Driver 1:
1.0 Drive
0.25 Break
0.75 POA (or Work, or some combination of Work/POA that adds up to 45 minutes)
3.5 Drive
0.5 Break
4.5 Drive
10.5 hrs total shift length
Driver2:
1.0 Drive
0.75 Break
0.25 POA (or Work, or some combination of Work/POA that adds up to 15 minutes)
4.5 Drive
0.75 Break
3.5 Drive
10.75 hrs total shift length - i.e. 15 minutes longer than Driver 1, for exactly the same reason that it was only 15 minutes longer in your original version.