Lego Duplo 10508 train does not pull up the bridge
Short answer: It's not a good train bridge and results are disappointing.
Longer answer:
We've tried two different Duplo trains (10874 Steam Train and 10875 Cargo Train) on the Duplo train bridge and they barely have enough power/traction to get over it even without any train cars attached. If you run a bare engine (no cover), it goes up fine. If you run the engine with a decorative cover (the &quot;top&quot; of the train), it will struggle. If you run it with train cars attached it seems like it's 50/50 whether it'll make it over.
You also could consider trying different types of batteries. Alkaline (non-rechargeable) batteries usually have higher voltage when they are new (but then drop off quickly), compared to rechargeable, which maintain a steady, but slightly lower voltage (reference).