the general consensus (at least among my fellow sig-leaders), is that when riding on the aero-bars, either your hands are too far removed from the brake levers to respond to an emergency (if the bars are clip-on and the brakes are on the drops of your regular bars), OR your weight is too far forward over the front wheel and adversly affecting handling to be able to respond to emergencies in a pace line.

the bottom line, aero-bars are for time-trial races where pacelining is not only not encouraged but allowed. they are not appropriate in a sig paceline where most riders are learning basic skills.

Former editor is right but doesn't go far enough. Aerobars aren't welcome in the STS (which is for experienced paceline riders) or, arguably, in any paceline rides for the same reasons they've been banned in the TdF and most pro racing (other than TTs) for at least the last 10 years. Aside from the location of the brakes and shifters, the bars themselves represent a hazard to other riders in the event of a paceline pile-up.

Delicate question which applies, I think, only to the STS and SIGs, since most regular group A rides don't specify that aerobars are prohibited. I've spent a little time checking this out with SIG and STS leaders and come back with a mixed bag of answers. Policy in the A Classic STS is flat out no aerobars. I don't know about the A Classic SIG but I hear it's the same. Policy in the A-19 SIG is a little vague--talk to Ed. A-19 STS policy is no aerobars on the bike, but there's probably a bit of leader discretion available for known skilled riders who absolutely won't use the aerobars on the ride and have brakes and shifters in conventional position on the main bar and/or downtube; even if you know the leaders and are a really solid rider, it's not a great idea to show up with aerobars unless you've cleared it with the leaders beforehand, because most leaders will just say no.