h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

the article missed something important- cyclists inhale
exhaust fumes very intensively as they need extra oxygen
for fuel and often they are right in the exhaust plumes. The
problem is potentially a big one deserving of research. I
was diagnosed with multiple myeloma, a cancer of the bone marrow,
after 4 decades of cycling, almost 3 of them in traffic. One of
the main triggers of this incurable cancer is benzene, something
to which I have never been exposed except via exhaust. This is
probably a coincidence, but I wanted to share this. Be careful!

There is some research that says the fumes are actually more concentrated in cars, but that doesn't stop cyclists being at risk too.

Thanks for pointing that out. But I remember many years
ago cycling along the Marylebone Road, keeping up with
traffic, and breathing very hard. When I got off the bike
I almost collapsed - I felt quite giddy/drunk, and it took
a while for me to collect my senses. The fact that cyclists breath so
hard brings carbon monoxide, dust, grit particles, etc. into
our lungs and bloodstream far faster than would occur
for any seated motorist- thus the intensity of the exposure
must be far higher for cyclists. That's the problem. I believe
what I experienced was carbon monoxide poisoning.