John, I think the point with masks like the Respro is to provide reasonable mitigation of particulates/VOCs along with higher airflow and less restricted breathing than you would typically get from the usual half-face respirators. I don't think anyone is claiming they are as effective as NIOSH/OSHA certified equipment, but then again those wouldn't be practical for the majority of bike commuters anyway. Afterall, the best protection is the one you'll actually wear. Ergonomics is a key.

Ultimately, a light-duty mask like the Respro, combined with your advice about reducing exposure (distance, shielding, etc.) is something everyone can easily get into and should go a long way towards minimizing the risk to an acceptable level.