HEPA spec. on a filter is removal of 99.97% of particulates of diameter 0.3 microns or greater.
Most diesel particulates (90% according to sites I just checked) are under 1 micron in diameter. I'm not sure you can count on the Insight filter to be that good given that it is described as a "micron" filter. It's certainly not HEPA.
Here's what I do to avoid smelling diesel fumes...
When I get the slightest sniff of Diesel fumes I switch my AC to recirculate mode. This prevents the nasty diesel fumes from being sucked in from the outside. After I pass the vehicle in question, I wait a tiny bit then switch back to fresh air circulation. Or if it's really bad I will completly shut off my AC untill I can get in front of suspect vehicle.
If you transport your dog in your insight or live on rural roads (dusty) you might shorten the replacement interval for the "micron" air filter to six or eight months instead of twelve.
Try rolling the window down and smell the diesel directly next time, you'll appreciate the filter. Recirculate helps too. One thing I would mention that I had a problem with. The origonal filter that comes in the car when new is different from the replacment one. The replacment one they well is the same as a CRV uses, convenient, but it's not exactly the same (and made in Germany?) when you replace it you have to put a pleat and a half over the hold down at the edge to get it to seal properly. If you just jam it in the plastic frame it will not seal. This is one problem I had with mine when I first replaced it. Now the origonal Japanese one just goes right in as it's supposed to. I want a japanese parts hook up.