Select rows where the 3rd column value is over xx

Shell Programming and Scripting
1

Hi All,
I've got a text file which is Postcode,Postcode, Travel_time and I want to select all of the rows where the 3rd column value is over 255. Can someone show me the magic on how to do this?
Originally it did contain 4 columns but i've managed to strip out the first 3 using:
cat textfile | awk -F, '{print $1, $2, $3}' > new_textfile

Thanks everyone

2 
awk -F, '$3>255' textfile
3

All in one:

awk -F, '{NF=3}$3>255' OFS="," textfile
4

To print the file,

awk -F, '$3>255 {print}' textfile