Transport Index Explained: What It Is and How to Calculate It

Why Transport Index Matters

The Transport Index isn't just a number you write on a label—it's the key value that controls how your package moves through the entire shipping chain. Carriers use TI to decide how many packages can go in one truck. Airlines use TI to determine cargo hold placement. Emergency responders use TI to assess hazard levels at accident scenes.

I've seen shipments delayed because the shipper didn't understand TI limits. A facility tried to ship five YELLOW-II packages in the same van, each with a TI of 0.8. The total TI was 4.0, which exceeded the non-exclusive use limit of 50 for the vehicle—but more importantly, it pushed them into needing specific loading configurations. The carrier refused the shipment until the packages could be spread across multiple vehicles.

Understanding TI helps you plan shipments efficiently, avoid carrier rejections, and ensure your packages are handled safely throughout transport.

Who Needs to Know This

This applies to anyone who:

• Measures radiation levels on packages
• Fills out radioactive material labels
• Prepares shipping papers for RAM
• Loads radioactive packages into vehicles
• Plans shipments involving multiple RAM packages

What is Transport Index?

The Transport Index is defined in 49 CFR 173.403 as the number expressing the maximum radiation level in mrem/hr at 1 meter (3.3 feet) from the external surface of the package.

Think of it this way: if you stood exactly 1 meter away from every side of the package and measured the radiation, the highest reading you get (in mrem/hr) becomes the basis for TI.

Why 1 Meter?

The 1-meter distance standardizes measurements across all packages regardless of size or shape. It provides a consistent way to compare radiation levels and predict dose to workers who handle packages at typical working distances.

How to Calculate Transport Index

Calculating TI involves measuring and rounding according to specific rules in 49 CFR 173.403.

Step 1: Measure at 1 Meter

Using a calibrated survey meter, measure the dose rate at 1 meter from each accessible surface of the package. For rectangular packages, this typically means measuring from all six sides. For cylindrical packages, measure around the circumference and from both ends.

Step 2: Take the Maximum Reading

The TI is based on the highest reading from any direction. If you measure 0.3 mrem/hr from one side and 0.8 mrem/hr from another, you use 0.8.

Step 3: Round Up to Nearest 0.1

Always round up to the first decimal place:

• 0.81 mrem/hr → TI = 0.9
• 0.15 mrem/hr → TI = 0.2
• 1.01 mrem/hr → TI = 1.1
• 2.00 mrem/hr → TI = 2.0

Exception: TI of Zero

If the measured dose rate at 1 meter is 0.05 mrem/hr or less, the TI is 0. This is the only case where you round down.

The most common mistake I see is rounding the wrong direction. Shippers measure 0.82 mrem/hr and write TI = 0.8 instead of TI = 0.9. This seems like a small error, but it can affect label category and vehicle loading calculations. Always round up unless you're at 0.05 or below.

How TI Determines Label Category

TI is one of two factors that determine which radioactive label your package needs. The other factor is surface dose rate.

Once you know your TI, there's another number you need for the label: the TI itself must be written in the designated space on the label. For WHITE-I packages (TI = 0), you still write “0” in the TI box.

TI and Vehicle Loading Limits

The total TI of all packages in a vehicle determines loading restrictions under 49 CFR 177.842.

Non-Exclusive Use Vehicles

For vehicles carrying radioactive material along with other freight or passengers:

• Total TI in the vehicle must not exceed 50
• Packages must be separated from people based on TI (see separation table below)

Exclusive Use Vehicles

For vehicles dedicated solely to radioactive cargo:

• No TI limit for the vehicle
• Higher surface dose rates allowed (up to 1000 mrem/hr with proper controls)
• Additional security and handling requirements apply

The exclusive use concept exists because you don't need to protect other freight or random passengers—everyone involved knows they're handling radioactive cargo and can take appropriate precautions.

TI and Separation Distances

Total TI determines how far radioactive packages must be kept from people and undeveloped film. These distances are specified in 49 CFR 177.842 Table 4.

The film distance matters because radiation can fog undeveloped photographic film. While film is less common today, some industrial applications still use it, and the regulations haven't been updated to reflect the digital age.

Calculating TI vs. Measuring TI

While TI is officially determined by measurement, you can often calculate expected dose rates before packaging to predict what TI you'll have. This helps with planning but shouldn't replace actual measurements.

When to Calculate

• Planning shipments before material arrives
• Estimating shielding requirements
• Verifying measurements are reasonable
• Training purposes

When to Measure

• Final TI determination for the label
• Regulatory compliance documentation
• Whenever carrier acceptance requires survey data

For routine shipments of identical packages, you may not need to measure every single one. If you ship the same source in the same packaging configuration repeatedly, you can establish a representative TI through initial measurements. But document your basis carefully—if anything changes (decay, different source, different shielding), you need new measurements.

How RadShip.com Helps

RadShip.com simplifies TI-related tasks by:

• LabelCalc – Enter your measured dose rate at 1 meter, and it automatically calculates TI with proper rounding and determines your label category.
• RAMcalc – Estimates expected dose rates based on nuclide, activity, and shielding to help you plan shipments before measurement.
• Proper TI rounding built in—no manual calculation errors.

TI calculation itself is straightforward, but the downstream effects—label selection, vehicle limits, separation distances—can get complex when you're shipping multiple packages. An automated tool ensures all these factors are considered together and your documentation is consistent.

Or skip the manual work and use LabelCalc to handle TI calculations automatically. Try it free for 7 days.

Common Questions

What if I can't measure at exactly 1 meter?

Use the inverse square law to adjust. If you measure at 0.5 meters, the dose rate at 1 meter would be approximately 1/4 of your reading. If you measure at 2 meters, it would be approximately 4 times your reading. However, this is an approximation—for regulatory compliance, try to measure at 1 meter.

Does TI change over time?

Yes, due to radioactive decay. As activity decreases, dose rates decrease, and TI decreases. For short-lived isotopes, you might ship at YELLOW-II but receive at WHITE-I. Always use the TI at time of shipment.

What if my TI exceeds 10?

You need exclusive use shipment. Packages with TI > 10 cannot be shipped in non-exclusive use vehicles. The package itself can have TI up to 10 for normal shipment; anything higher requires exclusive use arrangements.

Is TI the same for air and ground?

The calculation is the same, but limits differ. IATA has different vehicle/aircraft loading limits than DOT ground transport. Always check the applicable regulations for your mode of transport.

The most important thing to remember is that TI isn't just a number for the label—it's the basis for the entire system of controls that keep workers and the public safe during transport. Getting TI right means getting everything else right.

Summary: Your TI Calculation Checklist

Before finalizing TI, ensure:

• ☐ You've measured dose rate at 1 meter from all accessible surfaces
• ☐ You're using the highest reading from any direction
• ☐ You've rounded up to the nearest 0.1 (except ≤ 0.05 rounds to 0)
• ☐ You've also measured surface dose rate for label determination
• ☐ You've written the TI on the label
• ☐ You've verified total TI for the vehicle doesn't exceed limits

Or skip the manual work and use LabelCalc to handle TI calculations automatically.

Regulatory References

DOT Requirements:

• 49 CFR 173.403 – Definitions (Transport Index)
• 49 CFR 172.403 – Radioactive materials labeling
• 49 CFR 173.441 – Radiation level limitations
• 49 CFR 177.842 – Class 7 (radioactive) highway transport

IATA (Air Transport):

• IATA Dangerous Goods Regulations, Section 10 – Radioactive material requirements