Broomstick Question

[Jo Ann]

No: HPFGUIDX 94775

Heads up, Quidditch fans and canon experts!

My apologies if this has been dealt with previously, but can anyone 
tell me whether it's indicated in canon whether a racing broomstick 
can carry more than one person?

If it can be done, what effect does it have on speed, 
maneuverability, etc?

If it can't, what happens if one tries?

If it's not mentioned at all, can I get some opinions on the subject?

Thanks in advance...

J. Spencer