What measures have been most effective in decreasing transportation costs?

Three things I have seen in the past 12-months with clients around the globe include:
1. Implementation of a TMS solution or outsourcing logistics operations to a managed service provider.
2. Reduction in LTL -- utilizing more FTL.
3. Supplier contract management and freight audits to capture overages in invoicing for assessorial fees (as an example).

There are several measures that can be taken to decrease transportation costs. Here are some of them:

Creative and Out Of The Box Ideas: Becoming much more flexible and adaptable in your transport modes can really help to offset losses in ways you may not have taken into account.

Shipping Consolidation Opportunities: Explore shipping consolidation opportunities1.
Warehousing Services: Consider warehousing services.

Automatic Container Loading & Unloading System Reduces Labour Costs: Use Automatic container loading system to Reduce Labour Costs.

Use Preventive Maintenance: Use preventive maintenance to avoid breakdowns and keep your vehicles in top shape.

Logistics Cost Reduction: Focus On Logistics Cost Reduction (This blog will help further https://www.scmdojo.com/cost-reduction-strategies/)

Keep Customers Happy: Keep customers happy by listening to them.

Optimization of Available Storage Space to Increase the Storage Density: Focus on optimization of available storage space to increase the storage density.

I hope this helps! Let me know if you have any other questions.

Too much focus on transportation costs itself might be dangerous, it is more important to have a broader view of the whole supply chain. There are some options to decrease transportation costs based on better visibility and planning eq. DEM/DET optimization and decreasing free times. 

We implemented new software that helped decrease our transportation costs. With our old system, updating the freight lane costs was so difficult, which made us hesitant to go out to bid. As soon as we put in the new system, we had all of that available at our fingertips- we could go out to bid, do the analysis, and bring it back in. This particular software also had a benchmark within their ecosystem where you could see how you were doing in the lanes relative to your peers using the same system. This helped us target which areas we could try to attack with our carriers by just knowing we were out of alignment with that market.