The idea "Life is longer than any ride" capitalizes on the ending of the poem in which Frost emphasizes the promises he must keep and the miles he must travel before he sleeps.
Taken literally, miles before I sleep refers correctly to the many miles he will drive through a rural snow storm. Anyone who ever traveled through a snow storm knows this is a profoundly correct reflection: you are fully aware that you have miles and miles to go through blinding snow before you can sleep (or give up and stop at an inn on the roadside).
Taken figuratively, this is understood as Frost's contemplation of desired accomplishments or fulfilled responsibilities before his death.
Either way, considered literally or figuratively, the thought expressed is that a ride is something, anything, that lasts a period of time, while life, be it restorative sleep or accomplishments and responsibilities before death, is something that passes through many phases, many "rides," as it were. This is what you can muse on and comment on in your paper.
The woods are lovely, dark and deep.
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep.