I saw a couple riding bikes and using kayak's as their gear trailers behind their bikes leaving New Orleans during Katrina. They had the kayaks on some little bike wheel conflagaration of a makeshift trailer that hooked to the bike seat post and were just screaming down the road vs sitting in traffic.
Well thought out evac option if ya wait till the roads are jammed IMO....
I'd guess about 12 mph with the gear.
So six hours they are out of trouble.
Full Disclosure: If they were in Texas, heading towards Austin, they'd be in trouble. Those hills in Bastrop State Park are no fun at all.
Prayers for those evacuating.
Full Disclosure: Are all the Galveston and Houston hospitals equipped with handy basement-mounted generators like in N.O. ?