because of weather restrictions but also because of the practical impossibility of maneuvering in heavy traffic.

Checklist before departure

This is the minimum list of checks that any serious organizer of extraordinary transport must go through before the vehicle leaves: