I'm not going to let you keep old rolls for new actions. Even without the simple fact that dice pools are variable and there's no guarantee the same action will use the same number of dice, pre-knowledge of your roll results dramatically affects risk assessment when it comes to a roll.
For example, let's say you rolled 2 hits, and then 7 hits, and I told you 2 hits was enough and you kept that roll. You now have a 7 hit roll effectively in the bank that you can use at your leisure with relative confidence you'll succeed. The game doesn't work that way.
If you want to roll 3 times for every action, feel free, but your unused rolls are wasted.
Secondly, you should reconsider how many rolls ahead you want to toss out. Every action you declare and roll for, I will hold you to. Again, pre-knowledge of the results of your rolls dramatically changes your risk assessment. Just now you rolled a Matrix Perception to find a Firewall and check for Data bombs, then immediately rolled Hack on the Fly after. You got 5 hits on Hack on the Fly. If I said that it had a Firewall of 12, you might want to reconsider hacking it, but if I said the Firewall was only 4, you'd be happy with your roll and hack away. That's not a decision you get to make after already making the roll.
And what if I said there was a Data Bomb on that file? You just hacked it before I informed you of that, triggering the bomb.
Anyway, this is somewhat moot since you didn't need to do any hacking in the first place, as you have access to Knight Errant's traffic system, but this is relevant for future notice.
You pull up the video feed on the three cameras Skynet directed you to, however it'll take you awhile to comb through it, especially since you don't know what vehicle you're looking for. You will arrive at the building site before then if you start that search right now.
To comb through the video feed, roll Computer + Intuition [Data Processing] (6, 30 minutes) Extended Test, with a -4 penalty, since the only info you have is 'something like a roadmaster.' If you wait until after the investigation, you might find more evidence to go on that will give you better odds on that search.