Start from the bridge inventory, not from the brochure
Most bridge inspection vehicle selection mistakes happen at the first step: someone picks a truss length off a price list and then makes the bridge inventory fit the truck. The reverse is faster and cheaper. Your bridge inventory already has fixed numbers — under-deck clearance at each span, bridge width, approach road geometry, shoulder width, and whether the work is visual inspection or active repair. A good inspection vehicle choice is simply the smallest truss that still reaches the deepest soffit in your fleet. Below is the decision tree we run with customers, followed by the parameter definitions that bridge engineers usually argue about.
The decision tree: five questions before you spec a truck
1. Deepest under-deck clearance. Measure the vertical gap between the bridge deck and the water or ground below. Most urban bridges need 20 to 22 m; deep river crossings need 24 to 26 m. Spec the truss for the deepest span in your inventory.
2. Chassis axle count and road permits. A 3-axle chassis such as the 23 m truss vehicle is shorter and more maneuverable. A 4-axle chassis such as the 26 m 4-axle unit carries a longer truss. Check your country's weight and dimension permits.
3. Platform load for the work. Visual inspection needs a 2 to 3 person platform. Repair work with tools and materials needs a heavier platform. Spec the platform load for the heaviest planned crew.
4. Bridge width and shoulder access. Wide highways with shoulders let the truck park in one lane. Narrow urban bridges may need a vehicle that fits within a single lane without blocking traffic.
5. Budget and TCO. Compare purchase price, annual inspection, maintenance and downtime together. A slightly larger truss that covers every bridge in the fleet beats two smaller trucks that cannot reach the deep spans.
The parameters engineers actually argue about
These five terms are where two buyers "compare" inspection trucks that are not comparable at all. Get the definitions right and the table comparison becomes honest.
| Parameter | What it really means | How to use it in selection |
|---|---|---|
| Working depth (m) | Maximum vertical reach of the truss under the deck. | Must exceed the deepest under-deck clearance in your bridge inventory. |
| Truss length (m) | Horizontal reach of the articulated truss. | Must span from the bridge edge to the required inspection point under the deck. |
| Chassis axle count | 3-axle or 4-axle truck chassis. | Determines road permits, maneuverability and truss weight capacity. |
| Platform load (kg) | Maximum people and tools the under-bridge cage carries. | Must cover the heaviest planned repair crew. Overloading is unsafe. |
| Truss configuration | 2-section or 3-section telescopic truss. | More sections = longer reach in stowed position but more complex operation. |
| Working range | Side reach and rotation of the platform. | Must cover the full bridge width from one parked position on the shoulder. |
Match the truck to the bridge: urban, highway, long-span
Urban road bridges. Typically 8 to 16 m clearance with tight approach roads and narrow shoulders. A compact 3-axle 20 to 22 m unit such as the standard truss range navigates city streets and fits within one lane.
Highway viaducts and interchanges. 15 to 22 m clearance on wide multi-lane structures. A 4-axle 24 to 26 m unit such as the upgraded 26 m model reaches the soffit from the shoulder without blocking all lanes.
Long-span and river crossings. 20 to 26 m clearance over deep water. The Sinotruk Bawang 4-axle range such as the 26 m model or 3-section variant handles deep river spans and heavy platform loads.
Cable-stayed and special structures. Complex soffit geometry needs a specialized platform such as the cable-stayed bridge unit or the bridge inspection platform system.
Inspection vs repair: which work drives the spec
The honest comparison is not truss length on a spec sheet; it is what the crew actually does under the deck. Routine visual inspection needs a platform that holds 2 to 3 inspectors with cameras and measuring tools — a standard truss-type vehicle covers this. Active repair work (concrete patching, bearing replacement, waterproofing) needs a platform that carries power tools, materials and a larger crew, plus a longer working window under the same span. If your fleet does both inspection and repair, specify the heavier platform and longer truss even if the day-to-day work is inspection. A 24 m variant may be enough for inspection-only fleets, but repair crews will outgrow it within a season. Plan for the work you will do in three years, not the work you do today.
| Work type | Platform load | Truss length | Chassis | Best fit |
|---|---|---|---|---|
| Visual inspection only | Light (2-3 people) | 20-22 m | 3-axle | Urban bridges, routine inspections |
| Inspection plus light repair | Medium (tools + crew) | 23-24 m | 3-4 axle | Highway bridges, mixed duty |
| Active repair program | Heavy (materials + crew) | 25-26 m | 4-axle | Long spans, waterproofing, bearing work |
Five mistakes we see on real fleets
1. Under-sizing truss for the deepest bridge. A 20 m truck cannot reach a 22 m soffit, leaving that span uninspected. Spec for the deepest bridge in the inventory.
2. Ignoring road permits. A 4-axle oversize vehicle needs permits that vary by country. Confirm the destination's weight and dimension rules before ordering.
3. Light platform for repair work. A 2-person platform cannot carry a repair crew with tools. Spec platform load for the heaviest planned duty.
4. Buying for average clearance, not worst case. The average bridge may need 18 m, but the one deep river crossing needs 26 m. Design for the worst span.
5. Forgetting traffic management. The truck blocks a lane on every job. Narrow urban bridges may need a smaller vehicle that fits within one lane without a full closure.
Frequently asked questions
What working height of bridge inspection vehicle do I need?
Measure the clearance between the deck and the water or ground below. Most bridges fall in the 8 to 20 m range, covered by a 20 to 22 m truss. Deeper crossings need the 24 to 26 m class. Always spec for the deepest bridge in your fleet.
2-bridge or 3-bridge inspection vehicle?
A 2-axle or 3-axle vehicle is shorter and more maneuverable for urban bridges. A 4-axle vehicle carries a longer truss and heavier platform for highway viaducts. The axle count also determines road permit weight limits in your country.
How does platform load capacity affect the work?
The platform carries inspectors, tools and repair equipment. A standard platform holds 2 to 3 people plus light tools. If you carry repair crews with power tools or materials, specify a heavier platform. Overloading is a safety risk.
Truss-type or under-bridge platform?
A truss-type vehicle lowers an articulated truss over the edge and reaches under the deck from a parked position. A platform system provides a work cage that moves along the soffit. For routine visual inspection, a truss-type is standard. For repair work, a platform is more productive.
What chassis options are available?
Superstructures mount on mainstream heavy-duty chassis such as Sinotruk (Howo), in 3-axle and 4-axle configurations. The chassis must carry the truss weight and meet local road permits. Right-hand-drive variants are available for relevant markets.
Can the vehicle work on multi-lane highways?
Yes, but it requires lane closure and traffic control. The vehicle parks on the shoulder or a closed lane while the truss swings under the deck. Plan traffic management into every job. Narrow bridges may need a smaller vehicle.
What is the warranty and export lead time?
Standard configurations ship within 8 to 12 weeks due to custom truss fabrication. The vehicle carries a 12-month or 2,000-hour warranty with global spare-parts support. Right-hand-drive and local calibration options are available.
Send us your bridge inventory and we will size the truck
Tell us the bridge count, deepest under-deck clearance, average bridge width, shoulder geometry, and whether the work is inspection only or includes repair, and our special vehicle engineering team will match you to the right class across the Yutong bridge inspection vehicle range — from the 20 m urban class up to the 26 m 4-axle long-span units. We export to over 60 countries and build to FOB / CIF shipment terms with the full customs document set.