in my experince in both wearing and observing others, safty vest and screaming yellow jersey/wind jackets work really well during the day and in poor weather conditions during the day. like when its foggy or overecast the jacket literaly seems to glow. if your a driver and you just happen to glance in a direction, you will imedently see and identifty and cyclist in yellow. thats just how it is around here. in a normal jersey from 50yards away not so identifyable, a driver can't guess the speed, ect as quick as they would if in a saftey vest/sateren yellow jersey.

at night seems to be the down fall of safty vest. from a distance say 20feet or more in pitch black, half moon or dim lite conditions its not that great even with lots of large 2inch reflective bits with orange stripes. if i put my arm out to signal a turn its hard to tell what i am doing if your a car 30feet back going 20mph. safty vest only work with some aviable light, either full moon, street lights, or headlights. i know some vest come with flashing lights, but they are such weak led lights that can't even be seen from 10feet away. again useless.

i either use a mesh saefty vest or a jacket with lots of reflective bits but only at night, bad weather or if its windy out(its wind proof). i tend not to wear one during the day, imo its very efffective but i don't always wear one. lasty no vest is a replacment for lights. always use atleast 2 red lights in back and 2 up front, one flashing and one stready and both far apart.