Lane Load vs Truck Load Comparison Calculator

Calculator inputs

This tool uses a simply supported beam model for quick comparison. It is helpful for preliminary checks, planning reviews, and teaching examples.

Unit system

Span length (m)

Evaluation section x (m)

Lane uniform load w (kN/m)

Lane concentrated load P (kN)

Lane load factor

Include lane concentrated load

Place lane concentrated load at evaluation section

Lane point load position (m)

Truck axle 1 (kN)

Truck axle 2 (kN)

Truck axle 3 (kN)

Spacing 1 to 2 (m)

Spacing 2 to 3 (m)

Front axle position from left support (m)

Truck load factor

Truck impact allowance (%)

Example data table

Sample bridge screening values

Case	Span	Lane w	Lane P	Truck axles	Spacings	Section x
Metric teaching example	30 m	9.3 kN/m	110 kN	35, 145, 145 kN	4.3 m, 6.0 m	15 m
Imperial planning example	100 ft	0.64 kip/ft	18 kip	8, 32, 32 kip	14 ft, 30 ft	50 ft
Short-span screening	18 m	9.3 kN/m	80 kN	35, 120, 120 kN	3.8 m, 4.5 m	9 m

Formula used

Simply supported reactions

Uniform lane load: R_L = wL / 2 and R_R = wL / 2

Point load at distance a: R_L = P(L - a) / L and R_R = Pa / L

The calculator sums uniform load effects and every point load effect to build reactions, shears, and moments.

Shear at any section x

V(x) = R_L - wx - ΣP_i for all loads located at or left of x.

Moment at any section x

M(x) = R_Lx - wx² / 2 - Σ[P_i(x - a_i)] for loads positioned at or left of x.

This is a comparison calculator for preliminary review. Final design should still follow the governing code, load model, distribution method, and member configuration.

How to use this calculator

Choose metric or imperial units before entering loads.
Enter span length and the evaluation section location.
Fill the lane load inputs for uniform and concentrated effects.
Enter truck axle weights, spacings, front axle position, and any impact allowance.
Apply factors if you want a factored comparison instead of raw nominal loads.
Press Compare load cases to place the results above the form.
Review the table and Plotly graph to see which load case governs moment and shear.
Use the CSV or PDF buttons to export the summary for reports or review notes.

FAQs

1) What does this calculator compare?

It compares lane loading and truck loading on a simply supported beam span. It reports reactions, shear, moment, equivalent uniform load, and the governing case.

2) What is lane load?

Lane load represents traffic spread along a lane as a uniform load, often paired with a concentrated load. It is useful for modeling distributed traffic demand across longer spans.

3) What is truck load?

Truck load represents discrete axle forces placed at selected locations. It is useful when concentrated wheel group effects may control a specific section or a shorter span.

4) Why can the governing case change?

The controlling case depends on span length, axle spacing, impact allowance, evaluation section, and load magnitude. A longer span often favors lane effects, while a short span may favor truck effects.

5) Does this replace a full code design check?

No. This tool is for preliminary comparison only. Final bridge or construction design still needs the correct design code, distribution factors, combinations, member properties, and detailed load placement rules.

6) Why is the section location important?

Moment and shear vary along the span. A truck can govern near one section while a lane case governs elsewhere. Checking the selected section helps identify local demand differences.

7) Can I use metric and imperial values?

Yes. The form switches labels for length, force, line load, and moment. Enter values consistently in the chosen unit system and keep axle spacings inside the span.

8) Why are CSV and PDF exports useful?

They help you capture a fast comparison record for review notes, internal checks, presentations, or client discussions without copying each result manually from the page.