1. reckless - He wasn't exercising any caution. He wasn't being careful at all at a time when he should have been. 2. senseless - It wouldn't make any sense. It wouldn't be productive. Meaningless and senseless are very similar, but "senseless" collocates better in #2. I checked a few online dictionaries, and none of them can explain the difference between the two very clearly. It 's such a subtle distinction that's it's hard to put it in words.

In the context, the driver lacks sense -- meaning he lacks judgment or may not be paying attention. His driving is not sensible. So in the context, it means basically the same as reckless.