Yes, they more or less are. Both have two filaments, one for the parking light, and one for the brake light or turn signal. The parking light filament of the 3157 is a little brighter than the parking light filament of the 3057. The signal filaments of both bulbs are the same brightness.
Bad bulb socket? Broken Wire to socket?
Turn on that fast blinking signal light and check to see if the front and rear signal lights are both working, chances are you have a burned out bulb. If both front and rear bulbs are flashing fast, replace the flasher relay.
assuming you mean the light bulbs, see the answer to "how do you change turn signal lamps both front and rear on a 96 mercury grand marquis" right here in WikiAnswers.
Turn signal bulbs are in both front and rear of the vehicle.See "Related Questions" below for specific instructions for both fronts and rears.
Probably turn signal flasher is bad
You could have a faulty bulb. Check for contact in both bulbs if they are new.
If your blinker is blinking at a faster rate than normal, it usually means that one of the bulbs is out. For example, if the left turn signal blinks faster than usual, check either the front or the rear left turn signal. If both turn signals seem okay, check the front left parking light. (this is the front orange light that is on when your headlights are on)
The turn signal and brake light bulb on mine are one and the same. Once you get the tailight off, the bulb housing should just turn a quarter turn then be able to pull out. the bulb itself is just a push-in type. I always change bulbs in pairs or sets. Sometimes non-mated bulbs can blow out soon after.
short circuits in the turn signal and brake light circuits
Problem may be in the steering column turn signal not cancelling completely - try "jiggling" stalk and have assistant watch brake light
maybe wrong bulbs 2057 or 3157 or 1156